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
  • 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
  • F02B75/00—Other engines
  • F02B75/12—Other methods of operation
• • 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
  • F02B75/00—Other engines
  • F02B75/02—Engines characterised by their cycles, e.g. six-stroke
  • F02B2075/022—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle
  • F02B2075/027—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle four
• • 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
  • F02B2201/00—Fuels
  • F02B2201/06—Dual fuel applications
  • F02B2201/062—Liquid and 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
  • F02B3/00—Engines characterised by air compression and subsequent fuel addition
  • F02B3/06—Engines characterised by air compression and subsequent fuel addition with compression ignition

Definitions

• This invention relates to a four-stroke internal combustion engine. Over the last sixty years there have been many attempts to develop an engine that would bridge the gap between the pre-mixed spark ignited and the compression ignition cycles. This has not heretofore been achieved because the processes that control the burning of hydrocarbon fuels in the cylinder of the engine are complex and have not been fully understood. Combustion occurs between limited fuel-air ratios that will be affected by cylinder temperature, volatility and boiling point of the fuel, and method of introduction. After ignition takes place there is a minimum temperature that must be maintained for flame propogation to continue. Most fuels of the higher hydro-carbons have two temperature/pressure/ignition stages. There is a high temperature/ pressure region and a low temperature/pressure region.
• the next type of two stage injections is the pilot charge method.
• a small charge of fuel is injected ahead of the main charge in the compression ignition cycle. This commences to burn.
• the main charge is then injected. This is ignited on entry by the pilot charge. This reduces the delay so that combustion can progress smoothly.
• the secondary injection is generally less than the main injection. According to this method there is a phased difference between the two injections ranging from 320°-360° of crank shaft rotation.
• the essential conditions necessary to attain improved results is to inject a first fraction of the fuel charge into the hot residual gases remaining in the cylinder towards the end of the exhaust stroke.
• the pre-mixed spark ignited engine has a big power advantage over the compression ignition engine it is not as economical because at light load it has difficulty in igniting or maintaining combustion when the mixture content in the cylinder is less than 80% stoichiometric chemically correct, hereinafter referred to as by the abbreviation 'STO'.
• the lean limits of flammability can be extended (ie reduced) by raising the compression temperature, the compression ratio is governed by the fuel's resistance to pre-flame reaction and detonation.
• thermo-chemical ignition (cool flame) will occur regardless of the fuel's concentration but the leaner the mixture the lower the intensity of the reaction.
• pre-flame reaction will speed up spontaneous combustion
• the pre-mixing of fuel can only begin when the compression ignited defused flame combustion has raised the overall combustion chamber content to the temperature necessary for flame propogation to continue.
• the fuel is heated up in the injector nozzle. Under load the fuel will be over 200 °C at the start of injection.
• the speed of vaporization increases with the temperature, the bulk of diesel oils has a boiling temperature and evaporation lifetime that is too high for pre-mixing.
• diesel is injected into the cylinder early in the induction stroke the rate of evaporation will be retarded when the liquid fuel strikes the cool cylinder wall. Because of this the mixing will be incomplete and the engine efficiency will be impaired.
• the boiling point and the rate of vaporization are important factors to be taken into consideration.
• the fuel In the pre-mixed engine cycle the fuel must contain a reasonable proportion of low boiling point highly volatile fuel for cold starting. There must also be a fair proportion of less volatile, higher boiling point fuel for ease of starting when the engine is hot. There must also be fuel in the middle boiling range to meet the normal working requirements.
• a good pre-mixed engine fuel will have a boiling range from 25°C-210°C.
• fuel is injected into hot compressed air in the compression ignition engine there is no need for low boiling point highly volatile fuel for cold starting because the cylinder will always have sufficient heat for a percentage of the fuel to vaporize.
• the only requirement is that the boiling range must be at a level to maintain the vaporizing fuel in sufficient concentration for spontaneous combustion to take place.
