CN113404585B

CN113404585B - Combustion chamber and gas engine

Info

Publication number: CN113404585B
Application number: CN202110951817.7A
Authority: CN
Inventors: 李卫; 王慧; 吕顺; 周海磊; 潘洁
Original assignee: Weichai Power Co Ltd
Current assignee: Weichai Power Co Ltd
Priority date: 2021-08-19
Filing date: 2021-08-19
Publication date: 2021-12-21
Anticipated expiration: 2041-08-19
Also published as: CN113404585A

Abstract

The invention discloses a combustion chamber and a gas engine, wherein the combustion chamber comprises a combustion chamber pit which is downward sunken relative to the upper top surface of a piston, the combustion chamber pit comprises a main guide curved surface and a secondary guide curved surface which are sequentially extended and arranged from the upper circumferential edge of the combustion chamber pit to a bottom central area, the main guide curved surface comprises a first main guide curved surface and a second main guide curved surface which are distributed along the circumferential direction of the combustion chamber pit and are oppositely arranged, the first main guide curved surface and the second main guide curved surface are spherical arc surfaces which are downward sunken, the secondary guide curved surface comprises a first secondary guide curved surface which is extended from the lower side edge of the first main guide curved surface to the bottom central area and a second secondary guide curved surface which is extended from the lower side edge of the second main guide curved surface to the bottom central area, the first guide curved surface and the second guide curved surface are spherical arc surfaces which are downward sunken, and the bottom central area is upward convex relative to the secondary guide curved surface. The invention can maintain higher level of tumble and vortex and maintain the intake energy.

Description

Combustion chamber and gas engine

Technical Field

The invention relates to the technical field of engines, in particular to a combustion chamber and a gas engine.

Background

At present, natural gas engines are generally modified on the basis of diesel engines. For diesel engines, the swirl flow generated by the swirl flow duct helps to some extent the oil bundles to mix with the air, thereby achieving high efficiency combustion and low pollutant emissions. Most of the gas engines are premixed combustion, fuel is mixed with air in the air intake process, and after a spark plug is ignited to generate a fire core, high turbulent kinetic energy exists in a cylinder in the combustion process ideally. The increase of the turbulent kinetic energy can accelerate the flame propagation speed, which has great significance for improving the combustion process of the gas engine and reducing the cycle variation. If large-size flow such as vortex continues to exist in the gas engine, the flow rate near the spark plug is low at the end of compression, the longitudinal flow rate is also low, the vortex cannot be broken into small-size turbulence, and the turbulence energy cannot be improved.

The piston of the existing gas engine is generally formed by reforming on the basis of the piston of the diesel engine, and the combustion chamber 01 of the piston mostly adopts a shallow basin-shaped structure, as shown in figure 1. Simultaneously, current intake duct is mostly the whirl air flue, forms stronger vortex motion around cylinder central axis in the air intake process. Due to the existence of large-scale vortex, the vortex can be similar to rigid circular motion, so that the turbulent kinetic energy in the cylinder is maintained at a high level, but the large-scale flow can influence the flame development form and has high cyclic variation. Squish flow refers to the longitudinal and transverse air flow motion that occurs when a portion of the piston surface and the cylinder head are brought into close proximity. Due to the squish flow movement at the compression end stage, the flame transverse propagation speed is high, but the flame longitudinal propagation speed in the combustion chamber 01 is low, so that the premixed combustion of the gas fuel is not facilitated, as shown in fig. 1, the rectangular dashed-line frame area near the spark plug 03 is a flame propagation low-speed area 02, wherein the transverse direction refers to the radial direction of the cylinder, and the longitudinal direction refers to the axial direction of the cylinder. In addition, the piston crown edge area 04 is poorly cooled, and is an area where the risk of knocking is high. In high speed, high load areas, squish flow may blow out fire nuclei, adversely affecting fire stability.

In addition, the gas engine modified by the diesel engine has poor consistency of swirl ratio due to the middle gas inlet mode and casting deviation, and further has poor gas inlet consistency of each cylinder. On the premise that the valve rod cannot be inclined, although the air inlet channel can be improved to enable the air cylinder to generate large-scale weak tumble motion, the tumble strength in the air cylinder is low due to the fact that a roof type combustion chamber similar to a gasoline engine cannot be achieved, and premixed combustion of gas fuel is not facilitated.

