CN111412075A - Direct injection methanol engine in cylinder and working method of methanol engine combustion system - Google Patents

Direct injection methanol engine in cylinder and working method of methanol engine combustion system Download PDF

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Publication number
CN111412075A
CN111412075A CN202010346202.7A CN202010346202A CN111412075A CN 111412075 A CN111412075 A CN 111412075A CN 202010346202 A CN202010346202 A CN 202010346202A CN 111412075 A CN111412075 A CN 111412075A
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engine
injection
cylinder
fuel
methanol
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CN111412075B (en
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曾科
宁乐
刘兵
杨博
端启蒙
寇海亮
黄佐华
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Xian Jiaotong University
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Xian Jiaotong University
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    • 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
    • F02D41/38—Controlling fuel injection of the high pressure type
    • 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
    • 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
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/30—Controlling fuel injection
    • F02D41/38—Controlling fuel injection of the high pressure type
    • F02D41/40—Controlling fuel injection of the high pressure type with means for controlling injection timing or duration
    • F02D41/402—Multiple injections
    • 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
    • F02D41/38—Controlling fuel injection of the high pressure type
    • F02D41/40—Controlling fuel injection of the high pressure type with means for controlling injection timing or duration
    • F02D41/402—Multiple injections
    • F02D41/405—Multiple injections with post injections
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F1/00—Cylinders; Cylinder heads 
    • F02F1/24—Cylinder heads
    • F02F1/42—Shape or arrangement of intake or exhaust channels in cylinder heads
    • F02F1/4228—Helically-shaped channels 
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F1/00—Cylinders; Cylinder heads 
    • F02F1/24—Cylinder heads
    • F02F1/42—Shape or arrangement of intake or exhaust channels in cylinder heads
    • F02F1/4235—Shape or arrangement of intake or exhaust channels in cylinder heads of intake channels
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F3/00—Pistons 
    • F02F3/0084—Pistons  the pistons being constructed from specific materials
    • F02F3/0092—Pistons  the pistons being constructed from specific materials the material being steel-plate
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F3/00—Pistons 
    • F02F3/26—Pistons  having combustion chamber in piston head
    • 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
    • F02B2023/106—Tumble flow, i.e. the axis of rotation of the main charge flow motion is horizontal
    • 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
    • F02B2023/108—Swirl flow, i.e. the axis of rotation of the main charge flow motion is vertical
    • 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
    • F02D41/38—Controlling fuel injection of the high pressure type
    • F02D2041/389—Controlling fuel injection of the high pressure type for injecting directly into the cylinder
    • 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

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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)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Fuel-Injection Apparatus (AREA)

Abstract

The invention discloses a direct injection methanol engine in a cylinder and a working method of a methanol engine combustion system, wherein the methanol engine comprises a cylinder body, a cylinder cover arranged on the cylinder body, and a piston arranged in the cylinder; the cylinder cover is provided with an intake valve and an exhaust valve, the center of the cylinder cover is also provided with a spark plug, the cylinder cover is also provided with an in-cylinder direct injection fuel injector, the top surface of the piston is provided with a pit to form a combustion chamber, and main injection formed by the fuel injector faces the pit combustion chamber on the top of the piston. The working method of the engine comprises the following steps: the high compression ratio is adopted, a control strategy for controlling the advance angle and the injection times of the oil injection is adopted to inhibit the knocking combustion of the engine, and a strategy for organizing the air flow in different cylinders at different stages is also adopted. The invention further improves the thermal efficiency of the methanol engine in the prior art and improves the fuel economy of the engine.

Description

Direct injection methanol engine in cylinder and working method of methanol engine combustion system
Technical Field
The invention belongs to the field of methanol engines, and particularly relates to a direct injection methanol engine in a cylinder and a working method of a methanol engine combustion system.
