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WO2015132459A1 - Piston engine and method for operating a piston engine - Google Patents

Piston engine and method for operating a piston engine Download PDF

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Publication number
WO2015132459A1
WO2015132459A1 PCT/FI2015/050103 FI2015050103W WO2015132459A1 WO 2015132459 A1 WO2015132459 A1 WO 2015132459A1 FI 2015050103 W FI2015050103 W FI 2015050103W WO 2015132459 A1 WO2015132459 A1 WO 2015132459A1
Authority
WO
WIPO (PCT)
Prior art keywords
fuel
engine
operating mode
cylinder
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.)
Ceased
Application number
PCT/FI2015/050103
Other languages
French (fr)
Inventor
Ingemar Nylund
Johan DANBRATT
Joel KNIF
Lennart Haraldson
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.)
Wartsila Finland Oy
Original Assignee
Wartsila Finland Oy
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 Wartsila Finland Oy filed Critical Wartsila Finland Oy
Publication of WO2015132459A1 publication Critical patent/WO2015132459A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • 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
    • 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
    • F02D19/0649—Liquid fuels having different boiling temperatures, volatilities, densities, viscosities, cetane or octane numbers
    • F02D19/0652—Biofuels, e.g. plant oils
    • F02D19/0655—Biofuels, e.g. plant oils at least one fuel being an alcohol, e.g. ethanol
    • 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
    • F02B23/02—Other engines characterised by special shape or construction of combustion chambers to improve operation with compression ignition
    • F02B23/06—Other engines characterised by special shape or construction of combustion chambers to improve operation with compression ignition the combustion space being arranged in working piston
    • F02B23/0645—Details related to the fuel injector or the fuel spray
    • F02B23/0663—Details related to the fuel injector or the fuel spray having multiple injectors per 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
    • F02B69/00—Internal-combustion engines convertible into other combustion-engine type, not provided for in F02B11/00; Internal-combustion engines of different types characterised by constructions facilitating use of same main engine-parts in different types
    • F02B69/02—Internal-combustion engines convertible into other combustion-engine type, not provided for in F02B11/00; Internal-combustion engines of different types characterised by constructions facilitating use of same main engine-parts in different types for different fuel types, other than engines indifferent to fuel consumed, e.g. convertible from light to heavy fuel
    • 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
    • F02B7/00—Engines characterised by the fuel-air charge being ignited by compression ignition of an additional fuel
    • F02B7/02—Engines characterised by the fuel-air charge being ignited by compression ignition of an additional fuel the fuel in the charge being liquid
    • 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
    • F02B7/00—Engines characterised by the fuel-air charge being ignited by compression ignition of an additional fuel
    • F02B7/02—Engines characterised by the fuel-air charge being ignited by compression ignition of an additional fuel the fuel in the charge being liquid
    • F02B7/04—Methods of operating
    • 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
    • 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
    • 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
    • F02M43/00—Fuel-injection apparatus operating simultaneously on two or more fuels, or on a liquid fuel and another liquid, e.g. the other liquid being an anti-knock additive
    • F02M43/04—Injectors peculiar thereto
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02P—IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES
    • F02P19/00—Incandescent ignition, e.g. during starting of internal combustion engines; Combination of incandescent and spark ignition
    • F02P19/02—Incandescent ignition, e.g. during starting of internal combustion engines; Combination of incandescent and spark ignition electric, e.g. layout of circuits of apparatus having glowing plugs
    • F02P19/026—Glow plug actuation during engine operation
    • 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
    • F02M2200/00—Details of fuel-injection apparatus, not otherwise provided for
    • F02M2200/44—Valves, e.g. injectors, with valve bodies arranged side-by-side
    • 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

Definitions

  • the present invention relates to a piston engine in accordance with claim 1 .
  • the invention also concerns a method for operating a piston engine, as de- fined in the other independent claim.
  • Methanol CH 3 OH
  • methanol is an example of biofuel having a lot of potential for use as a fuel of large piston engines in ships and at power plants.
  • the use of methanol has many benefits. Since methanol is liquid at normal operating temperatures, it is easier to store than gaseous fuels. However, to be able to use methanol in engines operating on diesel cycle, the ignition of the methanol needs to be aided.
