CN111412075B

CN111412075B - In-cylinder direct injection methanol engine and working method of methanol engine combustion system

Info

Publication number: CN111412075B
Application number: CN202010346202.7A
Authority: CN
Inventors: 曾科; 宁乐; 刘兵; 杨博; 端启蒙; 寇海亮; 黄佐华
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2020-04-27
Filing date: 2020-04-27
Publication date: 2024-06-11
Anticipated expiration: 2040-04-27
Also published as: CN111412075A

Abstract

The invention discloses an in-cylinder direct injection methanol engine 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, a piston arranged in the cylinder, an air inlet pipe, a throttle body and the like, wherein the throttle body is arranged on the air inlet pipe and used for controlling the air inlet quantity of the engine; 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 the main injection of 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 method adopts a high compression ratio, adopts a control strategy for controlling the oil injection advance angle and the oil injection times to inhibit knocking combustion of the engine, and adopts a strategy for organizing air flows in different cylinders at different stages. The invention further improves the thermal efficiency of the methanol engine in the prior art and improves the fuel economy of the engine.

Description

In-cylinder direct injection methanol engine and working method of methanol engine combustion system

Technical Field

The invention belongs to the field of methanol engines, and particularly relates to an in-cylinder direct injection methanol engine and a working method of a methanol engine combustion system.

Background

Along with diversification of fuel of the engine, clean energy methanol gradually becomes a new trend, and the characteristic of poor ignition performance of the methanol fuel determines an ignition type combustion mode of the methanol engine, so that most of the current methanol engines work in a sequential multi-point electronic injection and ignition type combustion mode of an air inlet pipe.

In order to improve the combustion efficiency of an engine, it is one of the basic measures to improve the compression ratio, and the higher the compression ratio, the higher the thermal efficiency, but the improvement of the compression ratio is liable to cause knocking combustion (also called knocking) of the engine, which is not allowed. The mechanism of knocking combustion in a spark ignition engine is that abnormal combustion, called knocking combustion, which is generated by spontaneous combustion of a mixture gas at a high temperature at the tip end in a combustion chamber before normal flame propagation by ignition of a spark plug arrives, is harmful to engine performance and life, so that the engine is not allowed to operate under knocking, and the higher the compression ratio is, the greater the possibility of occurrence of knocking is. It is necessary to take measures to suppress the occurrence of knocking combustion of the engine when the compression ratio is increased.

In addition, about one third of the heat generated by the combustion of the engine fuel is generally used for work, one third is discharged in the form of exhaust heat, and the remaining third is absorbed by the cooling liquid of the engine. If the heat lost by the heat transfer through the piston top surface can be reduced, the thermal efficiency of the engine can be further improved.

The low heat value of the methanol is only 0.46 times of the heat value of the gasoline, and the methanol engine needs to inject more methanol fuel under the same power, and the evaporation latent heat of the methanol is 3.8 times of 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 easily gathered in an air inlet manifold of the engine after being injected into the air inlet manifold of the engine, and the problems of poor formation of mixed gas, uneven fuel distribution of each cylinder of the engine, fuel flow of the air inlet pipe and the like are easily generated, and are particularly prominent in the process of warming the vehicle after the engine is started. The recently disclosed technology, namely a multi-point sequential high-pressure injection system (application number: CN 201910631650.9) of an air inlet pipe of a methanol engine, discloses a technical scheme for sequentially injecting methanol at high pressure by adopting the air inlet pipe, wherein the technology adopts high-pressure injection methanol with injection pressure of 20-200bar so as to improve the spraying effect of the methanol, and the technical scheme can better solve the problems of poor fuel/air mixture and uneven distribution of each cylinder of the mixture. Since the high-pressure injection is adopted, if the high-pressure injection of the air inlet pipe is developed from the injection of the air inlet manifold to the direct injection of the high pressure in the cylinder, the configuration of parameters such as the injection pressure, the injection advance angle and the injection times of the methanol injection is more flexible, the optimization of the parameters is facilitated, the reasonable air movement in the cylinder is combined, the compression ratio of the engine is further greatly improved to improve the heat efficiency of the engine, and meanwhile, the heat transfer loss in the cylinder is reduced to improve the heat efficiency of the engine.

