阅读说明：本技术 稀薄燃烧系统、稀薄燃烧发动机及稀薄燃烧方法 (Lean combustion system, lean combustion engine and lean combustion method ) 是由 苏建业 习纲 叶俊亭 颜丙超 王华钰 王玉军 李挺 陈宇清 丁锋 王庆华 于 2019-09-26 设计创作，主要内容包括：本发明提供一种稀薄燃烧系统、稀薄燃烧发动机及稀薄燃烧方法。稀薄燃烧系统包括燃烧室、进气结构、低压喷射系统、高压喷射系统、点火系统、排气结构和活塞；进气结构和排气结构位于燃烧室顶部的两侧；低压喷射系统包括低压喷油器,低压喷油器位于进气道以向进气道喷射燃油；高压喷射系统和点火系统位于燃烧室顶部且位于进气结构和排气结构之间,高压喷射系统包括高压喷油器,高压喷油器设置在燃烧室的顶部以向燃烧室直接喷射燃油,点火系统包括点火线圈和火花塞,火花塞布置在燃烧室顶部且较高压喷油器靠近排气结构。本发明提供的方案可以解决现有技术中分层稀薄燃烧方式存在的NOx和颗粒物排放高、节油率低、成本高的问题。(The invention provides a lean combustion system, a lean combustion engine and a lean combustion method. The lean combustion system comprises a combustion chamber, an air inlet structure, a low-pressure injection system, a high-pressure injection system, an ignition system, an exhaust structure and a piston; the air inlet structure and the exhaust structure are positioned on two sides of the top of the combustion chamber; the low-pressure injection system comprises a low-pressure oil injector, and the low-pressure oil injector is positioned in the air inlet passage and used for injecting fuel oil to the air inlet passage; the high-pressure injection system and the ignition system are located at the top of the combustion chamber and located between the air inlet structure and the exhaust structure, the high-pressure injection system comprises a high-pressure oil injector, the high-pressure oil injector is arranged at the top of the combustion chamber to directly inject fuel oil into the combustion chamber, the ignition system comprises an ignition coil and a spark plug, and the spark plug is arranged at the top of the combustion chamber and is close to the exhaust structure through the higher-pressure oil injector. The scheme provided by the invention can solve the problems of high NOx and particulate matter emission, low oil saving rate and high cost in a layered lean combustion mode in the prior art.)

1. A lean combustion system is characterized by comprising a combustion chamber, an air inlet structure, a low-pressure injection system, a high-pressure injection system, an ignition system, an exhaust structure and a piston;

the piston moves up and down in the combustion chamber;

the air inlet structure and the exhaust structure are positioned on two sides of the top of the combustion chamber, the air inlet structure comprises an air inlet channel, an air inlet valve and an air inlet valve lift mechanism, and the exhaust structure comprises an exhaust channel, an exhaust valve and an exhaust valve lift mechanism;

the low-pressure injection system comprises a low-pressure injector which is positioned in the air inlet passage and used for injecting fuel to the air inlet passage;

the high-pressure injection system with ignition system is located the combustion chamber top just is located intake structure with between the exhaust structure, high-pressure injection system includes the high-pressure sprayer, the high-pressure sprayer sets up the top of combustion chamber is in order to the combustion chamber direct injection fuel, ignition system includes ignition coil and spark plug, the spark plug is arranged the combustion chamber top just compare the high-pressure sprayer is close to the exhaust structure.

2. The lean burn system of claim 1 wherein fuel injected by the high pressure injector is directed to a location near the spark plug but does not collide with the spark plug.

3. The lean burn system of claim 1 wherein the injection pressure of the low pressure injector does not exceed 10 bar.

4. The lean burn system of claim 1 wherein the low pressure injector is a solenoid driven multiple orifice injector for a port injected engine.