  • One way to assist the ignition of methanol is to use pilot fuel injection, in which a small amount of liquid pilot fuel, such as light fuel oil, is injected into the cylinders of the engine before the injection of methanol. The combustion of the pilot fuel ignites the methanol. Pilot fuel injection allows the use of diesel cycle, but some problems remain. The pilot fuel injection causes a large part of the nitrogen oxide emissions of the engine, and depending on the quality of the pilot fuel, also sulfur emissions may occur.
  • each cylinder is provided with a first fuel injector, which is configured for injecting liquid alcohol into the cylinder, with a second fuel injector, which is configured for injecting liquid hydrocarbo- naceous fuel into the cylinder, and with means for heating air/fuel mixture in the cylinder for aiding the ignition of the liquid alcohol.
  • the method according to the invention comprises a first operating mode, in which operating mode the engine is operated solely on liquid alcohol using means for heating air/fuel mixture in each cylinder of the engine for aiding the ignition of the alcoholic fuel, a second operating mode, in which operating mode the engine is operated on liquid alcohol using liquid hydrocarbonaceous fuel as a pilot fuel for aiding the ignition of the alcoholic fuel, and a third operating mode, in which operating mode the engine is operated solely on liquid hydrocarbonaceous fuel.
  • the means for heating the air/fuel mixture can be a glow plug or a passive heat retaining element.
  • a benefit of the passive heat retaining elements is their simplicity and reliability.
  • the glow plugs or the heat retaining elements can be arranged in a fuel injector body or directly in a cylinder head.
  • the engine is started in the second or the third operating mode.
  • the first operating mode can be used when the engine has reached a certain predetermined operating temperature.
  • Fig. 1 shows a simplified cross-sectional view of part of a cylinder and a cylin- der head of a piston engine according to a first embodiment of the invention
  • Fig. 2 shows a cross-sectional view of part of a cylinder and a cylinder head according to a second embodiment of the invention.
  • each cylinder 1 is provided with a reciprocating piston 2.
  • the engine is a large internal combustion engine, such as a main or an auxiliary engine of a ship or an engine that is used at a power plant for producing elec- tricity.
  • the engine is a dual-fuel engine, which is configured for using two different liquid fuels.
  • each cylinder 1 is provided with a first fuel injector 4 and a second fuel injector 5.
  • the first and second fuel injectors 4, 5 are arranged in a common fuel injector body 6.
  • the fuel injectors 4, 5 could also be provided with own fuel injector bodies.
  • Each fuel injector 4, 5 is provided with a plurality of nozzle holes 4C, 5C.
  • the fuel injectors 4, 5 are arranged in parallel, but the fuel injectors 4, 5 could also be arranged coaxially.
  • both fuel injectors 4, 5 are arranged to inject the fuel directly into the cylinder 1 , but one or both of the fuel injectors 4, 5 could also be arranged to inject the fuel into a prechamber.
  • the engine is provided with a first fuel tank 10, in which liquid alcoholic fuel, such as methanol is stored.
  • a first fuel feeding duct 8 connects the first fuel injector 4 to the first fuel tank 10.
  • the engine is provided with a first fuel pump 10 for delivering fuel at high pressure from the first fuel tank 10 to the first fuel in- jector 4.
  • the first fuel injector 4 is provided with an injector needle 4A for opening and closing fluid communication between the fuel feeding duct 8 and the nozzle holes 4C of the fuel injector 4.
  • the first fuel injector 4 is also provided with an actuator 4B for moving the injector needle 4A.
  • the actuator 4B can be for example an electrical or hydraulic actuator. Different arrangements can be used for pressurizing the fuel and supplying it to the first fuel injector 4.
  • the engine can be provided with one or more low-pressure pumps, high-pressure pumps and fuel rails.
  • a low-pressure pump supplies the fuel from the first fuel tank 10 to a high-pressure pump, from which the fuel is introduced into a fuel rail.
  • Each of the first fuel injectors 4 is connected to the fuel rail.
  • the alcoholic fuel could be pressurized by conventional fuel injection pumps, in which case each cylinder 1 of the engine would be provided with a fuel injection pump.