The prior Chinese patent 'a combustion system of a direct methanol injection engine and an alcohol injection strategy thereof' (application publication number CN 101915153A) disclose a combustion system structure and an alcohol injection strategy of a direct methanol injection engine in a cylinder so as to solve the problems of unstable ignition and incomplete combustion of methanol. The specific structure of the scheme is that an inlet valve area and an exhaust valve area with staggered height are arranged on the cylinder cover, a gas squeezing area communicated with the inlet valve and a combustion chamber communicated with the exhaust valve are formed among the cylinder cover, the cylinder body and the piston, the mixing of fuel and air is improved through tissue rolling flow in an air inlet stroke and strong squeezing flow in a compression stroke through the gas squeezing area stroke, a spark plug is arranged on the side wall of the combustion chamber between the inlet valve and the exhaust valve, a methanol injector is arranged towards the inlet valve and the top surface of the piston at an included angle of 30-60 degrees, and methanol is injected into the cylinder through the compression stroke of 20-50 CABTDC (the injection advance angle is 20-50 crank angle before compression top dead center, and the larger angle value is injected earlier) in the middle and small load, so that stratified combustion is realized; the problem with this solution is that the injection of alcohol is too late at medium and small loads, a good fuel-air mixture cannot be formed before normal ignition (ignition advance angle 20-40 CABTDC), resulting in unstable ignition combustion, and the solution is suitable for the above-mentioned specific structure.

The methanol engines sold in the market at present are basically developed on the platforms of gasoline engines of passenger cars or diesel engines of commercial cars, and two or four air valves are adopted, and spark plugs are basically arranged at the centers of the air valves on the original cylinder covers.

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 mode of high compression ratio and reducing heat transfer of a piston, so as to further improve the heat efficiency of the methanol engine in the prior art, solve the problems of poor formation of mixed gas, uneven distribution of each cylinder and the like in the working process of the methanol engine adopting an air inlet pipe injection mode by adopting a direct injection mode, and solve the problems of oil injection wetting wall by adopting a method of reasonable air movement organization, multiple injection and the like in the method, 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 valve body for controlling the air inlet quantity of the engine is arranged on the air inlet pipe; 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 provided with an oil sprayer, the top surface of the piston is provided with a pit, the pit and the cylinder body form a combustion chamber together, and main injection formed by the oil sprayer faces the combustion chamber at the pit on the top surface of the piston;

When the piston moves upwards to the end of the compression stroke, the spark plug ignites the fuel/air mixture to burn the fuel, and the gas in the cylinder expands to do work, so as to realize the working process of the engine.

The invention further improves that the piston is made of steel or is inlaid with a steel piston top.

The working method of the methanol engine combustion system is based on the direct injection methanol engine in a cylinder, and comprises the following steps:

the compression ratio adopted by the engine is 13-17;

The engine adopts a control strategy for controlling the oil injection advance angle and the main injection and the post injection, and the oil injection advance angle range of the main injection is 300-180 CABTDC, so that the fuel quantity in a high-temperature area at the upper part of the cylinder is small, the engine is in a lean mixed state, and the knocking combustion of the engine is restrained;

The engine adopts a strategy of organizing air flows in different cylinders at different stages, and organizes air inflow vortex flow in an air inflow stroke and air flows in cylinders which are compressed and extruded in a compression stroke, or organizes air inflow longitudinal vortex flow/tumble flow in the air inflow stroke and air flows in cylinders which are compressed and extruded in the compression stroke;

the methanol injection pressure of the engine ranges from 20 to 500bar.

The invention is further improved in that the methanol injection pressure of the engine is in the 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 more the fuel quantity of the post injection is, the earlier the injection is.

In the case where the injection amount of the main injection is large and the injection time is long, the main injection is performed 1 time to 2 to 3 times, and the interval of each injection is 1 to 2 milliseconds, in order to reduce the fuel injection to the wall surface.