Background
Along with diversification of fuel of an engine, methanol which is clean energy is gradually a new trend, ignition type combustion mode of the methanol engine is determined by the characteristic that the cetane number of the methanol fuel is low and the ignition performance is poor, and most of the existing methanol engines work by adopting air inlet pipe sequential multipoint electric injection and ignition type combustion modes.
In order to improve the combustion efficiency of the engine, it is one of the basic measures to increase the compression ratio, and the higher the compression ratio, the higher the thermal efficiency, but the increase in the compression ratio is liable to cause knocking combustion (also called knock) of the engine, which is not allowed. The mechanism of knocking combustion of a spark ignition engine is abnormal combustion, called knocking combustion, which is generated by self-ignition of a mixture at a high end temperature in a combustion chamber before normal flame propagation formed by ignition of a spark plug reaches, and the knocking combustion endangers the performance and the service life of the engine, so that the engine is not allowed to work under knocking, and the higher the compression ratio is, the higher the possibility of knocking is. It is necessary to take measures to suppress occurrence of knocking combustion in the engine when the compression ratio is increased.
In addition, approximately one third of the heat generated by the combustion of the engine fuel is used to perform work, one third is removed as exhaust heat, and the remaining third is absorbed by the engine coolant. The thermal efficiency of the engine can be further improved if the amount of heat lost by heat transfer through the top surface of the piston can be reduced.
The lower heat value of the methanol is only 0.46 times that of the gasoline, the methanol engine needs to inject more methanol fuel under the same power, and the latent heat of evaporation of the methanol is 3.8 times that of the gasoline. At present, a methanol engine generally adopts a mode of multi-point sequential injection of an air inlet pipe, the injection pressure is 3-5bar, a large amount of methanol is easy to gather in the air inlet manifold of the engine after being injected into the air inlet manifold of the engine, the problems of poor formation of mixed gas, uneven distribution of fuel of each cylinder of the engine, liquid flow of fuel in the air inlet pipe and the like are easily generated, and the problems are particularly prominent in the vehicle warming process after the engine is started. The recently published technology 'a methanol engine air inlet pipe multipoint sequential high-pressure injection system (application number: CN 201910631650.9)' discloses a technical scheme for sequentially injecting methanol by adopting an air inlet pipe, wherein the methanol is injected by adopting a high pressure with the injection pressure of 20-200bar in the technology so as to improve the spraying effect of the methanol, and the technical scheme can better solve the problems of poor fuel/air mixed gas and uneven distribution of each cylinder of the mixed gas. Since high-pressure injection is adopted, if the high-pressure injection of the air inlet pipe is developed into in-cylinder high-pressure direct injection from the injection of an air inlet manifold, the configuration of parameters such as the injection pressure, the injection advance angle and the injection frequency of methanol injection is more flexible, the optimization of the parameters is facilitated, the in-cylinder air motion with reasonable organization is combined, the thermal efficiency of the engine is further improved by greatly improving the compression ratio of the engine, and the thermal efficiency of the engine can be improved by reducing the heat transfer loss in the cylinder.
The existing Chinese patent 'methanol direct injection engine combustion system and alcohol injection strategy thereof' (application publication No. CN 101915153A) discloses a combustion system structure and an alcohol injection strategy of a direct injection methanol engine in a cylinder, so as to solve the problems of unstable ignition and incomplete methanol combustion. The specific structure of the scheme is that an air inlet valve area and an air outlet valve area which are staggered in height are arranged on an air cylinder cover, a squish area communicated with the air inlet valve and a combustion chamber communicated with the air outlet valve are formed among the air cylinder cover, the cylinder body and a piston, the mixing of fuel and air is improved by organizing tumble flow in an air inlet stroke and strongly squishing flow in a compression stroke through the squish area stroke, a spark plug is arranged on the side wall of the combustion chamber between the air inlet valve and the air outlet valve, a methanol fuel injector is arranged towards the air inlet valve and the top surface of the piston at an included angle of 30-60 degrees, and methanol is injected into the cylinder at 20-50 CABTDC (the injection advance angle is 20-50 crank rotation angles before the compression top dead center, the injection is earlier when the angle is larger, so that the stratified; the problem of this scheme is that it is too late to inject alcohol at medium and small loads, and good fuel-air mixture can not be formed before normal ignition (ignition advance angle is 20-40 CABTDC), resulting in unstable ignition combustion, and the scheme is suitable for the above specific structure.