  • one or more low-pressure pumps would be provided for supplying fuel to the fuel injection pumps. If conventional fuel pumps are used, the fuel injectors 4 do not need separate actuators 4B, but the injector needles 4A can be opened by the fuel pressure.
  • the engine also comprises a second fuel tank 1 1 , in which liquid hydrocarbo- naceous fuel, such as light fuel oil (LFO) is stored.
  • a second fuel feeding duct 9 connects the second fuel injector 5 to the second fuel tank 1 1 .
  • a second fuel pump 13 delivers fuel at high pressure from the second fuel tank 1 1 to the second fuel injector 5.
  • the second fuel injector 5 is provided with an injector needle 5A and an actuator 5B.
  • the second fuel injector 5 can be connected to a common rail system, which is provided with low- pressure pumps, high-pressure pumps and one or more fuel rails, or conventional fuel injection pumps can be used for pressurizing the fuel.
  • the engine can be operated with pilot fuel injection, which means that a small amount of hydrocarbonaceous fuel is injected into the cylinder 1 for aiding the ignition of the alcoholic fuel. However, this increases NOx emissions of the engine.
  • the engine is provided with means 7, 14 for heating air/fuel mixture in the cylinder 1 . When the temperature of the air/fuel mixture is increased locally in a small spot, the ignition is initiated in that spot and the resulting flame initiates the ignition in the rest of the cylinder 1 .
  • the means for heating the air/fuel mixture is a glow plug 7.
  • the glow plug 7 comprises an electrical heating element and can be used for increasing tempera- ture in the combustion chamber and thus aiding the ignition of the fuel.
  • the glow plug 7 is arranged directly in the cylinder head 3.
  • the glow plug 7 could also be arranged in the fuel injector body 6.
  • One of the nozzle holes 4C of the first fuel injector 4 is directed to- wards the glow plug 7. Part of the alcoholic fuel is thus injected towards the glow plug 7, which guarantees reliable ignition of the fuel.
  • FIG 2 shows a different embodiment of the invention.
  • the means for heating the air/fuel mixture is a passive heat retaining element 14, which protrudes into the combustion chamber.
  • the heat retaining element 14 is not heated by electricity or any other source of energy from the outside of the cylinder 1 , but the heat retaining element 14 is heated solely by the combustion of the fuel in the cylinder 1 .
  • the heat retaining element 14 is arranged in the fuel injector body 6, but the heat retaining element 14 could also be arranged directly in the cylinder head 3.
  • each cylinder 1 can be provided with more than one heat retaining elements 14.
  • the heat retaining element 14 is provided with a heat insulator 15.
  • the heat insulator 15 reduces thermal conduction to the fuel injector body 6 and to the cylinder head 3. During each power stroke of the engine, heat is conducted to the heat retaining element 14. Because of the heat insulator 15, the temperature of the heat retaining element 14 is kept relatively high until the next compression stroke and power stroke, during which part of the heat that is stored in the heat retaining element 14 is conducted and radiated to the air/fuel mixture. One of the nozzle holes 4C of the first fuel injector 4 is directed towards the heat retaining element 14. Part of the alcoholic fuel is thus injected towards the heat retaining element 14 to ensure reliable ignition.
  • the heat retaining element 14 is made of a material having high thermal capacity. The material needs also to be able to release the heat fast enough.
  • the heat retaining element 14 can be made of several parts.
  • the part of the heat retaining element 14 that protrudes into the combustion chamber is made of a material with high thermal capacity, whereas the part that is used for attaching the heat retaining element 14 to the fuel injector body 6 or the cylinder head 3 can be made of a material having low thermal conductivity to reduce heat conduction to the fuel injector body 6 and/or to the cylinder head 3.
  • the engine can be operated in several operating modes depending on the emission limits and available fuels. In a first operating mode, the engine is op- erated solely on liquid alcohol. The fuel is thus injected into the cylinders 1 of the engine through the first fuel injectors 4.
  • the glow plugs 7 or the heat retaining elements 14 are used for aiding the ignition of the fuel. With the operation on methanol or other liquid alcohol, the emis- sions of the engine can be minimized.