Therefore, how to further improve the combustion characteristics of the gas and improve the thermal efficiency of the gas engine is a technical problem that needs to be solved by those skilled in the art.

Disclosure of Invention

In view of the above, an object of the present invention is to provide a combustion chamber, which can make a gas mixture tumble in the combustion chamber to form a tumble flow, so as to accelerate flame propagation speed and increase turbulent kinetic energy, thereby improving gas combustion characteristics and thermal efficiency of a gas engine. Another object of the present invention is to provide a gas engine comprising the above combustion chamber.

In order to achieve the purpose, the invention provides the following technical scheme:

a combustion chamber comprises a combustion chamber pit which is positioned at the top of a piston and is downwards sunken relative to the top surface of the piston, the combustion chamber pit comprises a main guide curved surface and a secondary guide curved surface which are sequentially extended and arranged from the upper circumferential edge of the combustion chamber pit to a bottom central area, the main guide curved surface comprises a first main guide curved surface and a second main guide curved surface which are distributed along the circumferential direction of the combustion chamber pit and are oppositely arranged, the first main guide curved surface and the second main guide curved surface are downwards sunken spherical arc surfaces, the secondary guide curved surface comprises a first secondary guide curved surface which is extended from the lower side edge of the first main guide curved surface to the bottom central area and a second secondary guide curved surface which is extended from the lower side edge of the second main guide curved surface to the bottom central area, and the first secondary guide curved surface and the second secondary guide curved surface are downwards sunken spherical arc surfaces, the bottom central area protrudes upwards relative to the secondary flow guide curved surface.

Preferably, the radius of the first main guiding curved surface and the radius of the second main guiding curved surface are equal or different;

and/or the radius of the first secondary flow guiding curved surface is equal to or different from that of the second secondary flow guiding curved surface.

Preferably, the minimum radius of the primary air guiding curved surface is larger than the maximum radius of the secondary air guiding curved surface.

Preferably, the radius of the first main guiding curved surface and the radius of the second main guiding curved surface are both 0.3-0.36 times of the cylinder diameter;

and/or the radius of the first diversion curved surface and the radius of the second diversion curved surface are both 0.2-0.26 times of the cylinder diameter.

Preferably, the center of sphere of the first main guiding surface and the center of sphere of the second main guiding surface are both located above the upper top surface of the piston;

and/or the spherical center of the first secondary flow guiding curved surface and the spherical center of the second secondary flow guiding curved surface are both positioned below the upper top surface of the piston.

Preferably, the distance between the spherical center of the first main flow curved surface and the upper top surface of the piston and the distance between the spherical center of the second main flow curved surface and the upper top surface of the piston are both 0.04-0.08 times of the cylinder diameter;

and/or the distance between the spherical center of the first diversion curved surface and the upper top surface of the piston and the distance between the spherical center of the second diversion curved surface and the upper top surface of the piston are both 0.05-0.09 times of the cylinder diameter.

Preferably, the sphere center of the first main guiding surface and the sphere center of the second main guiding surface are arranged in a superposition manner or in a separation manner;

and/or the sphere center of the first secondary flow guiding curved surface and the sphere center of the second secondary flow guiding curved surface are arranged in a superposition manner or in a separation manner.

Preferably, the spherical center of the first main flow surface and the spherical center of the second main flow surface are arranged in a superposition way and are positioned on the axis of the piston;

and/or the spherical center of the first diversion curved surface and the spherical center of the second diversion curved surface are arranged in a superposition manner and are positioned on the axis of the piston.

Preferably, the whole of the main guide curved surface and/or the whole of the secondary guide curved surface is a spherical arc surface.

Preferably, the spherical center of the first main flow surface and the spherical center of the second main flow surface are respectively positioned at two sides of the axis of the piston;

and/or the spherical center of the first diversion curved surface and the spherical center of the second diversion curved surface are respectively positioned at two sides of the axis of the piston.

Preferably, a connecting line of the spherical center of the first main guide flow curved surface and the spherical center of the second main guide flow curved surface is arranged in parallel with a connecting line of an intake valve and an exhaust valve;

and/or the connecting line of the spherical center of the first diversion curved surface and the spherical center of the second diversion curved surface is arranged in parallel with the connecting line of the intake valve and the exhaust valve.