The methanol engine sold in the market at present is basically developed on a platform of a gasoline engine of a passenger vehicle or a diesel engine of a commercial vehicle, two valves or four valves are adopted, and a spark plug is basically arranged at the center of the valve on the original cylinder cover.
Disclosure of Invention
The invention aims to provide an efficient in-cylinder direct injection methanol engine and a working method of a methanol engine combustion system by adopting a high compression ratio and a mode of reducing piston heat transfer, so as to further improve the thermal efficiency of the methanol engine in the prior art, solve the problems of poor formation of mixed gas, uneven distribution of cylinders and the like in the working process of the methanol engine adopting an air inlet pipe injection mode simultaneously by adopting a direct injection mode, and solve the problem of oil injection wall wetting by adopting methods of air movement with reasonable organization, multiple injection and the like, so that the efficient methanol engine provided by the method is feasible.
The invention is realized by adopting the following technical scheme:
an in-cylinder direct injection methanol engine comprises a cylinder body, a cylinder cover arranged on the cylinder body and a piston arranged in the cylinder body; the engine is also provided with an air inlet pipe, and a throttle body for controlling the air inlet amount of the engine is arranged on the air inlet pipe; the cylinder cover is provided with an inlet valve and an exhaust valve, the center of the cylinder cover is also provided with a spark plug, the cylinder cover is provided with an oil sprayer, the top surface of the piston is provided with a pit which forms a combustion chamber together with the cylinder body, and a main injection formed by the oil sprayer faces the combustion chamber at the pit on the top surface of the piston;
when the engine is in an air inlet stroke and the piston moves downwards to the middle of the cylinder, the fuel injector adopts main injection to inject methanol fuel, or when the engine is in a compression stroke and the piston moves upwards to the middle of the cylinder, the fuel injector adopts post injection to inject the methanol fuel, the injected methanol is mixed with air entering in the air inlet stroke in the cylinder block to form fuel/air mixed gas, when the piston moves upwards to the final stage of the compression stroke, the fuel/air mixed gas is ignited by a spark plug to combust the fuel, and the gas in the cylinder block expands to do work, thereby realizing the working process of the engine.
The invention is further improved in that the piston is made of steel or is embedded with a steel piston top.
An operating method of a methanol engine combustion system is based on the in-cylinder direct injection methanol engine, and comprises the following steps:
the compression ratio adopted by the engine is 13-17;
the engine adopts a control strategy of controlling an oil injection advance angle and main injection and after injection, and the range of the oil injection advance angle of the main injection is 300-180 CABDC, so that the fuel in a high-temperature area at the upper part of a cylinder is less, the engine is in a lean mixed gas state, and the detonation combustion of the engine is inhibited;
the engine adopts a strategy of organizing air flows in different cylinders at different stages, and organizes air flow in an air inlet vortex and an air flow in a cylinder organizing compression flow in a compression stroke in an air inlet stroke, or organizes air inlet longitudinal vortex/tumble flow and an air flow in a cylinder organizing compression flow in a compression stroke in an air inlet stroke;
the methanol injection pressure range of the engine is 20-500 bar.
The invention is further improved in that the methanol injection pressure of the engine is in a range of 60-200 bar.
The invention is further improved in that the injection advance angle of the post injection is 150-60 CABTDC, the fuel quantity of the post injection is not more than 30% of the total fuel quantity, and the injection is earlier as the fuel quantity of the post injection is larger.