  • pilot fuel injection is used for aiding the ignition of the alcoholic fuel. If the engine is provided with heat retaining elements 14, the heat retaining elements 14 naturally work in the same way irrespective of whether the pilot fuel injection is in use or not.
  • the alcoholic fuel is injected into the cylinders 1 of the engine through the first fuel injectors 4, and the pilot fuel is injected into the cylinders 1 through the second fuel injectors 5.
  • the pilot fuel is liquid hydrocarbonaceous fuel, such as LFO.
  • the amount of the pilot fuel is small compared to the amount of the alcoholic fuel.
  • the energy content of the pilot fuel is preferably less than five per- cent of the total energy content of the fuel.
  • the engine is operated solely on liquid hydrocarbonaceous fuel.
  • the fuel is injected into the cylinders 1 through the second fuel injectors 5 and is ignited by compression by the pistons 2.
  • the second fuel injectors 5 are thus used for pilot fuel injection when alcoholic fuel is used and for normal fuel injection when hy- drocarbonaceous fuel is used.
  • the engine is started in the second operating mode or the third operating mode.
  • the engine can be operated in the first operating mode. Operation in the second or third oper- ating modes is needed for raising the temperature of the heat retaining elements 14 to a level that is high enough for the ignition of the alcoholic fuel.
  • the most suitable fuel can always be selected.
  • the engine thus provides increased flexibility and the emissions and operating costs of the engine can be minimized.

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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)
  • Life Sciences & Earth Sciences (AREA)
  • Biodiversity & Conservation Biology (AREA)
  • Biotechnology (AREA)
  • Botany (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Output Control And Ontrol Of Special Type Engine (AREA)
  • Combustion Methods Of Internal-Combustion Engines (AREA)
  • Fuel-Injection Apparatus (AREA)

Abstract

Each cylinder (1) of the piston engine is provided with a first fuel injector (4), which is configured for injecting liquid alcohol into the cylinder (1), with a second fuel injector (5), which is configured for injecting liquid hydrocarbonaceous fuel into the cylinder (1), and with means (7, 14) for heating air/fuel mixture in the cylinder (1) for aiding the ignition of the liquid alcohol.

Description

Piston engine and method for operating a piston engine Technical field of the invention
The present invention relates to a piston engine in accordance with claim 1 . The invention also concerns a method for operating a piston engine, as de- fined in the other independent claim.
Background of the invention
Due to the growing need to reduce carbon dioxide emissions of internal combustion engines, engines that are capable of using renewable fuels are becom- ing more and more attractive. Methanol (CH3OH) is an example of biofuel having a lot of potential for use as a fuel of large piston engines in ships and at power plants. The use of methanol has many benefits. Since methanol is liquid at normal operating temperatures, it is easier to store than gaseous fuels. However, to be able to use methanol in engines operating on diesel cycle, the ignition of the methanol needs to be aided. One way to assist the ignition of methanol is to use pilot fuel injection, in which a small amount of liquid pilot fuel, such as light fuel oil, is injected into the cylinders of the engine before the injection of methanol. The combustion of the pilot fuel ignites the methanol. Pilot fuel injection allows the use of diesel cycle, but some problems remain. The pilot fuel injection causes a large part of the nitrogen oxide emissions of the engine, and depending on the quality of the pilot fuel, also sulfur emissions may occur.
Summary of the invention An object of the present invention is to provide an improved piston engine, which solves at least some of the problems relating to the use of pilot fuel and offers improved fuel flexibility. The characterizing features of the engine according to the present invention are given in claim 1 . Another object of the invention is to provide an improved method for operating a piston engine. The characterizing features of the operating method are given in the other independent claim. In the engine according to the invention, each cylinder is provided with a first fuel injector, which is configured for injecting liquid alcohol into the cylinder, with a second fuel injector, which is configured for injecting liquid hydrocarbo- naceous fuel into the cylinder, and with means for heating air/fuel mixture in the cylinder for aiding the ignition of the liquid alcohol.