5. The lean burn system of claim 4 wherein the low pressure fuel injector is a multi-orifice swirl type fuel injector.

6. The lean burn system of claim 1 wherein the injection pressure of the high pressure injector is no less than 200 bar.

7. The lean burn system of claim 1 wherein the high pressure injector is a two-port injector or a single-port injector.

8. The lean-burn system of claim 1 wherein the piston is a high compression ratio piston.

9. A lean-burn engine comprising a plurality of the lean-burn systems as claimed in any one of claims 1 to 8.

10. A lean combustion method applied to the lean combustion engine according to claim 9, comprising:

under the working conditions of medium-low rotating speed and low load, aiming at one working cycle, injecting low-pressure fuel oil of an air inlet passage through the low-pressure fuel injector in a time period before an air inlet valve is opened, and injecting high-pressure fuel oil in a cylinder through the high-pressure fuel injector in the later stage of a compression stroke and before the ignition moment;

under the working conditions of medium and low rotation speed and medium load, aiming at one working cycle, the low-pressure fuel injection of an air inlet passage is carried out through the low-pressure fuel injector in the time period before an air inlet valve is opened, the high-pressure fuel injector finishes at least two times of in-cylinder high-pressure fuel injection in a compression stroke, the first time of in-cylinder high-pressure fuel injection occurs at the later stage of the compression stroke and before the moment close to ignition, and the last time of in-cylinder high-pressure fuel injection occurs during ignition or after ignition.

11. The lean-burn method of claim 10, further comprising:

under the working condition of high rotating speed or high load, aiming at one working cycle, the low-pressure fuel injection of the air inlet passage is carried out through the low-pressure fuel injector in the time period before the opening of the air inlet valve, or the low-pressure fuel injection of the air inlet passage is carried out through the low-pressure fuel injector in the time period from before the opening of the air inlet valve to after the opening of the air inlet valve, and the high-pressure fuel injection of the cylinder is carried out through the high-pressure fuel injector in.

12. The lean combustion method according to claim 10, wherein under the working conditions of medium-low rotation speed and low load, the time interval between the injection ending moment of the high-pressure injector and the ignition starting moment is 0-10 degrees of crankshaft angle.

13. The lean-burn method according to claim 10, wherein, under the medium-low rotation speed and medium-load conditions, the time interval from the end of the high-pressure fuel injection in the first cylinder to the start of ignition is 0 to 10 crank angle degrees, and the time interval from the start of the high-pressure fuel injection in the last cylinder to the start of ignition is 0 to 10 crank angle degrees.

14. The lean burn method of claim 10 wherein the high pressure fuel injector injects less than 1.5mg of fuel during a single operating cycle at medium to low speed, low load conditions.

Technical Field

The invention relates to the technical field of engines, in particular to a lean combustion system, a lean combustion engine and a lean combustion method.

Background

The development of gasoline engines with high efficiency and low fuel consumption is an important subject facing the automobile industry. From the view of the whole vehicle circulation working condition of the passenger vehicle, the working area of the engine is mainly concentrated on the working conditions of low speed, medium and low load. Therefore, the key point of reducing the oil consumption of the whole automobile is to improve the heat efficiency of the gasoline engine under the working condition of medium and low load. The main factors restricting the low-load thermal efficiency improvement of the gasoline engine comprise high pumping loss, large heat transfer loss, low specific heat ratio of mixed gas, high geometric compression ratio and the like. The lean combustion not only greatly reduces the pumping loss, but also reduces the heat transfer loss and improves the specific heat ratio of the mixture by forming the lean mixture. Therefore, lean combustion is an effective means for improving the thermal efficiency and reducing the fuel consumption of a gasoline engine.

At present, the main method for realizing spark ignition type lean combustion is to directly inject fuel oil in a cylinder to form a mixed gas with layered concentration in the cylinder, namely, a richer mixed gas is formed near a spark plug, and a leaner mixed gas is formed at a position far away from the spark plug, so that the mixed gas in the cylinder is lean as a whole. However, the layered lean combustion mode has the defects of high NOx and particulate matter emission, low oil saving rate and high cost.

