AU2013207569A1 - Dual Fuel Engine Control - Google Patents

Abstract

A kit of parts for modifying a dual fuel engine has a liquid cooled intercooler for input air to the engine, a heat exchanger coupled to the intercooler in which cold liquified gas fuel absorbs heat from the intercooler as the fuel changes from liquid to gaseous state, unions for connecting the exchanger to a fuel tank to accept liquid fuel and for connecting the exchanger to the engine manifold. Improvement in the use of the two fuels arise from the addition to the OEM electronic control unit of a supplementary electronic control unit, the latter detecting the same engine parameters as the OEM unit but additionally measuring throttle opening, gas pressure and gas temperature in order to vary the ratio of diesel to gas, whereby when the engine idles the injectors admit gas to render the fuel mix richer in gas than diesel. A kit of parts for modifying the operation of the OEM ECU is described. 2013-07-16,C:\UsersiShadeeDocumnnts SPECIFICATIONS\gastechcap 717.wpd,1 2

Description

1 TITLE OF INVENTION Dual Fuel Engine Control TECHNICAL FIELD [0001] This invention concerns the electronic control of dual fuel internal combustion engines. BACKGROUND [0002] The invention uses a hydrocarbon gas, namely liquefied natural gas [LNG] or compressed natural gas [CNG]. The hydrocarbon gas is injected into the inlet manifold, and delivered to the engine, in which it is controlled by an electronic control unit [ECU]. Thus the operator benefits from the economy of LNG or CNG fuel. Turbocharging is standard for such engines. Compression of the inflowing air increases its temperature and reduces its density. It is not unusual for the inlet air temperature to reach in excess of 70 degrees Celsius. This heat level is recorded even with the intervention of an air-to-air intercooler because intercoolers are cooled by the passage of air moving through them and, when the vehicle is in a queue or is stationery, the intercooler effectiveness falls. [0003] In a typical truck engine no throttle is fitted because the power is controlled by the quantity of diesel injected into the engine cylinder. Diesel self ignites near to the end of the compression stroke and continues to burn as more fuel is injected into the cylinder. For efficient power generation sufficient air must be present otherwise black smoke appears in the exhaust. [0004] EP0557927 describes a dual fuel engine which utilises a governor and a single electronic control unit (ECU) to control the ratio of gas to diesel. [0005] EP1546532 describes the conversion of a diesel engine to diesel plus gas operation in which control is by ECU. When the ECU is original equipment the engine is mapped and the ratio collected to determine how much gas to add to the diesel. The ECU is self- calibrating and 2013-07-16,C-\Users\Sharlene\DocumenIs\$PECIFICATIONSasteccap1 71T7wpd. i 2 ensures that minimal gas is added. [0006] US20120310509 uses electronically controlled liquid fuel injectors and an ECU which adjusts pump pulse duration. The ECU is part of the original equipment. Table 1 in the patent shows the percentages of natural gas at different loads. A second ECU meters gas supply for diesel fuel operation. [0007] EP2203633 describes the use of diesel and methane. A first ECU senses and emits output signals for the engine when running on diesel and a second ECU modifies the outputs when gas is admitted. The second ECU is a sleeve unit which intercepts signals from the parameter sensor on their way to the first ECU and modifies the quantity of diesel injected. The engine can swap modes. SUMMARY OF INVENTION [0008] The apparatus aspect of the invention provides a kit for modifying an engine using gas fuel and an intercooler, comprising a liquid cooled intercooler for input air to the engine, a heat exchanger coupled to the intercooler in which cold liquified gas fuel absorbs heat from the intercooler as the fuel changes from liquid to gaseous state, unions for connecting the exchanger to a fuel tank to accept liquid fuel and for connecting the exchanger to the engine manifold. The kit may include a header tank and a pump for circulating coolant from the exchanger to the intercooler. [0009] The use aspect of the invention presents the use of liquified gas fuel to cool the input air to an engine using gas fuel. A further apparatus aspect of the invention provides a cooling system for supplementing the air to air intercooler of a turbocharged engine, comprising a cooler for turbocharged air, a cooling circuit for the cooler, a heat exchanger in the cooling circuit, a liquid fuel inlet to the heat exchanger, a gas fuel outlet from the heat exchanger to the engine, whereby the cooling capacity of the phase change of the liquid fuel to gas is available to cool the