JP4082277B2 - In-cylinder direct injection CNG engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an in-cylinder direct injection CNG engine capable of directly injecting compressed natural gas (CNG) into a cylinder and switching between stratified combustion and homogeneous combustion according to engine operating conditions. The present invention relates to an in-cylinder direct injection CNG engine that can realize both stratified combustion and homogeneous combustion with a simple configuration.
[0002]
[Prior art]
In recent years, from the viewpoints of energy and environmental measures, compressed natural gas (CNG) has been used as a fuel for automobile internal combustion engines, and CNG fuel has been injected into the cylinder to improve fuel efficiency and output. In-cylinder direct injection CNG engine (hereinafter referred to as “CNG engine” where appropriate) that can directly switch between stratified combustion and homogeneous combustion according to engine operating conditions has been actively developed. Has been proposed.
[0003]
For example, an in-cylinder direct injection CNG engine (see Patent Document 1) having a cavity on the piston top surface and an in-cylinder direct injection CNG engine (see Patent Document 2) having a convex portion on the piston top surface are disclosed.
[0004]
A two-cycle direct injection LPG (liquefied natural gas) engine (see Patent Document 3) having a piston without a cavity and an intake / exhaust port in a cylinder block is disclosed.
[0005]
[Patent Document 1]
JP 2000-328997 A [Patent Document 2]
JP 2002-221037 A [Patent Document 3]
Japanese translation of PCT publication No. 2000-503745
[Problems to be solved by the invention]
In the first and second prior arts, in order to perform stratified combustion, a cavity is formed in the piston, thereby guiding a fuel spray, which is a combustible air-fuel mixture, in the vicinity of the spark plug.
[0007]
However, at the time of homogeneous combustion, there is a problem that due to the action of the cavity, the heat efficiency is lowered due to the concentration of the rich air-fuel mixture near the spark plug, and the torque is also lowered due to the poor homogeneity of the air-fuel mixture. That is, stratified combustion and homogeneous combustion were not compatible.
[0008]
Moreover, since the cavity is formed in the piston, there is a problem that the cost is increased.
[0009]
Furthermore, in the third prior art, although it has a flat piston, it is a technology related to a two-cycle direct injection LPG engine, which is essentially different in engine configuration and has a simple configuration for a direct injection CNG engine. No means is disclosed for establishing both stratified and homogeneous combustion.
[0010]
The present invention has been made in view of the above, and an object thereof is to provide an in-cylinder direct injection CNG engine that can achieve both stratified combustion and homogeneous combustion with a simple configuration.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, an in-cylinder direct injection CNG engine according to the present invention is an in-cylinder direct injection CNG engine that switches between stratified combustion and homogeneous combustion in accordance with the operating conditions of the engine. A flat piston having substantially no cavity on the top surface, a fuel injection valve disposed on the intake side of the combustion chamber and directly injecting CNG fuel into the combustion chamber, and disposed substantially at the center of the combustion chamber. The angle between the direction of the injection hole of the fuel injection valve and the top surface of the flat piston is such that the fuel spray injected during stratified combustion in a low load and low rotation region While being formed, it is reflected on the top surface of the flat piston and guided to the vicinity of the spark plug, while the fuel spray injected at the time of homogeneous combustion in a high load and high rotation region forms an air-fuel mixture. It is characterized in that the is configured as guided to the spark plug vicinity by utilizing the top surface and the exhaust side of the cylinder bore wall of the flat piston while.
[0012]
Since CNG fuel is a gaseous fuel, problems such as adhesion to the piston and bore flushing (oil dilution) do not occur like liquid fuel (for example, gasoline). In addition, since the fuel spray speed is high and there is no momentum reduction due to vaporization, it is easy to use reflection on the surface forming the combustion chamber. Based on these features, the configuration as described above results in the following operational effects.
[0013]
In other words, at low load and low speed range, the fuel injection period is short and the mixing time with air is short, so the fuel spray is reflected at the top surface of the intake side piston and the mixture is guided to the vicinity of the spark plug. The stratified charge combustion is realized by optimizing the injection timing and the ignition timing on the retarded angle side.
