EP3092399A1 - Dual fuel internal combustion engine - Google Patents

Dual fuel internal combustion engine

Info

Publication number
EP3092399A1
EP3092399A1 EP14806730.9A EP14806730A EP3092399A1 EP 3092399 A1 EP3092399 A1 EP 3092399A1 EP 14806730 A EP14806730 A EP 14806730A EP 3092399 A1 EP3092399 A1 EP 3092399A1
Authority
EP
European Patent Office
Prior art keywords
combustion chamber
gasoline
mixture
fuel
air
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP14806730.9A
Other languages
German (de)
French (fr)
Inventor
Thomas Ma
Hua Zhao
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Brunel University
Original Assignee
Brunel University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Brunel University filed Critical Brunel University
Publication of EP3092399A1 publication Critical patent/EP3092399A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B43/00—Engines characterised by operating on gaseous fuels; Plants including such engines
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D13/00—Controlling the engine output power by varying inlet or exhaust valve operating characteristics, e.g. timing
    • F02D13/02—Controlling the engine output power by varying inlet or exhaust valve operating characteristics, e.g. timing during engine operation
    • F02D13/0261—Controlling the valve overlap
    • F02D13/0265—Negative valve overlap for temporarily storing residual gas in the cylinder
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B17/00—Engines characterised by means for effecting stratification of charge in cylinders
    • F02B17/005—Engines characterised by means for effecting stratification of charge in cylinders having direct injection in the combustion chamber
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B43/00—Engines characterised by operating on gaseous fuels; Plants including such engines
    • F02B43/02—Engines characterised by means for increasing operating efficiency
    • F02B43/04—Engines characterised by means for increasing operating efficiency for improving efficiency of combustion
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D13/00—Controlling the engine output power by varying inlet or exhaust valve operating characteristics, e.g. timing
    • F02D13/02—Controlling the engine output power by varying inlet or exhaust valve operating characteristics, e.g. timing during engine operation
    • F02D13/0203—Variable control of intake and exhaust valves
    • F02D13/0207—Variable control of intake and exhaust valves changing valve lift or valve lift and timing
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/0639—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed characterised by the type of fuels
    • F02D19/0642—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed characterised by the type of fuels at least one fuel being gaseous, the other fuels being gaseous or liquid at standard conditions
    • F02D19/0647—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed characterised by the type of fuels at least one fuel being gaseous, the other fuels being gaseous or liquid at standard conditions the gaseous fuel being liquefied petroleum gas [LPG], liquefied natural gas [LNG], compressed natural gas [CNG] or dimethyl ether [DME]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/08—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed simultaneously using pluralities of fuels
    • F02D19/081—Adjusting the fuel composition or mixing ratio; Transitioning from one fuel to the other
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0027—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures the fuel being gaseous
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0047—Controlling exhaust gas recirculation [EGR]
    • F02D41/006—Controlling exhaust gas recirculation [EGR] using internal EGR
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/30—Controlling fuel injection
    • F02D41/3011—Controlling fuel injection according to or using specific or several modes of combustion
    • F02D41/3017—Controlling fuel injection according to or using specific or several modes of combustion characterised by the mode(s) being used
    • F02D41/3023—Controlling fuel injection according to or using specific or several modes of combustion characterised by the mode(s) being used a mode being the stratified charge spark-ignited mode
    • F02D41/3029—Controlling fuel injection according to or using specific or several modes of combustion characterised by the mode(s) being used a mode being the stratified charge spark-ignited mode further comprising a homogeneous charge spark-ignited mode
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/30—Controlling fuel injection
    • F02D41/3094—Controlling fuel injection the fuel injection being effected by at least two different injectors, e.g. one in the intake manifold and one in the cylinder
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/01—Internal exhaust gas recirculation, i.e. wherein the residual exhaust gases are trapped in the cylinder or pushed back from the intake or the exhaust manifold into the combustion chamber without the use of additional passages
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B23/00—Other engines characterised by special shape or construction of combustion chambers to improve operation
    • F02B23/08—Other engines characterised by special shape or construction of combustion chambers to improve operation with positive ignition
    • F02B23/10—Other engines characterised by special shape or construction of combustion chambers to improve operation with positive ignition with separate admission of air and fuel into cylinder
    • F02B23/101—Other engines characterised by special shape or construction of combustion chambers to improve operation with positive ignition with separate admission of air and fuel into cylinder the injector being placed on or close to the cylinder centre axis, e.g. with mixture formation using spray guided concepts
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B37/00—Engines characterised by provision of pumps driven at least for part of the time by exhaust
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/0663—Details on the fuel supply system, e.g. tanks, valves, pipes, pumps, rails, injectors or mixers
    • F02D19/0686—Injectors
    • F02D19/0692—Arrangement of multiple injectors per combustion chamber
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0002—Controlling intake air
    • F02D41/0007—Controlling intake air for control of turbo-charged or super-charged engines
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/30—Use of alternative fuels, e.g. biofuels
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Definitions

