IL299283A

IL299283A - Dual-fuel diesel engine and system and method for adapting diesel engines for dual-fuel use

Info

Publication number: IL299283A
Application number: IL299283A
Authority: IL
Inventors: SHMUELI Lior; Sebastian GUELER Rodrigo; GOLDWINE Gideon
Original assignee: Dor Chemicals Ltd; SHMUELI Lior; Sebastian GUELER Rodrigo; GOLDWINE Gideon
Priority date: 2022-12-20
Filing date: 2022-12-20
Publication date: 2024-07-01
Also published as: IL299283B1

Description

DUAL-FUEL DIESEL ENGINE AND SYSTEM AND METHOD FOR ADAPTING DIESEL ENGINES FOR DUAL-FUEL USE FIELD OF THE INVENTION [0001]This invention relates in general to dual-fuel engines that run on a combination of diesel fuel and a secondary fuel. It relates more specifically to systems and methods with improved injection of the secondary fuel and to systems and methods for adapting existing diesel engines to dual-fuel use.

BACKGROUND OF THE INVENTION [0002]Diesel is widely used as a fuel for engines and generators. Because of increasingly strict limitations on emissions from combustion of diesel fuel, finding strategies for reducing emissions of pollutants and particulates during diesel fuel combustion has become a problem of significant current concern. One approach to the problem has been to develop dual-fuel systems in which diesel is combined with a secondary fuel that is more environmentally friendly. One such secondary fuel is methanol. Methanol is a clean-burning fuel, has a high energy density, and is commonly available and inexpensive. Because methanol has a low cetane number, it cannot be used easily in compression-ignition engines such as typical diesel engines. Further, methanol is not highly miscible with diesel fuel, making use of methanol-diesel blends impractical. Thus, alternative approaches to design of dual-fuel engines that combine diesel with a secondary fuel are needed. id="p-3"

[0003]British Pat. No. 1593852 (henceforth "GB852") discloses a dual-fuel methanol-diesel engine system in which methanol is stored in an auxiliary tank attached to the chassis of the vehicle. Reference is now made to FIG. 1 , which presents a schematic diagram of the system disclosed in GB852. In the system as it is depicted in the figure, the methanol is passed by a fuel pump to a carburetor that is fitted to the air intake of the engine. A heat exchanger jacket is fitted around the air intake downstream of the carburetor and connected to the exhaust manifold so that the exhaust gases from the engine pass through the jacket before they enter the exhaust pipe. The exhaust gases heat the air/methanol mixture, causing the methanol to vaporize. The vaporized methanol is provided to the engine via inlet manifold. id="p-4"

[0004]Japanese Pat. Appl. No. JPS6375322 discloses a "methanol diesel engine." The system disclosed therein incorporates two fuel tanks, one containing methanol and the other the usual fuel for the engine. The methanol passes through a heat exchanger that is heated by waste heat from the engine. The system includes a heat sensor and a control mechanism that determines whether or not the temperature of the engine is sufficiently high to allow operation using methanol alone. When this temperature is reached, the valve to the main fuel tank is closed. When the engine is shut down, the valve to the methanol tank is closed and that to the main fuel tank opened in order to flush the methanol from the engine so that the next time the engine is operated, it will start by burning the diesel fuel rather than methanol. id="p-5"

[0005]International (PCT) Pat. Appl. Pub. No. WO2006/037155 discloses a dual-fuel diesel engine in which a "co-fuel" characterized by a melting point below -10 °C and boiling point above 35 °C is vaporized in a liquid-to-gas converter interposed between the co-fuel's storage tank and the combustion chamber(s) of the engine. The gaseous co-fuel is then passed to the combustion chamber. id="p-6"

[0006]Udayakumar et al. (Udayakumar, R., Sundaram, S., and Sivakumar, K., "Engine Performance and Exhaust Characteristics of Dual Fuel Operation in DI Diesel Engine with Methanol," SAE Technical Paper 2004-01-0096, 2004) performed a series of laboratory tests of the performance of a model dual-fuel diesel/methanol engine. They noted that direct injection of methanol into the engine inlet air would cause absorption of a large amount of heat from the vaporization of the methanol, and therefore heated the inlet air through which the methanol passed by wrapping the inlet air pipe with electrical heating tape. This solution is clearly not practical for use in actual dual-fuel engines. id="p-7"

[0007]Guan et al. (Guan, W.; Wang, X.; Zhao, H.; Liu, H., "Exploring the High Load Potential of Diesel-Methanol Dual-Fuel Operation with Miller Cycle, EOR, and Intake Air Cooling on a Heavy-Duty Diesel Engine," Int. J. Engine Res. 2021 , 22, 2318 – 2336) performed a study in which engine operating parameters of a dual-fuel diesel-methanol engine were examined in order to determine the conditions that maximized engine efficiency and performance. They reported that engine performance can be compromised because of the high latent heat of vaporization of methanol, leading to lowering of the engine temperature. id="p-8"

[0008]Dierickx et al. (Dierickx, J.; Verbiest, J.; Janvier, T.; Peeters, J.; Sileghem, L.; Verhelst, S., "Retrofitting a High-Speed Marine Engine to Dual-Fuel Methanol-Diesel Operation: a Comparison of Multiple and Single Point Methanol Port Injection," Fuel Comm. 2021 , 7, 100010) investigated the effect of varying the methanol injection point on engine performance when a diesel engine is retrofitted for dual fuel diesel-methanol operation. They found that single point injection provides the lowest retrofit cost, but that multiple point injection maximizes the methanol energy fraction and minimizes NOx emissions. They reported that condensation of methanol in the intake line should be avoided, and therefore vaporized the methanol by removal of the intercooler or by use of the heat of the valves. id="p-9"

[0009]It is clear from the foregoing that while extensive research has been performed regarding the design of dual-fuel diesel-based engines, an improved system characterized by efficiency, low cost, and ease of construction, especially for retrofitting to existing diesel engines, remains a long-felt, but as yet unmet need.

SUMMARY OF THE INVENTION [0010]It is therefore an object of this invention to disclose an add-on system for adapting a diesel engine system for dual-fuel use, id="p-11"

[0011] said diesel engine system comprising: id="p-12"

[0012] a diesel engine comprising an engine block ( 100 ), an engine controller ( 110 ), an engine mix input ( 120 ), an air filter ( 130 ); and at least one turbocharger ( 140 ); and, id="p-13"

[0013] a diesel fuel supply system ( 160 ) adapted to supply diesel fuel to said diesel engine, said diesel fuel supply system comprising a diesel fuel storage container ( 450 ), a diesel fuel pump in fluid connection with said diesel fuel storage container, and a diesel fuel delivery passage ( 470 ) providing a fluid connection between an output of said diesel fuel pump and said engine mix input; id="p-14"

[0014] and said add-on system comprising: (a) a first passage ( 600 ), said first passage providing a fluid connection between a source of a flow of heated air and said engine mix input; (b) at least one first injector ( 300 ) adapted to inject a secondary fuel into said first passage; (c) a secondary fuel delivery system for delivering said secondary fuel to said at least one first injector; (d) at least one first fuel delivery passage ( 420 ) providing a fluid connection between said secondary-fuel delivery system and said at least one first injector; and, (e) a control system ( 500 ) in electrical connection with said engine controller, an electrical system of said engine, and said at least one first injector; id="p-15"

[0015] wherein (a) said control system is programmed to determine a load on said engine and to control said at least one first injector such that said at least one first injector injects said secondary fuel into said first passage at a variable rate, said variable rate depending on said load on said engine; and, (b) said secondary fuel is selected from the group consisting of alcohols, ketones, ethers, and mixtures thereof, and is characterized by a net caloric value greater than 15 MJ/liter and a boiling point at a pressure of 1 atm that is greater than 50 °C. id="p-16"

[0016]It is a further object of this invention to disclose such an add-on system, wherein said first passage is in thermal contact with a heating body. id="p-17"

[0017]It is a further object of this invention to disclose an add-on system as defined in any of the above, wherein: id="p-18"

[0018] said engine additionally comprises a radiator ( 150 ); and, id="p-19"

[0019] said system additionally comprises: (a) a heat exchanger ( 200 ), said heat exchanger comprising (a1) a primary side ( 210 ) comprising a primary side inlet ( 211 ) and a primary side outlet ( 212 ); and (a2) a secondary side ( 220 ) comprising a secondary side inlet ( 221 ) and a secondary side outlet ( 222 ); said primary side inlet in fluid connection with said first passage, and said primary side outlet in fluid connection with said first passage at a point upstream of said at least one first injector; (b) a second passage ( 700 ), said second passage providing a fluid connection between said radiator and said engine block ( 100 ) and adapted to transfer engine coolant fluid between said radiator and said engine block; (c) a third passage ( 710 ), said third passage providing a fluid connection between said engine block and said secondary side inlet and adapted to transfer engine coolant fluid between said engine block and said heat exchanger; (d) a fourth passage ( 720 ), said fourth passage providing a fluid connection between said secondary side exit and said radiator and adapted to transfer engine coolant fluid between said heat exchanger and said radiator; (e) at least one second injector ( 310 ) adapted to inject said secondary fuel at a constant rate into said first passage at a point upstream of said primary side inlet of said heat exchanger; and, (f) at least one second fuel delivery passage ( 430 ) providing a fluid connection between said secondary fuel delivery system and said at least one second injector; id="p-20"

[0020] and further wherein said secondary fuel delivery system is arranged to deliver fuel to said at least one first injector and to said at least one second injector. id="p-21"

[0021]In some preferred embodiments of the invention, said secondary fuel has a boiling point at 1 atm that is not greater than 200 °C. In some other preferred embodiments of the invention, said secondary fuel has a boiling point at 1 atm that is not greater than 90 °C. id="p-22"

[0022]It is a further object of this invention to disclose the add-on system as defined in any of the above, additionally comprising: id="p-23"

[0023] a bypass passage ( 800 ), said bypass passage providing a fluid connection between two points in said first passage: (a) if said system does not comprise a second injector, said bypass passage providing a fluid connection between a first point located upstream of said at least one first injector and a second point located downstream of said at least one first injector; (b) if said system comprises a second injector, said bypass passage providing a fluid connection between a first point located upstream of said at least one second injector and a second point located downstream of said at least one first injector; and, id="p-24"

[0024] a three-way valve ( 810 ) disposed within said first passage, said three-way valve switchable between: (a) a first configuration in which said three-way valve provides a fluid connection between said source of said flow of heated air and said bypass passage, thereby bypassing said at least one first injector and, if present, said at least one second injector; and, (b) a second configuration in which said three-way valve provides a fluid connection between said source of said flow of heated air and said at least one first injector and, if present, said at least one second injector, thereby bypassing said bypass passage. id="p-25"