The invention has at least the following beneficial technical effects:

The invention provides a direct injection methanol engine in a cylinder, when the engine is in an air inlet stroke and a piston moves downwards to the middle part of the cylinder, a fuel injector adopts main injection to inject fuel, so that the fuel quantity in a high-temperature area at the upper part of the cylinder is small and is in a lean mixture state, the occurrence of knocking is restrained, or the engine is in a compression stroke and the piston moves upwards to the fuel injector in the middle part of the cylinder and then injects methanol fuel, the injected methanol is mixed with air entering in the air inlet stroke of the cylinder to form fuel/air mixture, when the piston moves upwards to the end of the compression stroke, the fuel/air mixture is ignited by a spark plug, the fuel is combusted, and the gas in the cylinder expands to do work, so that the working process of the engine is realized. The concentration of the mixed gas in the cylinder of the methanol engine sprayed by the air inlet pipe is more uniform, knocking is more easily caused in a high-temperature area with the concentration of the mixed gas being consistent with the surrounding area, the compression ratio cannot be generally increased to be more than 13, and the compression ratio can be increased to be 13-17 by the scheme, so that the thermal 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 technical measures of the efficient methanol engine. The advantage of the high-efficiency methanol engine that adopts the steel piston or inlay the piston of steel piston top has two points, firstly the steel piston top surface that contacts with methyl alcohol can be better to the hot corrosion resistance of methyl alcohol than aluminium piston, secondly the steel piston top surface can reduce the heat transfer loss of piston in the stroke of doing work, is favorable to further improving the thermal efficiency of engine, if combine other like booster technique or variable valve timing technique, this point becomes more obvious, and steel material also enables the piston to bear higher burst pressure simultaneously.

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 mixture is formed, the fuel combustion is quick and sufficient, and meanwhile, the engine can obtain high combustion efficiency due to the high compression ratio of the engine; due to the adoption of a mode of multiple spraying, the penetration distance of spraying beams can be effectively shortened, and the wall wetting phenomenon caused by spraying beams 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 formation of mixed gas and uneven fuel quantity distribution of each cylinder.

Drawings

FIGS. 1 and 2 are diagrams of one embodiment of a high efficiency methanol engine in accordance with the present invention; FIG. 1 is a schematic structural diagram of a piston when it is near intake top dead center (330 CABTDC), including a main injection of methanol at this time;

Fig. 2 is a schematic diagram showing the arrangement of intake valves, exhaust valves, spark plugs and 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 an embodiment when the piston is at position 270CABTDC in the intake stroke.

FIG. 4 is a schematic block diagram of an embodiment when the piston is in position 210CABTDC during an intake stroke.

FIG. 5 is a schematic block diagram of an embodiment when the piston is at 150CABTDC in the intake stroke.

Reference numerals illustrate:

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 region, 10 is main injection, 11 is a cylinder block, 12 is a cylinder head, 13 is an intake vortex, 14 is an intake longitudinal vortex, and 15 is post injection.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

As shown in fig. 1 and 2, the in-cylinder direct injection methanol engine provided by the invention comprises a cylinder block 11, a cylinder head 12 arranged on the cylinder block 11, a piston 7 arranged in the cylinder block 11, an air inlet pipe 5, and a throttle body 6 for controlling the air inlet amount of the engine, wherein the throttle body 6 is arranged on the air inlet pipe 5; the cylinder cover 12 is provided with an intake valve 2 and an exhaust valve 1, the center of the cylinder cover 12 is also provided with a spark plug 3, the cylinder cover 12 is also provided with an oil sprayer 4, the top surface of the piston 7 is provided with a pit 8, the pit and the cylinder cover 12 together form a combustion chamber, and the main injection 10 generated by the oil sprayer 4 is directed to the combustion chamber at the pit 8 on the top surface of the piston 7.

When the engine is in an air intake stroke and the piston 7 moves downwards to the middle of the cylinder, the fuel injector adopts the 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 the post injection 15 to inject methanol fuel, the injected methanol is mixed with air in the cylinder body 11 to form fuel/air mixture, and when the piston 7 moves upwards to the end of the compression stroke, the spark plug 3 ignites the fuel/air mixture to burn the fuel, so that the gas in the cylinder body 11 expands to do work, and the working process of the engine is realized.

The control of the amount of air taken in the engine cylinder is realized by adjusting the throttle opening of a throttle 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 employs a high compression ratio, preferably 13 to 17.