[0014]
Also, in the region where the load and the rotational speed are higher than in the above case, the fuel injection period is long and the mixing time with air is long, so that the fuel spray is reflected at the top surface of the exhaust side piston at the initial stage of injection, and the exhaust side cylinder bore wall Is used to guide the air-fuel mixture to the vicinity of the spark plug. That is, stratified combustion is realized by optimizing the injection timing and the ignition timing on the advance side as compared with the case of the low load and low rotation range.
[0015]
Also, at high load and high speed, fuel spray needs to be mixed with air throughout the combustion chamber, so the fuel injection timing is set to the more advanced side (first half of the compression stroke or second half of the intake stroke) and the piston top surface And the whole combustion chamber is mixed using the exhaust side cylinder bore wall.
[0016]
Therefore, according to the present invention, both stratified combustion and homogeneous combustion can be established. Moreover, since the flat piston which does not have a cavity substantially is provided, the cost of piston manufacture can be reduced.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a direct injection CNG engine according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.
[0018]
Since CNG fuel is a gaseous fuel, problems such as adhesion to the piston and bore flushing (oil dilution) do not occur like liquid fuel (for example, gasoline). Moreover, since the fuel spraying speed is high and there is no momentum reduction due to vaporization, it is easy to use reflection on each wall surface forming the combustion chamber. In view of these features, the present invention is configured as follows.
[0019]
Here, FIG. 1 is a cross-sectional view showing a schematic configuration of the in-cylinder direct injection CNG engine according to the embodiment of the present invention, and schematically shows the flow of fuel spray in the combustion chamber.
[0020]
FIG. 2 is a schematic view showing a state in which the fuel spray is reflected on the exhaust side of the flat top surface while forming an air-fuel mixture and guided to the vicinity of the spark plug using the cylinder bore wall on the exhaust side.
[0021]
FIG. 3 is a schematic view showing a state in which the fuel spray is reflected on the intake side of the flat top surface while forming an air-fuel mixture and guided to the vicinity of the spark plug.
[0022]
FIG. 4 is a schematic view showing how fuel spray forms an air-fuel mixture using the entire flat top surface and cylinder bore wall.
[0023]
As shown in FIG. 1, the CNG engine 10 is a direct injection type in which CNG fuel is directly injected into the combustion chamber 10a by an injector 23, which will be described later. The CNG engine 10 is configured almost in the same manner as a normal direct injection type gasoline engine. It is configured to be able to switch between stratified combustion and homogeneous combustion according to operating conditions.
[0024]
The combustion chamber 10 a of the CNG engine 10 is composed of a cylinder bore 11, a cylinder head 13, and a flat piston 12 that is reciprocally disposed in the cylinder bore 11. The top surface of the flat piston 12 has substantially no cavity, and is formed as a substantially flat flat top surface 12a.
[0025]
A spark plug 14 for igniting the air-fuel mixture is disposed substantially at the center of the combustion chamber 10a. An intake valve 16 is disposed at the intake port 15 facing the combustion chamber 10a, and an exhaust valve 20 is disposed at the exhaust port 18 facing the combustion chamber 10a. An injector 23 that directly injects CNG fuel into the combustion chamber 10a is disposed near the intake valve 16 in the combustion chamber 10a.
[0026]
The angle formed by the direction of the injection hole of the injector 23 and the flat top surface 12a, that is, the injection angle θ is set so as to satisfy all the mixture formation patterns shown in FIGS.
[0027]
That is, as shown in FIG. 3, the fuel spray 23a injected at the time of stratified combustion in a low load and low rotation region reflects to the flat top surface 12a while forming an air-fuel mixture, as shown in FIG. It is set to be guided to.
[0028]
In the region where the load and the rotational speed are higher than in the above case, the injection angle θ is reflected by the flat top surface 12a on the exhaust side as shown in FIG. The cylinder bore wall 11a is used to be guided to the vicinity of the spark plug 14.
[0029]
Further, as shown in FIG. 4, the injection angle θ is such that the fuel spray 23a injected at the time of homogeneous combustion in a high load and high rotation region forms an air-fuel mixture on the flat top surface 12a and the exhaust-side cylinder bore wall 11a. It is set so as to be guided to the vicinity of the spark plug 14 by use.
