CN114810328A - Combustion chamber and gas engine - Google Patents

Abstract

The invention discloses a combustion chamber and a gas engine, belonging to the technical field of engines, wherein the combustion chamber is used for the gas engine reformed by a diesel engine, the combustion chamber is combined with a weak tumble cylinder cover structure for use, the 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, any plane passing through the axis of the piston is a longitudinal central plane of the piston, the intersection line of the combustion chamber pit and the longitudinal central plane of the piston is a combustion chamber pit molded line, the combustion chamber pit molded line comprises a section of smooth curve or a plurality of sections of smooth curves which are sequentially connected in a smooth transition mode, the curvature center of each smooth curve is positioned above the top surface of the piston, and the compression clearance of the combustion chamber is 0.05-0.2 times of the radius of the piston. The invention overcomes the design concept of using small compression clearance of diesel engine in the existing design, adopts the shallow basin type piston to increase the compression clearance, and improves the flame propagation speed in the compression clearance, thereby being beneficial to improving the combustion characteristic of fuel gas.

Description

A combustion chamber and gas engine

technical field

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

Background technique

At present, the design and development of heavy-duty natural gas engines are generally carried out on the basis of diesel engines. For diesel engines, the eddy current generated by the swirling air passages helps to mix the oil beam with the air to a certain extent, so as to achieve high-efficiency combustion and low-efficiency combustion. Emissions. The gas engine is premixed combustion, the fuel has been mixed with air during the intake process, and after the spark plug is ignited to generate a fire nucleus, the ideal state is that there is a high turbulent kinetic energy in the cylinder during the combustion process. The increase of turbulent kinetic energy will speed up the flame propagation speed, which is of great significance for improving the combustion process of the gas engine and reducing the cyclic variation. If the large-scale flow such as eddy current continues to exist in the gas engine, at the end of compression, the flow velocity near the spark plug is low, and the longitudinal flow velocity is also low, and the vortex cannot be broken into small-scale turbulence, resulting in low turbulent kinetic energy. Therefore, large-scale vortex motion cannot be It is beneficial to the premixed combustion of the gas engine, and the cycle fluctuation is large. For gas engines, appropriately increasing the tumble intensity of the mixture can increase the turbulent kinetic energy, thereby improving the combustion characteristics of the gas. Among them, eddy flow refers to the organized large-scale swirl movement of the gas around the central axis of the cylinder; tumble flow refers to the organized large-scale swirl movement of the gas around the axis perpendicular to the central axis of the cylinder; in addition, turbulent flow is different from laminar flow, turbulent flow It refers to the small-scale swirls with many directions that are not fixed in the flow field when the airflow velocity is high.

Due to the intermediate air intake mode and casting deviation of the diesel engine, the consistency of the swirl ratio will be poor, and the consistency of each cylinder will be poor. Under the premise that the valve stem of the diesel engine cannot be tilted, it is impossible to achieve a roof-type combustion chamber similar to that of a gasoline engine. Therefore, the tumble flow intensity is low. In order to cooperate with the tumble flow, the gas engine usually adopts a straight piston, and the current combustion speed of the gas engine It is still relatively slow, and it is necessary to further optimize the piston, strengthen the degree of tumble flow, increase the speed of flame propagation, and improve the thermal efficiency of the engine.