In order to achieve high efficiency of the engine, a high compression ratio is adopted, and the preferable value of the engine is 13-17, which is much higher than the compression ratio of the existing engine 9-12.

The high-efficiency engine adopts a control strategy for controlling the oil injection advance angle and the main injection plus post injection to inhibit knocking combustion of the engine.

The preferable oil injection advance angle of the main injection is 300-180 CABTDC.

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 is the highest temperature in the space of the whole combustion chamber at this time, and is Wen Moduan of the whole combustion chamber, and knocking is most likely to occur when the mixture concentration therein is high (lambda=0.9 to 1.1). In order to suppress knocking, the mixture concentration in the high temperature region 9 is reduced as much as possible. Therefore, a control strategy for controlling the oil injection advance angle and the oil injection times is adopted.

First, the oil injection advance angle is controlled.

As shown in fig. 1, at the beginning of the intake stroke of the engine, the piston 7 is near the top dead center, and as the piston 7 moves downward, if the injector 4 starts injecting fuel 1 st time, the earlier the injected fuel, the easier the main injection 10 is injected to the surface of the pit 8 on the top surface of the piston 7, and the more likely it is to collide with the surface and bounce back onto 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, since this area is the high temperature area 9 where the temperature in the cylinder is highest, and is further away from the intake valve, the air movement intensity is weaker here than other nearby areas, so the more the fuel quantity of this area is than the other nearby areas, and the more the fuel quantity of this high temperature area is easy to form knocking combustion in the latter stage of the compression stroke. The fuel injection is properly delayed in the air intake stroke, so that the injected fuel is prevented from bouncing to the surface of the cylinder cover at the exhaust valve side through the top surface of the piston, the fuel quantity at the upper part of the cylinder, particularly in the high temperature region 9, is less, and the knocking combustion of the engine can be restrained in a lean state; on the premise of properly delaying fuel injection and avoiding the fuel injection from rebounding to the high-temperature region 9, the injection is performed as early as possible, so that the longer the mixed gas stays in the cylinder, the more uniform the formed mixed gas is, the higher the formed quality of the mixed gas is, and the stable combustion of the mixed gas is facilitated.

When the piston moves downwards to the middle part of the cylinder (as shown in fig. 3), if the fuel injector starts to inject at the moment, the oil beam stroke of the fuel injector is longer, at the moment, the middle and rear sections of the main injection 10 are injected to the surface of the piston, compared with the situation in fig. 1, the fuel is less prone to rebound to a high temperature region 9, the fuel enters into a pit 8 on the top surface of the piston, part of the fuel in the injection bounces to the air through the surface of the piston, part of the fuel is accumulated on the surface of the pit 8, and part of the fuel accumulated on the surface of the piston is further volatilized under the heating action of the hot surface of the piston, so that good fuel/air mixture is formed.

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 bundle stroke of the injector is long, the periphery of the side surface of the rear end of the oil bundle touches the inner wall surface of the cylinder block 11, the fuel is partially volatilized, and the wet wall phenomenon is caused by partial accumulation on the inner wall surface of the cylinder block, the oil film on the surface of the cylinder liner is diluted by the partial accumulation on the inner wall surface of the cylinder block, poor lubrication and more abrasion are caused, and meanwhile, the phenomenon that liquid methanol flows into the engine oil pan through the gap between the piston and the inner wall of the cylinder block can occur when the partial accumulation on the inner wall surface of the cylinder block is too much, so that the possibility of occurrence of the warm-up working condition with lower engine temperature is higher, and the wet wall phenomenon should be avoided as much as possible.

Post injection 15 is also included in the injection control strategy.

The main injection 10 is generated early in the intake stroke or the compression stroke, and the present operation mode mainly uses the homogeneous combustion mode, so that the main injection is satisfied.