[0025]It is a further object of this invention to disclose the add-on system as defined in any of the above, wherein said diesel engine is a generator. id="p-26"

[0026]It is a further object of this invention to disclose the add-on system as defined in any of the above, wherein said diesel engine is an engine of a motor vehicle. id="p-27"

[0027]It is a further object of this invention to disclose the add-on system as defined in any of the above, wherein said control system ( 500 ) is programmed to activate said system only when said engine is running. id="p-28"

[0028]It is a further object of this invention to disclose the add-on system as defined in any of the above, wherein said control system ( 500 ) is programmed to activate said system when said engine achieves a predetermined speed. id="p-29"

[0029]It is a further object of this invention to disclose the add-on system as defined in any of the above, wherein said control system controls said injector or injectors such that said injector or injectors deliver said secondary fuel in pulses. In some preferred embodiments of the invention, said pulses are characterized by a pulse width of 6 ms. In some preferred embodiments of the invention, said control system is programmed to shut down said add-on system if said pulses exceed a predetermined pulse width. In some preferred embodiments of the invention, said control system is programmed to shut down said add-on system if said pulses exceed a pulse width of 6 ms. id="p-30"

[0030]It is a further object of this invention to disclose the add-on system as defined in any of the above, wherein said control system comprises data transmitting means adapted to transmit data regarding at least one characteristic selected from the group consisting of engine status and at least one engine operating parameter. id="p-31"

[0031]It is a further object of this invention to disclose the add-on system as defined in any of the above, wherein said control system comprises protection against cyberattack. id="p-32"

[0032]It is a further object of this invention to disclose the add-on system as defined in any of the above, wherein said control system comprises a controller ( 510 ) in electrical and/or data connection with said engine and with said injector or injectors, said controller adapted: (a) to obtain from an engine or generator controller data regarding engine status, and, (b) to provide signals for controlling said injector or injectors. In some preferred embodiments of the invention, said data regarding engine status comprises at least one of engine current and engine load. In some preferred embodiments of the invention, the data connection from the engine to the controller is an analog connection. In some preferred embodiments of the invention, said data connection is selected from the group consisting of MODBUS protocol; CANBUS protocol; and direct connection to phase current of said engine. id="p-33"

[0033]In some preferred embodiments of the invention in which said control system comprises a controller ( 510 ), said controller obtains data regarding engine status via a direct connection to said phase current of said engine; said controller uses a low voltage system of said engine as its voltage source; said controller obtains values of current on each of said engine's three phases as analog inputs ( 511 ); said controller determines said load on said engine from said current values; and, said controller provides separate digital outputs to said injector or injectors ( 310 , 311 ). In some preferred embodiments of the invention, said controller ( 510 ) obtains a digital input ( 514 ) from said engine controller ( 110 ) indicating whether or not said engine is running. id="p-34"

[0034]It is a further object of this invention to disclose the add-on system as defined in any of the above, wherein said secondary fuel is an aliphatic alcohol. In some preferred embodiments of the invention, said aliphatic alcohol is selected from the group consisting of methanol, ethanol, and mixtures thereof. In some especially preferred embodiments of the invention, said secondary fuel is methanol. id="p-35"

[0035]It is a further object of this invention to disclose the add-on system as defined in any of the above, wherein said system is adapted to supply sufficient secondary fuel to provide a secondary fuel : diesel caloric ratio of 1:1 under no-load conditions, and a secondary fuel : diesel caloric ratio of 7:3 under full-load conditions. In some preferred embodiments of the invention in which said secondary fuel is methanol, said system is adapted to supply said methanol to said engine so as to provide a methanol:diesel volume ratio of 2:1 under no-load conditions and a methanol:diesel volume ratio of 4:1 when said engine is operated at full load. In some preferred embodiments of the invention in which said secondary fuel is methanol, said system comprises at least one first injector and at least one second injector, and said at least one second injector is adapted to supply a total of 0.4 liters of methanol per kWh. id="p-36"

[0036]It is a further object of this invention to disclose the add-on system as defined in any of the above, wherein said system is adapted to be implemented without requiring any modifications of the engine other than installation of the system itself. id="p-37"

[0037]It is a further object of this invention to disclose the add-on system as defined in any of the above, wherein said system does not comprise any means for measuring engine temperature in which temperature measurements made by said means for measuring engine temperature are used by said control system ( 500 ) as part of any control mechanism for setting a rate or volume of injection of said secondary fuel. id="p-38"

[0038]It is a further object of this invention to disclose a method for adapting a diesel engine system to dual-fuel use, id="p-39"

[0039] said diesel engine system comprising: id="p-40"

[0040] a diesel engine comprising an engine block ( 100 ), an engine controller ( 110 ), an engine mix input ( 120 ), an air filter ( 130 ); and at least one turbocharger ( 140 ); and, id="p-41"

[0041] a diesel fuel supply system ( 160 ) adapted to supply diesel fuel to said diesel engine, said diesel fuel supply system comprising a diesel fuel storage container ( 450 ), a diesel fuel pump in fluid connection with said diesel fuel storage container, and a diesel fuel delivery passage ( 470 ) providing a fluid connection between an output of said diesel fuel pump and said engine mix input; id="p-42"

[0042] said method comprising: (a) providing a first passage ( 600 ), said first passage providing a fluid connection between a source of a flow of heated air and said engine mix input; (b) providing at least one first injector ( 300 ) adapted to inject a secondary fuel into said first passage; (c) providing a secondary fuel delivery system arranged to deliver said secondary fuel to said at least one first injector; (d) providing a fluid connection between said secondary fuel delivery system and said at least one first injector; and, (e) providing a control system ( 500 ) in electrical connection with said engine controller, an electrical system of said engine, and said injector or injectors; id="p-43"

[0043] wherein (a) said secondary fuel is selected from the group consisting of alcohols, ketones, ethers, and combinations thereof, and is characterized by a net caloric value greater than 15 MJ/liter and a boiling point at a pressure of 1 atm that is greater than 50 °C; and, (b) said step of providing at least one first injector comprises providing at least one first injector adapted to inject said secondary fuel into said first passage at a variable rate, said variable rate depending on said load of said engine. id="p-44"

[0044]In some preferred embodiments of the method, said secondary fuel is characterized by a boiling point at a pressure of 1 atm that does not exceed 200 °C. In some preferred embodiments of the method, said secondary fuel is characterized by a boiling point at a pressure of 1 atm that does not exceed 90 °C. id="p-45"

[0045]It is a further object of this invention to disclose such a method for adapting a diesel engine system for dual-fuel use, wherein said method further comprises: (a) providing a heating body; and, (b) placing said first passage in thermal contact with said heating body. id="p-46"

[0046]It is a further object of this invention to disclose the method for adapting a diesel engine system for dual-fuel use as defined in any of the above, wherein said engine additionally comprises a radiator ( 150 ) and said method additionally comprises: (a) providing a heat exchanger ( 200 ), said heat exchanger comprising: (a1) a primary side ( 210 ) comprising a primary side inlet ( 211 ) and a primary side outlet ( 212 ); and, (a2) a secondary side ( 220 ) comprising a secondary side inlet ( 221 ) and a secondary side outlet ( 222 ); (b) providing at least one second injector ( 310 ) in fluid connection with said secondary fuel delivery system, said at least one second injector adapted to inject said secondary fuel into said first passage at a point upstream of said primary side inlet of said heat exchanger; (c) placing said primary side outlet in fluid connection with said first passage at a point upstream of said at least one first injector; (d) providing a second passage ( 700 ), said second passage providing a fluid connection between said radiator and said engine block ( 100 ) and adapted to transfer engine coolant fluid between said radiator and said engine block; (e) providing a third passage ( 710 ), said third passage providing a fluid connection between said engine block and said secondary side inlet and adapted to transfer engine coolant fluid between said engine block and said heat exchanger; and (f) providing a fourth passage ( 720 ), said fourth passage providing a fluid connection between said secondary side exit and said radiator and adapted to transfer engine coolant fluid between said heat exchanger and said radiator; and further wherein said control system is programmed: (1) to determine a load on said engine; (2) to control said at least one first injector to inject said secondary fuel into said first passage at a variable rate, said variable rate depending on said load on said engine; and (3) to control said at least one second injector to inject said secondary fuel into said first passage at a constant rate. id="p-47"

[0047]It is a further object of this invention to disclose the method for adapting a diesel engine system for dual-fuel use as defined in any of the above, additionally comprising: id="p-48"

[0048](a) providing a bypass passage ( 800 ), said bypass passage providing a fluid connection between two points in said first passage: id="p-49"

[0049] (A) if said system does not comprise a second injector, said bypass passage providing a fluid connection between a first point located upstream of said at least one first injector and a second point located downstream of said at least one first injector; id="p-50"

[0050] (B) if said system comprises a second injector, said bypass passage providing a fluid connection between a first point located upstream of said at least one second injector and a second point located downstream of said at least one first injector located downstream of said downstream injector; and, id="p-51"

[0051](b) providing a three-way valve ( 810 ) disposed within said first passage, said three-way valve switchable between: (b1) a first configuration in which said three-way valve provides a fluid connection between said source of said flow of heated air and said bypass passage, thereby bypassing said at least one first injector and, if present, said at least one second injector; and, (b2) a second configuration in which said three-way valve provides a fluid connection between said source of said flow of heated air and said at least one first injector and, if present, said at least one second injector, thereby bypassing said bypass passage. id="p-52"

[0052]It is a further object of this invention to disclose the method for adapting a diesel engine system for dual-fuel use as defined in any of the above, wherein said diesel engine is a generator. id="p-53"

[0053]It is a further object of this invention to disclose the method for adapting a diesel engine system for dual-fuel use as defined in any of the above, wherein said diesel engine is an engine of a motor vehicle. id="p-54"

[0054]It is a further object of this invention to disclose the method for adapting a diesel engine system for dual-fuel use as defined in any of the above, wherein said control system ( 500 ) is programmed to activate said system only when said engine is running. id="p-55"

[0055]It is a further object of this invention to disclose the method for adapting a diesel engine system for dual-fuel use as defined in any of the above, wherein said control system ( 500 ) is programmed to activate said system when said engine achieves a predetermined speed. id="p-56"

[0056]It is a further object of this invention to disclose the method for adapting a diesel engine system for dual-fuel use as defined in any of the above, wherein steps of providing injectors comprises providing injectors adapted to inject said secondary fuel into said first passage in pulses. In some preferred embodiments of the method, said control system is programmed to shut down said system if said pulses exceed a predetermined pulse width. In some preferred embodiments of the method, said control system is programmed to shut down said system if said pulses exceed a pulse width of 6 ms. id="p-57"

[0057]It is a further object of this invention to disclose the method for adapting a diesel engine system for dual-fuel use as defined in any of the above, wherein said control system comprises protection against cyberattack. id="p-58"