turbocharged air. 2013-07-16,C:\Users\Sharlene\Documents\SPECIFICAT[ONS\gastechcapl 717.wpd,2 3 [0010] When large capacity engines operate continually at large throttle openings the cost of fuel is an important economic factor to the operator and the availability of fuel is a concern particularly in remote areas. It is an advantage if an engine can deliver adequate power from a choice of fuels, for example diesel and hydrocarbon gas. Many large diesel engines suffer power reduction as the diesel fuel temperature rises and or the air temperature entering the engine rises even at modest ambient air temperatures. [0011] If the engine is to use diesel and hydrocarbon gas as a mix the ratio must change to optimise the combination. The engine therefore is mapped, taking measurements during dynamometer tests to determine the operating values across the rpm/load range of the engine. These parameters are data for the ECU which controls the operation of engine when running on a single fuel but the use of an additional fuel adds to the parameters and supplementary ECU becomes necessary. [0012] The first apparatus aspect of the invention provides a dual fuel multi-cylinder internal combustion engine operable to accept diesel and hydrocarbon gas fuels, having an OEM electronic control unit for controlling the performance of the diesel injectors, the inlet manifold with multiple ports for admitting hydrocarbon gas, a primary heat exchanger for changing liquid hydrocarbon into gaseous fuel, a secondary heat exchanger for cooling the diesel fuel by heat exchange with the liquified hydrocarbon gas, multiple sensors for detecting the same engine parameters as the OEM electronic control unit including throttle opening, an additional sensor for hydrocarbon gas pressure, an additional sensor for hydrocarbon gas temperature, and a supplementary electronic control unit for varying the ratio of diesel to hydrocarbon gas in response to the throttle opening in dependence upon the above parameters, whereby when the engine idles the injectors admit gas to render the fuel mix richer in hydrocarbon gas than diesel. [0013] The parameters utilised by the supplementary electronic control unit may comprise air temperature coolant temperature, gas pressure, gas temperature, diesel temperature, lubricant pressure, lubricant temperature and diesel temperature. [0014] The flow of air and hydrocarbon gas in the manifold may be controlled by a motorised 2013-07-16,C:\Users\Shadene\Docuients\SPECIFICATIONS\gastech cap177.wpd,3 4 valve in turn controlled by the supplementary electronic control unit. [0015] The diesel injectors' performance may be controlled by the combined outputs of the OEM and supplementary electronic control units. [0016] The diesel heat exchanger for cooling the diesel may be in series with the heat exchanger which cools the air charge to the inlet manifold. [0017] The diesel heat exchanger is preferably downstream of the heat exchanger for cooling the air charge to the inlet manifold. [0018] Long individual intake pipes are fitted to ensure cylinder to cylinder air mass induced equally. This is important to ensure equal Air Fuel ratio in between cylinders remains equal. [0019] Fuel delivery is via sequentially timed port gas injection. This enables reduced gas emission loss during valve overlap period and superior transient Air Fuel Ratio control during acceleration. [0020] Operators of vehicles can correct the engine to accept hydrocarbon gas fuel by using a kit of parts. [0021] The second apparatus aspect of the invention provides a kit of parts for converting a hydrocarbon gas engine to a dual fuel engine consisting of a diesel fuel cooler with pipes to connect the cooler inlet to a source of diesel fuel and to connect the cooler output to diesel injectors, a manifold with at least one gas port for the admission of hydrocarbon gas, a motorised valve in the manifold for adjusting manifold flow, a sensor for hydrocarbon gas pressure, a sensor for hydrocarbon gas temperature, an electronic control unit for supplementing the OEM electronic unit in the gas engine to vary the proportion of diesel/hydrocarbon gas in the fuel mix in response to throttle opening. [0022] A primary heat exchanger is fitted to transform the liquid methane into a gaseous state 20 13-07-16,C:\Uses\Shadene\Documents\SPECIFICATIONSgastechsap1x717.wpd,4 5 utilizing the heat from the warm air exiting from the originally fitted intercooler. This lowers the inlet air 20-30 degrees Celsius that supplies air to the cylinders and thereby reducing the combustion process vulnerability to ping or knock. The lower air temperature reduces the end of compression temperature and gives a smooth combustion process. [0023] Cooling the diesel fuel with its own heat exchanger and utilizing the LNG that has passed through