However, in the case where the engine is designed to have a high compression ratio, when the engine is in a large load state and knocking is more likely to occur, in order to better suppress the occurrence of knocking, a post injection 15 (shown in fig. 5) following the main injection 10 may be performed to further reduce the temperature of the in-cylinder compression late-stage mixture by further utilizing the characteristic that the methanol fuel is large in vaporization latent heat. The post injection occurs in the middle of the compression stroke, the fuel quantity of the injection should not exceed 30% of the total fuel quantity, if the injection is too late, such as in the later injection of the compression stroke, the fuel volatilization time is too short, which is not beneficial to the formation of the mixture, and the temperature of the mixture in the center of the cylinder is also reduced more, which is not beneficial to the ignition of the mixture by the spark plug in the later compression stage. The post injection is beneficial to reducing knocking, forming a mixture gas with concentration thicker than that of the mixture gas deviated from the center of the cylinder in the center of the cylinder for a lean-burn engine, stabilizing spark ignition, accelerating flame propagation and reducing combustion cycle variation. The preferred crank angle for the post injection is 150-60 CABTDC, the greater the amount of post injected fuel, the earlier the injection.

In the case of large injection quantity and long injection time of the main injection, in order to reduce the phenomenon of wetting wall caused by fuel injection to the wall surface, the main injection performed 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 of each injection is controlled to be smaller than the wall collision distance of the spray. According to the spray theory, in order to avoid wall collision, for the condition that the injection pressure is 20Mpa and the diameter of the spray hole is 0.2 millimeter, the penetration distance of 1.5 milliseconds of injection can reach 100 millimeters, so that a large amount of wall collision of fuel can be avoided when the duration of each injection is controlled between 1 and 2 milliseconds, and the higher the pressure, the shorter the injection time of each injection. In the case of starting injection when the piston is in the upper middle portion of the cylinder (fig. 3), even if injection is allowed earlier to cause a large amount of fuel to be injected into the pit on the piston crown, the phenomenon of wet wall of the cylinder wall is not caused although the fuel is accumulated in the pit, and the fuel forms a good combustible air mixture with air under the heating action of the top surface of the pit of the piston and the entrainment action of the compressed air squeeze flow, and the main injection is not necessarily divided into multiple injections.

The high-efficiency methanol engine adopts strategies for organizing air flows in different cylinders at different stages.

In order to achieve high efficiency of the engine, the engine employs in-cylinder air flow that organizes intake swirl 13 during the intake stroke and compression squish during the compression stroke.

In order to achieve high efficiency of the engine, the engine either employs in-cylinder air flow that organizes intake air longitudinal swirl 14 (tumble) during the intake stroke and compression squish during the compression stroke.

After the in-cylinder direct injection method is adopted instead of the intake pipe injection method, the fuel injection is evaporated and the time for forming good combustible gas mixture by mixing with air is short, so that proper form and strong air movement are required to be organized to improve the in-cylinder fuel/air mixture forming quality.

The intake swirl 13 is organized by designing the intake ports in the cylinder head in a tangential or spiral air passage fashion to improve the mixing of fuel and air during intake.

The intake air longitudinal swirl 14 is organized by designing the intake air passage on the cylinder head as a tangential intake air passage to improve the mixing of fuel and air during intake.

The provision of a pit 8 shaped combustion chamber, such as a typical bathtub shaped combustion chamber, atop the piston 7 creates a compression squish flow during the compression stroke and a reverse squish flow during the expansion stroke, which facilitates a generally more uniform mixture of methanol fuel and air after injection into the cylinder for flame propagation and combustion.

The high efficiency methanol engine has a methanol injection pressure in the range of 20 to 500bar, preferably 60 to 200bar.

In order to achieve good fuel spraying effect, different fuel injection pressures are adopted according to different injected fuel amounts of the engine under different working conditions, and the higher the fuel amount is, the higher the fuel injection pressure is. The injection pressure ranges from 20 to 500bar, preferably from 60 to 200bar. When the methanol engine adopts an air inlet pipe injection mode, the injection pressure is 3-5 bar, and after direct injection in a cylinder is adopted, the injection pressure range is 20-500 bar, so that the methanol engine has a good spraying effect. Meanwhile, in order to reduce the power consumption of the methanol high-pressure oil pump, the methanol oil injection pressure is preferably 60-200 bar on the premise of meeting the direct injection spraying effect of the methanol.

The injection pressure, the injection advance angle and the injection times of the engine under different operation conditions are all determined by carrying out matching calibration test optimization on the engine.