Preferably, the spherical center of the first main flow curved surface and the spherical center of the second main flow curved surface are symmetrically distributed on two sides of the axis of the piston;

and/or the spherical center of the first diversion curved surface and the spherical center of the second diversion curved surface are symmetrically distributed on two sides of the axis of the piston.

Preferably, the distance between the spherical center of the first main flow surface and the axis of the piston and the distance between the spherical center of the second main flow surface and the axis of the piston are both 0.04-0.07 times of the cylinder diameter;

and/or the distance between the spherical center of the first diversion curved surface and the axis of the piston and the distance between the spherical center of the second diversion curved surface and the axis of the piston are both 0.06-0.11 times of the cylinder diameter.

The working principle of the invention is as follows:

when the gas engine enters air, the inlet valve is opened, the inlet airflow enters the pit of the combustion chamber along the main guide flow curved surface, and generates large-scale tumble motion under the guide effect of the main guide flow curved surface, and when the airflow moves to the area near the bottom of the pit of the combustion chamber, the secondary guide flow curved surface guides the airflow to form vortex motion around the central area of the bottom, so that the large-scale tumble motion and the vortex motion are formed in the pit of the combustion chamber, and the maintenance of inlet energy is facilitated.

The invention has the following beneficial effects:

1) the tumble flow is enhanced through the main guide flow curved surface, the strength of the turbine is maintained at a higher level through the secondary guide flow curved surface, the maintenance of the air inlet energy is facilitated, and the rule of the offset between the vortex flow and the tumble flow in the prior art is broken;

2) the invention has higher adaptability and universality, can adapt to the air inlet channels (including a vertical air inlet channel and an inclined air inlet channel) of the current mainstream gas engine, and has no requirement on the installation direction of the piston.

The invention also provides a gas engine comprising a combustion chamber as described above. The derivation process of the beneficial effect of the gas engine is substantially similar to the derivation process of the beneficial effect brought by the combustion chamber, and therefore, the description is omitted.

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 view of a prior art shallow basin combustion chamber;

FIG. 2 is a schematic view of the overall structure of a combustor in an embodiment of the present invention;

FIG. 3 is a schematic perspective cross-sectional view of a combustion chamber in an embodiment of the invention;

FIG. 4 is a schematic longitudinal cross-sectional view of a main flow surface of a combustor in an embodiment of the present invention;

FIG. 5 is a schematic longitudinal cross-sectional view of a secondary curved flow guide surface of a combustor in an embodiment of the present invention;

FIG. 6 is a schematic illustration of intake airflow creating tumble flow in the combustion chamber in an exemplary embodiment of the present invention;

FIG. 7 is a graph showing the change in tumble strength at a calibration point;

FIG. 8 is a graph showing the variation of the eddy current intensity in the calibration point cylinder;

FIG. 9 is a plot of the evolution of the heat release rate at the calibration point;

FIG. 10 is a plot of calibration point cylinder pressure variation;

FIG. 11 is a graph comparing the velocity field of the compressed gas flow for a combustor provided by the present invention with a shallow basin combustor of the prior art;

FIG. 12 is a flame plane comparison of a combustion chamber provided by the present invention and a shallow basin combustion chamber of the prior art.

The reference numerals in fig. 1 have the following meanings:

01-combustion chamber, 02-flame propagation low velocity zone, 03-spark plug, 04-piston crown edge zone;

the reference numerals in fig. 2 to 12 have the following meanings:

