JPH0742558A - Structure of combustion chamber for diesel engine - Google Patents

Abstract

PURPOSE:To suppress the generation of NOx by a method wherein, in a low load operation region, a mixing ratio is further concentrated than a stoichiometric air-fuel ratio. CONSTITUTION:An approximately columnar piston combustion chamber 14 is recessed in the top part of a piston 10 and a fuel injection valve 15 is arranged to a cylinder head 12 so that an injection nozzle is caused to front on the interior of the piston combustion chamber 14. A hollow columnar protrusion 16 the upper end of which is opened is protruded from the bottom part of the piston combustion chamber 14 approximately concentrically with the piston combustion chamber 14. The interior of the piston combustion chamber 14 is partitioned into inner and outer chambers 14a and 14b by means of a protrusion 16. Further, the position of the upper end 16a of the protrusion 16 is situated in a level lower than that of a piston top surface 10a and the upper end is arranged so that spray axis A injected through the injection nozzle of a fuel injection valve 15 is collided in the vicinity of the top dead center of the piston with the upper inner wall 16b of the protrusion 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a combustion chamber of a diesel engine, and more particularly to a technique for improving the structure of a combustion chamber of a direct injection diesel engine which suppresses NOx generation.

[0002]

2. Description of the Related Art As a conventional structure of a combustion chamber of a direct injection type diesel engine, there is, for example, that shown in FIG. 3 (see Japanese Utility Model Laid-Open No. 56-127326). That is,
As shown in the figure, this one causes an air flow formed by the shape of the intake port provided in the cylinder head 1 to flow into the piston combustion chamber 3 provided at the top of the piston 2 to generate swirl, and The piston combustion chamber 3
A plurality of protrusions 4 are detachably planted at the bottom, and the intensity of the small vortex flow generated in the swirl is adjusted by changing the protrusions 4, and the fuel is supplied to the small vortex flow from the injection valve 5 at the approximate center position of the piston combustion chamber 3. Is configured to be ejected.

The air sucked in the cylinder 6 during the intake stroke is compressed as the piston 2 moves upward in the compression stroke, and the compressed high-temperature and high-pressure air enters the piston combustion chamber 3. Pushed in. Then, when the piston 2 reaches the compression top dead center, fuel is injected and supplied from the fuel injection valve 5 to the piston combustion chamber 3, and the injected fuel is
It atomizes, evaporates, mixes with air, and self-ignites to burn.

In such a case, in order to obtain good combustion, a lateral swirl flow (swirl) is applied to the intake air during the intake stroke and introduced into the combustion chamber 3. This swirl
It collides with the turbulent flow generation projection 4 extending from the bottom surface of the combustion chamber 3, and a violent turbulent flow is generated downstream thereof. As a result, the mixing of fuel and air is promoted, and good combustion is obtained, so smoke (black smoke) is suppressed,
Fuel economy is improved.

[0005]

However, in such a conventional structure of the combustion chamber of the diesel engine, smoke (black smoke) is suppressed by good combustion and fuel consumption is improved particularly in the low load operation region. However, since the mixing ratio is slightly leaner than the theoretical mixing ratio due to the promotion of mixing of fuel and air, there is a problem that the combustion temperature becomes high and the production of nitrogen oxides (NOx) increases. It was

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and in a low load operation region, the mixing ratio is made thicker than the theoretical mixing ratio so that the combustion of a diesel engine in which the generation of NOx is suppressed is suppressed. The purpose is to provide the structure of the chamber.

[0007]

For this reason, according to the first aspect of the present invention, there is provided a substantially cylindrical piston combustion chamber having a recess at the top of the piston, and a cylinder head for exposing the injection hole in the piston combustion chamber. In a structure of a combustion chamber of a diesel engine including a mounted fuel injection valve, a hollow cylindrical projection having an upper end opened at a bottom surface of the piston combustion chamber is provided so as to project substantially concentrically with the piston combustion chamber. An inner chamber and an outer chamber are formed in the combustion chamber, the upper end position of the projection is below the piston top surface, and the spray axis of the fuel injection valve collides with the upper inner wall of the projection near the piston top dead center. It is configured so that it is located.