the primary exchanger ensures that the all the LNG has changed its state to gaseous and that the methane gas temperature is above 10 degrees Celsius. This lowers the diesel temperature by about 20-40 degrees Celsius and reduces engine ping or knock in the combustion process. Tests have shown that more stable smooth combustion takes place. [0024] These two installed heat exchangers allows the dual fuel diesel/LNG engine to maintain the rated engine power at high ambient temperatures. [0025] If any fault occurs in the control imposed by the supplementary ECU, the operator reverts to control by the OEM electronic unit. [0026] The electronic control unit may comprise an ECU for diesel fuel admission to the injectors and a separate ECU for gas admission to the gas ports in the manifold. Advantageous Effects of Invention [0027] 1. Being able to utilise two different fuels eases availability problems especially in remote areas. [0028] 2. Overall fuel economy is improved. BRIEF DESCRIPTION OF DRAWINGS [0029] Embodiments of the invention are now described with reference to the accompanying drawings in which: 2013-07-16,C:\U 5sher\ edDocuments\SPECIFICATIONSigastecap1717.npd,5 6 [0030] Figure 1 is a flow diagram. [0031] Figure 2 is a diagram of the circuit modification to Figure 1 showing the position of the diesel cooler. [0032] Figure 3 is a diagram of an engine electronic control unit as supplied with a multi cylinder diesel engine and a supplementary electronic control unit. [0033] Figure 4 is a perspective of the manifold indicted in Figure 3. [0034] Figure 5 is a perspective of the throttle valve attached to the manifold of Figure 4. [0035] Figure 6 is a table showing fuel ratios at 75% throttle. [0036] Figure 7 is a table showing fuel mix ratios at 25% throttle. DESCRIPTION OF EMBODIMENTS [0037] Referring to the drawing, a 141 truck engine (not shown) with a conventional turbo charger delivers air at a pressure through an air-to-air intercooler 2. A duct 4 directs the compressed air at up to 70-75 degrees Celsius through a water-cooled intercooler 6 then to the engine. The water-cooled cooler 6 is tubular (500mm x 200mm) and delivers cooler air at 20-25 degrees Celsius lower than the incoming charge air before it reaches the engine intake manifold. [0038] The water-fuelled cooler 6 has a cold coolant inlet 8 and a warm coolant outlet 10 which returns coolant to a header tank 12. The contents of the header tank create extra volume for the system to prime the coolant pump 14, which feeds the heat exchanger 16. This compartment is 900mm x 200mm and houses a multi-passage heat exchanger element which receives LNG at -160 degrees Celsius from an insulated fuel tank (not shown). Contact with the warm coolant of the exchanger 16 changes the liquid to the gaseous form, at which point the liberated gas leaves the exchanger through the outlet 18, passes through a gas filter 20 and reaches the regulator 22 20 13-07-16,C-\Us s\SharndDocumntnls\SPECIFICATION\gastechcap1 717wpd,6 7 before entering the injector fuel manifold. [0039] The continuous flow of liquid fuel to the exchanger provides a steady heat sink capable of cooling the coolant arriving from the intercooler by about 20 degrees Celsius with a consequent density increase in air for the engine. The advantage of increased inlet-air cooling is evident when the truck travels up a sustained incline: with such extra cooling the truck engine's power is sustained. With charge-air temperatures normally at 25-45 degrees Celsius, but which can reach up to 70-75 degrees Celsius at maximum load, it falls to between 45 degrees Celsius and 55 degrees Celsius with the addition of the heat exchanger 16. [0040] Referring now to Figure 2, an air to air intercooler 2 supplies pre-cooled air to water cooled heat exchanger 6. Exchanger 6 further cools the pressurised air blown into the inlet manifold (not shown) which is cooled by exchange with the LNG heat exchanger 16. The LNG conduit 24 leaves exchanger 16 and enters diesel oil cooler 26 and transfers fuel to filter 20. The cooled diesel passes through conduit 28 to be directed to the injector pumps beside the engine. [0041] Referring now to Figure 3, the ECU 30 supplied with the engine by the manufacturer as original equipment is in a housing fixed to engine exterior and connected by electrical leads to engine components. In a six cylinder engine there is a lead 32 from the ECU 30 to each injector to vary the injector pulse. A lead 34 connects to the accelerator pedal sensor 36. The ECU 30 collects input from Sync sensor 38, reference sensor 40, diesel temperature 42, oil temperature 44, oil pressure 46, coolant temperature 48, air temperature 50 and map sensor 52. These inputs allow the unit 30 to change the pulse period of the injectors to respond to the throttle