1-piston, 2-piston axis, 3-inlet valve, 4-exhaust valve, 5-tumble schematic, 11-upper top surface of piston, 12-main guide flow curved surface, 13-secondary guide flow curved surface, 14-bottom center area, 121-first main guide flow curved surface, 122-second main guide flow curved surface, 123-first spherical center, 124-second spherical center, 131-first secondary guide flow curved surface, 132-second secondary guide flow curved surface, 133-third spherical center and 134-fourth spherical center.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 2 to 12, in order to solve the problems of the conventional gas engine, the present invention provides a combustion chamber for a gas engine, the combustion chamber is combined with a cylinder cover structure of a weak tumble rapid combustion system for use, so that the tumble strength in the cylinder can be further improved, wherein, the cylinder head structure of the weak tumble fast combustion system refers to the cylinder head described in the invention patent (a weak tumble fast combustion system and a gas engine, with the publication number of CN 111287860A), the cylinder cover structure is formed by reforming a cylinder cover of the diesel engine, the top surface of a combustion chamber formed by the cylinder cover structure is of a flat-top structure, that is, the valve stem of the cylinder head is arranged along a direction parallel to the axial direction of the piston, and the air inlet passage of the cylinder head is a weak tumble air passage, specifically, the air inlet passage of the cylinder head can enable intake air flow to generate large-scale weak tumble motion in the cylinder, and specific weak tumble structure design features thereof are not repeated herein. Specifically, the combustion chamber provided by the invention comprises a combustion chamber pit which is positioned at the top of a piston 1 and is downwards concave relative to an upper top surface 11 of the piston, the combustion chamber pit comprises a main guiding curved surface 12 and a secondary guiding curved surface 13 which are sequentially extended from the upper circumferential edge of the combustion chamber pit to a bottom central area 14, the main guiding curved surface 12 comprises a first main guiding curved surface 121 and a second main guiding curved surface 122 which are distributed along the circumferential direction of the combustion chamber pit and are oppositely arranged, the first main guiding curved surface 121 and the second main guiding curved surface 122 are both downwards concave spherical curved surfaces, the secondary guiding curved surface 13 comprises a first secondary guiding curved surface 131 which is extended from the lower side edge of the first main guiding curved surface 121 to the bottom central area 14 and a second secondary guiding curved surface 132 which is extended from the lower side edge of the second main guiding curved surface 122 to the bottom central area 14, and the first guiding curved surface 131 and the second guiding curved surface 132 are both downwards concave spherical curved surfaces, the bottom central region 14 is convex upward relative to the minor pilot curved surface 13.

The working principle of the invention is as follows:

referring to fig. 6, when the gas engine is intake, the intake valve 3 is opened, the intake air flow enters the combustion chamber pit along the main guiding curved surface 12, and generates a large-scale tumble motion (as shown in the tumble flow schematic 5 shown in fig. 6) under the guiding action of the main guiding curved surface 12, when the air flow moves to the area near the bottom of the combustion chamber pit, because the secondary guiding curved surface 13 forms a small annular concave surface feature around the bottom central area 14, the secondary guiding curved surface 13 guides the air flow to more easily form a vortex motion around the bottom central area 14, and the rotating speed is higher, which is beneficial to improving the turbulent kinetic energy of the area, therefore, the large-scale tumble motion and the vortex motion are formed in the combustion chamber pit, which is beneficial to maintaining the intake energy, and is beneficial to breaking the air flow into small-scale turbulent motion at the end of the compression stroke, thereby improving the turbulent kinetic energy in the combustion chamber, the flame propagation speed is accelerated, the effect of quick combustion is achieved, and the heat efficiency of the gas engine is improved.

It should be noted that there are generally three large-scale flow patterns for the air flow inside the engine cylinder: the piston comprises a piston body, a cylinder, a piston cover, a piston surface, a cylinder cover, a vortex, and a squish, wherein the vortex refers to the rotational motion of gas organized around the axial direction of the cylinder, the vortex refers to the rotational motion of gas perpendicular to the central axis of rotation and the axial direction of the cylinder, and the squish refers to the longitudinal and transverse airflow motion generated when a certain part of the piston surface and the cylinder cover are close to each other. The three flow forms affect each other in the intake structure and the combustion process, and have different degrees of influence on the combustion process. The invention achieves the purposes of improving combustion and improving heat efficiency by reasonably distributing different flow forms.