Disclosure of Invention

The invention aims to provide a lean combustion system, a lean combustion engine and a lean combustion method, which aim to solve the problems of high NOx and particulate matter emission, low oil saving rate and high cost in a layered lean combustion mode in the prior art. The specific technical scheme is as follows:

in order to solve the technical problem, the invention provides a lean combustion system, which comprises a combustion chamber, an air inlet structure, a low-pressure injection system, a high-pressure injection system, an ignition system, an exhaust structure and a piston, wherein the combustion chamber is provided with a combustion chamber;

the piston moves up and down in the combustion chamber;

the air inlet structure and the exhaust structure are positioned on two sides of the top of the combustion chamber, the air inlet structure comprises an air inlet channel, an air inlet valve and an air inlet lift mechanism, and the exhaust structure comprises an exhaust channel, an exhaust valve and an exhaust lift mechanism;

the low-pressure injection system comprises a low-pressure injector which is positioned in the air inlet passage and used for injecting fuel to the air inlet passage;

the high-pressure injection system with ignition system is located the combustion chamber top just is located intake structure with between the exhaust structure, high-pressure injection system includes the high-pressure sprayer, the high-pressure sprayer sets up the top of combustion chamber is in order to the combustion chamber direct injection fuel, ignition system includes ignition coil and spark plug, the spark plug is arranged the combustion chamber top just compare the high-pressure sprayer is close to the exhaust structure.

Alternatively, the fuel injected by the high-pressure injector is directed to a position close to the ignition plug but does not collide with the ignition plug.

Optionally, the injection pressure of the low-pressure fuel injector does not exceed 10 bar.

Optionally, the low-pressure injector is a multi-hole injector driven by a solenoid valve of a port injection engine.

Optionally, the low-pressure oil injector is a porous swirl oil injector.

Optionally, the injection pressure of the high-pressure fuel injector is not lower than 200 bar.

Optionally, the high-pressure fuel injector is a two-hole fuel injector or a single-hole fuel injector.

Optionally, the piston is a high compression ratio piston.

Based on the same inventive concept, the invention also provides a lean-burn engine comprising a plurality of lean-burn systems as described in any one of the above.

Based on the same inventive concept, the invention also provides a lean-burn method applied to the lean-burn engine, comprising:

under the working conditions of medium-low rotating speed and low load, aiming at one working cycle, injecting low-pressure fuel oil of an air inlet passage through the low-pressure fuel injector in a time period before an air inlet valve is opened, and injecting high-pressure fuel oil in a cylinder through the high-pressure fuel injector in the later stage of a compression stroke and before the ignition moment;

under the working conditions of medium and low rotation speed and medium load, aiming at one working cycle, the low-pressure fuel injection of an air inlet passage is carried out through the low-pressure fuel injector in the time period before an air inlet valve is opened, the high-pressure fuel injector finishes at least two times of in-cylinder high-pressure fuel injection in a compression stroke, the first time of in-cylinder high-pressure fuel injection occurs at the later stage of the compression stroke and before the moment close to ignition, and the last time of in-cylinder high-pressure fuel injection occurs during ignition or after ignition.

Optionally, the lean combustion method further comprises:

under the working condition of high rotating speed or high load, aiming at one working cycle, the low-pressure fuel injection of the air inlet passage is carried out through the low-pressure fuel injector in the time period before the opening of the air inlet valve, or the low-pressure fuel injection of the air inlet passage is carried out through the low-pressure fuel injector in the time period from before the opening of the air inlet valve to after the opening of the air inlet valve, and the high-pressure fuel injection of the cylinder is carried out through the high-pressure fuel injector in.

Optionally, under the working conditions of medium-low rotating speed and low load, the time interval between the oil injection ending moment of the high-pressure oil injector and the ignition starting moment is 0-10 degrees of crankshaft angle.

Optionally, under the working conditions of medium and low rotation speeds and medium load, the time interval between the injection ending time of the high-pressure fuel oil in the cylinder for the first time and the ignition starting time is 0-10 crank angle degrees, and the time interval between the injection starting time of the high-pressure fuel oil in the cylinder for the last time and the ignition starting time is 0-10 crank angle degrees.