[0058]It is a further object of this invention to disclose the method for adapting a diesel engine system for dual-fuel use as defined in any of the above, wherein: (a) said control system comprises a controller ( 510 ) in electrical and/or data connection with said engine and with said injector or injectors, said controller adapted (a) to obtain from an engine or generator controller data regarding engine status, and (b) to provide signals for controlling said injector or injectors. In some preferred embodiments of the system, said data regarding engine status comprises at least one of engine current and engine load. In some preferred embodiments of the system, said data connection comprises at least one analog input to said controller. In some preferred embodiments of the invention, said data connection is selected from the group consisting of MODBUS protocol; CANBUS protocol; and direct connection to phase current of said engine. id="p-59"

[0059]It is a further object of this invention to disclose the method for adapting a diesel engine system for dual-fuel use as defined in any of the above, wherein: (a) said control system comprises a controller ( 510 ); (b) said controller uses a low voltage system of said engine as its voltage source; (c) said controller obtains values of current on each of said engine's three phases as analog inputs ( 511 ); (d) said controller determines said load on said engine from said current values; and, (e) said controller provides separate digital outputs to said injector or injectors ( 310 , 311 ). In some preferred embodiments of the invention, said controller ( 510 ) obtains a digital input ( 514 ) from said engine controller ( 110 ) indicating whether or not said engine is running. id="p-60"

[0060]It is a further object of this invention to disclose the method for adapting a diesel engine system for dual-fuel use as defined in any of the above, wherein said secondary fuel is an aliphatic alcohol. In some preferred embodiments of the method, said secondary fuel is selected from the group consisting of ethanol, methanol, and mixtures thereof. In some particularly preferred embodiments of the method, said secondary fuel is methanol. id="p-61"

[0061]It is a further object of this invention to disclose the method for adapting a diesel engine system for dual-fuel use, as defined in any of the above, wherein said system is adapted to supply sufficient secondary fuel to provide a secondary fuel : diesel caloric ratio of 1:1 under no-load conditions, and a secondary fuel : diesel caloric ratio of 7:3 under full-load conditions. In some preferred embodiments of the method in which said secondary fuel is methanol, said method comprises supplying said methanol to said engine so as to provide a methanol:diesel volume ratio of 2:1 under no-load conditions and a methanol:diesel volume ratio of 4:1 when said engine is operated at full load. In some preferred embodiments of the method in which said secondary fuel is methanol, said at least one second injector is adapted to supply a total of 0.4 liters of methanol per kWh. id="p-62"

[0062]It is a further object of this invention to disclose the method for adapting a diesel engine system for dual-fuel use as defined in any of the above, wherein said method does not comprise any additional step that requires modification of said engine. id="p-63"

[0063]It is a further object of this invention to disclose the method for adapting a diesel engine for dual-fuel use as defined in any of the above, wherein said method does not include any step of providing means for measuring engine temperature as part of said control system ( 500 ). In preferred embodiments of the invention, said method does not comprise any step of measuring engine temperature that is not part of said engine's normal operation. id="p-64"

[0064]It is a further object of this invention to disclose the method for adapting a diesel engine for dual-fuel use as defined in any of the above, wherein said engine comprises an intercooler and said step of providing a first passage ( 600 ) comprises providing said first passage so as to provide a fluid connection between said source of a flow of heated air and said engine mix input that bypasses said intercooler. id="p-65"

[0065]It is a further object of this invention to disclose a method for operating a diesel engine system as a duel-fuel engine system, id="p-66"

[0066] said diesel engine system comprising: id="p-67"

[0067]a diesel engine comprising an engine block ( 100 ), an engine controller ( 110 ), an engine mix input ( 120 ), an air filter ( 130 ); and at least one turbocharger ( 140 ); and, id="p-68"

[0068]a diesel fuel supply system ( 160 ) adapted to supply diesel fuel to said diesel engine, said diesel fuel supply system comprising a diesel fuel storage container ( 450 ), a diesel fuel pump in fluid connection with said diesel fuel storage container, and a diesel fuel delivery passage ( 470 ) providing a fluid connection between an output of said diesel fuel pump and said engine mix input; id="p-69"

[0069]said method comprising: (a) providing a flow of heated air in a first passage that provides a fluid connection between a source of said flow and said engine mix input; (b) injecting a secondary fuel selected from the group consisting of alcohols, ketones, ethers, and combinations thereof that is characterized by a net caloric value greater than 15 MJ/liter and a boiling point at a pressure of 1 atm that is greater than 50 °C into at least one first point in said flow of heated air, said injecting characterized by a first injection rate; (c) maintaining said flow of heated air between said at least one first point and at least one second point located downstream of said first point at a temperature sufficient to ensure complete vaporization of said secondary fuel; and, (d) determining a load on said engine; wherein said first injection rate is varied according to said load on said engine. id="p-70"

[0070]It is a further object of this invention to disclose such a method for operating a diesel engine system as a dual-fuel engine system, wherein said step of maintaining said flow of heated air at a temperature sufficient to ensure complete vaporization of said secondary fuel comprises placing said first passage in thermal contact with a heating body. id="p-71"

[0071]It is a further object of this invention to disclose the method for operating a diesel engine system as a dual-fuel engine system as defined in any of the above, wherein: said engine comprises a radiator ( 150 ), and said method additionally comprises: (a) providing a heat exchanger ( 200 ), said heat exchanger comprising a primary side ( 210 ) comprising a primary side inlet ( 211 ) and a primary side outlet ( 212 ); and a secondary side ( 220 ) comprising a secondary side inlet ( 221 ) and a secondary side outlet ( 222 ); (b) providing at least one second injector ( 310 ) in fluid connection with said secondary fuel delivery system, said at least one second injector adapted to inject said secondary fuel into said first passage at a point upstream of said primary side inlet of said heat exchanger; (c) placing said primary side outlet in fluid connection with said first passage at a point upstream of said at least one first injector; (d) providing a second passage ( 700 ), said second passage providing a fluid connection between said radiator and said engine block ( 100 ) and adapted to transfer engine coolant fluid between said radiator and said engine block; (e) providing a third passage ( 710 ), said third passage providing a fluid connection between said engine block and said secondary side inlet and adapted to transfer engine coolant fluid between said engine block and said heat exchanger; and, (f) providing a fourth passage ( 720 ), said fourth passage providing a fluid connection between said secondary side exit and said radiator and adapted to transfer engine coolant fluid between said heat exchanger and said radiator; and further wherein said control system is programmed: (1) to determine a load on said engine; (2) to control said at least one first injector to inject said secondary fuel into said first passage at a variable rate, said variable rate depending on said load on said engine; and, (3) to control said at least one second injector to inject said secondary fuel into said first passage at a constant rate. id="p-72"

[0072]It is a further object of this invention to disclose the method for operating a diesel engine system as a dual-fuel engine system as defined in any of the above, wherein said method comprises fixing at least one of said first injection rate and said second injection rate by use of a control system that is programmed to determine the engine load and determine the rate of injection of said secondary fuel from the measured engine load. In some preferred embodiments of the method, said step of determining said load on said engine comprises determining said load on said engine from measurements of an electrical current of said engine. id="p-73"

[0073]It is a further object of this invention to disclose the method for operating a diesel engine system as a dual-fuel engine system as defined in any of the above, wherein said secondary fuel is an aliphatic alcohol. In some preferred embodiments of the method, said secondary fuel is selected from the group consisting of methanol, ethanol, and mixtures thereof. In some especially preferred embodiments of the method, said secondary fuel is methanol. id="p-74"

[0074]It is a further object of this invention to disclose the method for operating a diesel engine system as a dual-fuel engine system as defined in any of the above, wherein steps of providing injectors comprises providing injectors adapted to inject said secondary fuel into said first passage in pulses. In some preferred embodiments of the method, said control system is programmed to shut down said system if said pulses exceed a predetermined pulse width. In some preferred embodiments of the method, said control system is programmed to shut down said system if said pulses exceed a pulse width of 6 ms. id="p-75"

[0075]It is a further object of this invention to disclose the method for operating a diesel engine system as a dual-fuel engine system as defined in any of the above, wherein said system is adapted to supply sufficient secondary fuel to provide a secondary fuel : diesel caloric ratio of 1:1 under no-load conditions, and a secondary fuel : diesel caloric ratio of 7:under full-load conditions. In some preferred embodiments of the method in which the secondary fuel is methanol, said step of injecting methanol comprises injecting methanol so as to provide a methanol:diesel volume ratio of 2:1 under no-load conditions and of 4:1 under full load conditions. In some preferred embodiments of the method in which said secondary fuel is methanol, said method comprises injecting said secondary fuel into said flow of heated air at a downstream point located downstream of said heat exchanger, said injecting characterized by a second injection rate and said second injection rate is 0.4 liters of methanol per kWh. id="p-76"

[0076]It is a further object of this invention to disclose a kit for adapting a diesel engine system to dual-fuel use, wherein said kit comprises:a first fluid connection means adapted to provide a fluid connection between a source of a flow of heated air and an engine mix input of said diesel engine; at least one injector; secondary fuel source connecting means for making a fluid connection between a source of a secondary fuel and said at least one injector; a control system for controlling rate and volume of injection of secondary fuel according to a measured load on the engine; and, electrical and data connection means for providing electrical and/or data connections from an electrical system of said diesel engine electrical system and said at least one injectors to said control system. id="p-77"

[0077]It is a further object of this invention to disclose such a kit, wherein said kit further comprises a secondary fuel delivery system, said secondary fuel delivery system comprising at least one component selected from the group consisting of a secondary fuel tank, a secondary fuel pump, and fluid connection means for providing a fluid connection between a secondary fuel tank and said at least one injector. id="p-78"

[0078]It is a further object of this invention to disclose the kit as defined in any of the above, wherein said kit further comprises: (a) a heat exchanger, said heat exchanger comprising a primary side and a secondary side; (b) second fluid connection means for making a fluid connection between an engine block of said engine and an entrance of said secondary side of said heat exchanger; and, (c) third fluid connection means for making a fluid connection between said exit of said secondary side and a radiator of said engine. id="p-79"

[0079]It is a further object of this invention to disclose the kit as defined in any of the above, wherein said kit further comprises: (a) fourth fluid connection means for making a fluid connection between two points in said first fluid connection means; and, (b) a three-way valve.