Compared with the technical scheme that the existing weak tumble air passage is matched with a straight-mouth type combustion chamber structure, the invention accelerates combustion by changing the intensity distribution of tumble and vortex, and the method is specifically divided into the following two stages:

in the first stage, large-scale tumble and vortex are formed in the air intake process, specifically, under the guiding action of a weak tumble air passage, most of intake air flows to a combustion chamber pit, and because the main guide curved surface 12 is a spherical arc surface, the intake air can be guided to form large-scale tumble, and when gas flows near the bottom central area 14 of the combustion chamber pit, because the secondary guide curved surface 13 forms an annular spherical arc surface surrounding the bottom central area 14, the air flow is easy to keep large-scale vortex motion at the position, so that the tumble and the vortex can be kept to have high intake energy simultaneously in the air intake process, and the intake air can be broken into turbulence in the compression process;

in the second stage, in the compression process, along with the upward movement of the piston 1, the space in the cylinder is gradually reduced, the main guide flow curved surface 12 can further enhance the tumble strength in the gas compression process, when the piston reaches the position near the top dead center, namely, the final stage of the compression process, the tumble trend is still obvious, after the spark plug is ignited, the tumble can be further continuously broken into turbulence, the flame propagation speed is favorably increased, and meanwhile, the vortex motion at the bottom of the pit of the combustion chamber can also collide with the tumble and the turbulence and be broken into the turbulence, so that the flame propagation speed near the spark plug is further increased.

Referring to FIG. 11, FIG. 11 is a graph comparing the velocity field of the compressed gas flow in the combustion chamber of the present invention with that of the shallow-bowl combustion chamber of the prior art. The three top-down rows on the left side of fig. 11 are schematic diagrams of the airflow velocity field varying with the progress of the compression stroke when the shallow-basin-shaped combustion chamber is matched with the weak tumble air passage structure in the prior art (i.e. the original scheme), the three top-down rows on the right side of fig. 11 are schematic diagrams of the airflow velocity field varying with the progress of the compression stroke when the combustion chamber pit is matched with the weak tumble air passage structure provided by the invention (i.e. the scheme), the right side of the longitudinal section of each combustion chamber in fig. 11 is an air inlet side, the left side is an air outlet side, and many small arrows in the combustion chamber represent the airflow velocity field. The three lines from top to bottom in fig. 11 show the gas flow velocity field at the start of compression, the gas flow velocity field at the early middle stage of compression, and the gas flow velocity field at the end of compression, respectively. As can be seen from fig. 11, in the compression starting stage (150 degrees before compression top dead center), the large-scale tumble motion trend formed by the scheme is more obvious and is important for maintaining the intake energy. In the middle stage of the compression process (90 degrees before the compression top dead center), the scheme continues to strengthen the tumble motion. At the end stage of compression (24 degrees before the compression top dead center), the tumble trend of the scheme is still obvious, and the tumble can be further and continuously broken in the flame propagation process, so that the method is favorable for accelerating the flame propagation speed.

It should be noted that the radius R1 of the first principal streamlining surface 121 and the radius R2 of the second principal streamlining surface 122 are equal or different;

and/or the radius R3 of the first quadric 131 and the radius R4 of the second quadric 132 may be equal or different.

Preferably, the smallest radius of the primary air guiding surface is larger than the largest radius of the secondary air guiding surface. By the arrangement, the airflow can be guided to form large-scale tumble motion by the main guide curved surface with larger radius, and the airflow around the central part of the piston is organized into vortex motion by the annular spherical arc surface formed by the secondary guide curved surface with smaller radius.

Preferably, the radius R1 of the first main curved surface 121 and the radius R2 of the second main curved surface 122 are both 0.3 to 0.36 times the cylinder diameter D (as shown in fig. 4), i.e., R1 is (0.3 to 0.36) D; r2 ═ (0.3-0.36) D; this feature affects the direction of tumble motion by controlling the radius of the two portions of the main streamlining surface 12 to determine how much airflow is directed as it enters the combustion bowl, as shown in fig. 4;

and/or the radius R3 of the first secondary air guiding curved surface 131 and the radius R4 of the second secondary air guiding curved surface 132 are both 0.2 to 0.26 times the cylinder diameter D, namely, R3 is (0.2 to 0.26) D, and R4 is (0.2 to 0.26) D; as shown in fig. 5, the secondary curved guide surface 13 is arranged tangentially to the primary curved guide surface 12, R3 and R4 determine the form of airflow tumbling inside the combustion chamber pit, the larger R3 and R4, the smoother airflow tumbling, and the stronger tumbling.

Preferably, the center of sphere (e.g., the first center of sphere 123 shown in fig. 4) of the first mainflow curved surface 121 and the center of sphere (e.g., the second center of sphere 124 shown in fig. 4) of the second mainflow curved surface 122 are both located above the upper top surface 11 of the piston; and/or the center of the first subsidiary flow guiding curved surface 131 (e.g., the third center 133 shown in fig. 5) and the center of the second subsidiary flow guiding curved surface 132 (e.g., the fourth center 134 shown in fig. 5) are both located below the upper piston top surface 11.