Existing gas engine pistons are generally transformed on the basis of diesel engine pistons. The combustion chamber 01 of the piston mostly adopts a basin-shaped structure with a straight mouth, as shown in Figure 1. Due to the large-scale eddy current motion, the flame development shape will be affected. In addition, the height of the top of the piston is the same, and the intensity of squeezing flow generated on both sides of the intake valve and exhaust valve is similar, so that the speed near the spark plug 03 is low, the turbulent kinetic energy is low and the distribution is unreasonable, resulting in flame propagation in the early stage of ignition lower speed. As shown in FIG. 1 , the dotted frame area indicated near the spark plug 03 is the flame propagation low speed area 02 . At the same time, the lower flame propagation velocity on the exhaust valve side increases the knock tendency. Among them, squish flow refers to the vertical and lateral airflow movement generated when a certain part of the piston surface and the cylinder head are close to each other; knocking refers to the fact that after the gas is ignited in the combustion chamber, the flame wave has not been fully diffused, and the unburned gas in the distance is caused by high temperature. Or high pressure and spontaneous combustion, the flame wave collides with the normal combustion flame wave to generate great pressure, which makes the engine produce abnormal knocking sound. The lateral direction mentioned herein refers to the radial direction of the cylinder, and the longitudinal direction refers to the axial direction of the cylinder.

In the design process of diesel engines in the prior art, it is generally considered that the compression clearance (the clearance between the piston top and the cylinder head when the piston is at the top dead center) is a harmful volume. Therefore, the compression clearance of the diesel engine is designed to be very small ( Usually only 1-2mm), in the design process of diesel engine to gas engine, it is also deeply influenced by this design concept, so the current gas engine compression clearance is also designed to be very small.

Therefore, how to optimize the combustion chamber structure of the gas engine to improve the combustion characteristics of gas is a technical problem that those skilled in the art need to solve urgently.

The invention adopts the weak tumble air passage and transforms the combustion chamber, so that the mixed gas tumbles in the combustion chamber to form a tumble flow. The turbulent kinetic energy near the spark plug is improved, thereby improving the combustion characteristics of gas and reducing gas consumption.

SUMMARY OF THE INVENTION

In view of this, the purpose of the present invention is to provide a combustion chamber and a gas engine. By optimizing the structure of the combustion chamber and combining the existing weak tumble air passages, the present invention is beneficial to the organization of the tumble flow in the cylinder, thereby improving the flame Propagation speed, improve gas combustion characteristics.

In order to achieve the above object, the present invention provides the following technical solutions:

A combustion chamber for a gas engine converted from a diesel engine, the combustion chamber is used in combination with a weak tumble flow cylinder head structure, the combustion chamber includes a combustion chamber pocket located on the top of the piston and recessed downward relative to the upper top surface of the piston , any plane passing through the axis of the piston is the longitudinal center plane of the piston, and the intersection of the combustion chamber pit and the longitudinal center plane of the piston is the combustion chamber pit profile line, and the combustion chamber pit profile line includes One segment of smooth curve or multiple segments of smooth curves connected by smooth transitions in turn, the center of curvature of each smooth curve is located above the top surface of the piston, and the compression clearance of the combustion chamber is 0.05 to 0.2 times the radius of the piston .

Preferably, the surface of the combustion chamber pit is a spherical arc surface.

Preferably, the radius of curvature of the surface of the combustion chamber pit is 0.8 to 2 times the radius of the piston.

Preferably, the depth of the combustion chamber pit is 0.2-0.5 times the radius of the piston.

Preferably, the radius of the upper edge of the combustion chamber pit is 0.6-0.8 times the radius of the piston.

Preferably, the center of curvature of the combustion chamber pocket is located on the axis of the piston.

Preferably, the top surface of the piston is a plane structure.

The working principle of the present invention is as follows:

Compared with the traditional straight-port piston, the invention adopts a shallow basin-shaped piston structure, so that more gas can enter into the better streamlined combustion chamber pit, thereby increasing the tumble flow intensity. At the same time, the invention overcomes the design concept of using the small compression clearance of the diesel engine in the existing design, and finds that the too small compression clearance will cause the quenching effect of the flame in the compression clearance of the gas engine. The compression clearance is not a harmful volume, and a new design concept that appropriately increases the compression clearance is beneficial to combustion is adopted. When the piston runs to the vicinity of the top dead center, the airflow in the compression clearance will still be subject to tumble flow, thereby increasing the airflow velocity in the compression clearance. At the same time, the flame quenching effect caused by the too narrow compression clearance is overcome. The flame propagation speed in the compression clearance is improved, which is beneficial to improve the combustion characteristics of gas.