Optionally, under the working conditions of medium-low rotating speed and low load, the amount of fuel injected by the high-pressure fuel injector in one working cycle is less than 1.5 mg.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects:

compared with the existing layered lean combustion technology, the original emission of NOx is reduced to the level without a lean combustion catalyst, and meanwhile, the emission of particles is greatly reduced because the wholly uniform lean mixed gas is formed in the combustion chamber;

the lean-burn engine can realize lean combustion in each cylinder, and reduce the original emission of NOx and particulate matters;

according to the lean combustion method, the low-pressure oil injector positioned in the air inlet channel and the high-pressure oil injector positioned in the combustion chamber work cooperatively in one working cycle, and the injection time of the low-pressure oil injector and the high-pressure oil injector is reasonably configured in one working cycle, so that the uniform mixed gas lean combustion with high efficiency and low NOx and particulate matter emission is realized.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic diagram of a lean burn system according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of fuel injection from a two-orifice fuel injector according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of the operation of the homogeneous lean combustion engine according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a strategy for lean-burn of homogeneous charge under low-load conditions at medium-low rotation speed by the lean-burn method according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a lean burn strategy for lean burn at medium and low rpm under medium load conditions according to an exemplary embodiment of the present invention;

FIG. 6 is a schematic diagram of a homogeneous lean combustion strategy for a lean combustion method at high speed or high load conditions according to an embodiment of the present invention;

FIG. 7 is a schematic diagram of another strategy for homogeneous lean combustion at high speed or high load using the lean combustion method of the present invention.

Detailed Description

As described in the background art, the existing stratified lean combustion mode has the problems of high NOx and particulate matter emission, low oil saving rate and high cost, and is mainly expressed in the following aspects:

1) although the stratified lean combustion mode is very lean in the overall air-fuel ratio and is beneficial to reducing NOx emission, in order to stabilize combustion, a rich mixture is formed around a spark plug, so that the original NOx concentration generated by the first half-stage combustion is high, and therefore, an NOx aftertreatment technology is required to treat NOx;

2) the conversion efficiency of the existing three-way catalyst to NOx is close to zero under the Lean-burn condition, and a NOx Lean-burn catalyst, such as LNT (Lean NOx Trap), needs to be configured, which not only increases the system cost, but also leads to great reduction in the fuel saving potential of Lean combustion due to the fact that the LNT needs to be regenerated through periodic enrichment combustion in the regeneration process, and also leads to great increase in particulate matter emission, which brings new challenges to meeting the current increasingly stringent particulate matter emission regulations worldwide.

In summary, in order to save oil and reduce particulate matter emission and reduce cost as much as possible, it is necessary to solve the technical bottleneck of the stratified lean combustion and realize a combustion system with the best overall performance starting from the gas mixture organization and the combustion mode.

Based on the above, the invention provides a high-efficiency low-NOx and particulate matter emission homogeneous mixed gas lean-burn combustion system, which is used for solving the problems that the existing stratified lean-burn combustion is high in NOx original emission and needs an additional lean-burn catalyst, and greatly reducing particulate matter emission which is more and more important in the industry while realizing lean-burn fuel saving. Generally, a desired homogeneous charge lean combustion mode is achieved by a low pressure injector located in an intake port and a high pressure injector located in a combustion chamber working together in one cycle. Compared with stratified lean combustion, the invention can reduce the original emission of NOx to the level without a lean combustion catalyst because of the homogeneous lean combustion of the mixed gas, and meanwhile, the emission of particulate matters is greatly reduced because of the formation of the wholly homogeneous lean mixed gas in the combustion chamber.

The present invention will be described in detail with reference to the accompanying drawings in order to make the objects and features of the present invention more comprehensible, however, the present invention may be realized in various forms and should not be limited to the embodiments described above.

FIG. 1 is a schematic diagram of a lean-burn combustion system according to an embodiment of the present invention. Referring to fig. 1, a lean burn system includes a combustion chamber 10, an intake structure 20, a low pressure injection system 30, a high pressure injection system 40, an ignition system 50, an exhaust structure 60, and a piston 70.

The piston 70 moves up and down in the combustion chamber 10, and preferably, the piston 70 is a high compression ratio piston, and the high compression ratio piston can enable the geometric compression ratio of the combustion chamber 10 to reach more than 12:1, so that lean combustion can be better realized.