Preferably, the distance H1 between the center of sphere (the first center of sphere 123) of the first main flow curved surface 121 and the piston upper top surface 11 and the distance H2 between the center of sphere (the second center of sphere 124) of the second main flow curved surface 122 and the piston upper top surface 11 are both 0.04 to 0.08 times of the cylinder diameter D, that is, H1 is (0.04 to 0.08) D, and H2 is (0.04 to 0.08) D; h1 and H2 may be designed to be equal or unequal;

and/or the distance H3 between the center of the first curved flow guiding surface 131 (the third center 133) and the top surface 11 of the piston and the distance H4 between the center of the second curved flow guiding surface 132 (the fourth center 134) and the top surface 11 of the piston are both 0.05 to 0.09 times of the cylinder diameter D, that is, H3 is (0.05 to 0.09) D, and H4 is (0.05 to 0.09) D. H3 and H4 may be designed to be equal or unequal.

Preferably, the spherical center (first spherical center 123) of the first mainflow curved surface 121 and the spherical center (second spherical center 124) of the second mainflow curved surface 122 are arranged in a superposition manner or in a separation manner;

and/or the sphere center (third sphere center 133) of the first secondary flow guiding curved surface 131 and the sphere center (fourth sphere center 134) of the second secondary flow guiding curved surface 132 are arranged in a superposition manner or in a separation manner.

The first spherical center 123, the second spherical center 124, the third spherical center 133, and the fourth spherical center 134 may be located on the axis of the piston 1 (the piston axis 2) or may be located at a distance from the piston axis 2. In a preferred scheme, the spherical center (first spherical center 123) of the first main pilot curved surface 121 and the spherical center (second spherical center 124) of the second main pilot curved surface 122 are arranged in a superposition way and are positioned on the axis (piston axis 2) of the piston 1;

and/or the sphere center (third sphere center 133) of the first secondary flow guiding curved surface 131 and the sphere center (fourth sphere center 134) of the second secondary flow guiding curved surface 132 are arranged in a superposition way and are positioned on the piston axis 2.

Preferably, the entirety of the primary air guiding curved surface 12 and/or the entirety of the secondary air guiding curved surface 13 is a spherical curved surface. That is, the radius R1 of the first leading curved surface 121 is equal to the radius R2 of the second leading curved surface 122, and the first spherical center 123 and the second spherical center 124 are arranged to overlap, and/or the radius R3 of the first secondary leading curved surface 131 is equal to the radius R4 of the second secondary leading curved surface 132, and the third spherical center 133 and the fourth spherical center 134 are arranged to overlap. By the arrangement, the processing difficulty of the combustion chamber pit can be reduced.

In another preferred scheme, the spherical center (first spherical center 123) of the first main laminar surface 121 and the spherical center (second spherical center 124) of the second main laminar surface 122 are respectively positioned on two sides of the piston axis 2; and/or the center of the first secondary flow guiding curved surface 131 (third center of sphere 133) and the center of the second secondary flow guiding curved surface 132 (fourth center of sphere 134) are respectively positioned at two sides of the piston axis 2.

Preferably, a connecting line of the first spherical center 123 and the second spherical center 124 is arranged in parallel with a connecting line of the intake valve and the exhaust valve; and/or the connecting line of the third spherical center 133 and the fourth spherical center 134 is arranged in parallel with the connecting line of the intake valve and the exhaust valve. So arranged, the air flow can be made to flow below the exhaust valve 4 after entering the main curved flow surface 12.

In the present embodiment, the distances between the first spherical center 123 and the second spherical center 124 and the piston axis 2 may be the same or different. When the two are the same, the centre of rotation of the combustion chamber pit coincides with the piston axis 2. When the two are different, the rotation center of the combustion chamber pit is not coincident with the piston axis 2, and at the moment, the combustion chamber pit can be designed to deviate towards one direction, so that the direction of the tumble flow can be controlled in a targeted manner.