• a good diesel fuel to meet these requirements will have a boiling range from 150°C -350°C.
• the pre-mixed fuel is pre-heated in the injector nozzle a wide boiling range fuel can be used.
• the invention provides a method of operating a four-stroke compression ignition internal combustion engine including a cylinder whose volume varies cyclically, and which is provided with means for injecting a hydrocarbon fuel into the cylinder during a compression stroke of the engine, wherein over a lower part of a power range thereof, from tickover up to a transition point, engine power is varied by varying the quantity of a main injection of fuel late in the compression stroke from a minimum at tick-over up to higher value at the transition point, and wherein over a higher part of the power range from the transition point up to full power, the main injection of fuel is supplemented by a secondary introduction of the same fuel, which is initiated earlier in the compression stroke and which mixes with air in the cylinder to form a combustible mixutre which is burnt simultaneously with the main injection of fuel, the secondary injection of fuel taking place under conditions of temperature and pressure which ensure evaporation thereof, and sufficiently early to allow a pre-flame reaction to occur in the mixture of secondary fuel and air before the main injection of fuel.
• low octane non-leaded fuel in the Kerosene and Gasoline boiling range can be burned at high compression ratios without knock with fuel-air ratios that are continuously variable from 15% to 100% stochiometric (chemically correct).
• Fig. 1 is a set of diagrams illustrating operation of a conventional compression ignition engine
• Fig. 2 is a similar set for a first preferred engine of the invention
• Fig. 3 is a similar set for a second preferred engine of the invention.
• Fig. 4 is a similar set for a third preferred engine of the invention.
• Fig. 5 is a similar set for a fourth, but with a lower BP fuel
• Fig. 6 is a similar set for a fifth, but with higher resistance to pre-flame reaction.
• TDC top dead centre in a cylinder of a reciprocatingpiston engine, other angles being given in relation to TDC.
• a main injection of fuel is indicated by vertical hatching, and a secondary introduction of fuel by horizontal hatching.
• STO is used as an abbreviation for stoichiometric.
• the far left-hand diagram (A) illustrates lowest power (tickover) and the far right diagram (C or D) indicates full power.
• diagram (B) indicates a transition point.
• Fig. 1 In the conventional compression-ignition engine using " diesel"fuel, illustrated in Fig. 1, there is a single main injection of fuel which usually commences at or about 25° before TDC. At this point the cylinder is hot enough to initiate ignition of the injected fuel and the combustion starts immediately after injection commences, and finishes shortly after injection ceases. At full power injection may continue up to or beyond TDC, although 70% STO tends to be a maximum, value, higher values causing a smoky exhaust.
• the diagrams are drawn to illustrate progressively longer periods of injection from low to high power, consistent with an injector construction and size wherein the rate of injection is constant the quantity of fuel injected being varied by varying the period of operation of the injector.
• a first preferred embodiment of engine operating in accordance with a first preferred method of the invention is identical to the Fig. 1 engine over a lower part of its power range from A to B.
• the transition point B is chosen in relation to the characteristics of the fuel to occur at that position wherein after combustion of the main fuel portion the temperature within the cylinder is everywhere greater than 1200°C. This is usually at a position wherein the quantity of fuel injected in the main injection is about 35%-45% of and usually 40% STO.
• the quantity of the main fuel injection is progressively increased up to 60% STO at full power, but the increase is less than would occur in the conventional engine of Fig. 1.
• the engine of Fig. 2 uses an additional fuel injection from the same injector as supplies the main fuel charge, and this can very simply be achieved in a conventional injector arrangement by a relatively minor modification to the reciprocating pump member of the injector arrangement.
• the quantity of fuel in the secondary charge varies from 0%STO at B up to 25%STO at maximum power. Because the additional fuel is pre-mixed, it is possible by this means to increase the maximum power of the engine.
• the maximum power is that which is generated by an 85%STO mixture rather than 70%STO in a conventional diesel without a smoky exhaust.
• a liquid fuel such as kerosene or petrol in the boiling range 100°C-280°C must be used.
• a liquid fuel such as kerosene or petrol in the boiling range 100°C-280°C must be used.