The present invention also provides a gas engine comprising the above combustion chamber. The derivation process of the beneficial effect produced by the gas engine is generally similar to the derivation process of the beneficial effect brought by the above-mentioned combustion chamber, so it is not repeated here.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

Fig. 1 is the structural representation of the straight mouth basin-shaped combustion chamber in the prior art;

2 is a schematic diagram of a combustion chamber arrangement structure using a smaller compression clearance in the prior art;

3 is a schematic structural diagram of a combustion chamber in a specific embodiment of the present invention;

4 is a schematic diagram of the size and position of a combustion chamber in a specific embodiment of the present invention;

5 is a schematic diagram of a cross-sectional position in a specific embodiment of the present invention;

6 is a schematic diagram of the motion form of the intake air flow of a traditional straight-port piston;

7 is a schematic diagram of the motion form of the intake air flow in the combustion chamber in a specific embodiment of the present invention;

FIG. 8 is a schematic diagram of the airflow inside the combustion chamber when the conventional straight-port piston reaches the vicinity of the top dead center;

FIG. 9 is a schematic diagram of the airflow inside the combustion chamber when the shallow basin type piston reaches the vicinity of the top dead center in the specific embodiment of the present invention.

The meanings of the reference numerals in Figures 1 and 2 are as follows:

01-combustion chamber, 02-flame propagation low speed area, 03-spark plug;

The meanings of the reference numerals in Figures 3 to 9 are as follows:

1- the top surface of the piston, 2- the combustion chamber pit, 3- intake valve, 4- exhaust valve, 5- piston centerline.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Please refer to FIG. 3 to FIG. 9 , FIG. 3 is a schematic structural diagram of a combustion chamber in a specific embodiment of the present invention;

4 is a schematic diagram of the size and position of the combustion chamber in the specific embodiment of the present invention; FIG. 5 is a schematic diagram of the cross-sectional position in the specific embodiment of the present invention; FIG. Schematic diagram of the motion form of the intake air flow in the combustion chamber in the specific embodiment of the invention; Fig. 8 is a schematic diagram of the airflow inside the combustion chamber when the traditional straight-port piston reaches the vicinity of the top dead center; Fig. 9 is a shallow basin type piston in a specific embodiment of the invention. Schematic diagram of the airflow inside the combustion chamber when it reaches near top dead center.

The present invention provides a combustion chamber for a gas engine transformed from a diesel engine. The combustion chamber is used in combination with a weak tumble flow cylinder head structure. For the weak tumble flow cylinder head structure, please refer to the invention patent ("A weak tumble flow cylinder head structure Rapid combustion system and a gas engine", the cylinder head described in the publication number CN111287860A), the cylinder head structure is transformed from a diesel engine cylinder head, and the top surface of the combustion chamber formed by the cylinder head is a flat-top type structure, that is, the The valve rod of the cylinder head is arranged along the axial direction of the piston, and the intake port of the cylinder head is a weak tumble flow port. Specifically, the intake port of the cylinder head can make the intake air flow generate a large-scale weak tumble flow movement in the cylinder. This paper The specific design features of the weak tumble flow structure are not repeated here. The combustion chamber includes a combustion chamber pit 2 located on the top of the piston and concave downward relative to the upper top surface 1 of the piston. Any plane passing through the axis of the piston is the longitudinal center plane of the piston. The intersection line is the pit profile of the combustion chamber. The pit profile of the combustion chamber includes a segment of smooth curve or multiple segments of smooth transitions connected in turn. The center of curvature of each smooth curve is located above the top surface 1 of the piston. The compression clearance H1 is 0.05-0.2 times the radius R1 of the piston, as shown in FIG. 4 , H1=(0.05-0.2) R1.