BRIEF DESCRIPTION OF THE DRAWINGS [0080]The invention will now be described with reference to the drawings, wherein: id="p-81"

[0081]FIG. 1 is a schematic block diagram of a diesel-methanol dual-fuel engine known in the prior art; id="p-82"

[0082]FIG. 2 is a schematic block diagram of an add-on system for adapting a diesel-fueled engine to dual-fuel use according to one non-limiting embodiment of the invention disclosed herein; id="p-83"

[0083]FIG. 3 is a schematic block diagram of an add-on system for adapting a diesel-fueled engine to dual-fuel use according to a second non-limiting embodiment of the invention disclosed herein; id="p-84"

[0084]FIG. 4 is a schematic block diagram of an add-on system for adapting a diesel-fueled engine to dual-fuel use according to a third non-limiting embodiment of the invention disclosed herein; id="p-85"

[0085]FIG. 5 is a schematic block diagram of one non-limiting embodiment of a control system for the add-on dual-fuel system of the invention disclosed herein; id="p-86"

[0086]FIG. 6 is a flowchart illustrating one non-limiting embodiment of the method by which the instant invention controls the injection of methanol into the dual diesel-methanol system of the invention disclosed herein; and, id="p-87"

[0087]FIG. 7 is a photograph of a non-limiting example of an add-on system for adapting a diesel engine for dual-fuel use, constructed according to one embodiment of the invention disclosed herein. id="p-88"

[0088]In FIGs. 2 – 4 , arrows indicate the direction of fluid flow through the system, parallel solid lines indicate passages that provide fluid connections between system components, and dotted lines indicate electrical and data connections.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0089]In the following description, various aspects of the invention will be described. For the purposes of explanation, specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent to one skilled in the art that there are other embodiments of the invention that differ in details without affecting the essential nature thereof. Therefore, the invention is not limited by that which is illustrated in the figures and described in the specification, but only as indicated in the accompanying claims, with the proper scope determined only by the broadest reasonable interpretation of said claims. In some cases, for clarity or conciseness, individual elements of the invention are discussed separately. Nonetheless, any combination of individual elements of the invention disclosed herein that is not self-contradictory is considered by the inventors to be within the scope of the invention. id="p-90"

[0090]In all cases in which an embodiment is described as "comprising" a set of components or a series of method steps, i.e. the embodiment of the invention may include components or method steps in addition to those explicitly listed, the scope of invention is to be understood to include embodiments in which the invention "consists of" the listed components or method steps, i.e. embodiments that include the listed components or method steps and no others, and to include as well embodiments in which the invention "consists essentially of" the listed components or method steps, i.e. embodiments that do not include any components or method steps not listed that would materially affect the basic and novel characteristics of the invention. id="p-91"

[0091]In the description and drawings of the various embodiments, like reference numbers refer to the same component of the invention. id="p-92"

[0092]Unless specifically stated otherwise, any range disclosed herein is understood to include within its scope the stated endpoints of the range and any subrange. As non-limiting examples, if a range is stated to be "1 – 10%," ranges of >1% – <10%, 1 – 5%, 2 – 9%, etc., are considered by the inventors to be within the scope of the invention; similarly, if a range is stated to be "less than 50%," ranges of less than 40%, less than 25%, less than 10%, etc., are considered to be within the scope of the invention. id="p-93"

[0093]As used herein, with reference to numerical quantities, the term "about" refers to a tolerance of ±25% about the nominal value. id="p-94"

[0094]As used herein, unless explicitly defined otherwise, the term "engine" is used to describe a device that converts chemical energy to kinetic energy via combustion of an inflammable fuel. Unless explicitly defined otherwise, the term is used generically both to describe generators (devices in which the engine's mechanical energy is converted to electrical energy, and which generally run at a constant speed) as well as engines for powering vehicles. As used herein, unless explicitly defined otherwise, the term "diesel engine" is used to refer to an engine as defined above that uses diesel fuel as the source of chemical energy, without any restriction on the mechanical design of the engine. id="p-95"

[0095]As used herein, unless the context or explicit definition to the contrary makes it clear, the term "control system" is used to describe a system that is designed to control the add-on system for adapting a diesel engine to dual-fuel disclosed herein. id="p-96"

[0096]As used herein, unless explicitly defined otherwise, the word "passage" is used to describe a device or component thereof that creates a fluid connection between devices or components thereof to which it is connected. Non-limiting examples of passages as the term is used herein include pipes and tubes. id="p-97"

[0097]As used herein, unless explicitly defined otherwise, the term "fuel ratio" is used to describe the ratio between the secondary fuel and the diesel fuel in the dual-fuel system disclosed herein. Depending on the context, the term may refer to a volume ratio or to a ratio according to caloric value. id="p-98"

[0098]As used herein, unless explicitly defined otherwise, the term "net caloric value" is used to describe the amount of heat produced by combustion of a fuel in which the products of combustion include water vapor, i.e., the heat produced without recovery of any of the heat content of the water vapor produced in the combustion. This value is also known as the "lower calorific value," the "net calorific value," and the "lower heating value." id="p-99"

[0099]The instant invention provides a novel add-on system and a novel method for adapting a standard diesel engine to dual-fuel use. The add-on system and method are based on a novel control system that optimizes the ratio of diesel fuel to secondary fuel as a function of the load on the engine. The add-on system and method can be used to adapt to dual-fuel use diesel generators that operate at constant speed as well as variable-speed diesel engines such as those that are used in diesel-powered vehicles. id="p-100"

[0100]In preferred embodiments, the instant invention comprises an addition to an existing diesel engine, and a method for adapting an existing diesel engine for dual-fuel use. The system and method described herein for adaptation of a diesel engine for dual-fuel use with a secondary fuel. Any secondary fuel with a sufficiently high caloric content, a sufficiently low boiling temperature such that it will be fully vaporized in the inventive system, and that will not foul or damage the engine or system may be used. In preferred embodiments of the invention, the secondary fuel is selected from the group consisting of alcohols, ketones, ethers, and mixtures thereof, and is characterized by a net caloric value greater than MJ/liter and a boiling point at a pressure of 1 atm that is greater than 50 °C. In typical embodiments of the invention, the upper limit on the boiling point of the secondary fuel is set by the temperature of the engine exhaust, and hence, in typical non-limiting embodiments of the invention, the 1 atm boiling point of the secondary fuel is less than or equal to 200 °C. As described below, in some embodiments of the invention, the system includes a heat exchanger through the cold side of which air carrying vapor of the secondary fuel passes. In these embodiments, the upper limit on the boiling point of the secondary fuel is set by the fluid on the hot side of the heat exchanger. In typical non-limiting embodiments of the invention in which the heat exchanger is used to transfer heat from the engine's radiator to the air carrying the fuel vapor, the 1 atm boiling point of the secondary fuel is less than or equal to 90 °C. In some preferred embodiments of the invention, the secondary fuel is an aliphatic alcohol. In some more preferred embodiments of the invention, the secondary fuel is methanol, ethanol, or an ethanol-methanol mixture. In the most preferred embodiments of the invention, the secondary fuel is methanol. id="p-101"

[0101]For clarity of presentation, in the accompanying description and figures, only those parts of the existing engine that are connected to or are modified by the add-on system of the invention disclosed herein, or are necessarily in use when the system (existing engine + the add-on disclosed herein) is operated in dual-fuel mode, are shown or described. In the following description of preferred embodiments of the invention, unless a modification to the existing engine is explicitly described, the embodiment is assumed to incorporate and operate the engine as originally constructed, without any modification. In the most preferred embodiments of the invention, no modifications are made to the engine other than the installation of the add-on system disclosed herein. In particular, in preferred embodiments of the invention disclosed herein, in contrast to similar systems known in the prior art, dual-fuel operation of a diesel engine to which the add-on system disclosed herein has been connected does not require any measurement of engine temperature in order to determine the amount or rate of addition of secondary fuel. While in some embodiments of the invention, the add-on system may include means for measuring engine temperature as part of its general data measurement system, the measurements of engine temperature are not used by the add-on system's control system in any way to determine or set the rate or volume of injection of secondary fuel. id="p-102"

[0102]Reference is now made to FIG. 2 , which presents a schematic block diagram illustrating one non-limiting embodiment 10 of the instant invention. A flow of heated air is provided via first passage 600 ; in the embodiment shown in FIG. 2 , the air passes through an air filter 130 and the engine's turbocharger 140 . In the embodiments shown in the figures, for simplicity, systems in which the engine includes a single turbocharger are shown. Embodiments in which the engine includes multiple turbochargers are considered by the inventors to be within the scope of the invention, however. The engine exhaust ( 610 ) is likewise indicated in the figure. Secondary fuel is provided by a secondary fuel delivery system that in preferred embodiments comprises a dedicated secondary fuel storage container 400 and a dedicated secondary fuel pump 410 in fluid connection with the secondary fuel storage container. The secondary fuel storage container may be connected physically to the engine or to the vehicle carrying the engine, or it may be a self-standing unit. The secondary fuel is introduced into the flow of heated air via at least one first injector 300 that receives secondary fuel from the secondary fuel storage container via the secondary fuel pump and passage 420 . In the embodiment illustrated in FIG. 2 , a single injection apparatus is illustrated. While the first injector may be a single injector, embodiments in which the "first injector" comprises a plurality of individual injector units that are arranged to operate in tandem are considered by the inventors to be within the scope of the invention. For clarity of presentation, in the following discussion, the invention is discussed in terms of a single first injector. A person of ordinary skill in the art will readily understand the straightforward adaptations necessary to incorporate additional injection units into the first injector and how to make and use embodiments of the invention in which the first injector comprises a plurality of individual injector units. id="p-103"

[0103]The first injector injects secondary fuel into first passage 600 , where it is entrained in the flow of heated air and vaporized to create a mixture of air and vapor; the secondary fuel is injected into the flow of air far enough upstream of the engine to ensure that the mixture is homogeneous by the time that it reaches the engine. The first injector is adapted to inject the secondary fuel into the air flow at a variable rate that depends on the engine load, as described in detail below. In typical embodiments of the invention, first injector 300 is adapted to provide sufficient secondary fuel to yield a 1:1 secondary fuel : diesel ratio by caloric value under no-load conditions, and 7:3 ratio by caloric value under full-load conditions. When the secondary fuel is methanol, this caloric value ratio is equivalent to a 2:1 volume ratio under no-load conditions and a 4:1 volume ratio under full-load conditions. The rates and amounts of injection of the secondary fuel are determined by control system 500 , as described in detail below. As is shown in the figure, the system for introducing the secondary fuel into the engine is independent of the engine's own diesel fuel supply system ( 160 ). id="p-104"

[0104]The injectors may be any commercially available type that is compatible with use in a dual-fuel diesel engine system, i.e., one that is compatible with diesel fuel and the selected secondary fuel. Passages that carry the air and the air carrying vapor of the secondary fuel may be made of any material that is compatible with use in the instant invention may be used. Non-limiting examples include tubes made of metal, chemical- and heat-resistant plastic, and rubber. The dedicated secondary fuel pump 410 may be of any commercially available type that is compatible with use in the system disclosed herein. id="p-105"