The invention is further improved in that under the condition that the fuel injection quantity of the main injection is large and the injection time is long, in order to reduce the condition that fuel is injected to the wall surface, the main injection of 1 time is divided into 2-3 times, and the interval of each injection is 1-2 milliseconds.
The invention has at least the following beneficial technical effects:
the invention provides an in-cylinder direct injection methanol engine, when the engine is in an air inlet stroke and a piston moves downwards to the middle of an air cylinder, an oil injector adopts main injection to inject fuel, so that the fuel quantity in a high-temperature region at the upper part of the air cylinder is small, the engine is in a lean gas mixture state, the occurrence of detonation is inhibited, or when the engine is in a compression stroke and the piston moves upwards to the middle of the air cylinder, the methanol fuel is injected, the injected methanol is mixed with air entering in the air inlet stroke in the air cylinder to form fuel/air mixed gas, when the piston moves upwards to the end of the compression stroke, the fuel/air mixed gas is ignited by a spark plug, the fuel is combusted, the gas in the air cylinder expands to do work, and the working process of the engine is realized. The concentration of the mixed gas in the cylinder of the methanol engine injected by the air inlet pipe is more uniform, the concentration of the mixed gas and a high-temperature area with the same periphery are easy to knock, the compression ratio can not be increased to more than 13 generally, and the scheme can increase the compression ratio to 13-17, so that the heat efficiency of the engine is improved. Preferably, the piston in the basic structure of the engine is preferably a steel piston or a piston inlaid with a steel piston top, which is one of the technical measures of the high-efficiency methanol engine. The high-efficiency methanol engine has two advantages that the steel piston or the piston embedded with the steel piston top is adopted, firstly, the heat corrosion resistance of the steel piston top surface contacted with the methanol to the methanol can be better than that of an aluminum piston, secondly, the heat transfer loss of the piston in the working stroke can be reduced by the steel piston top surface, the heat efficiency of the engine can be further improved, if other technologies such as a supercharging technology or a variable valve timing technology are combined, the point can be more obvious, and meanwhile, the steel material can also enable the piston to bear higher explosion pressure.
After the working method of the methanol engine combustion system provided by the invention is adopted, the knocking of the engine can be effectively avoided under the condition of high compression ratio, good air/fuel mixed gas is formed, the fuel is quickly and sufficiently combusted, and meanwhile, the engine can obtain high combustion efficiency due to the high compression ratio of the engine; due to the adoption of a multi-time spraying mode, the penetration distance of the spray can be effectively shortened, and the wall wetting phenomenon caused by the spray is reduced.
In addition, compared with the existing air inlet pipe injection technical scheme, the direct injection technical scheme can effectively solve the problems of poor mixed gas formation and uneven fuel quantity distribution of each cylinder.
Drawings
FIGS. 1 and 2 are diagrams of one embodiment of a high efficiency methanol engine according to the present invention; FIG. 1 is a schematic block diagram of a piston as it approaches intake top dead center (330CABTDC), including a main injection resulting from a methanol injection at this time;
fig. 2 is a schematic diagram showing the arrangement of the valves, the exhaust valves, the spark plugs and the injectors on the 2-valve cylinder head and the 4-valve cylinder head, respectively, in the embodiment, wherein (a) in fig. 2 is the case of the 2-valve cylinder head, and (b) in fig. 2 is the case of the 4-valve cylinder head.
FIG. 3 is a schematic block diagram of the embodiment when the piston is at the 270CABTDC position during the intake stroke.
FIG. 4 is a schematic block diagram of the embodiment when the piston is at the 210 CABDC position during the intake stroke.
FIG. 5 is a schematic block diagram of the embodiment when the piston is at the 150CABTDC position during the intake stroke.