The method according to the invention comprises a first operating mode, in which operating mode the engine is operated solely on liquid alcohol using means for heating air/fuel mixture in each cylinder of the engine for aiding the ignition of the alcoholic fuel, a second operating mode, in which operating mode the engine is operated on liquid alcohol using liquid hydrocarbonaceous fuel as a pilot fuel for aiding the ignition of the alcoholic fuel, and a third operating mode, in which operating mode the engine is operated solely on liquid hydrocarbonaceous fuel. With the engine and the method according to the invention, the flexibility of engines can be increased. Suitable operating mode and combination of fuels can be selected according to the applicable emission limits and the availability of different fuels. The emissions and operating costs can thus be minimized.
The means for heating the air/fuel mixture can be a glow plug or a passive heat retaining element. A benefit of the passive heat retaining elements is their simplicity and reliability. The glow plugs or the heat retaining elements can be arranged in a fuel injector body or directly in a cylinder head.
If the engine is provided with passive heat retaining elements, the engine is started in the second or the third operating mode. The first operating mode can be used when the engine has reached a certain predetermined operating temperature.
Features of further embodiments of the invention are disclosed in the dependent claims. Brief description of the drawings
Embodiments of the invention are described below in more detail with reference to the accompanying drawings, in which
Fig. 1 shows a simplified cross-sectional view of part of a cylinder and a cylin- der head of a piston engine according to a first embodiment of the invention, and
Fig. 2 shows a cross-sectional view of part of a cylinder and a cylinder head according to a second embodiment of the invention.
Description of embodiments of the invention
In the figures is shown part of a cylinder 1 and a cylinder head 3 of a piston engine, where each cylinder 1 is provided with a reciprocating piston 2. The engine is a large internal combustion engine, such as a main or an auxiliary engine of a ship or an engine that is used at a power plant for producing elec- tricity. The engine is a dual-fuel engine, which is configured for using two different liquid fuels. For introducing the fuel into the cylinders 1 of the engine, each cylinder 1 is provided with a first fuel injector 4 and a second fuel injector 5. The first and second fuel injectors 4, 5 are arranged in a common fuel injector body 6. However, the fuel injectors 4, 5 could also be provided with own fuel injector bodies. Each fuel injector 4, 5 is provided with a plurality of nozzle holes 4C, 5C. In the embodiment of the figures, the fuel injectors 4, 5 are arranged in parallel, but the fuel injectors 4, 5 could also be arranged coaxially. In the embodiment of the figures, both fuel injectors 4, 5 are arranged to inject the fuel directly into the cylinder 1 , but one or both of the fuel injectors 4, 5 could also be arranged to inject the fuel into a prechamber.
The engine is provided with a first fuel tank 10, in which liquid alcoholic fuel, such as methanol is stored. A first fuel feeding duct 8 connects the first fuel injector 4 to the first fuel tank 10. The engine is provided with a first fuel pump 10 for delivering fuel at high pressure from the first fuel tank 10 to the first fuel in- jector 4. The first fuel injector 4 is provided with an injector needle 4A for opening and closing fluid communication between the fuel feeding duct 8 and the nozzle holes 4C of the fuel injector 4. The first fuel injector 4 is also provided with an actuator 4B for moving the injector needle 4A. The actuator 4B can be for example an electrical or hydraulic actuator. Different arrangements can be used for pressurizing the fuel and supplying it to the first fuel injector 4. For instance, the engine can be provided with one or more low-pressure pumps, high-pressure pumps and fuel rails. A low-pressure pump supplies the fuel from the first fuel tank 10 to a high-pressure pump, from which the fuel is introduced into a fuel rail. Each of the first fuel injectors 4 is connected to the fuel rail. Instead of this kind of common rail system, the alcoholic fuel could be pressurized by conventional fuel injection pumps, in which case each cylinder 1 of the engine would be provided with a fuel injection pump. In addition, one or more low-pressure pumps would be provided for supplying fuel to the fuel injection pumps. If conventional fuel pumps are used, the fuel injectors 4 do not need separate actuators 4B, but the injector needles 4A can be opened by the fuel pressure. The engine also comprises a second fuel tank 1 1 , in which liquid hydrocarbo- naceous fuel, such as light fuel oil (LFO) is stored. A second fuel feeding duct 9 connects the second fuel injector 5 to the second fuel tank 1 1 . A second fuel pump 13 delivers fuel at high pressure from the second fuel tank 1 1 to the second fuel injector 5. Also the second fuel injector 5 is provided with an injector needle 5A and an actuator 5B. Like the first fuel injector 4, the second fuel injector 5 can be connected to a common rail system, which is provided with low- pressure pumps, high-pressure pumps and one or more fuel rails, or conventional fuel injection pumps can be used for pressurizing the fuel.