[0105]In the embodiment shown in FIG. 2 , the first passage is connected to the engine block ( 100 ) via engine mix inlet 120 . The air carrying the vapor of secondary fuel is introduced at this point into the inlet manifold where it is introduced into the engine's cylinders along with the diesel/air mixture provided by the engine's own fuel supply system 160 , in a ratio determined according to the load on the engine, as described in detail below. Under normal operating conditions, the diesel fuel is supplied to the engine continuously and in rates and quantities determined by the engine's own control system. id="p-106"

[0106]In order to optimize the performance of the system, it is critical that the secondary fuel be vaporized to provide a mixture of air and secondary fuel vapor rather than a mixture of air and droplets of liquid secondary fuel. Thus, if the air flowing through first passage 600 is insufficiently hot to vaporize the secondary fuel and to maintain an air/vapor mixture, it is necessary to heat the passage. In some embodiments (not shown in the figures), first passage 600 is placed in thermal contact with a heating body. As non-limiting examples, first passage 600 can be partially or entirely wrapped with heating tape or be in thermal contact with any other heating system known in the art compatible with the add-on system and the engine. id="p-107"

[0107]Many existing diesel engine systems include an intercooler to cool the exhaust air. Because in the invention disclosed herein, evaporation of the secondary fuel will necessarily cool the air into which the secondary fuel is injected, when the add-on system of the invention disclosed herein is used, the necessity for use of an intercooler is reduced or eliminated. Therefore, in preferred embodiments of the invention in which the engine comprises an intercooler (not shown in the figures), first passage 600 is connected to the engine so as to bypass the intercooler. id="p-108"

[0108]Reference is now made to FIG. 3 , which presents a schematic block diagram of a second non-limiting embodiment 20 of the instant invention. In this embodiment, the system includes a heat exchanger 200 . The heat exchanger comprises a primary side 210 , which comprises primary side inlet 211 and primary side outlet 212 , and a secondary side 220 , which comprises secondary side inlet 221 and secondary side outlet 222 . In this embodiment, the fluid flow (air + any secondary fuel that has been introduced upstream of the heat exchanger) through the first passage passes through the primary side of the heat exchanger. The upstream portion of the first passage (indicated in the figure as 600a ) is connected to the primary side inlet upstream of first injector 300 . The downstream portion of the first passage (indicated in the figure as 600b ), into which first injector 300 injects the secondary fuel, provides a fluid connection between primary side outlet 212 and the engine mix inlet. In embodiments in which the system comprises a heat exchanger, the system additionally comprises at least one second injector 310 that is adapted to inject secondary fuel at a predetermined constant rate into one or more points in the portion of the first passage ( 600a ) that is upstream of the heat exchanger. Analogously to the description of the first injector given above, in the embodiment illustrated in FIG. 3 , a single injection apparatus is illustrated. As was the case with the first injector, while the second injector may be a single injector unit, embodiments in which the "second injector" comprises a plurality of individual injectors that are arranged to operate in tandem are considered by the inventors to be within the scope of the invention. For clarity of presentation, in the following discussion, the invention is discussed in terms of a single second injector. A person of ordinary skill in the art will readily understand the straightforward adaptations necessary to incorporate additional injection units into the second injector and how to make and use embodiments of the invention in which the second injector comprises a plurality of individual injector units. id="p-109"

[0109]A fluid connection between the second injector 310 and the secondary fuel tank and fuel pump ( 400 / 410 ) is provided by a second fuel delivery passage ( 430 ). In preferred embodiments of the invention, a single output from the fuel pump provides secondary fuel to the two passages, as is shown in the figure. As with the first injector, the second injector may comprise a single injector or a plurality of individual injectors, and of any type that is compatible with use in the dual-fuel system and that can inject the secondary fuel at the appropriate rate. id="p-110"

[0110]The heat exchanger heats the air carrying vapor of the secondary fuel that passes through the heat exchanger's primary side by transferring heat from the engine's coolant system to the air carrying vapor of secondary fuel. The engine's radiator 150 passes coolant fluid to the engine block via second passage 700 . The coolant fluid flows from the engine block to secondary side inlet 221 via a third passage 710 . The coolant fluid passes through the secondary side of the heat exchanger and then returns to the radiator via a fourth passage 720 . id="p-111"

[0111]In typical embodiments of the invention, the air stream initially has a temperature of about 35 °C. When second injector 310 injects secondary fuel into the air stream, the evaporation of the secondary fuel cools the air; the temperature of the air carrying the vapor of secondary fuel is typically about 10 °C at the inlet to the heat exchanger. The temperature of the engine coolant entering the secondary side of the heat exchanger is typically about °C, and its temperature when it exits the heat exchanger is typically about 70 – 85 °C. Complete vaporization of the secondary fuel is thus accomplished by use of the engine's own waste heat. The fuel that is injected by first injector 300 into the air/secondary fuel mixture exiting the heat exchanger cools down the mixture, typically to a temperature of about 20 °C, as required for the operation of the engine. id="p-112"

[0112]Any commercially available heat exchanger that is compatible with a dual-fuel engine that operates on diesel fuel and the particular secondary fuel may be used. Passages 700 – 720 may be constructed of any material that is compatible with use in the dual-fuel system, i.e., that is chemically inert to the secondary fuel, oil, and diesel fuel, capable of withstanding the engine temperature without significant degradation, and of any diameter that will enable the fluids that pass through the system to flow at the desired rate. Non-limiting examples of such materials include metal, oil-resistant plastics, and oil-resistant rubbers. In some preferred embodiments, the passages are constructed from reinforced synthetic rubber that is resistant to oil, ozone, and abrasion, is capable of continuous use over a temperature range of -20 °C to +80 °C, and has an inside diameter of 25 – 51 mm, a wall thickness of 10 mm, and is rated at a working pressure of 10 bar and a burst pressure of 30 bar. id="p-113"

[0113]As with the embodiment shown in Fig. 2 , in embodiments such as the one shown in FIG. 3 in which the secondary fuel system includes means for heating the flow of air in which the secondary fuel is entrained, the secondary fuel system is independent of the engine's diesel fuel supply system 160 . id="p-114"

[0114] Reference is now made to FIG. 4 , which presents a schematic block diagram of a third non-limiting embodiment of the system of the instant invention. In the embodiment illustrated in the figure, the system includes a bypass passage ( 800 ) that connects a point in the first passage located upstream of the second injector to a point in the first passage that is downstream of the first injector. In embodiments of the invention that lack a second injector, the bypass passage connects a point in the first passage located upstream of the first injector to a point in the first passage that is downstream of the first injector. The embodiment illustrated schematically in FIG. 4 further includes a three-way valve ( 810 ) that can be switched reversibly between a first configuration in which it provides a fluid connection between the first passage and the bypass passage while diverting the flow of air through the first passage from passing by the injector or injectors, and a second configuration in which it provides a fluid connection for the air to flow past the injector or injectors, while closing off the air flow to the bypass passage. In typical embodiments of the invention, the three-way valve is manually operated, but embodiments in which the valve is remotely operated (e.g. electrically, pneumatically, or electropneumatically) are considered by the inventors to be within the scope of the invention. The bypass system allows the user to choose to operate the engine on diesel fuel alone and to control when the system is open to dual-fuel use. It is emphasized that FIG. 4 , which illustrates a bypass system in an embodiment of the invention in which the system includes a heat exchanger, is not intended to limit the use of a bypass system to those embodiments in which a heat exchanger is present, but only to assist a person of ordinary skill in the art to make and use the bypass system. A person of ordinary skill in the art will readily understand that the bypass system can be adapted to any embodiment of the system disclosed herein, including those in which the system does not include a heat exchanger or other means for heating the air flow through first passage 600 . id="p-115"

[0115]The heart of the instant invention is its unique control system 500 , which controls the rate and volume of injection of the secondary fuel into the add-on system described above for supplying secondary fuel to the engine. Control system 500 operates independently of the control systems of the generator and motor. In preferred embodiments of the invention, the control system is sealed against contamination by dust or liquid, most preferably with an IP rating of at least 65, and sealed against humidity sufficient to prevent condensation at a relative humidity of at least 95%. In preferred embodiments, the control system is protected against vibration to an acceleration of at least 4g, and a deviation of no more than 1.6 mm at a vibration frequency of 25 – 100 Hz. In preferred embodiments, the control system is protected against shocks up to an acceleration of at least 200 m s-1. The control system preferably has a working temperature over a range of at least -20 °C – +70 °C. In preferred embodiments of the invention, the control system is protected against stray electromagnetic fields according to at least one of international standards EN 50082-2:97; EN 50082-1:99; and EN 50081-2:96. id="p-116"

[0116]In some embodiments of the invention, the control system includes means for transmitting data regarding engine status. In these embodiments, any appropriate wired or wireless means for monitoring and transmitting the data may be used. In some embodiments of the invention, the control system includes protection against cyberattack; any means (hardware or software) known in the art that is compatible with the control system and for use under the engine's operating conditions may be used. id="p-117"

[0117]Preferred embodiments of the control system incorporate one or more fail-safe systems. For example, in some preferred embodiments, the control system is programmed to activate the injection of the secondary fuel only when the engine is running. In some preferred embodiments, the control system includes a mechanism to shut down the injection of the secondary fuel if the width of the pulses (i.e. the time when the injectors are open) exceeds a predetermined value, typically 6 ms. In some preferred embodiments, the control system includes protection against secondary fuel overpressure or underpressure, said protection including a subsystem that comprises means for measuring the pressure of the secondary fuel, means for controlling the secondary fuel pump, and electrical switching means to turn the secondary fuel system on and off if the pressure exceeds a maximum set value or is below a minimum set value. id="p-118"

[0118]In contrast to systems known in the art, the dual-fuel system and its control system disclosed herein are designed as add-ons to an existing engine or generator, and except for making the connections described herein between the dual-fuel system and its control system on the one hand and the engine or generator on the other, no modifications to the existing engine or generator are necessary for the construction or operation of the invention disclosed herein. In addition, in contrast to systems known in the art, the volume and rate of delivery of the secondary fuel to the engine is determined by the engine load, as described in detail below. It is further emphasized that, in contrast to dual-fuel systems known in the art, the instant invention is not designed or intended to include a state in which the engine runs entirely on the secondary fuel. At all times during which the system is in operation, at least about 20% by volume of the fuel supplied to the engine is diesel fuel, which in preferred embodiments is supplied entirely by the engine's own supply system. In addition, in contrast to systems known in the art, no temperature measurements are necessary in order to determine the engine load or the optimal fuel mixture; rather, control system 500 is connected to the engine's own control system, from which it receives a signal indicating the rate of fuel supply to the engine as a function of the engine load, and defines the amount of secondary fuel to be delivered to the engine accordingly. Consequently, in preferred embodiments of the add-on system disclosed herein, it does not comprise any means for measuring or monitoring engine temperature that is used to determine or to help determine the rate or volume of introduction of secondary fuel. Furthermore, in contrast to systems known in the art, the system for supplying the secondary fuel to the engine operates independently of the engine's own fuel supply system. id="p-119"