In a preferred embodiment, the first spherical center 123 and the second spherical center 124 are symmetrically distributed on both sides of the piston axis 2; and/or the third spherical center 133 and the fourth spherical center 134 are symmetrically distributed on both sides of the piston axis 2. In this embodiment, the first and second

spherical centers

123, 124 are equidistant from the piston axis 2, and/or the third and fourth

spherical centers

133, 134 are equidistant from the piston axis 2.

Preferably, the distance S1 between the first spherical center 123 and the piston axis 2 and the distance S2 between the second spherical center 124 and the piston axis 2 are both 0.04 to 0.07 times of the cylinder diameter D, i.e., S1 is (0.04 to 0.07) D and S2 is (0.04 to 0.07) D;

and/or the distance S3 between the third spherical center 133 and the piston axis 2 and the distance S4 between the fourth spherical center 134 and the piston axis 2 are both 0.06 to 0.11 times the cylinder diameter D, i.e., S3 is (0.06 to 0.11) D and S4 is (0.06 to 0.11) D.

The secondary curved surface 13 of the combustion chamber pit is arranged tangentially to the primary curved surface 12, which determines the form of tumbling after the airflow enters the combustion chamber pit, and S3 and S4 cooperate with S1 and S2 to determine the overall structure and width of the combustion chamber.

Further, a distance L1 between the first spherical center 123 and the second spherical center 124 is (0.08 to 0.13) D; the purpose of the design is to control the whole width of the combustion chamber pit and avoid the combustion chamber pit from being too wide. The distance L2 between the third spherical center 133 and the fourth spherical center 134 is (0.12 to 0.22) D.

Next, the original scheme and the scheme of the invention are compared through experimental simulation, a calibration point (ignition time is-25 degrees CA) is selected as a calculation condition, and a three-dimensional simulation calculation software is used for comparing simulation results of the original scheme and the scheme of the invention. Referring to fig. 7 to 10, fig. 7 is a graph showing the variation of the tumble flow strength in the calibration point cylinder; FIG. 8 is a graph showing the variation of the eddy current intensity in the calibration point cylinder; FIG. 9 is a plot of the evolution of the heat release rate at the calibration point; fig. 10 is a calibration point cylinder pressure change curve. In fig. 7 to 10, a solid line or a dotted line with dots represents a variation curve of the present invention (i.e., the present solution), and another solid line or a dotted line without dots represents a variation curve of the prior art (i.e., the original solution).

As can be seen from fig. 7, in the compression process, the tumble flow of the scheme is rapidly strengthened, and at the end of the compression stroke, the tumble flow is broken, and the tumble ratio is sharply reduced. As can be seen from fig. 8, the present solution is able to maintain a high intensity of swirling motion both during the intake phase and during the compression.

As can be seen from fig. 9, the instantaneous heat release rate of the present solution at the initial stage of combustion is significantly higher than that of the original solution, i.e., the present invention can increase the combustion speed at the initial stage of combustion because the enhanced tumble flow and the stronger vortex flow of the present invention can effectively increase the small-scale turbulence in the cylinder at the final stage of compression, which is more beneficial to the flame propagation and the increase of the combustion speed, and the increase of the heat release rate at the initial stage of combustion directly increases the utilization rate of the total energy of the fuel, i.e., the present invention makes the main heat release stage of combustion more in the working process. It can also be seen from fig. 9 that in the late stage combustion phase (after 20 ° CA), the late stage combustion of the present scheme is slower, which is beneficial for maintaining low load exhaust temperatures, while the aftertreatment conversion efficiency can be improved and the NOx production can be reduced. Referring to fig. 12, fig. 12 is a flame surface comparison diagram of the combustion chamber of the present invention and a shallow-basin combustion chamber in the prior art. The flame in fig. 12 is a flame schematic of a 1500K temperature isosurface, the left column is a flame surface variation schematic of a shallow-basin-shaped combustion chamber scheme (i.e., the original scheme) in the prior art, and the right column is a flame surface variation schematic of a combustion chamber pit scheme (i.e., the scheme) in the invention. As can be seen from figure 12, when the crank angle is 0 CA-20 CA, the lower area of the exhaust side of the original scheme still burns, and more flames are in the pits of the combustion chamber, while the lower area of the exhaust side of the scheme and the pits of the combustion chamber basically burn completely, and most of the flames reach the space of the combustion chamber above the piston, so that the combustion speed of the scheme in the early stage of combustion is faster. Compared with the prior art, the scheme has the advantages that the combustion speed at the later stage is low, namely, after-combustion is delayed, the heat emission is favorably maintained, and the after-treatment effect is improved.