The intake structure 20 and the exhaust structure 60 are located on two sides of the top of the combustion chamber 10, the intake structure 20 includes an intake passage 21, an intake valve 22, and an intake lift mechanism (not shown), and the exhaust structure 60 includes an exhaust passage 61, an exhaust valve 62, and an exhaust lift mechanism (not shown), which can continuously change the opening timings of the intake valve 22 and the exhaust valve 62.

The low pressure injection system 30 includes a low pressure injector 31, and the low pressure injector 31 is located in the intake passage 21 to inject fuel (i.e., low pressure fuel spray 311) into the intake passage 21. Preferably, the injection pressure of low-pressure injector 31 does not exceed 10 bar. The low-pressure injector 31 may be a multi-hole injector driven by a solenoid valve of a port injection engine, and preferably uses a hole swirl injector.

As shown in fig. 1, the low-pressure injection system 30 may further include a low-pressure fuel rail 32, a gasoline tank, and a low-pressure fuel supply module 33, where the low-pressure fuel injector 31 is connected to the low-pressure fuel rail 32 through a pipeline, the low-pressure fuel rail 32 is connected to the gasoline tank and the low-pressure fuel supply module 33 through a pipeline, and the low-pressure fuel rail 32 is used for storing fuel, and simultaneously suppressing pressure fluctuation generated by injecting fuel into the gasoline tank and the low-pressure fuel supply module 33 and the low-pressure fuel injector 31, so as to ensure stable pressure of.

The high-pressure injection system 40 and the ignition system 50 are located at the top of the combustion chamber 10 and between the air intake structure 20 and the exhaust structure 60, the high-pressure injection system 40 includes a high-pressure fuel injector 41, and the high-pressure fuel injector 41 is arranged at the top of the combustion chamber 10 to directly inject fuel (i.e., high-pressure fuel spray 411) into the combustion chamber 10. Preferably, the injection pressure of the high-pressure fuel injector 10 is not lower than 200bar, and the high-pressure fuel injector 10 is a two-hole fuel injector or a single-hole fuel injector.

The ignition system 50 includes an ignition coil 51 and an ignition plug 52, and the ignition plug 52 is disposed at the top of the combustion chamber 10 and closer to the exhaust structure 60 than the high-pressure fuel injector 41, so that the high-pressure fuel injector 41 can be disposed on the intake side, otherwise if the ignition plug is disposed on the intake side, the high-pressure fuel injector 41 must be disposed on the exhaust side, and the temperature on the exhaust side is too high, so that the fuel injector 41 cannot accommodate the high temperature.

The fuel injected by the high-pressure injector 41 (i.e., the high-pressure fuel spray 411) is guided to a position close to the ignition plug 52 without colliding with the ignition plug 52, and fig. 2 shows a schematic diagram of high-pressure direct injection fuel injection when the high-pressure injector 41 is a two-port injector, and two high-pressure fuel sprays 411 generated by the two-port injector are respectively guided to positions close to the ignition plug 52 from both sides of the ignition plug 52 without colliding with the ignition plug 52, so that combustion stability and robustness of lean combustion can be ensured. It is understood that when the high-pressure fuel injector 41 is a single-hole fuel injector, a high-pressure fuel spray 411 generated by the single-hole fuel injector injection may be directed from a side of the ignition plug 52 to a position close to the ignition plug 52, but does not collide with the ignition plug 52.

As shown in fig. 1, the high-pressure injection system further includes a high-pressure fuel rail 42 and a high-pressure fuel pump 43, the high-pressure fuel injector 41 is connected to the high-pressure fuel rail 42 through a pipeline, and the high-pressure fuel rail 42 is connected to the high-pressure fuel pump 43 through a pipeline. The high-pressure oil pump 43 is connected to the gasoline tank and the low-pressure fuel supply module 33 through pipes, so that the high-pressure injection system 40 and the low-pressure injection system 30 share one tank. The high-pressure rail 42 is used for storing fuel, and simultaneously, pressure fluctuation generated by injecting fuel by the high-pressure fuel pump 43 and the high-pressure fuel injector 41 is restrained, so that the pressure of the high-pressure injection system 40 is ensured to be stable.