[0119]The control system obtains data regarding the status of the engine via the generator (engine) controller. Data obtained from the generator controller comprises the current or load. This data can be obtained to the controller in any appropriate way known the art. Non-limiting examples include providing a data connection between control system 500 and the engine via a data transfer protocol known in the art such as the MODBUS or the CANBUS protocol. Reference is now made to FIG. 5 , which presents a schematic block diagram of one non-limiting embodiment of the control system 500 and its connections to the dual-fuel system in which the control system is connected to the engine's phase current. The heart of the control system is controller 510 . Any commercially available chip or card that can meet the requirements of the control system may be used. The controller uses the low voltage system of the engine as its voltage source ( 515 ). In some non-limiting embodiments of the invention, the controller is adapted to operate on an input voltage of 12 – 24 VDC. In some other non-limiting embodiments of the invention, the controller is adapted to operate on an input voltage of 5 VDC. In embodiments in which the low-voltage output of the engine (typically 24 VDC) does not match the controller's input voltage, DC/DC voltage converter 520 is used to provide the appropriate input voltage to the controller. The controller is grounded to the generator's electrical ground via electrical connection 512 ; in the schematic diagram of FIG. 5 , ground connections are indicated by the letter "G." The controller also obtains the values of the current on each of the generator's three phases as analog inputs 511 , the three phases marked as "A1," "A2," and "A3," respectively, from engine controller 110 . Digital input 514 is an ON/OFF signal indicating the engine's status, obtained from engine controller 110 . In embodiments in which the engine provides its ON/OFF signal at a voltage incompatible with the input voltage of controller 510 , DC/DC voltage converter 525 is used to convert the voltage to the appropriate value. id="p-120"

[0120]Controller 510 provides separate digital outputs to injectors 300 and 310 that regulate each injector's state (open or closed). In the non-limiting embodiment depicted in FIG. 5 , the digital signals to the injectors are sent via MOSFETs 530A and 530B , respectively, with the controller providing the gate voltage. A person of ordinary skill in the art will understand that the output voltage of the digital outputs will depend on the requirements of the particular injectors used. In typical embodiments of the invention, the digital output to the injectors is – 5 VDC. The engine's low-voltage output is used to drive the injectors ( 516 ). id="p-121"

[0121]The control system may be activated manually. In preferred embodiments of the invention, it is activated automatically. In the case of a generator, in preferred embodiments of the invention, the control system is programmed to activate the secondary fuel injection system when the generator's speed reaches its working value (typically 1500 rpm for a 50 Hz generator or 1800 rpm for a 60 Hz generator). In the case of an engine that drives a vehicle, in some embodiments of the invention, the control system is programmed to be activated when the engine speed or engine load indicates that the engine is not idling. Once the control system is activated, it controls the injectors, and hence the secondary fuel : diesel ratio, by setting the injection rate of the secondary fuel as a function of the measured engine load. Reference is now made to FIG. 6 , which shows a flowchart illustrating the control process. Controller 510 receives as an analog input from the engine controller (genset controller in the case of a generator) 110 , which determines the current on each of the engine current's phases. This analog signal is converted to a total current measurement (step 1000 ).

From the total current measured, the load on the engine is calculated (step 1010 ). The amount of secondary fuel to be injected is then calculated from the engine load (step 1020 ). In typical embodiments of the invention, under no-load conditions, sufficient secondary fuel is provided to yield a secondary fuel : diesel caloric ratio of 1:1; when the secondary fuel is methanol, this caloric ratio corresponds to a 2:1 volume ratio. When the engine is operated at full load, sufficient secondary fuel is provided to provide a secondary fuel : diesel caloric ratio of 7:3; when the secondary fuel is methanol, this caloric ratio corresponds to a 4:volume ratio. When the engine is operating under an intermediate load, the fuel ratio is adjusted appropriately. Once the proper fuel ratio has been defined, the controller directs the injectors to inject the secondary fuel into first passage 600 as described above (step 1030 ). In typical embodiments of the invention, the secondary fuel is injected in pulses (i.e., the injectors are not open continuously), in which the ON state of the injector duty cycle (i.e., the injector provides a fluid connection between the methanol storage tank and the first passage) is preferably no longer than 6 ms. As described above, the second injector 310 injects secondary fuel at a fixed rate. In typical embodiments of the invention, second injector 310 injects sufficient secondary fuel to provide a net caloric value of about 6 MJ/kWh; in the case in which the secondary fuel is methanol, this rate is equivalent to about 0.4 liter/kWh (about l/h for a 32kW generator), while first injector 300 injects secondary fuel at a variable rate, determined as described above, in order to provide the desired fuel ratio. id="p-122"

[0122]The instantaneous engine load may change due to changes in operating conditions or to the combustion of the secondary fuel/diesel combination in place of pure diesel ( 1040 ), thereby changing the electrical current (step 1050 ). This change in electrical current will be measured by the current sensors (step 1060 ), which will input the updated information to the controller. Thus, the control system is designed to adapt the fuel ratio in real time according to the instantaneous requirements of the engine. id="p-123"

[0123]In some embodiments of the invention, the control system may require a one-time calibration in order to set the appropriate rates and volumes of injection of secondary fuel as a function of engine load. In some embodiments of the invention, the calibration comprises optimizing and setting the injection rate of one or both of the injectors at the load endpoints (no load and full load). In other embodiments of the invention, the calibration includes determination and setting of optimal methanol injection rates of one or both of the injectors at one or more intermediate load values. id="p-124"

[0124]It is also within the scope of the invention to provide a method for modifying a diesel engine to dual-fuel use. In preferred embodiments of the method, except for alterations necessary to make connections between the system for providing secondary fuel and the engine, no modifications of the existing engine are necessary, and the method is performed without any alterations to the engine itself. The method comprises obtaining the components of the system described above, some embodiments of which are illustrated schematically in FIGs. 2 – 4 , and connecting them to the existing engine as illustrated in the figures and description. A person of ordinary skill in the art will readily understand that the physical and technical requirements of components added as part of the method described below are identical to those of the corresponding components of the system described above, some embodiments of which are depicted schematically in FIGs. 2 – 4 . A person of ordinary skill in the art will also readily that the description discloses certain preferred embodiments of the method, and that other embodiments of the method that are based on incorporation of elements of the system described above into a dual-fuel system are within the scope of the invention. id="p-125"

[0125]The method comprises producing a flow of heated air through a first passage 600 that provides a fluid connection between the source of the flow (e.g., from the engine's turbocharger or turbochargers) and the engine mix input 120 . A secondary fuel is injected into the flow of heated air via at least one first injector 300 , which is adapted to inject secondary fuel at a variable rate. The injector is in fluid connection with a dedicated secondary fuel tank ( 410 ). In preferred embodiments of the invention, the secondary fuel is injected into the flow of air in pulses, in which the injector is open for a predetermined period of time, typically 6 ms. The rate of injection of secondary fuel via the first injector varies according to the engine load. id="p-126"

[0126]In some embodiments of the method, in addition to the at least one first injector, the system includes at least one second injector 310 that injects secondary fuel into the flow of heated air at a constant rate at a point upstream of the first injector. The flow of heated air carrying vapor of secondary fuel is passed through the primary (cold) side of a heat exchanger that is located downstream of second injector 310 and upstream of first injector 300 . In preferred embodiments of the invention, the method comprises passing engine coolant fluid through the secondary (hot) side of the heat exchanger, thereby transferring waste heat from the engine to the flow of heated air carrying vapor of the secondary fuel. id="p-127"

[0127]In preferred embodiments of the method, the rate of injection of secondary fuel is controlled via a control system 500 that is programmed to measure the engine load and to control the rate of injection of secondary fuel via injectors 300 and 310 according to the measured engine load, as described above. id="p-128"

[0128]In some other embodiments of the method, the method includes providing a bypass passage 800 that creates a fluid connection from a point in the first passage that is upstream of the most upstream injector to a point that is downstream of most downstream injector, and placing a three-way valve 810 at the upstream connection between the first passage and the bypass passage, the three-way valve adapted to provide a fluid connection between the source of the flow of air either through the first passage or through the bypass passage, thereby enabling manual bypass of the system for injecting methanol into the engine. id="p-129"

[0129]It is also within the scope of the invention to disclose a method for operating a diesel engine using a dual-fuel mixture. In preferred embodiments, the method does not involve any modification of the diesel engine other than installation of the components necessary for injection of a secondary fuel into the engine and for controlling the rate of injection of the secondary fuel. The method comprises providing a flow of heated air in a first passage that provides a fluid connection between the source of the flow and the mix inlet of the engine. The heated air is preferably obtained from the engine's own turbocharger or exhaust system. A secondary fuel is injected into the flow of heated air. The injection is preferably performed in pulses, most preferably having a pulse width (i.e. time during which methanol is injected) of no more than 6 ms. The air flow is maintained at a temperature sufficient to ensure complete vaporization of the secondary fuel. In some preferred embodiments of the invention, the secondary fuel is injected into the flow of heated air at two points or sets of points, an upstream point or set of points at which the secondary fuel is injected at a constant rate and a downstream point or set of points at which the secondary fuel is injected at a variable rate that depends on the engine load. In especially preferred embodiments of the invention, the air flow passes through the primary (cold) side of a heat exchanger that is located between the upstream and downstream points. The downstream injection may cool the methanol-air mixture to the temperature of the engine's own diesel-air mixture. The method includes measurement of the engine load, and varying the upstream injection rate according to the measured engine load. In preferred embodiments of the invention, the method does not involve any step of running the engine on secondary fuel alone, or of measuring the engine temperature. id="p-130"

[0130]In preferred embodiments of the invention in which the method comprises passing the flow of heated air through a heat exchanger, the method comprises passing engine coolant fluid from the engine block to the engine's radiator via the secondary side of the heat exchanger, thereby using waste heat from the engine to heat the air carrying the vapor of secondary fuel. id="p-131"

[0131]In preferred embodiments of the invention in which the engine comprises an intercooler, the method comprises directing the flow of heated air so as to bypass the intercooler. id="p-132"

[0132]In particularly preferred embodiments of the invention, the rate of injection of the secondary fuel is fixed by a control system that is programmed to determine the engine load and determine the rate of injection of the secondary fuel from the measured engine load. In some preferred embodiments of the invention, the control system determines the engine load from measurements of the engine electrical current. id="p-133"