With most alcoholic fuels, compression by the piston 2 does not increase the temperature in the cylinder 1 enough for reliable ignition of the alcoholic fuel. The engine can be operated with pilot fuel injection, which means that a small amount of hydrocarbonaceous fuel is injected into the cylinder 1 for aiding the ignition of the alcoholic fuel. However, this increases NOx emissions of the engine. To be able to operate the engine solely on alcoholic fuel, the engine is provided with means 7, 14 for heating air/fuel mixture in the cylinder 1 . When the temperature of the air/fuel mixture is increased locally in a small spot, the ignition is initiated in that spot and the resulting flame initiates the ignition in the rest of the cylinder 1 . In the embodiment of figure 1 , the means for heating the air/fuel mixture is a glow plug 7. Depending on the size of the engine, there can be more than one glow plug 7 in each cylinder 1 . The glow plug 7 comprises an electrical heating element and can be used for increasing tempera- ture in the combustion chamber and thus aiding the ignition of the fuel. In the embodiment of figure 1 , the glow plug 7 is arranged directly in the cylinder head 3. However, the glow plug 7 could also be arranged in the fuel injector body 6. One of the nozzle holes 4C of the first fuel injector 4 is directed to- wards the glow plug 7. Part of the alcoholic fuel is thus injected towards the glow plug 7, which guarantees reliable ignition of the fuel.
Figure 2 shows a different embodiment of the invention. In the embodiment of figure 2, the means for heating the air/fuel mixture is a passive heat retaining element 14, which protrudes into the combustion chamber. The heat retaining element 14 is not heated by electricity or any other source of energy from the outside of the cylinder 1 , but the heat retaining element 14 is heated solely by the combustion of the fuel in the cylinder 1 . In the embodiment of figure 2, the heat retaining element 14 is arranged in the fuel injector body 6, but the heat retaining element 14 could also be arranged directly in the cylinder head 3. Depending on the size of the engine, each cylinder 1 can be provided with more than one heat retaining elements 14. The heat retaining element 14 is provided with a heat insulator 15. The heat insulator 15 reduces thermal conduction to the fuel injector body 6 and to the cylinder head 3. During each power stroke of the engine, heat is conducted to the heat retaining element 14. Because of the heat insulator 15, the temperature of the heat retaining element 14 is kept relatively high until the next compression stroke and power stroke, during which part of the heat that is stored in the heat retaining element 14 is conducted and radiated to the air/fuel mixture. One of the nozzle holes 4C of the first fuel injector 4 is directed towards the heat retaining element 14. Part of the alcoholic fuel is thus injected towards the heat retaining element 14 to ensure reliable ignition. The heat retaining element 14 is made of a material having high thermal capacity. The material needs also to be able to release the heat fast enough. The heat retaining element 14 can be made of several parts. The part of the heat retaining element 14 that protrudes into the combustion chamber is made of a material with high thermal capacity, whereas the part that is used for attaching the heat retaining element 14 to the fuel injector body 6 or the cylinder head 3 can be made of a material having low thermal conductivity to reduce heat conduction to the fuel injector body 6 and/or to the cylinder head 3. The engine can be operated in several operating modes depending on the emission limits and available fuels. In a first operating mode, the engine is op- erated solely on liquid alcohol. The fuel is thus injected into the cylinders 1 of the engine through the first fuel injectors 4. In the first operating mode, the glow plugs 7 or the heat retaining elements 14 are used for aiding the ignition of the fuel. With the operation on methanol or other liquid alcohol, the emis- sions of the engine can be minimized. In a second operating mode, the engine is operated on liquid alcohol, but instead of using the glow plugs 7, pilot fuel injection is used for aiding the ignition of the alcoholic fuel. If the engine is provided with heat retaining elements 14, the heat retaining elements 14 naturally work in the same way irrespective of whether the pilot fuel injection is in use or not. The alcoholic fuel is injected into the cylinders 1 of the engine through the first fuel injectors 4, and the pilot fuel is injected into the cylinders 1 through the second fuel injectors 5. The pilot fuel is liquid hydrocarbonaceous fuel, such as LFO. The amount of the pilot fuel is small compared to the amount of the alcoholic fuel. The energy content of the pilot fuel is preferably less than five per- cent of the total energy content of the fuel. In a third operating mode, the engine is operated solely on liquid hydrocarbonaceous fuel. The fuel is injected into the cylinders 1 through the second fuel injectors 5 and is ignited by compression by the pistons 2. The second fuel injectors 5 are thus used for pilot fuel injection when alcoholic fuel is used and for normal fuel injection when hy- drocarbonaceous fuel is used.