Description of reference numerals:
1 is an exhaust valve, 2 is an intake valve, 3 is a spark plug, 4 is an oil injector, 5 is an intake pipe, 6 is a throttle body, 7 is a piston, 8 is a pit, 9 is a high-temperature zone, 10 is main injection, 11 is a cylinder block, 12 is a cylinder head, 13 is intake swirl, 14 is intake longitudinal swirl, and 15 is after-injection.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
As shown in fig. 1 and fig. 2, the direct injection methanol engine in the cylinder provided by the present invention comprises a cylinder block 11, a cylinder head 12 mounted on the cylinder block 11, and a piston 7 mounted in the cylinder block 11, wherein the engine further comprises an intake pipe 5, and a throttle body 6 for controlling the intake air amount of the engine is mounted on the intake pipe 5; an intake valve 2 and an exhaust valve 1 are mounted on the cylinder cover 12, an ignition plug 3 is further mounted in the center of the cylinder cover 12, an oil injector 4 is further mounted on the cylinder cover 12, a pit 8 is formed in the top surface of the piston 7 and forms a combustion chamber together with the cylinder cover 12, and a main injection 10 generated by the oil injector 4 faces the combustion chamber at the pit 8 in the top surface of the piston 7.
When the engine is in an air inlet stroke and the piston 7 moves downwards to the middle of the cylinder, the fuel injector adopts main injection 10 to inject fuel, or when the engine is in a compression stroke and the piston 7 moves upwards to the middle of the cylinder, the fuel injector 4 adopts post injection 15 to inject methanol fuel, the injected methanol is mixed with air in the cylinder block 11 to form fuel/air mixed gas, when the piston 7 moves upwards to the end of the compression stroke, the fuel/air mixed gas is ignited by the ignition plug 3 to burn the fuel, and the gas in the cylinder block 11 expands to do work, so that the working process of the engine is realized.
The control of the air quantity entering the engine cylinder is realized by adjusting the opening degree of a throttle valve body arranged on an air inlet pipe of the engine.
The fuel/air mixture ratio (air/fuel ratio) in the engine cylinder is achieved by controlling the amount of fuel injected by the injector.
The invention provides a working method of a methanol engine combustion system, which comprises the following steps:
the engine adopts a high compression ratio, and the optimal value of the high compression ratio is 13-17.
In order to realize high efficiency of the engine, the engine adopts a high compression ratio, the preferable value is 13-17, and the compression ratio is much higher than the compression ratio of the existing engine of 9-12.
The high-efficiency engine adopts a control strategy of controlling an oil injection advance angle and main injection plus after injection to inhibit the detonation combustion of the engine.
The preferable range of the fuel injection advance angle of the main injection is 300-180 CABDC.
At the end of the compression stroke, the area of the surface of the cylinder head 12 near the exhaust valve 1 and the wall surface of the cylinder block 11 is a high temperature zone 9, which has the highest temperature in the entire combustion chamber space at this time and is the high temperature end in the entire combustion chamber, and when the mixture concentration is high (L ambda is 0.9 to 1.1), knocking is most likely to occur.
Firstly, the fuel injection advance angle is controlled.
As shown in fig. 1, when the engine intake stroke starts, the piston 7 is located near the top dead center, and as the piston 7 moves downward, if the injector 4 starts injecting fuel for the 1 st time, the earlier the fuel is injected, the main injection 10 is more likely to be injected to the surface of the top surface dimple 8 of the piston 7, and to bounce against the surface of the cylinder head 12 and the surface of the exhaust valve 1 or the area near the surface of the cylinder head 12 and the surface of the exhaust valve 1 after colliding with the surface, and since this area is a high temperature area 9 where the temperature in the cylinder is the highest and is further away from the intake valve, the intensity of air movement is weaker than other nearby areas, the amount of fuel in this area is greater than other nearby areas, and the greater the amount of fuel in this high temperature area is, the more likely knocking combustion is formed later in the. The fuel injection is properly delayed in the air inlet stroke, so that the injected fuel is prevented from rebounding to the surface of a cylinder cover on the exhaust valve side through the top surface of a piston, the fuel quantity of the upper part of a cylinder, particularly the high-temperature region 9, is small, and the upper part of the cylinder is in a lean mixture state, and the detonation combustion of an engine can be inhibited; on the premise of properly delaying fuel injection and avoiding the fuel injection beam from rebounding to the high-temperature area 9, the fuel injection is also carried out as early as possible, so that the longer the time of the mixed gas staying in the cylinder is, the more uniform the formed mixed gas is, the higher the quality of the formed mixed gas is, and the more favorable the stable combustion of the mixed gas is.