opening. [0042] Referring to Figures 4 and 5, each group of cylinders in the engine receives air from the booster, diesel fuel from the fuel cooler and gas from the heat exchanger. Manifold 52 provides a connnon air supply to individual inlet passages 54. A gas feed 56 discharges into each passage 54. The entry end of the manifold is fitted with a throttle valve 60 consisting of a butterfly valve housing 62, the spindle 64 of valve 66 being rotated by a servo motor contained in the P-shaped housing 68. Cable 70 supplies current to this drive by wire throttle which is commanded from the supplementary ECU 72 to maintain a maximum lean A/F ratio. The throttle controls the 20130746,C:\Users\Shlene\Documenis\SPECIFICATIONSkgastechcap171ipd,7 8 amount of air entering the engine. If the Air Fuel ratio is too lean (no throttle control), then the natural gas (methane) that has started to burn after the pilot diesel injection, will burn too slowly and incompletely and therefore green house emission will rise as well as fuel consumption. The substitution ratio of methane versus diesel falls and the cost benefit is significantly reduced. By having this throttle control the substitution of methane can be utilised in almost all load conditions even at idle. [0043] The supplementary ECU 54 requires inputs from the same sensors referred to above and in addition there is input from hydrocarbon gas pressure sensor 56 and gas temperature sensor 58. The ECU 54 has leads 60 to the six diesel injectors, leads 62 to six gas injectors 64 in the manifold and a lead 66 to the servo meter (not shown) which rotates the flap valve 68 in the manifold. The supplementary ECU 54 is connected to the injectors by sharing the lead used by the ECU 30 and in a variant a changeover switch allows the operator to cancel the sharing. All parameters are controlled via the supplementary ECU 54 and the ECU 30 is only monitoring the engine parameters but not controlling. [0044] If any problems were to arise the original ECU 30 would take over control of the engine and run under full diesel mode, and the supplementary ECU 54 switched off. [0045] Referring now to the Table in Figure 4, at 75% throttle and 1500rpm the fuel mix is 20% diesel, 80% gas. [0046] Referring now to the Table in Figure 5, at 25% throttle and 1500rpm the mix is 3% diesel and 97% gas. As vehicles idle for a substantial portion of their journey, this saves on emissions. [0047] The effect of the combination of the algorithm controlling diesel/gas ratio and ECU adjustment of the motorised throttle value over the power range is as follows, when the dual fuel engine is delivering full power a pilot (small ) amount of diesel is injected into the cylinder and a large amount of secondary fuel is added via inlet manifold. The sum of fuels added will always need to be rich enough for the burn rate to be of sufficient speed to create the maximum cylinder 2013-07- 16,C:\Users\$bared1ocumnts\$PEC1FICAIONS ~gastechcpt717.opd,8 9 pressure early in the power stroke. [0048] At mid-power level, say 50% power, a pilot amount of diesel is again injected into the cylinder and a reduced amount of secondary fuel added. Obviously a power reduction but also a leaner Air fuel ratio. The burn rate has also slowed down but is still sufficient to burn properly. [0049] At mid to low power level, say 25% power, a pilot amount of diesel is again injected into the cylinder, but this time a much lesser amount of secondary fuel is added in inlet manifold. This time the power reduction is greater that would be expected from the lesser amount of fuel. This is because the burn rate has slowed and incomplete combustion has occurred and much lower cylinder temperatures and pressures. The air fuel ratio is too lean. But restriction in the inlet manifold is imposed (add throttle) this reduces the amount of air entering the cylinder and the air fuel ratio will richen. Now combustion burn rate will improve, combustion efficiency will increase and emissions reduced. [0050] At low power levels, say <10%, the proportion of pilot injection to added secondary fuel increases and the typical diesel characteristics dominate. The air flow is still restricted but combustion of the secondary fuel is enhanced by the combustion of diesel fuel. [0051] It is to be understood that the word "comprising" as used throughout the specification is to be interpreted in its inclusive form, ie. use of the word "comprising" does not exclude the addition of other elements. [0052] It is to be understood that various modifications of and/or additions to the invention can be made without departing from the basic nature of the invention. These modifications and/or additions are therefore considered to fall within the scope of the invention. 2013-07-6,C:\sers\Sharene\Docunens\PECIlCAlONS~gasteccap1717.wpd,9