  • the present invention relates of a dual fuel internal combustion engine operative to burn in a combustion chamber a main charge comprising a mixture of a gaseous hydrocarbon fuel, preferably natural gas, and air and to initiate combustion of the main charge by means of a liquid fuel that is injected directly into the combustion chamber.
  • gaseous fuels such as natural gas (which is predominantly methane), or propane which are readily available in large quantities and have the potential to burn more cleanly than gasoline or diesel with very low hydrocarbon an carbon monoxide
  • the compression ignition of the diesel fuel acts in the same way as a powerful spark, the homogeneous lean charge is burnt by flame propagation and this results in localised areas of high temperature that create NOx. Also if the compression temperature of the homogeneous lean charge is high, there is a risk of auto-ignition occurring
  • the present invention seeks therefore to provide an engine that can reliably ignite a lean mixture of a gaseous hydrocarbon fuel and air without having to resort to a high compression ratio.
  • a dual fuel internal combustion engine operative to burn in a combustion chamber a main charge comprising a mixture of a gaseous hydrocarbon fuel and air and to initiate combustion of the main charge by igniting a liquid fuel injected directly into the combustion chamber, characterised in that the liquid fuel is gasoline and a spark plug is provided within the combustion chamber to ignite the gasoline, and in that the gaseous hydrocarbon fuel and air mixture is a lean mixture that is pressurised by means of a turbocharger or supercharger.
  • a lean homogeneous mixture of gaseous hydrocarbon fuel and air is used in order to reduce NOx emissions and to avoid the need for a high compression ratio, combustion is initiated by injecting gasoline and igniting the gasoline using a spark.
  • the intake charge is pressurised by means of a turbocharger or supercharger.
  • the gasoline is injected directly into the combustion chamber in such a manner as to create a stratified charge with the gasoline concentrated in the vicinity of the spark plug.
  • the gaseous hydrocarbon fuel may suitably be introduced into the combustion chamber by port injection so that a homogeneously premixed mixture of gaseous fuel and air is admitted into the combustion chamber.
  • exhaust gases from a first combustion cycle are retained within, or reintroduced into, the combustion chamber during a
  • the selected compression ratio and the regulated amount of hot EGR set the temperature and pressure of the charge to a point slightly below the conditions necessary for auto- ignition.
  • the spark ignition of the injected gasoline then raises the temperature and pressure sufficiently to create the necessary conditions for auto-ignition of the lean homogenous mixture, thereby enabling the timing of the auto- ignition to be controlled.
  • the gaseous fuel is preferably natural gas but other hydrocarbon gases such as propane may be used.
  • a method of operating an internal combustion engine having a combustion chamber which comprises filling the combustion chamber homogeneously with a lean mixture of a gaseous hydrocarbon fuel and ambient air, the pressure of the mixture being greater than the ambient atmospheric pressure, compressing the mixture, injecting gasoline directly into the combustion chamber towards the end of the compression step and igniting the gasoline and air charge by means of a spark plug to initiate combustion of the gaseous hydrocarbon fuel and air charge.
  • Figure 1 is a schematic diagram of one cylinder of an internal combustion engine having a gasoline direct injector and at least one natural gas injector located in the intake port, and
  • Figures 2a to 2d show various valve timing diagrams to achieve high temperature internal EGR (internal exhaust gas recirculation) in a four stroke engine.
  • EGR internal exhaust gas recirculation
  • Figure 1 shows a schematic view of a cylinder 10 of a reciprocating internal combustion engine operating with a 2- stroke cycle or 4-stroke cycle.
  • a piston 12 connected to a crankshaft by a connecting rod 14, reciprocates within the cylinder 10 to define a variable volume working chamber 16.
  • the working chamber 16 has at least one intake valve 22 operated by a cam 28 and one exhaust valve 24 operated by a cam 30.
  • a direct injection liquid fuel injector 20 in the cylinder head injects liquid fuel directly into the working chamber 16 and a spark plug 18 is provided for the spark ignition of the injected liquid fuel in the working chamber.
  • a port gaseous fuel injector 26 supplies natural gas into the intake port 32 to form a premixed homogeneous lean mixture of natural gas and air.
  • the engine has at least one turbocharger and/or supercharger which is not shown in the drawing. Turbochargers and superchargers are well known equipment and may be assumed to operate in a conventional manner.
  • the injector 20 is shown as being positioned immediately adjacent the spark plug 18 but it may
  • the engine may also have an exhaust back pressure valve which is not shown in the drawing.
  • the back pressure valve serves to increase the exhaust back pressure in the engine in order to promote sufficient internal EGR into the pressurised intake charge when required.
  • the natural gas injected by the injector 26 mixes with pressurised air in the intake port 32 and fills the working chamber 16 with a premixed homogeneous lean mixture of gaseous fuel and air at the commencement of the compression process.
  • Direct injection of gasoline from the injector 20 is timed to occur in the later part of the compression stroke in order to form a stratified charge with a rich or near stoichiometric gasoline and air region near the spark plug 18, which is optimised both by appropriate positioning and orientation of the injector 20 and the geometry of the piston crown and cylinder head.
  • Combustion starts with spark ignition of the stratified gasoline and air mixture.
  • the resulting combustion kernel formed around the spark plug then spreads to the homogeneous lean gaseous fuel and air mixture.
  • the homogeneous lean gaseous fuel and air charge may be preheated by mixing with hot EGR gases, in the manner to be explained below. Its temperature will rise during the compression stroke to a value near TDC that is just short of the auto-ignition temperature of the gaseous fuel and air mixture. The increased temperature and pressure created by the ignition of the gasoline fuel will then raise the temperature to above the auto-ignition point to cause the entire contents of the combustion chamber to auto-ignite and undergo low temperature combustion.
  • Figure 2 shows various known valve timing diagrams for obtaining hot internal EGR. In all these valve timing diagrams, exhaust event are shown in solid lines and intake events in dashed lines.
  • hot internal EGR is achieved by a secondary opening of the exhaust valve during the intake stroke .
  • hot internal EGR is achieved by a secondary opening of the intake valve during the exhaust stroke .
  • early exhaust valve closing results in a high proportion of hot exhaust gases being retained within the combustion chamber. The intake valve does not open until after TDC to prevent the compressed residual gases from being expelled through the intake valve into the intake port.
  • hot internal EGR is achieved by a large overlap between the opening periods of the intake and exhaust valves .
  • Internal EGR can also be implemented in a known manner in two-stroke engines .