When the piston moves downwards to the middle of the cylinder (as shown in figure 3), if the fuel injector starts to inject at the moment, the oil beam stroke of the fuel injector is longer, and the middle section and the rear section of the main injection 10 are injected to the surface of the piston at the moment, compared with the situation in figure 1, the fuel oil is less prone to rebounding to the high-temperature area 9, the fuel oil enters the pit 8 on the top surface of the piston, part of the fuel in the injection beam rebounds to the air through the surface of the piston, part of the fuel is gathered on the surface of the pit 8, and the portion gathered on the surface of the piston is further volatilized under the heating action of the glowing surface of the piston, so that good fuel/.
When the piston moves to the vicinity of the lower end of the cylinder (as shown in fig. 4), if the injector starts to inject at this time, the oil beam stroke of the injector is long, the periphery of the side surface of the rear end of the oil beam touches the inner wall surface of the cylinder block 11, part of the fuel volatilizes, and part of the fuel is gathered on the inner wall surface of the cylinder block to cause a wall wetting phenomenon, the wall wetting phenomenon can dilute the oil film on the surface of the cylinder sleeve on the part of the inner wall surface of the cylinder block to cause poor lubrication and more wear, and meanwhile, when the part of the fuel gathered on the inner wall surface of the cylinder block is too much, the phenomenon that liquid methanol flows into an oil pan of the engine through a gap between the piston and the inner wall of the cylinder block can occur.
Post injection 15 is also included in the injection control strategy.
The main injection 10 is generated in the early stage of the intake stroke or the compression stroke, and the main injection is satisfied because the working mode mainly adopts the mode of homogeneous mixed gas combustion.
However, in the case where the engine is designed to have a high compression ratio, when the engine is under a heavy load condition and knocking is more likely to occur, in order to suppress the occurrence of knocking more effectively, post injection 15 (as shown in fig. 5) may be performed after main injection 10 to further reduce the temperature of the mixture in the late stage of in-cylinder compression by utilizing the characteristic of large latent heat of vaporization of methanol fuel. The post injection occurs in the middle stage of the compression stroke, the fuel quantity of the injection is not more than 30% of the total fuel quantity, if the injection is too late, such as the injection in the later stage of the compression stroke, the formation of the mixed gas cannot be facilitated due to too short time for fuel volatilization, and the temperature of the mixed gas in the center of the cylinder is reduced more, so that the mixed gas is not ignited by a spark plug in the later stage of the compression. The post-injection is beneficial to reducing the occurrence of knocking, and is also beneficial to forming mixed gas with concentration richer than that deviating from the center of the cylinder in the center of the cylinder for a lean burn engine, thereby being beneficial to the stability of spark ignition, accelerating flame propagation and reducing the combustion cycle variation. The preferable crank angle of the post injection is 150-60 CABDC, and the more the fuel quantity of the post injection is, the earlier the injection is.