[0030]
Since the other configuration of the CNG engine 10 is substantially the same as the configuration of a normal direct injection gasoline engine, description thereof is omitted.
[0031]
The flat piston 12, spark plug 14, intake valve 16, exhaust valve 20, injector 23, etc. of the CNG engine 10 are controlled by an electronic control unit (ECU) (not shown) based on various sensor information.
[0032]
The CNG engine 10 configured as described above is controlled as follows. That is, as shown in FIG. 3, in a low load and low rotation range, the fuel injection period is short and the mixing time with air is short, so the fuel spray 23a is reflected by the flat top surface 12a on the intake side and mixed. Stratified combustion is realized by optimizing the injection timing and the ignition timing on the relatively retarded angle side so as to guide the air to the vicinity of the spark plug 14.
[0033]
In addition, as shown in FIG. 2, in the region where the load and the rotational speed are higher than in the above case, the fuel injection period is long and the mixing time with air is also long. The air-fuel mixture is reflected by the top surface 12a and guided to the vicinity of the spark plug 14 using the cylinder bore wall 11a on the exhaust side. That is, stratified combustion is realized by optimizing the injection timing and the ignition timing on the advance side as compared with the case of the low load and low rotation range.
[0034]
Further, as shown in FIG. 4, in a high load and high rotation range, the fuel spray 23a needs to be mixed with air in the entire combustion chamber 10a, so that the fuel injection timing is further advanced (the first half of the compression stroke or the intake stroke). In the second half), the entire combustion chamber 10a is mixed using the flat top surface 12a and the cylinder bore wall 11a on the exhaust side.
[0035]
As described above, according to the CNG engine 10 according to this embodiment, both stratified combustion and homogeneous combustion can be established. In addition, since the CNG engine 10 includes the flat piston 12 that does not substantially have a cavity, the cost for manufacturing the piston can be reduced.
[0036]
【The invention's effect】
As described above, according to the direct injection CNG engine according to the present invention, both stratified combustion and homogeneous combustion can be established. Moreover, since this in-cylinder direct injection CNG engine is provided with the flat piston which does not have a cavity substantially, it can aim at the cost reduction of piston manufacture.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a schematic configuration of an in-cylinder direct injection CNG engine according to an embodiment of the present invention.
FIG. 2 is a schematic view showing a state in which fuel spray is reflected on the exhaust side of the flat top surface while forming an air-fuel mixture and guided to the vicinity of a spark plug using a cylinder bore wall on the exhaust side.
FIG. 3 is a schematic view showing a state in which fuel spray is reflected on the intake side of the flat top surface while forming an air-fuel mixture and guided to the vicinity of a spark plug.
FIG. 4 is a schematic diagram showing how fuel spray forms an air-fuel mixture using the entire flat top surface and cylinder bore wall.
[Explanation of symbols]
θ Injection angle 10 CNG engine 10a Combustion chamber 11 Cylinder bore 11a Cylinder bore wall 12 Flat piston 12a Flat top surface 13 Cylinder head 14 Spark plug 15 Intake port 16 Intake valve 18 Exhaust port 20 Exhaust valve 23 Injector (fuel injection valve)
23a Fuel spray

Claims (1)

In the in-cylinder direct injection CNG engine that switches between stratified combustion and homogeneous combustion according to engine operating conditions,
A flat piston that is reciprocally provided in the cylinder bore and has substantially no cavity on the top surface;
A fuel injection valve disposed on the intake side of the combustion chamber and directly injecting CNG fuel into the combustion chamber;
A spark plug disposed substantially in the center of the combustion chamber;
Comprising at least
The angle formed by the direction of the injection hole of the fuel injection valve and the top surface of the flat piston is
While the fuel spray injected at the time of stratified combustion in a low load and low rotation region is reflected to the top surface of the flat piston while forming an air-fuel mixture, it is guided to the vicinity of the spark plug,
The fuel spray injected at the time of homogeneous combustion in a high load and high rotation range is guided to the vicinity of the spark plug using the top surface of the flat piston and the cylinder bore wall on the exhaust side while forming an air-fuel mixture.
An in-cylinder direct injection CNG engine characterized by being set.

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