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Output Control And Ontrol Of Special Type Engine (AREA)
  • Combustion Methods Of Internal-Combustion Engines (AREA)

Abstract

A dual fuel internal combustion engine is disclosed that is operative to burn in a combustion chamber a main charge comprising a mixture of a gaseous hydrocarbon fuel and air and to initiate combustion of the main charge by igniting a liquid fuel injected directly into the combustion chamber. In the invention, the liquid fuel is gasoline and a spark plug is provided within the combustion chamber to ignite the gasoline. The gaseous hydrocarbon fuel and air mixture is a lean mixture that is pressurised by means of a turbocharger or supercharger.

Description

DUAL FUEL INTERNAL COMBUSTION ENGINE
Field of the invention The present invention relates of a dual fuel internal combustion engine operative to burn in a combustion chamber a main charge comprising a mixture of a gaseous hydrocarbon fuel, preferably natural gas, and air and to initiate combustion of the main charge by means of a liquid fuel that is injected directly into the combustion chamber.
Background of the invention
It is desirable to be able to run an engine on gaseous fuels, such as natural gas (which is predominantly methane), or propane which are readily available in large quantities and have the potential to burn more cleanly than gasoline or diesel with very low hydrocarbon an carbon monoxide
emissions. However, using normal combustion, engines running on such gases will produce NOx and it is desirable to use leaner mixtures (below stoichiometry) in order to reduce NOx by reducing combustion temperature.
The problem with lean mixtures is that they are difficult to ignite reliably by spark ignition alone. For this reason, dual fuel engines have previously been proposed that use diesel injection to initiate combustion of the lean gaseous fuel and air mixture. Such engines must of necessity employ a high compression ratio for the injected diesel fuel to ignite by compression ignition.
If the compression ignition of the diesel fuel acts in the same way as a powerful spark, the homogeneous lean charge is burnt by flame propagation and this results in localised areas of high temperature that create NOx. Also if the compression temperature of the homogeneous lean charge is high, there is a risk of auto-ignition occurring
prematurely and causing engine damage.
Object of the invention
The present invention seeks therefore to provide an engine that can reliably ignite a lean mixture of a gaseous hydrocarbon fuel and air without having to resort to a high compression ratio.
Summary of the invention
According to a first aspect of the present invention, there is provided a dual fuel internal combustion engine operative to burn in a combustion chamber a main charge comprising a mixture of a gaseous hydrocarbon fuel and air and to initiate combustion of the main charge by igniting a liquid fuel injected directly into the combustion chamber, characterised in that the liquid fuel is gasoline and a spark plug is provided within the combustion chamber to ignite the gasoline, and in that the gaseous hydrocarbon fuel and air mixture is a lean mixture that is pressurised by means of a turbocharger or supercharger. In the invention, a lean homogeneous mixture of gaseous hydrocarbon fuel and air is used in order to reduce NOx emissions and to avoid the need for a high compression ratio, combustion is initiated by injecting gasoline and igniting the gasoline using a spark. In order to compensate for the reduced output power that results from burning a weak mixture in a cylinder having a low compression ratio, the intake charge is pressurised by means of a turbocharger or supercharger.
Conveniently, the gasoline is injected directly into the combustion chamber in such a manner as to create a stratified charge with the gasoline concentrated in the vicinity of the spark plug.
The gaseous hydrocarbon fuel may suitably be introduced into the combustion chamber by port injection so that a homogeneously premixed mixture of gaseous fuel and air is admitted into the combustion chamber.
It is desirable to promote auto-ignition of the homogeneous lean charge, which is a known low temperature combustion process resulting in negligible amounts of NOx . Such combustion can be achieved by a combination of a high concentration of hot EGR and low compression ratio but the timing of the auto-ignition is unpredictable and may occur prematurely resulting in engine damage.
In some embodiments of the invention, exhaust gases from a first combustion cycle are retained within, or reintroduced into, the combustion chamber during a
subsequent cycle to raise the temperature of the charge in the subsequent cycle so as to promote auto-ignition of the homogeneous gaseous fuel and air mixture but only subsequent to spark ignition of the gasoline mixture. In this case, the selected compression ratio and the regulated amount of hot EGR set the temperature and pressure of the charge to a point slightly below the conditions necessary for auto- ignition. The spark ignition of the injected gasoline then raises the temperature and pressure sufficiently to create the necessary conditions for auto-ignition of the lean homogenous mixture, thereby enabling the timing of the auto- ignition to be controlled.