• Such a fuel mixes well at the temperatures apertaining to the conventional compression ignition engine. Any increase in volatility in the conventional compression ignition engine will retard the onset of spontaneous combustion. This will be detrimental at speed and load. It is an object of the present invention to overcome this delay by using the thermo-chemical changes that take place when pre-mixed fuel is subjected to compression.
• pre-flame reaction as a trigger mechanism to speed up the onset of spontaneous combustion a wide range of fuels can be used in the compression ignition engine cycle.
• Fig. 3 illustrates a variation on the method illustrated in Fig. 2 in which a low boiling point fuel in the kerosene petrol range with a higher resistance to pre-flame reaction.
• the principles are the same as those described in relation to Fig. 2 except that the main charge increases after the transition point B from 40% STO up to a maximum of say 50% STO at about three quarters power (C) and thereafter remains constant up to full power.
• the quantity of the second charge rises slowly from 0%C STO at B to 10%STO at C and more rapidly from 10% STO at C to 40% at D (full power)
• Fig. 4 illustrates a variation on the method illustrated in Fig. 2 in which high boiling point fuel
• diesel is injected via a second injector on to the back of the hot inlet valve during the induction stroke of the engine to provide a pre-mixed charge prior to the main charge. Because of its high boiling point diesel fuel will not evaporate when injected into the asperated air in the inlet manifold during the induction stroke of the engine because it requires a temperature of 300 °C at atmospheric pressure to vaporize.
• the inlet valve or valves of the compression ignition engine vary in temperature from 350°-450 °C and in an engine operating in accordance with the preferred method of this invention will reach a temperature over 300°C at the transition point B.
• Fig. 5 illustrates a method identical to the method illustrated in Fig. 4 but the fuel used is in the kerosene, petrol boiling range and has a low resistance to pre-flame reaction.
• Fig. 6 illustrates a variation on the method illustrated in Fig. 4 and Fig. 5 in which a low boiling point fuel in the kerosene, petrol boiling range, with a higher resistance to pre-flame reaction is used. This cycle would be suitable for use in a supercharged engine wherein temperaturesare higher.
• tion engines in which there is cyclic variation of the size of a working chamber (conveniently referred to as a "cylinder").
• a cylinder a working chamber
• the methods of the invention allow “diesel” engines to have much higher power than present diesels and a much livier response without excessively high compression ratios and without excessively smoky exhausts.
• unleaded fuel can be used without problems of pre-ignition and with the economies that the use of low octane and the elimination of pre-ignition suppression agents can bring.
• the petrol engine has a low quantity of unwanted products of combustion in its exhaust and its economics are good.
• the invention is equally applicable to a direct-injected diesel two-stroke engine.
• the secondary fuel will normally be injected prior to the main injection after closure of the scavenge ports, but it is possible to use an injection into the air as pivoted via the crank-case, provided lubricant is added or the problems of crank-case lubrication is otherwise considered.
• the average temperature of the inlet valve is between 350°C to 450°C in the diesel engine at full load.
• the fuel is impinged on the inlet valve during the induction stroke so that instantaneous vaporization takes place at the time of maximum air speed through the inlet port. This causes instantaneous and complete mixing.
• the amount of fuel injected must be governed by but the leaner the mixture the lower the intensity of the reaction. Although pre-flame reaction will speed up spontaneous combustion, the pre-mixing of fuel can only begin when the compression ignited defused flame combustion has raised the overall combustion chamber content to the temperature necessary for flame propogation to continue.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Combustion Methods Of Internal-Combustion Engines (AREA)

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• 1985
  • 1985-01-05 GB GB858500270A patent/GB8500270D0/en active Pending
  • 1985-08-08 GB GB858519987A patent/GB8519987D0/en active Pending
• 1986
  • 1986-01-03 WO PCT/GB1986/000002 patent/WO1986004111A1/en unknown
  • 1986-01-03 AU AU53047/86A patent/AU5304786A/en not_active Abandoned
  • 1986-01-03 EP EP19860900607 patent/EP0207970A1/de not_active Withdrawn
  • 1986-01-03 GB GB08600101A patent/GB2169960B/en not_active Expired

Non-Patent Citations (1)

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