According to the second aspect of the present invention, a substantially cylindrical piston combustion chamber is provided at the top of the piston, and a fuel injection unit mounted on a cylinder head so as to expose a plurality of injection holes in the piston combustion chamber. A valve and a structure of a combustion chamber of a diesel engine, in which a plurality of projections located in the spray axis direction of the fuel injection valve are concentrically arranged with respect to the piston combustion chamber to form an inner chamber in the piston combustion chamber. And the outer chamber are formed, and the upper end position of the protrusion is below the piston top surface,
In addition, the spray shaft of the fuel injection valve is positioned near the top dead center of the piston so as to collide with the upper inner wall of the protrusion.

[0009]

According to this structure, the invention described in claim 1 has the following operation. First, since the fuel injection amount is set small under the low load operating condition of the engine, the injection period from the start of injection to the end of injection is shorter than that under the high load operating condition.

Therefore, in the vicinity of the top dead center of the piston, the fuel spray collides with the upper inner wall of the projection and is concentratedly supplied to the hollow cylindrical inner chamber surrounded by the projection. As a result, excessive mixing is avoided and combustion is performed in a mixture state that is richer than the theoretical mixing ratio, so the temperature does not rise and NOx production is suppressed, and unburned hydrocarbons resulting from excessive mixing are also suppressed. Is also suppressed.

Next, under high load operating conditions, the fuel injection amount increases and the injection period becomes longer, so if the injection start timing is the same, the injection end timing will be later than under low load operating conditions. become. Therefore, a predetermined period from the start of injection,
That is, in the vicinity of the top dead center of the piston, the fuel spray collided with the inner wall of the upper part of the projection and was concentratedly supplied to the hollow cylindrical inner chamber surrounded by the projection, as under the low load operation condition, and was concentrated. Mixed combustion occurs and NOx generation is suppressed, but in the latter half of the injection period, the piston descends from the vicinity of top dead center, so that the fuel spray crosses the protrusion and is surrounded by the outer wall of the protrusion and the inner wall of the piston combustion chamber. Is supplied centrally to the open room.

As a result, the mixing ratio in the inner chamber and the outer chamber is made uniform, and it is possible to prevent smoke (black smoke) and deterioration of fuel efficiency. Further, according to the invention described in claim 2, since the inner chamber and the outer chamber are communicated with each other by the passage formed between the plurality of protrusions under the high load operation condition, the change of the fuel injection amount or the injection is performed. Even if the mixing ratio of the inner chamber and the outer chamber becomes non-uniform due to the delay of the timing or the like, the non-uniformity can be eliminated promptly and the mixing ratio can be made uniform.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 showing an embodiment of the present invention shows the structure of a combustion chamber of a diesel engine, and shows the relationship between the cylinder body 11 and the piston 10 in the vicinity of the top dead center of the piston 10.

That is, in the figure, the cylinder body 11 is
It consists of a cylinder head 12 and a cylinder block 13,
At the top of the piston 10, a substantially cylindrical piston combustion chamber 1
A fuel injection valve 15 is attached to the cylinder head 12 in order to expose the injection hole in the piston combustion chamber 14. On the bottom surface of the piston combustion chamber 14, a hollow cylindrical projection 16 having an open upper end is provided so as to be substantially concentric with the piston combustion chamber 14, and the projection 16
As a result, the inside of the piston combustion chamber 14 becomes
It is formed by being partitioned into b and b.

The position of the upper end 16a of the protrusion 16 is
It is formed below the piston top surface 10a. [For example, in a small engine with a piston diameter of around 90 mm, 1.5-2 m
It should be about m below. Further, this value slightly changes depending on the inner diameter of the piston combustion chamber 14, the diameter of the hollow cylindrical protrusion 16, the injection angle of the fuel injection valve 15 (the angle of the spray axis with respect to the cylinder axis or the horizontal plane), and the like.
Set an optimal value as appropriate. ].

Further, the spray axis A injected from the injection hole of the fuel injection valve 15 is positioned near the top dead center of the piston so as to collide with the upper inner wall 16b of the projection 16. That is,
In the vicinity of the piston top dead center (when the difference between the piston top surface 10a and the position of the upper end 16a of the protrusion 16 is set to about 1.5 to 2 mm, 10 ° to 15 ° BT across the top dead center)
(Between DC and 10 ° to 15 ° ATDC), the fuel injection collides with the upper inner wall 16b of the protrusion 16 and is supplied to the inner chamber 14a, but when the piston 10 is slightly lowered from the vicinity of the top dead center, the fuel injection exceeds the protrusion 16. And collides with the outer wall 14c of the outer chamber 14b to supply fuel injection to the outer chamber 14b.