The gaseous fuel is preferably natural gas but other hydrocarbon gases such as propane may be used.
The invention is equally applicable to two stroke and four stroke engines . According to a second aspect of the invention, there is provided a method of operating an internal combustion engine having a combustion chamber which comprises filling the combustion chamber homogeneously with a lean mixture of a gaseous hydrocarbon fuel and ambient air, the pressure of the mixture being greater than the ambient atmospheric pressure, compressing the mixture, injecting gasoline directly into the combustion chamber towards the end of the compression step and igniting the gasoline and air charge by means of a spark plug to initiate combustion of the gaseous hydrocarbon fuel and air charge.
Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which :
Figure 1 is a schematic diagram of one cylinder of an internal combustion engine having a gasoline direct injector and at least one natural gas injector located in the intake port, and
Figures 2a to 2d show various valve timing diagrams to achieve high temperature internal EGR (internal exhaust gas recirculation) in a four stroke engine.
Detailed description of the preferred embodiment ( s )
Figure 1 shows a schematic view of a cylinder 10 of a reciprocating internal combustion engine operating with a 2- stroke cycle or 4-stroke cycle. A piston 12, connected to a crankshaft by a connecting rod 14, reciprocates within the cylinder 10 to define a variable volume working chamber 16. The working chamber 16 has at least one intake valve 22 operated by a cam 28 and one exhaust valve 24 operated by a cam 30. A direct injection liquid fuel injector 20 in the cylinder head injects liquid fuel directly into the working chamber 16 and a spark plug 18 is provided for the spark ignition of the injected liquid fuel in the working chamber.
A port gaseous fuel injector 26 supplies natural gas into the intake port 32 to form a premixed homogeneous lean mixture of natural gas and air. The engine has at least one turbocharger and/or supercharger which is not shown in the drawing. Turbochargers and superchargers are well known equipment and may be assumed to operate in a conventional manner. The injector 20 is shown as being positioned immediately adjacent the spark plug 18 but it may
alternatively be possible to position an injector in the side of the combustion chamber and to rely on air motion to transport the injected liquid fuel to the vicinity of the spark plug. The engine may also have an exhaust back pressure valve which is not shown in the drawing. The back pressure valve serves to increase the exhaust back pressure in the engine in order to promote sufficient internal EGR into the pressurised intake charge when required.
The natural gas injected by the injector 26 mixes with pressurised air in the intake port 32 and fills the working chamber 16 with a premixed homogeneous lean mixture of gaseous fuel and air at the commencement of the compression process. Direct injection of gasoline from the injector 20 is timed to occur in the later part of the compression stroke in order to form a stratified charge with a rich or near stoichiometric gasoline and air region near the spark plug 18, which is optimised both by appropriate positioning and orientation of the injector 20 and the geometry of the piston crown and cylinder head. Combustion starts with spark ignition of the stratified gasoline and air mixture. The resulting combustion kernel formed around the spark plug then spreads to the homogeneous lean gaseous fuel and air mixture. The homogeneous lean gaseous fuel and air charge may be preheated by mixing with hot EGR gases, in the manner to be explained below. Its temperature will rise during the compression stroke to a value near TDC that is just short of the auto-ignition temperature of the gaseous fuel and air mixture. The increased temperature and pressure created by the ignition of the gasoline fuel will then raise the temperature to above the auto-ignition point to cause the entire contents of the combustion chamber to auto-ignite and undergo low temperature combustion.
Figure 2 shows various known valve timing diagrams for obtaining hot internal EGR. In all these valve timing diagrams, exhaust event are shown in solid lines and intake events in dashed lines.
In Figure 2a, hot internal EGR is achieved by a secondary opening of the exhaust valve during the intake stroke .
In Figure 2b, hot internal EGR is achieved by a secondary opening of the intake valve during the exhaust stroke . In Figure 2c, early exhaust valve closing results in a high proportion of hot exhaust gases being retained within the combustion chamber. The intake valve does not open until after TDC to prevent the compressed residual gases from being expelled through the intake valve into the intake port.
In Figure 2d, hot internal EGR is achieved by a large overlap between the opening periods of the intake and exhaust valves .
Internal EGR can also be implemented in a known manner in two-stroke engines .