[0133]The flow of air into which the secondary fuel has been entrained is introduced into the engine mix input ( 120 ) of the engine. The diesel fuel is supplied to the engine via the engine's own diesel fuel supply system ( 160 ), which in typical embodiments comprises a diesel fuel storage container ( 450 ), a diesel fuel pump ( 460 ) in fluid connection with the diesel fuel storage container, and a diesel fuel delivery passage ( 470 ) that provides a fluid connection between the exit of the diesel fuel pump and the engine mix input. The diesel fuel is supplied to the engine mix input independent of the secondary fuel according to the normal operation of the engine. Thus, in typical embodiments, the diesel fuel is delivered continuously to the engine mix input at a rate determined by the engine's control system. id="p-134"

[0134]It is within the scope of the invention to disclose the method for operating a diesel engine using a dual-fuel mixture in which the method is performed by using the system as described above. id="p-135"

[0135]It is also within the scope of the invention to provide a kit for conversion of a diesel engine to dual-fuel use. The kit includes a first fluid connection means (for providing a fluid connection between a source of a flow of heated air and the engine mix inlet; two injectors; fluid connection means for making fluid connections between a source of methanol and the injectors; a control system for controlling the rate and volume of methanol injection according to the load on the engine; and electrical and data connection means for connecting the control system to the engine's electrical system and the injectors. In some embodiments of the invention, kit includes a delivery system for the secondary fuel, which may include one or more components selected from a secondary fuel tank, a secondary fuel pump, and fluid connection means for providing a fluid connection between the secondary fuel tank and the injectors. In preferred embodiments of the invention, the kit additionally includes a heat exchanger that comprises a primary side and a secondary side, second fluid connection means for making a fluid connection between the engine block and the entrance of the secondary side, and third fluid connection means for making a fluid connection between the exit of the secondary side and the engine's radiator. In some embodiments of the invention, the kit also includes fourth fluid connection means for making a fluid connection between two points in the first fluid connection means and a three-way valve.

Example [0136]The following example is intended to assist a person of ordinary skill in the art to make and use the invention as described in the instant specification, and is not intended to be limiting in any way. id="p-137"

[0137]A diesel generator was modified for dual-fuel operation by installation of a system according to the invention disclosed herein. Reference is now made to FIG. 7 , which presents a photograph of the generator as modified by installation of the system of the invention disclosed herein. id="p-138"

[0138]The system illustrated in the figure was constructed for introduction of methanol as the secondary fuel. The passages that carry the air and methanol/air mixture are 1/2" synthetic rubber tubes having an internal diameter of 13 mm, and external diameter of mm, a nominal working pressure of 20 bar, a burst pressure of 60 bar, and a working temperature range of -40 °C – +120 °C. id="p-139"

[0139]The system illustrated in the figure includes a bypass passage that includes a manual three-way ball valve for directing the flow of heated air either past the injectors or to bypass them so that the system runs entirely on diesel fuel. id="p-140"

[0140]The secondary fuel (methanol) is supplied to the system by a VIKING model FH4cast iron gear pump, which has a nominal flow rate of 3 gallons/min (11.36 liters/min) and pressure of 250 psi (1.72 MPa). The secondary fuel is injected into the system by BOSCH 0280158040 fuel injectors. id="p-141"

[0141]The system illustrated in the figure includes both first and second injectors, and a WTK model P12-50 heat exchanger that is attached to the system as described above. The heat exchanger has a rated capacity of about 50 kW, a flow rate through each side of about 4.4 m/h at a nominal flow rate of 0.13 m/s, and a pressure drop across the heat exchanger of about 6 – 7 kPa.

ABSTRACT A system and method for conversion of a diesel-fueled engine to dual-fuel use is disclosed. A secondary fuel, typically methanol, is injected into a flow of heated air. In preferred embodiments of the invention, the system comprises two injectors, an upstream injector that injects the secondary fuel at a constant rate and a downstream injector that injects it at a variable rate. The mixture of air and secondary fuel vapor is introduced into the engine mix inlet, where it is combined with the engine's own diesel-air mixture. In preferred embodiments of the invention, the mixture of air and the secondary fuel passes through a heat exchanger, where it is heated by waste heat from the engine to ensure complete vaporization. In contrast to systems and methods known in the art, the rate and volume of injection of the secondary fuel are determined as a function of engine load.

Claims

CLAIMS We claim:

1. An add-on system for adapting a diesel engine system for dual-fuel use, said diesel engine system comprising: a diesel engine comprising: an engine block ( 100 ); an engine controller ( 110 ); an engine mix input ( 120 ); an air filter ( 130 ); and, at least one turbocharger ( 140 ); and, a diesel fuel supply system ( 160 ) adapted to supply diesel fuel to said diesel engine, said diesel fuel supply system comprising: a diesel fuel storage container ( 450 ); a diesel fuel pump ( 460 ) in fluid connection with said diesel fuel storage container; and, a diesel fuel delivery passage ( 470 ) providing a fluid connection with an output of said diesel fuel pump and said engine mix input; said add-on system comprising: a first passage ( 600 ), said first passage providing a fluid connection between a source of a flow of heated air and said engine mix input; at least one first injector ( 300 ) adapted to inject a secondary fuel into said first passage; a secondary fuel delivery system for delivering said secondary fuel to said at least one first injector; at least one first fuel delivery passage ( 420 ) providing a fluid connection between said secondary-fuel delivery system and said at least one first injector; and, a control system ( 500 ) in electrical connection with said engine controller, an electrical system of said engine, and said at least one first injector; wherein: said control system is programmed to determine a load on said engine and to control said at least one first injector such that said at least one first injector injects said secondary fuel into said first passage at a variable rate, said variable rate depending on said load on said engine; and, said secondary fuel is selected from the group consisting of alcohols, ketones, ethers, and mixtures thereof, and is characterized by a net caloric value greater than MJ/liter and a boiling point at a pressure of 1 atm that is greater than 50 °C.

2. The add-on system according to claim 1 , wherein said first passage is in thermal contact with a heating body.

3. The add-on system according to claim 1 , wherein: said diesel engine additionally comprises a radiator ( 150 ); and, said system additionally comprises: a heat exchanger ( 200 ), said heat exchanger comprising: a primary side ( 210 ) comprising a primary side inlet ( 211 ) and a primary side outlet ( 212 ); and, a secondary side ( 220 ) comprising a secondary side inlet ( 221 ) and a secondary side outlet ( 222 ); said primary side inlet in fluid connection with said first passage, and said primary side outlet in fluid connection with said first passage at a point upstream of said at least one first injector; a second passage ( 700 ), said second passage providing a fluid connection between said radiator and said engine block ( 100 ) and adapted to transfer engine coolant fluid between said radiator and said engine block; a third passage ( 710 ), said third passage providing a fluid connection between said engine block and said secondary side inlet and adapted to transfer engine coolant fluid between said engine block and said heat exchanger; a fourth passage ( 720 ), said fourth passage providing a fluid connection between said secondary side exit and said radiator and adapted to transfer engine coolant fluid between said heat exchanger and said radiator; at least one second injector ( 310 ) adapted to inject said secondary fuel at a constant rate into said first passage at a point upstream of said primary side inlet of said heat exchanger; and, at least one second fuel delivery passage ( 430 ) providing a fluid connection between said secondary fuel delivery system and said at least one second injector; and further wherein said secondary fuel delivery system is arranged to deliver fuel to said at least one first injector and to said at least one second injector.

4. The add-on system according to claim 3 , wherein said secondary fuel has a boiling point at atm that is not greater than 90 °C.

5. The add-on system according to any one of the preceding claims, additionally comprising: a bypass passage ( 800 ), said bypass passage providing a fluid connection between two points in said first passage: if said system does not comprise a second injector, said bypass passage providing a fluid connection between a first point located upstream of said at least one first injector and a second point located downstream of said at least one first injector; if said system comprises a second injector, said bypass passage providing a fluid connection between a first point located upstream of said at least one second injector and a second point located downstream of said at least one first injector; and, a three-way valve ( 810 ) disposed within said first passage, said three-way valve switchable between: a first configuration in which said three-way valve provides a fluid connection between said source of said flow of heated air and said bypass passage, thereby bypassing said at least one first injector and, if present, said at least one second injector; and, a second configuration in which said three-way valve provides a fluid connection between said source of said flow of heated air and said at least one first injector and, if present, said at least one second injector, thereby bypassing said bypass passage.

6. The add-on system according to any one of the preceding claims, wherein said diesel engine is a generator.

7. The add-on system according to any one of the preceding claims, wherein said diesel engine is an engine of a motor vehicle.

8. The add-on system according to any one of the preceding claims, wherein said control system ( 500 ) is programmed to activate said system only when at least one condition from the group consisting of (a) said engine is running; and (b) said engine achieves a predetermined speed; is met.

9. The add-on system according to any one of the preceding claims, wherein said control system controls said injector or injectors such that said injector or injectors deliver said secondary fuel in pulses.

10. The add-on system according to claim 9 , wherein said control system is programmed to shut down said system if said pulses exceed a predetermined pulse width.

11. The add-on system according to any one of the preceding claims, wherein said control system comprises data transmitting means adapted to transmit data regarding at least one characteristic selected from the group consisting of: engine status; and, at least one engine operating parameter.

12. The add-on system according to any one of the preceding claims, wherein said control system comprises protection against cyberattack.

13. The add-on system according to any one of the preceding claims, wherein said control system comprises a controller ( 510 ) in electrical and/or data connection with said engine and with said injector or injectors, said controller adapted: to obtain from an engine or generator controller data regarding engine status; and, to provide signals for controlling said injector or injectors.

14. The add-on system according to claim 13 , wherein said data regarding engine status comprises at least one of engine current and engine load.

15. The add-on system according to claim 13 , wherein said data connection is selected from the group consisting of MODBUS protocol; CANBUS protocol; and direct connection to phase current of said engine.

16. The add-on system according to claim 15 , wherein: said controller obtains data regarding engine status via a direct connection to said phase current of said engine; said controller uses a low voltage system of said engine as its voltage source; said controller obtains values of current on each of said engine's three phases as analog inputs ( 511 ); said controller determines said load on said engine from said current values; and, said controller provides separate digital outputs to said injector or injectors ( 310 , 311 ).

17. The add-on system according to claim 13 , wherein said engine controller ( 110 ) is adapted to transmit a digital input ( 514 ) to said controller ( 510 ) indicating whether or not said engine is running.

18. The add-on system according to any one of the preceding claims, wherein said secondary fuel is methanol.

19. The add-on system according to claim 18 , wherein said system comprises at least one first injector and at least one second injector, and further wherein said at least one second injector is adapted to supply a total of 0.4 liters of methanol per kWh.

20. The add-on system according to any one of the preceding claims, wherein said add-on system does not comprise any means for measuring engine temperature in which temperature measurements made by said means for measuring engine temperature are used by said control system ( 500 ) as part of any control mechanism for setting a rate or volume of injection of said secondary fuel.