Under the conditions of large fuel injection quantity and long injection time of the main injection, in order to reduce the wall wetting phenomenon caused by fuel injection to the wall surface, the main injection carried out for 1 time can be divided into continuous multiple injections, the interval of each injection is 1-2 milliseconds, and the penetration distance of the spray beam of each injection is controlled to be smaller than the wall collision distance of the spray beam. According to the spraying theory, in order to avoid wall collision, the penetration distance of 1.5 milliseconds of injection can reach 100 millimeters under the conditions that the injection pressure is 20Mpa and the diameter of a spray hole is 0.2 millimeter, so that a large amount of fuel can be prevented from colliding with the wall by controlling the injection time length of each time within 1-2 milliseconds, and the injection time of each time is shorter as the pressure is higher. In the case of starting the injection when the piston is in the upper middle of the cylinder (fig. 3), even if the injection earlier causes a large amount of fuel to be injected into the pit at the top of the piston, this is permissible, and in this case, although the fuel will collect in the pit, it will not cause the phenomenon of wall wetting of the cylinder wall, and this fuel will form a good combustible air mixture with the air under the heating action of the top surface of the piston pit and the entrainment action of the squish of the compressed air, and it is not necessary to divide the main injection into multiple injections.
The high-efficiency methanol engine adopts a strategy of organizing air flow in different cylinders at different stages.
To achieve high efficiency of the engine, the engine employs an in-cylinder air flow that organizes the intake swirl flow 13 during the intake stroke and the compression squish flow during the compression stroke.
To achieve high efficiency of the engine, the engine either employs an in-cylinder air flow that organizes an intake longitudinal swirl 14 (tumble flow) during the intake stroke and a compression squish flow during the compression stroke.
After the in-cylinder direct injection mode is adopted to replace the intake pipe injection mode, because the time for evaporating and mixing with air to form good combustible mixture after fuel injection is short, the formation quality of the in-cylinder fuel/air mixture must be improved by organizing a proper form and strong air movement.
The intake swirl 13 is organized by designing the intake passage on the cylinder head in such a way that it acts tangentially or as a spiral duct to improve the mixing of fuel and air during the intake process.
The intake longitudinal swirl 14 is organized by designing the intake passage on the cylinder head as a tangential intake passage to improve the mixing of fuel and air during intake.
The provision of a combustion chamber in the form of a dimple 8, such as the typical bath type combustion chamber, atop the piston 7 creates a compression squish flow during the compression stroke and a counter squish flow during the expansion stroke, which facilitates the mixing of the methanol fuel with air after injection into the cylinder to create a generally more homogeneous mixture for flame propagation and combustion.
The methanol injection pressure range of the high-efficiency methanol engine is 20-500 bar, and the preferred value is 60-200 bar.
In order to realize good fuel spraying effect, different fuel injection pressures are adopted according to different injected fuel quantities of the engine under different working conditions, and the more the fuel quantity is, the higher the fuel injection pressure is. The oil injection pressure range is 20-500 bar, and the preferable value is 60-200 bar. When the methanol engine adopts an air inlet pipe injection mode, the oil injection pressure is 3-5bar, and after in-cylinder direct injection is adopted, the oil injection pressure range is 20-500 bar, so that a good spraying effect is achieved. Meanwhile, in order to reduce the power consumption of the methanol high-pressure oil pump, the preferential methanol oil injection pressure is 60-200 bar on the premise of meeting the methanol direct injection spraying effect.
The injection pressure, the injection advance angle and the injection times of the engine under different operating conditions are determined by optimizing the engine through a matching calibration test.
The piston in the basic structure of the engine is preferably a steel piston or a piston embedded with a steel piston top, which is one of the preferable technical measures of the high-efficiency methanol engine. The high-efficiency methanol engine has two advantages of adopting a steel piston or a piston inlaid with a steel piston top, wherein the steel piston top surface contacted with methanol can better resist heat corrosion to the methanol than an aluminum piston, and the steel piston top surface can reduce heat transfer loss of the piston in a power stroke, so that the heat efficiency of the engine is further improved.