If the engine is provided with heat retaining elements 14, the engine is started in the second operating mode or the third operating mode. When the engine has reached a certain predetermined operating temperature, the engine can be operated in the first operating mode. Operation in the second or third oper- ating modes is needed for raising the temperature of the heat retaining elements 14 to a level that is high enough for the ignition of the alcoholic fuel.
Because of the means 7, 14 for heating the air/fuel mixture in the cylinder 1 and the separate fuel injectors 4, 5 for different fuels, the most suitable fuel can always be selected. The engine thus provides increased flexibility and the emissions and operating costs of the engine can be minimized.
It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, but may vary within the scope of the appended claims.

Claims

Claims
1 . A piston engine, where each cylinder (1 ) of the engine is provided with a first fuel injector (4), which is configured for injecting liquid alcohol into the cylinder (1 ), with a second fuel injector (5), which is configured for injecting liquid hydrocarbonaceous fuel into the cylinder (1 ), and with means (7, 14) for heating air/fuel mixture in the cylinder (1 ) for aiding the ignition of the liquid alcohol.
2. An engine according to claim 1 , characterized in that the means for heating the air/fuel mixture is a glow plug (7).
3. An engine according to claim 1 , characterized in that the means for heating the air/fuel mixture is a passive heat retaining element (14).
4. An engine according to claim 3, characterized in that the heat retaining element (14) is provided with a heat insulator (15) for reducing heat conduction from the heat retaining element (14) to the fuel injectors (4, 5) and/or to a cylinder head (3).
5. An engine according to any of the preceding claims, characterized in that the means (7, 14) for heating the air/fuel mixture are arranged in a cylinder head (3).
6. An engine according to any of claims 1 -4, characterized in that the means (7, 14) for heating the air/fuel mixture are arranged in a fuel injector body (6).
7. An engine according to any of the preceding claims, characterized in that the first fuel injector (4) is configured for injecting methanol.
8. An engine according to any of the preceding claims, characterized in that the first fuel injector (4) and the second fuel injector (5) are arranged in a common fuel injector body (6).
9. A method for operating a piston engine, the method comprising a first operating mode, in which operating mode the engine is operated solely on liquid alcohol using means (7, 14) for heating air/fuel mixture in each cylinder (1 ) of the engine for aiding the ignition of the alcoholic fuel, a second operating mode, in which operating mode the engine is operated on liquid alcohol using liquid hydrocarbonaceous fuel as a pilot fuel for aiding the ignition of the alco- holic fuel, and a third operating mode, in which operating mode the engine is operated solely on liquid hydrocarbonaceous fuel.
10. A method according to claim 9, characterized in that the air/fuel mixture is heated in the first operating mode by a glow plug (7).
1 1 . A method according to claim 9, characterized in that the air/fuel mixture is heated in the first operating mode by a passive heat retaining element (14).
12. A method according to claim 1 1 , characterized in that the engine is started in the second or the third operating mode, and the engine is operated in the first operating mode after the engine has reached a predetermined op- erating temperature.
13. A method according to any of claims 8-12, characterized in that the liquid alcohol is methanol.
PCT/FI2015/050103 2014-03-06 2015-02-23 Piston engine and method for operating a piston engine Ceased WO2015132459A1 (en)

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