21. A method for adapting a diesel engine system to dual-fuel use, said diesel engine system comprising: a diesel engine comprising: an engine block ( 100 ); an engine controller ( 110 ); an engine mix input ( 120 ); an air filter ( 130 ); and, at least one turbocharger ( 140 ); and, a diesel fuel supply system ( 160 ) for supplying diesel fuel to said diesel engine, said diesel fuel supply system comprising: a diesel fuel storage container ( 450 ); a diesel fuel pump ( 460 ) in fluid connection with said diesel fuel storage container; and, a diesel fuel delivery passage ( 470 ) providing a fluid connection between an output of said diesel fuel pump and said engine mix input; said method comprising: providing a first passage ( 600 ), said first passage providing a fluid connection between a source of a flow of heated air and said engine mix input; providing at least one first injector ( 300 ) adapted to inject a secondary fuel into said first passage; providing a secondary fuel delivery system arranged to deliver said secondary fuel to said at least one first injector; providing a fluid connection between said secondary fuel delivery system and said at least one first injector; and, providing a control system ( 500 ) in electrical connection with said engine controller, an electrical system of said engine, and said injector or injectors; wherein: said secondary fuel is selected from the group consisting of alcohols, ketones, ethers, and combinations thereof, and is characterized by a net caloric value greater than MJ/liter and a boiling point at a pressure of 1 atm that is greater than 50 °C; and, said step of providing at least one first injector comprises providing at least one first injector adapted to inject said secondary fuel into said first passage at a variable rate, said variable rate depending on said load of said engine.

22. The method according to claim 21 , wherein said method further comprises: providing a heating body; and, placing said first passage in thermal contact with said heating body.

23. The method according to claim 21 , wherein said diesel engine additionally comprises a radiator ( 150 ) and said method additionally comprises: providing a heat exchanger ( 200 ), said heat exchanger comprising: a primary side ( 210 ) comprising a primary side inlet ( 211 ) and a primary side outlet ( 212 ); and, a secondary side ( 220 ) comprising a secondary side inlet ( 221 ) and a secondary side outlet ( 222 ); providing at least one second injector ( 310 ) in fluid connection with said secondary fuel delivery system, said at least one second injector adapted to inject said secondary fuel into said first passage at a point upstream of said primary side inlet of said heat exchanger; placing said primary side outlet in fluid connection with said first passage at a point upstream of said at least one first injector; providing a second passage ( 700 ), said second passage providing a fluid connection between said radiator and said engine block ( 100 ) and adapted to transfer engine coolant fluid between said radiator and said engine block; providing a third passage ( 710 ), said third passage providing a fluid connection between said engine block and said secondary side inlet and adapted to transfer engine coolant fluid between said engine block and said heat exchanger; and, providing a fourth passage ( 720 ), said fourth passage providing a fluid connection between said secondary side exit and said radiator and adapted to transfer engine coolant fluid between said heat exchanger and said radiator; and further wherein said control system is programmed: to determine a load on said engine; to control said at least one first injector to inject said secondary fuel into said first passage at a variable rate, said variable rate depending on said load on said engine; and, to control said at least one second injector to inject said secondary fuel into said first passage at a predetermined constant rate.

24. The method according to any one of claims 21 – 23 , additionally comprising: providing a bypass passage ( 800 ), said bypass passage providing a fluid connection between two points in said first passage: if said system does not comprise a second injector, said bypass passage providing a fluid connection between a first point located upstream of said at least one first injector and a second point located upstream of said at least one first injector; if said system comprises a second injector, said bypass passage providing a fluid connection between a first point located upstream of said at least one second injector and a second point located downstream of said at least one first injector; and, providing a three-way valve ( 810 ) disposed within said first passage, said three-way valve switchable between: a first configuration in which said three-way valve provides a fluid connection between said source of said flow of heated air and said bypass passage, thereby bypassing said at least one first injector and, if present, said at least one second injector; and, a second configuration in which said three-way valve provides a fluid connection between said source of said flow of heated air and said at least one first injector and, if present, said at least one second injector, thereby bypassing said bypass passage.

25. The method according to any one of claims 21 – 24 , wherein said diesel engine is a generator.

26. The method according to any one of claims 21 – 24 , wherein said diesel engine is an engine of a motor vehicle.

27. The method according to any one of claims 21 – 26 , wherein said control system is programmed to activate said system only when at least one condition selected from the group consisting of (a) said engine is running; and (b) said engine has achieved a predetermined speed; is met.

28. The method according to any one of claims 21 – 27 , wherein steps of providing injectors comprises providing injectors adapted to inject said secondary fuel into said first passage in pulses.

29. The method according to claim 28 , wherein said control system is programmed to shut down said system if said pulses exceed a predetermined pulse width.

30. The method according to any one of claims 22 – 29 , wherein said control system comprises protection against cyberattack.

31. The method according to any one of claims 21 – 30 , wherein said control system comprises a controller ( 510 ) in electrical and/or data connection with said engine and with said injector or injectors, said controller adapted: to obtain from an engine or generator controller data regarding engine status, and, to provide signals for controlling said injector or injectors.

32. The method according to claim 31 , wherein said data regarding engine status comprises at least one of engine current and engine load.

33. The method according to claim 31 , wherein said data connection is selected from the group consisting of MODBUS protocol; CANBUS protocol; and direct connection to phase current of said engine.

34. The method according to claim 31 , wherein: said controller obtains data regarding engine status via a direct connection to said phase current of said engine; said controller uses a low voltage system of said engine as its voltage source; said controller obtains values of current on each of said engine's three phases as analog inputs ( 511 ); said controller determines said load on said engine from said current values; and, said controller provides separate digital outputs to said injector or injectors ( 310 , 311 ).

35. The method according to claim 31 , wherein said controller ( 510 ) obtains a digital input ( 514 ) from said engine controller ( 110 ) indicating whether or not said engine is running.

36. The method according to any one of claims 21 – 35 , wherein said secondary fuel is methanol.

37. The method according to claim 21 – 36 , wherein said secondary fuel is methanol and said at least one second injector is adapted to supply a total of 0.4 liters of methanol per kWh.

38. The method according to any one of claims 21 – 37 , wherein said method does not comprise any additional step that requires modification of said engine.

39. The method according to any one of claims 21 – 38 , wherein said method does not include any step of providing means for measuring engine temperature as part of said control system ( 500 ).

40. The method according to any one of claims 21 – 39 , wherein said engine comprises an intercooler and said step of providing a first passage ( 600 ) comprises providing said first passage so as to provide a fluid connection between said source of a flow of heated air and said engine mix input that bypasses said intercooler.

41. A method for operating a diesel engine system as a dual-fuel engine system, said diesel engine system comprising: a diesel engine comprising: an engine block ( 100 ); an engine controller ( 110 ); an engine mix input ( 120 ); an air filter ( 130 ); and, at least one turbocharger ( 140 ), and, a diesel fuel supply system ( 160 ) adapted to supply diesel fuel to said diesel engine, said diesel fuel supply system comprising: a diesel fuel storage container ( 450 ); a diesel fuel pump ( 460 ) in fluid connection with said diesel fuel storage container; and, a diesel fuel delivery passage ( 470 ) providing a fluid connection between an output of said diesel fuel pump and said engine mix input; said method comprising: providing a flow of heated air in a first passage that provides a fluid connection between a source of said flow and said engine mix input; injecting a secondary fuel selected from the group consisting of alcohols, ketones, ethers, and combinations thereof that is characterized by a net caloric value greater than 15 MJ/liter and a boiling point at a pressure of 1 atm that is greater than 50 °C into at least one first point in said flow of heated air, said injecting characterized by a first injection rate; maintaining said flow of heated air between said at least one first point and at least one second point located downstream of said first point at a temperature sufficient to ensure complete vaporization of said secondary fuel; delivering diesel fuel from said diesel fuel storage tank to said engine mix input via said diesel fuel supply system; and, determining a load on said engine; wherein said first injection rate is varied according to said load on said engine.

42. The method according to claim 41 , wherein said step of maintaining said flow of heated air at a temperature sufficient to ensure complete vaporization of said secondary fuel comprises placing said first passage in thermal contact with a heating body.

43. The method according to claim 41 , wherein: said diesel engine comprises a radiator ( 150 ); said step of maintaining said flow of heated air at a temperature sufficient to ensure complete vaporization of said secondary fuel comprises: passing said flow of heated air into which said secondary fuel has been injected through a primary side of a heat exchanger, said heat exchanger located downstream of said first point; and, passing engine coolant fluid from said engine block to said radiator via a secondary side of said heat exchanger, thereby using waste heat from said engine to heat said flow of heated air into which said secondary fuel has been injected; said method additionally comprises injecting said secondary fuel into said flow of heated air upstream of said heat exchanger, said injecting characterized by a second injection rate; said first injection rate is varied according to said load on said engine; and, said second injection rate is constant.

44. The method according to any one of claims 41 – 43 , wherein said method further comprises fixing at least one of said first injection rate and said second injection rate by use of a control system that is programmed to determine the engine load and determine the rate of injection of said secondary fuel from the measured engine load.

45. The method according to claim 44 , wherein said step of determining said load on said engine comprises determining said load on said engine from measurements of an electrical current of said engine.

46. The method according to any one of claims 41 – 45 , wherein at least one of said steps of injecting said secondary fuel comprises injecting said secondary fuel in pulses.

47. The method according to any one of claims 41 – 46 , wherein said secondary fuel is methanol.

48. A kit for adapting a diesel engine to dual diesel-methanol use, wherein said kit comprises: a first fluid connection means adapted to provide a fluid connection between a source of a flow of heated air and an engine mix input of said diesel engine; at least one injector; secondary fuel source connecting means for making a fluid connection between a source of a secondary fuel and said at least one injector; a control system for controlling rate and volume of injection of secondary fuel according to a measured load on the engine; and, electrical and data connection means for providing electrical and/or data connections from an electrical system of said diesel engine electrical system and said at least one injectors to said control system..

49. The kit according to claim 48 , wherein said kit further comprises a secondary fuel delivery system, said secondary fuel delivery system comprising at least one component selected from the group consisting of a secondary fuel tank, a secondary fuel pump, and fluid connection means for providing a fluid connection between a secondary fuel tank and said at least one injector.

50. The kit according to either one of claim 48 or claim 49 , wherein said kit further comprises: a heat exchanger, said heat exchanger comprising a primary side and a secondary side; second fluid connection means for making a fluid connection between an engine block of said engine and an entrance of said secondary side of said heat exchanger; and, third fluid connection means for making a fluid connection between said exit of said secondary side and a radiator of said engine; and, optionally: fourth fluid connection means for making a fluid connection between two points in said first fluid connection means; and, a three-way valve.