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 preferable technical measures of the efficient methanol engine. The advantage of the high-efficiency methanol engine that adopts the steel piston or the piston that inlays steel piston top has two points, firstly the steel piston top surface that contacts with methyl alcohol can be better to the hot corrosion resistance of methyl alcohol than aluminium piston, secondly the steel piston top surface can reduce the heat transfer loss of piston in the stroke of doing work, is favorable to further improving the thermal efficiency of engine, if combine other like booster technique or variable valve timing technique, this point becomes more obvious, also enables the piston to bear higher burst pressure simultaneously.

Example actual measurement effect

An air-cooled single-cylinder natural air-suction engine (model 192F) with a cylinder diameter of 92mm modified by a diesel engine has a discharge capacity of about 0.5 liter, a 2-valve and a spiral air inlet channel to generate air inlet vortex, a spark plug is arranged between an air inlet valve and exhaust, a pit on the top of a piston is bathtub-shaped, and the compression ratio is 15. When the working condition of the engine is that a throttle valve is fully opened, the rotating speed is 2500 rpm, lambda=1 (theoretical mixing ratio), if the oil injection advance angle is earlier than 330CABTDC, knocking combustion can occur, when the oil injection advance angle is later than 300CABTDC, knocking combustion can not occur, and when the oil injection advance angle is 270CABTDC, the effective thermal efficiency of the engine can reach 37%, which is a good level for a single-cylinder engine. When the injection advance angle is less than 180CABTDC, the thermal efficiency of the engine is reduced. Therefore, the preferable oil injection advance angle is 300-180 CABTDC.

By now it will be appreciated by those skilled in the art that while the invention has been shown and described in detail, many other variations or modifications of the invention can be directly ascertained or inferred from the teachings of the present disclosure and which remain within the principles of the present invention without departing from the spirit and scope thereof. Accordingly, the scope of the present invention should be understood and deemed to cover all such other variations or modifications.

Claims

1. A method of operating a methanol engine combustion system, the method being based on a direct injection methanol engine in a cylinder, comprising:

the compression ratio adopted by the engine is 13-17;

The direct injection methanol engine in the cylinder adopted by the working method of the methanol engine combustion system comprises a cylinder block (11), a cylinder head (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 amount of the engine is arranged on the air inlet pipe (5); an air inlet valve (2) and an air outlet valve (1) are arranged on a cylinder cover (12), a spark plug (3) is arranged in the center of the cylinder cover (12), an oil sprayer (4) is arranged on the cylinder cover (12), a pit (8) is formed in the top surface of a piston (7), a combustion chamber is formed together with a cylinder body (11), and main injection (10) formed by the oil sprayer (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 part of the cylinder, the fuel injector (4) adopts main injection (10) to inject methanol fuel, or when the engine is in a compression stroke and the piston (7) moves upwards to the middle part of the cylinder, the fuel injector (4) adopts post injection (15) to inject methanol fuel, the injected methanol is mixed with air entering in an air inlet stroke of the cylinder body (11) to form fuel/air mixture, and when the piston (7) moves upwards to the end of the compression stroke, the spark plug (3) ignites and ignites the fuel/air mixture to burn the fuel, and the air in the cylinder body (11) expands to do work, so that the working process of the engine is realized;

In the case of large injection quantity and long injection time of the main injection, in order to reduce the situation that the fuel is injected to the wall surface, the main injection performed 1 time is divided into 2 to 3 times, and the interval of each injection is 1 to 2 milliseconds;

the methanol injection pressure range of the engine is 20-500 bar;

The engine adopts a strategy of organizing air flows in different cylinders at different stages, and organizes air flows in an air intake vortex and a compression squeezing flow in a compression stroke in an air intake stroke, or organizes air flows in an air intake longitudinal vortex/rolling flow and the compression squeezing flow in the compression stroke in the air intake stroke.

2. A method of operating a methanol engine combustion system according to claim 1, characterized in that the piston (7) is a steel piston or a piston with a steel piston top.

3. A method of operating a methanol engine combustion system as in claim 1 wherein the engine has a methanol injection pressure in the range of 60 to 200bar.

4. A method of operating a methanol engine combustion system as in claim 1 wherein the post injection has an injection advance of 150 to 60CABTDC, the amount of post injected fuel is no more than 30% of the total fuel and the more post injected fuel is, the earlier the injection.