As can be seen from FIG. 10, the cylinder pressure in the scheme can reach 13.42MPa (134.2 bar), which is significantly higher than 12.306MPa (123.06 bar) in the original scheme, which means that the invention can further increase the pressure released in the combustion process, improve the combustion characteristics and improve the engine efficiency.

The invention has the following beneficial effects:

It should be noted that, the vertical air intake duct described herein specifically means that a central connecting line of two intake valves is arranged perpendicular or nearly perpendicular to the axial direction of the crankshaft; the inclined air inlet channel specifically means that a certain included angle exists between the central connecting line of the two air inlet valves and the axis direction of the crankshaft.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A combustion chamber is characterized by comprising a combustion chamber pit which is positioned at the top of a piston and is downwards sunken relative to the top surface of the piston, wherein the combustion chamber pit comprises a main guide curved surface and a secondary guide curved surface which are sequentially extended from the circumferential edge of the upper side of the combustion chamber pit to a central area of the bottom and are tangentially arranged, the main guide curved surface comprises a first main guide curved surface and a second main guide curved surface which are distributed along the circumferential direction of the combustion chamber pit and are oppositely arranged, the first main guide curved surface and the second main guide curved surface are both downwards sunken spherical arc surfaces, the secondary guide curved surface comprises a first secondary guide curved surface which is extended from the lower side edge of the first main guide curved surface to the central area of the bottom and a second secondary guide curved surface which is extended from the lower side edge of the second main guide curved surface to the central area of the bottom, and the first secondary guide curved surface and the second secondary guide curved surface are both downwards sunken spherical arc surfaces, the bottom central area protrudes upwards relative to the secondary flow guide curved surface;

the radius of the first main guiding curved surface and the radius of the second main guiding curved surface are equal or different, and/or the radius of the first secondary guiding curved surface and the radius of the second secondary guiding curved surface are equal or different;

the minimum radius of the main flow guide curved surface is larger than the maximum radius of the secondary flow guide curved surface;

the radius of the first main guide flow curved surface and the radius of the second main guide flow curved surface are both 0.3-0.36 times of the cylinder diameter, and/or the radius of the first secondary flow guide curved surface and the radius of the second secondary flow guide curved surface are both 0.2-0.26 times of the cylinder diameter.

2. The combustion chamber of claim 1 wherein the center of sphere of the first mainflow surface and the center of sphere of the second mainflow surface are both above the top surface of the piston;

3. The combustion chamber of claim 2, wherein the distance between the spherical center of the first main flow surface and the upper top surface of the piston and the distance between the spherical center of the second main flow surface and the upper top surface of the piston are both 0.04-0.08 times of the cylinder diameter;

4. The combustion chamber according to any of claims 1 to 3, characterized in that the spherical centers of the first and second main streamers are arranged in coincidence or in separation;

5. The combustion chamber of claim 4 wherein the spherical centers of the first and second leading streamers are arranged in coincidence and on the axis of the piston;

6. The combustor of claim 4, wherein the entirety of the primary flow guiding curved surface and/or the entirety of the secondary flow guiding curved surface is a spherical curved surface.

7. The combustion chamber of claim 4 wherein the center of sphere of the first leading surface and the center of sphere of the second leading surface are located on opposite sides of the axis of the piston;

8. The combustion chamber as set forth in claim 7, wherein a line connecting the spherical centers of the first and second mainflow surfaces is arranged in parallel with a line connecting intake and exhaust valves;

9. The combustion chamber of claim 7 wherein the spherical centers of the first and second leading cambered surfaces are symmetrically distributed on both sides of the axis of the piston;

10. The combustion chamber as claimed in any one of claims 7 to 9, characterized in that the distance between the spherical center of the first main flow surface and the axis of the piston and the distance between the spherical center of the second main flow surface and the axis of the piston are both 0.04 to 0.07 times of the cylinder diameter;

11. A gas engine, characterized in that it comprises a combustion chamber according to any one of claims 1 to 10.