Claims

1. A dual fuel internal combustion engine operative to burn in a combustion chamber (16) a main charge
comprising a mixture of a gaseous hydrocarbon fuel and air and to initiate combustion of the main charge by igniting a liquid fuel injected directly into the combustion chamber, characterised in that the liquid fuel is gasoline and a spark plug (18) is provided within the combustion chamber to ignite the gasoline, and in that the gaseous hydrocarbon fuel and air mixture is a lean mixture that is pressurised by means of a turbocharger or supercharger.
2. A dual fuel internal combustion engine as claimed in claim 1, wherein an injector (20) is provided to inject the gasoline directly into the combustion chamber in such a manner as to create a stratified charge with the gasoline concentrated in the vicinity of the spark plug.
3. A dual fuel internal combustion engine as claimed in Claim 1 or 2, wherein the gaseous hydrocarbon fuel is introduced into the combustion chamber by an injector (26) located in an intake port (32) so that a homogeneously premixed mixture of gaseous hydrocarbon fuel and air is admitted into the combustion chamber (16) .
4. A dual fuel internal combustion engine as claimed in claim 3, wherein hot exhaust gases from a first
combustion cycle are retained within, or reintroduced into, the combustion chamber during a subsequent cycle to raise the temperature of the charge in the subsequent cycle so as to promote auto-ignition of the homogeneous gaseous fuel and air mixture but only subsequent to spark ignition of the gasoline mixture.
5. A dual fuel internal combustion engine as claimed in claim 4, wherein the reintroduction of hot exhaust gases is achieved by simultaneous opening of intake and exhaust valves of the combustion chamber.
6. A dual fuel internal combustion engine as claimed in any preceding claim, wherein the gaseous fuel is natural gas .
7. A dual fuel internal combustion engine as claimed in any preceding claim, wherein the engine is a four-stroke engine.
8. A dual fuel internal combustion engine as claimed in any one of claims 1 to 6, wherein the engine is a two- stroke engine.
9. A method of operating an internal combustion engine having a combustion chamber which comprises filling the combustion chamber homogeneously with a lean mixture of a gaseous hydrocarbon fuel and ambient air, the pressure of the mixture being greater than the ambient atmospheric pressure, compressing the mixture, injecting gasoline directly into the combustion chamber towards the end of the compression step and igniting the gasoline and air charge by means of a spark plug to initiate combustion of the gaseous hydrocarbon fuel and air charge.
10. A method as claimed in claim 9, wherein the direct injection of gasoline serves to create a stratified gasoline and air charge within the combustion chamber, a richer region of the latter charge being located in the vicinity of the spark plug.
EP14806730.9A 2013-11-05 2014-10-31 Dual fuel internal combustion engine Withdrawn EP3092399A1 (en)

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GB1319554.0A GB2520017A (en) 2013-11-05 2013-11-05 Dual fuel internal combustion engine
PCT/IB2014/065750 WO2015068090A1 (en) 2013-11-05 2014-10-31 Dual fuel internal combustion engine

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