Next, the operation will be described. First, under low load operating conditions, the fuel injection timing is usually near the piston top dead center and the fuel injection amount is small, so the injection period from the start of injection to the end of injection is relatively short. Therefore, FIG.
As shown in (b), the fuel spray A collides with the upper inner wall 16 b of the protrusion 16 and is concentratedly supplied into the hollow cylindrical inner chamber 14 a surrounded by the protrusion 16. Therefore,
Excessive mixing is avoided and combustion is performed in a mixture that is richer than the theoretical mixing ratio, so the temperature does not become too high, NOx generation is suppressed, and at the same time unburned hydrocarbon generation due to excessive mixing is also generated. Suppressed.

However, even if it is said that the mixture is concentrated,
Smoke (black smoke) is not generated and the fuel consumption is not concentrated to the extent that it deteriorates, so smoke and deterioration of fuel consumption can be avoided. Next, under high load operating conditions, the fuel injection amount increases and the injection period becomes longer, so if the injection start timing is the same, the injection end timing will be later than under low load operating conditions. become. Therefore, for a predetermined period from the start of injection, the fuel spray A collides with the inner wall of the projection 16 near the top dead center of the piston and is concentrated in the hollow cylindrical piston combustion chamber 14 inner chamber 14 a surrounded by the projection 16. Is supplied to. As a result, the mixed combustion becomes concentrated, and the generation of NOx is suppressed. However, in the latter half of the injection period, as the piston 10 descends from the vicinity of the top dead center, the fuel spray A crosses the protrusion 16 and enters the outer chamber 14b surrounded by the outer wall of the protrusion 16 and the inner wall of the piston combustion chamber 14. Supplied centrally. As a result, the mixing ratio in the inner chamber 14a and the outer chamber 14b becomes uniform, and it is possible to prevent smoke (black smoke) and deterioration of fuel efficiency.

The EGR operation during which a part of the exhaust gas is recirculated to the intake system in order to reduce NOx production will be described. First, in low load operation, NOx by EGR
The effect of reducing the generation can be obtained as it is. Also,
Although there is also a NOx reduction method that lowers the temperature by delaying the injection timing, the injection timing can be delayed in the present invention until the piston 10 descends from the vicinity of the top dead center and the injected fuel reaches the position beyond the projection 16. Absent. However, even in the conventional combustion chamber structure, in the low load EGR operation, a large delay in the injection timing leads to the generation of unburned hydrocarbons due to the low temperature in the combustion chamber, so it was difficult to adopt it, so compared to the conventional example. Is not inferior.

Next, in high load operation, NO by EGR
The effect of reducing x generation can be obtained as it is. Regarding the combination with the delay of the injection timing, the fuel distribution ratio between the inner chamber 14a of the combustion chamber 14 and the outer chamber 14b changes due to the delay of the injection timing in the first half of the injection period, and both chambers 14a, 14b are changed.
However, when the latter half of the injection period comes, the piston 10 descends from the vicinity of the top dead center so that the fuel spray A passes over the projection 16 and the outer wall of the projection 16 and the piston combustion chamber 14. Is supplied to the outer chamber 14b surrounded by the inner wall of the. As a result, the gas in the inner chamber 14a and the gas in the outer chamber 14b are mixed, and the mixing ratio of both chambers 14a and 14b becomes uniform,
It is possible to minimize the occurrence of smoke (black smoke) and the deterioration of fuel efficiency.

Next, another embodiment will be described with reference to FIG. That is, this is one in which the fuel is intensively injected and supplied to the inner chamber 14a of the piston combustion chamber 14 under the low load operating condition, and the inner chamber of the piston combustion chamber 14 is supplied under the high load operating condition. 14 is the same as that of the embodiment shown in FIG. 1 in that a protrusion 16 for dispersing and supplying fuel to the outer chamber 14b and the outer chamber 14b is formed, but the configuration of the protrusion 16 is different. Therefore, the same components as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

That is, the plurality of projections 16 are arranged concentrically with respect to the piston combustion chamber 14 along the spray axis direction of the fuel injection valve 15, and the inner chamber formed in the piston combustion chamber 14 is independent. 14a and the outer chamber 14b are configured to communicate with each other by a passage 17 formed between the adjacent protrusions 16. The position of the upper end 16a of the projection 16 is formed below the piston top surface 10a, and the spray axis A injected from the injection hole of the fuel injection valve 15 in the vicinity of the piston top dead center has the projection axis A of the projection 16. The structure positioned so as to collide with the upper inner wall 16b is the same as that of the embodiment shown in FIG.