The working principle of the present invention is as follows:

Compared with the traditional straight-port piston, the invention adopts a shallow basin-shaped piston structure, so that more gas can enter into the better streamlined combustion chamber pit, thereby increasing the tumble flow intensity. At the same time, the invention overcomes the design concept of using the small compression clearance of the diesel engine in the existing design, and finds that the too small compression clearance will cause the quenching effect of the flame in the compression clearance of the gas engine. The compression clearance is not a harmful volume, and a new design concept that appropriately increases the compression clearance is beneficial to combustion is adopted. When the piston runs to the vicinity of the top dead center, the airflow in the compression clearance will still be subject to tumble flow, thereby increasing the airflow velocity in the compression clearance. At the same time, the flame quenching effect caused by the too narrow compression clearance is overcome. The flame propagation speed in the compression clearance is improved, which is beneficial to improve the combustion characteristics of gas.

It should be noted that the surface of the combustion chamber pit 2 can be designed as a spherical arc surface, or an ellipsoid arc surface, or a combination form of a spherical arc surface and an ellipsoid arc surface, preferably, the combustion chamber depression 2 in this solution The surface is a spherical arc surface.

Further preferably, as shown in FIG. 4 , the curvature radius R3 of the surface of the combustion chamber pit 2 is 0.8-2 times the radius R1 of the piston, that is, R3=(0.8-2) R1. This arrangement can ensure that the overall shape of the combustion chamber pit 2 is a shallow basin-shaped pit structure with better streamline shape, which can make it easier for the airflow in the combustion chamber to form a tumble flow.

Further preferably, the depth H2 of the combustion chamber pit 2 is 0.2˜0.5 times the radius R1 of the piston, as shown in FIG. 4 , that is, H2=(0.2˜0.5) R1 .

It should be noted that the combustion chamber pit 2 in this scheme is a concave structure with a revolving shape, and the upper edge of the combustion chamber pit 2 is a circular edge. The radius R2 of the upper edge is 0.6-0.8 times the radius R1 of the piston, that is, R2=(0.6-0.8)R1.

Preferably, the center of curvature of the combustion chamber pocket 2 is located on the axis of the piston (ie the piston centerline 5 shown in FIG. 3 ). Of course, in this solution, the center of curvature of the combustion chamber pit 2 can also be designed to be at a certain distance from the centerline 5 of the piston.

It should be noted that the upper top surface 1 of the piston is a plane structure, which can ensure that the squeezing flow intensity around the piston is consistent during the compression process of the piston.

The invention is based on the new concept that the compression clearance of the diesel engine to the gas engine is not a harmful volume, and an appropriate increase in the compression clearance is beneficial to combustion. flow intensity, and avoid the flame quenching phenomenon caused by too small compression clearance near the top dead center, and improve the flame propagation speed. The following uses a new type of large compression clearance piston and a common straight-port piston flow field diagram to illustrate.

Figures 6 to 9 show cross-sectional views of the combustion chamber, and the cross-sectional position is the A-A cross-section shown in Figure 5. It can be seen that the engine cylinder to which it is applied is correspondingly provided with two intake valves 3 and two exhaust valves 4 , the two hollow arrows in Figure 5 represent the total intake direction and the total exhaust direction, respectively.

As shown in Figure 6, during the intake process, the intake air rushes to the top surface of the piston, and the traditional straight-port piston is prone to reverse flow in the B1 area in Figure 6, thus hindering the generation of tumble flow. At the same time, the combustion chamber pit of the straight-port piston has a cylindrical cavity structure as a whole, which is not conducive to the enhancement of tumble flow.

As shown in FIG. 7 , during the intake process, the shallow basin-shaped combustion chamber structure provided by the present invention can reduce the airflow directly impacting the top surface of the piston, as shown in the C1 area in FIG. 7 , which can make more airflow smoothly into the combustion chamber pit 2 of the piston, in addition, because the combustion chamber pit 2 of this solution is more streamlined, it can more effectively guide the airflow to roll in the cylinder, thereby reducing the energy loss during the tumble flow.