In this embodiment, a lean mixture that is uniform as a whole can be formed in the combustion chamber 10, and the preparation of the uniform mixture is mainly completed by the low-pressure injection system 30 that is injected by the intake passage and the high-pressure injection system 40 that is injected in the combustion chamber. Compared with a multi-hole (4-hole) oil sprayer used by a conventional gasoline direct injection engine, the two-hole oil sprayer or the single-hole oil sprayer is adopted in the embodiment, and the problem that the conventional multi-hole oil sprayer forms over-rich mixed gas around a spark plug is solved by reducing the quality of fuel oil injection.

Based on the same inventive concept, an embodiment of the invention also provides a lean-burn engine which comprises a plurality of lean-burn systems described in the above embodiments. Specifically, the lean-burn engine comprises at least one cylinder, and each cylinder can be correspondingly provided with the lean-burn system, so that lean combustion can be realized in each cylinder. Because the cylinder of the lean-burn engine can form uniform lean mixture, compared with the existing layered lean-burn engine, the original emission of NOx can be reduced to the level without a lean-burn catalyst, and meanwhile, because the cylinder forms the uniform lean mixture, the emission of particulate matters is greatly reduced.

Based on the same inventive concept, an embodiment of the invention further provides a lean combustion method, which is applied to the lean combustion engine of the embodiment, and the lean combustion of the homogeneous mixture is realized by the cooperative work of a low-pressure fuel injector positioned in an air inlet passage and a high-pressure fuel injector positioned in a cylinder in a working cycle.

Fig. 3 shows a lean combustion region in the whole operating condition diagram of the engine, wherein a region I is a medium-low rotating speed and low load condition, a region II is a medium-low rotating speed and medium load condition, and a region III is a high rotating speed or high load condition. The homogeneous mixing lean combustion mode is mainly applied to a region I and a region II which influence the fuel consumption of the whole vehicle most importantly, and a combustion mode of a theoretical air-fuel ratio can be adopted in the region III. The combustion strategies employed by these three regions are described in detail below.

Fig. 4 shows the homogeneous lean combustion strategy at medium and low speed, low load conditions in region I, and fig. 5 shows the homogeneous lean combustion strategy at medium and low speed, medium load conditions in region II.

Referring to fig. 4, in the middle-low speed and low load condition of the region I, the lean-burn method is: and aiming at one working cycle, injecting low-pressure fuel of an air inlet passage through the low-pressure fuel injector in a time period before an air inlet valve is opened, and injecting high-pressure fuel in a cylinder through the high-pressure fuel injector in the later period of a compression stroke and before the ignition moment. Preferably, the time interval between the oil injection end time and the ignition start time of the high-pressure oil injector is 0-10 crank angle degrees.

As with the intake, fuel and ignition strategy shown in FIG. 4, low pressure port fuel injection occurs during the time period before the engine intake valve is opened, i.e., a closed-valve injection strategy, to ensure sufficient time to form a homogeneous mixture before ignition. The high-pressure injection moment of the high-pressure fuel injector occurs in the later period of the compression stroke and is close to the ignition moment. The time interval between the end of injection of the high-pressure injection and the ignition is defined as Δ (crank angle), which is typically 0 to 10 degrees. A small amount of fuel (less than 1.5mg) is injected through the two-hole fuel injector, so that a large-area over-rich area is not formed around the spark plug, namely, the problems of high particulate matter emission and high NOx generation in the latter half of combustion caused by the large-area over-rich area formed around the spark plug by the traditional layered lean combustion are solved. Meanwhile, the high-pressure oil injector has higher injection pressure, and high-speed spraying improves the turbulence intensity around the spark plug, so that the propagation speed of initial flame is increased, and homogeneous lean mixed gas can be stably combusted.