Claims (9)

1. A dual fuel multi-cylinder internal combustion engine modified by the addition of a kit to accept diesel and hydrocarbon gas having an OEM electronic control unit for controlling the performance of the diesel injectors, an inlet manifold with multiple parts for admitting hydrocarbon gas, a primary heat exchanger for changing liquid hydrocarbon into gaseous fuel, a secondary heat exchanger for cooling the diesel fuel by heat exchange with the liquified hydrocarbon gas, multiple sensors for detecting the same engine parameters as the OEM electronic control unit including throttle position, an additional sensor for hydrocarbon gas pressure, an additional sensor for hydrocarbon gas temperature, a motorised throttle valve for inlet air control and a supplementary electronic control for releasing sufficient diesel to cause ignition over the power range but varying the ratio of diesel to hydrocarbon gas in response to power demand in dependence on the above parameters, whereby the throttle position is compressed to the required power output and the throttle valve position adjusts the air supply to cause efficient burn.

2. A dual fuel engine as claimed in Claim 1, wherein the parameters utilised by the supplementary electronic control unit are air temperature coolant temperature, gas pressure, gas temperature, diesel temperature, lubricant pressure, lubricant temperature and diesel temperature.

3. A dual fuel engine as claimed in Claim 1 or 2, wherein the flow of air and hydrocarbon gas in the manifold is controlled by a motorised valve in turn controlled by the supplementary electronic control unit.

4. A dual fuel engine as claimed in any one of Claims 1-3, wherein the diesel injectors' performance is controlled by the combined outputs of the OEM and supplementary electronic control units.

5. A dual fuel engine as claimed in Claim 7, wherein the diesel heat exchanger downstream of the heat exchanger for cooling the air charge to the inlet manifold.

2013-07-16,C:\Users\ShadenelDocuments\SPECIFICAI[ONS\gastech cap 1717.wpd, 10 11

6. A dual fuel multi-cylinder internal combustion engine as claimed in Claim 3, wherein the motorised valve is a rotary valve, the rotary position of which is reported to the ECU.

7. A dual fuel engine as claimed in any one of Claims 1-6, wherein the engine capacity is 2.5-131.

8. A kit of parts for converting a diesel engine to a dual fuel engine where the extra fuel is hydrocarbon gas consisting of a diesel fuel cooler with unions to connect the cooler inlet to a source of diesel fuel and to connect the cooler output to diesel injectors, a manifold with a gas post for each cylinder, a motororised valve controlling air input to the manifold, a sensor for gas pressure, a sensor for gas temperature, an electronic control unit for supplementing the OEM electronic unit in the diesel engine to vary the proportion of diesel to gas in the fuel mix and to adjust to the motorised valve in relation to the power demand to give efficient burn.

9. A dual fuel multi-cylinder internal combustion engine operable to accept diesel and hydrocarbon gas fuel, having a electronic control unit for controlling the performance of diesel injectors, an inlet manifold with multiple ports for admitting hydrocarbon gas, multiple sensors for detecting accelerator pedal position, which unit utilises parameters which follow synchronicity, gas pressure, gas temperature, diesel temperature, oil temperature, oil pressure, coolant temperature, air temperature, and mapping in order to change the pulse period of the diesel injectors to respond to throttle opening, a motorised throttle valve controlling air supply to the manifold, whereby the electronic control releases sufficient diesel over the speed range to cause diesel injection, the algorithm controls the addition of hydrocarbon gas to meet power requirements and adjusts the throttle valve to ensure sufficient burn. 2013-07-16,C:\Uers\Shden'Documents\SPECIFICATIONSgastech.cap1 717.wpd, il