As shown in Figure 8, when the piston runs near the top dead center, the compression clearance of the traditional straight-port piston is very small, and the air flow energy is very weak in the small space of the compression clearance (in the B2 area shown in Figure 8). In addition, due to the squeezing flow at the top of the piston, two rotating motions on the left and right sides are formed in the combustion chamber, so that the turbulent kinetic energy is mainly distributed at the bottom of the combustion chamber, and the gas flow near the spark plug is slow, which is not conducive to the ignition of the spark plug.

As shown in FIG. 9 , in the solution of the present invention, the large compression clearance allows the piston to retain a large space when it runs to the vicinity of the top dead center. Therefore, a strong airflow disturbance is also generated in the large compression clearance, thereby accelerating the Part of the gas combustion speed can still maintain the tumble flow from the intake valve to the exhaust valve in the cylinder, thereby accelerating the flow of airflow near the spark plug and accelerating the speed of flame propagation in the early stage.

All in all, there are three large-scale flow forms in the gas engine cylinder: tumble flow, eddy flow and squish flow. The three flow modes affect each other in the intake structure and the combustion process, and have different degrees of influence on the combustion process. The invention designs a shallow basin-type piston shape with a large compression clearance, and has three core ideas: 1) Under the condition that the weak tumble flow air passage remains unchanged, the tumble flow in the cylinder and the air flow disturbance intensity in the compression clearance near the top dead center are enhanced to Accelerate combustion, specifically, increase the compression clearance, reduce the airflow directly impacting the top of the piston, so that more airflow enters the combustion chamber, which in turn forms a stronger tumble flow, which accelerates the speed of early flame propagation. Near the dead center, the large compression clearance makes the airflow in the clearance more turbulent, accelerates the flame propagation speed in the clearance, and shortens the overall duration of combustion; 2) It adopts a shallow basin-shaped combustion chamber line, which is similar to the traditional straight piston. Compared with the streamlined shape, the energy loss is smaller when guiding the airflow to generate tumble flow; 3) The compression clearance is increased, no valve pit design is required, and there is no sharp corner feature, which improves the overall anti-knock performance.

The present invention also provides a gas engine comprising the above combustion chamber. The derivation process of the beneficial effect produced by the gas engine is generally similar to the derivation process of the beneficial effect brought by the above-mentioned combustion chamber, so it is not repeated here.

The above description of the disclosed embodiments enables 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 implemented in 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 (8)

1. A combustion chamber is used for a gas engine reformed by a diesel engine, and is combined with a weak tumble cylinder cover structure for use, and the 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, any plane passing through the axis of the piston is a longitudinal central plane of the piston, the intersection line of the combustion chamber pit and the longitudinal central plane of the piston is a combustion chamber pit molded line, the combustion chamber pit molded line comprises one section of smooth curve or a plurality of sections of smooth curves which are sequentially connected in a smooth transition mode, the curvature center of each smooth curve is positioned above the top surface of the piston, and the compression clearance of the combustion chamber is 0.05-0.2 times of the radius of the piston.

2. The combustor of claim 1, wherein the surface of said combustion bowl is spherically curved.

3. The combustion chamber of claim 2 wherein the surface of the combustion pocket has a radius of curvature of 0.8 to 2 times the radius of the piston.

4. The combustion chamber of claim 3 wherein the depth of the combustion pocket is 0.2 to 0.5 times the radius of the piston.

5. The combustion chamber of claim 3 wherein the radius of the upper edge of the combustion pocket is 0.6 to 0.8 times the radius of the piston.

6. The combustion chamber of any one of claims 2-5 wherein the center of curvature of the combustion pocket is located on the axis of the piston.

7. The combustor of claim 1, wherein said top piston surface is a planar structure.

8. A gas engine comprising a combustion chamber according to any one of claims 1 to 7.

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