According to this, under high load operating conditions,
Even if the fuel injection amount changes or the injection timing is delayed, the inner chamber 14a and the outer chamber 14b communicate with each other through the passage 17 formed between the plurality of protrusions 16, so that the combustion chamber 14
It is possible to quickly eliminate the non-uniformity of the mixing ratio between the inner chamber 14a and the outer chamber 14b, thereby preventing the generation of smoke (black smoke) and the deterioration of fuel efficiency.

[0024]

As described above, according to the first aspect of the invention, a hollow cylindrical projection is provided on the bottom surface of the piston combustion chamber so as to be substantially concentric with the piston combustion chamber, and the hollow cylindrical projection is provided. The upper end position of the projection of is below the piston top surface, and
Since the spray shaft of the fuel injection valve is positioned so as to collide with the upper end of the projection near the piston top dead center position, the fuel spray collides with the inner wall of the projection near the piston top dead center under low load operating conditions. Then, it is concentratedly supplied to the hollow cylindrical inner chamber surrounded by the projections. As a result, excessive mixing is avoided and combustion is performed in a mixture that is richer than the theoretical mixing ratio, so the temperature does not become too high and NOx production is suppressed,
Generation of unburned hydrocarbons due to excessive mixing is also suppressed.

According to the second aspect of the present invention, a plurality of projections are concentrically arranged with respect to the piston combustion chamber along the spray axis direction of the fuel injection valve, so that the piston combustion chamber has an inner chamber and an outer chamber. The chamber is formed, and the upper end position of the projection is positioned below the piston top surface and in such a manner that the spray axis of the fuel injection valve collides with the upper inner wall of the projection near the piston top dead center. Since it is configured, even if the fuel injection amount changes or the injection timing is delayed, etc., under high load operating conditions,
The passage formed between the plurality of protrusions allows the inner chamber and the outer chamber to communicate with each other, thereby promptly eliminating the non-uniformity of the mixing ratio between the inner chamber and the outer chamber of the combustion chamber, thereby producing smoke (black smoke). ) And the deterioration of fuel efficiency can be prevented.

[Brief description of drawings]

FIG. 1A is a plan view showing a structure of a combustion chamber according to an embodiment of the present invention, and FIG. 1B is a sectional view taken along line XX of FIG.

2A is a plan view showing the structure of a combustion chamber according to another embodiment of the present invention, and FIG. 2B is a sectional view taken along line YY of FIG.

FIG. 3A is a plan view showing a structure of a conventional combustion chamber,
(B) is ZZ sectional drawing of (a).

[Explanation of symbols]

 Reference Signs List 10 piston 10a piston top surface 11 cylinder body 12 cylinder head 13 cylinder block 14 piston combustion chamber 14a inner chamber 14b outer chamber 15 fuel injection valve 16 protrusion 16a upper end 16b upper inner wall 17 passage A spray axis

Claims (2)

[Claims] 1. A combustion chamber of a diesel engine, comprising: a substantially cylindrical piston combustion chamber recessed at the top of the piston; and a fuel injection valve mounted on a cylinder head so that an injection hole faces the piston combustion chamber. In the structure, a hollow cylindrical protrusion having an open upper end on the bottom surface of the piston combustion chamber is provided so as to project substantially concentrically with the piston combustion chamber to form an inner chamber and an outer chamber in the piston combustion chamber. Combustion chamber of a diesel engine, characterized in that the upper end position is located below the piston top surface and in the vicinity of the piston top dead center so that the spray axis of the fuel injection valve collides with the upper inner wall of the projection. Structure. 2. A combustion of a diesel engine, which comprises a substantially cylindrical piston combustion chamber recessed in the top of the piston, and a fuel injection valve mounted on a cylinder head so as to expose a plurality of injection holes in the piston combustion chamber. In the structure of the chamber, a plurality of protrusions located in the spray axis direction of the fuel injection valve are concentrically arranged with respect to the piston combustion chamber to form an inner chamber and an outer chamber in the piston combustion chamber, and The upper end position of the projection is located below the piston top surface, and the spray shaft of the fuel injection valve is located near the piston top dead center so as to collide with the upper inner wall of the projection. Structure of the combustion chamber.