Examples measured Effect
An air-cooled single-cylinder natural air-breathing engine (model 192F) modified by a diesel engine and having a cylinder diameter of 92mm has the discharge capacity of about 0.5 liter, 2 valves, a spiral air inlet channel generates air inlet vortex, an ignition plug is arranged between an air inlet valve and exhaust, a pit at the top of a piston is of a bathtub type, and the compression ratio is 15. when the engine is under the working condition that a throttle valve is fully opened, the rotating speed is 2500 rpm, and L ambda is 1 (theoretical mixing ratio), if the fuel injection advance angle is earlier than 330 CABDC, knocking combustion can occur, if the fuel injection advance angle is later than 300 CABDC, the knocking combustion cannot occur, and when the fuel injection advance angle is 270 CABDC, the effective thermal efficiency of the engine can reach 37 percent, which is a good level for the single-cylinder engine.
Thus, it will be appreciated by those skilled in the art that while the present invention has been particularly shown and described with reference to exemplary embodiments thereof, many other variations and modifications can be made in accordance with the principles of the invention without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be understood and interpreted to cover all such other variations or modifications.

Claims (6)

1. An in-cylinder direct injection methanol engine is characterized by comprising a cylinder block (11), a cylinder cover (12) arranged on the cylinder block (11) and a piston (7) arranged in the cylinder block (11); the engine is also provided with an air inlet pipe (5), and a throttle body (6) for controlling the air inlet quantity of the engine is arranged on the air inlet pipe (5); an intake valve (2) and an exhaust valve (1) are mounted on a cylinder cover (12), a spark plug (3) is further mounted at the center of the cylinder cover (12), an oil sprayer (4) is mounted on the cylinder cover (12), a pit (8) is formed in the top surface of a piston (7) and forms a combustion chamber together with a cylinder block (11), and a main injection (10) formed by the oil sprayer (4) faces the pit (8) in the top surface of the piston (7) to form the combustion chamber;
when the engine is in an air inlet stroke, the piston (7) moves downwards to the middle of the cylinder, the fuel injector (4) adopts main injection (10) to inject methanol fuel, or the engine is in a compression stroke, the piston (7) moves upwards to the middle of the cylinder, the fuel injector (4) adopts post injection (15) to inject the methanol fuel, the injected methanol is mixed with air entering in the air inlet stroke in the cylinder block (11) to form fuel/air mixed gas, when the piston (7) moves upwards to the end of the compression stroke, the fuel/air mixed gas is ignited by the ignition plug (3) to combust the fuel, the gas in the cylinder block (11) expands to do work, and the working process of the engine is realized.
2. The direct injection methanol engine according to claim 1, characterized in that the piston (7) is a steel piston or a piston with a steel piston crown.
3. An operating method of a methanol engine combustion system, characterized in that the operating method is based on the in-cylinder direct injection methanol engine of claim 1 or 2, and comprises the following steps:
the compression ratio adopted by the engine is 13-17;
the engine adopts a control strategy of controlling an oil injection advance angle and main injection and after injection, and the range of the oil injection advance angle of the main injection is 300-180 CABDC, so that the fuel in a high-temperature area at the upper part of a cylinder is less, the engine is in a lean mixed gas state, and the detonation combustion of the engine is inhibited;
the engine adopts a strategy of organizing air flows in different cylinders at different stages, and organizes air flow in an air inlet vortex and an air flow in a cylinder organizing compression flow in a compression stroke in an air inlet stroke, or organizes air inlet longitudinal vortex/tumble flow and an air flow in a cylinder organizing compression flow in a compression stroke in an air inlet stroke;
the methanol injection pressure range of the engine is 20-500 bar.
4. The method of claim 1, wherein the methanol injection pressure of the engine is in the range of 60-200 bar.
5. The operating method of the methanol engine combustion system as claimed in claim 1, characterized in that the injection advance angle of the post injection is 150-60 CABTDC, the fuel quantity of the post injection is not more than 30% of the total fuel quantity, and the more the fuel quantity of the post injection is, the earlier the injection is.
6. The operating method of the combustion system of the methanol engine is characterized in that under the condition that the fuel injection quantity of the main injection is large and the injection time is long, in order to reduce the condition that fuel is injected to the wall surface, the main injection of 1 time is divided into 2-3 times, and the interval of each injection is 1-2 milliseconds.
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