Referring to fig. 5, in the middle-low speed and middle-load operating condition of the region II, the lean-burn method is as follows: and aiming at a working cycle, injecting low-pressure fuel of an air inlet passage through the low-pressure fuel injector in a time period before an air inlet valve is opened, completing high-pressure fuel injection in a cylinder at least twice in a compression stroke by the high-pressure fuel injector, wherein the high-pressure fuel injection in the cylinder for the first time occurs at the later stage of the compression stroke and before the moment close to ignition, and the high-pressure fuel injection in the cylinder for the last time occurs during ignition or after ignition. Preferably, the time interval between the end moment of the high-pressure fuel injection in the first cylinder and the ignition start moment is 0-10 crank angle degrees, and the time interval between the start moment of the high-pressure fuel injection in the last cylinder and the ignition start moment is 0-10 crank angle degrees.

As with the intake, fuel and ignition strategy shown in fig. 5, a homogeneous lean burn strategy is still employed for this condition, but differs from region I in the injection strategy of the high pressure injector. The fuel injection from the low-pressure injector of the air inlet channel is carried out in the time period before the opening of the air inlet valve of the engine, namely the valve closing injection strategy, so that enough time is ensured to form uniform air mixture before ignition. And the high-pressure injection of the high-pressure injector is completed at least twice. The first high-pressure injection occurs late in the compression stroke, near the time of ignition, and the last injection occurs during or after ignition. Fig. 5 shows two injections by the high-pressure injector as an example, where the time interval from the end of the first high-pressure injection to the start of ignition is defined as Δ 1 (crank angle), the time interval from the start of ignition to the start of the second high-pressure injection is defined as Δ 2 (crank angle), and both Δ 1 and Δ 2 are typically 0 to 10 crank angle degrees. The first high-pressure fuel injection, which is performed before ignition, produces a very small fuel injection amount (about 1mg or so), and particulate matter and NOx emissions can be reduced. And for the second high-pressure fuel injection carried out at the beginning of ignition (delta 2 is less than or equal to the ignition pulse width) or at the end of ignition (delta 2 is greater than the ignition pulse width), a very small amount of fuel (about 1 mg) is injected to the periphery of a spark plug gap, so that the turbulence intensity around the spark plug is improved, the formation of a fire core and the propagation of flame are promoted, and the combustion is stabilized.

Fig. 6 and 7 show two homogeneous charge lean burn strategies at high speed or high load conditions in region III.

Referring to fig. 6 and 7, under high speed or high load conditions, shown in region III, the lean burn method is: and aiming at one working cycle, performing low-pressure fuel injection of an air inlet passage through the low-pressure fuel injector in a time period before an air inlet valve is opened, or performing low-pressure fuel injection of the air inlet passage through the low-pressure fuel injector in a time period from the time before the air inlet valve of the engine is opened to the time after the air inlet valve is opened, and performing in-cylinder high-pressure fuel injection through the high-pressure fuel injector in an air inlet stroke.

Intake, fuel, and ignition control strategies are shown in fig. 6 and 7 for the stoichiometric combustion mode for region III. According to the requirement of the engine for preparing the mixture under different load and rotating speed conditions, the fuel injection of the low-pressure injector in the air inlet passage can be carried out in the time period before the opening of an air inlet valve of the engine shown in the figure 6, namely the valve closing injection strategy, or in the time period from the opening of the air inlet valve to the opening of the air inlet valve shown in the figure 7, namely the strategy of the partial valve opening injection and the partial valve closing injection. The high-pressure injector completes one-time high-pressure injection in the intake stroke, and the fuel injection quality is higher than that of the areas I and II. The ignition timing is usually before or after the top dead center of the compression stroke, with the maximum heat efficiency being the target, and the limiting factors such as knocking are taken into account.

Based on the above strategy, the lean-burn method provided by this embodiment forms a fully-mixed homogeneous lean-burn mixture by spraying from the low-pressure injector located in the intake port and spraying from the high-pressure injector located in the cylinder at a high pressure, and finally realizes the homogeneous lean-burn with high efficiency, low NOx and particulate matter emission by reasonably configuring the timings of low-pressure injection and high-pressure injection in one cycle.

It should be noted that, in the present specification, all the embodiments are described in a related manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments.

In this document, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The above description is only for the purpose of describing the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention, and any variations and modifications made by those skilled in the art based on the above disclosure are within the scope of the appended claims.