JP2003254105A - Diesel engine and its operating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and inexpensively provide a diesel engine capable of performing diesel combustion even by using the fuel of high self-ignition temperature. <P>SOLUTION: This diesel engine comprises a fuel injection means 5 for spark ignition, capable of forming a concentrated air-fuel mixture for spark ignition in a predetermined spark ignition area 1a of a combustion chamber by injecting the fuel fs to the new air taken in the combustion chamber 1, a spark ignition means 7 generating spark in the spark ignition area 1a for combusting the concentrated air-fuel mixture by spark ignition, and a fuel injection means 5 for diesel combustion for performing the diesel combustion by directly injecting the fuel fd to the combustion chamber 1 after the spark ignition. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine in which fuel is directly injected into fresh air compressed in a combustion chamber to perform diesel combustion, and a method of operating the same. In particular, the engine has a self-ignition temperature as compared with diesel oil. TECHNICAL FIELD The present invention relates to a diesel engine that can be used as a fuel even in highly natural gas.

[0002]

2. Description of the Related Art Conventionally, a diesel engine performs diesel combustion in which fuel such as light oil is injected into high temperature air which is sucked into a combustion chamber and compressed to self-ignite and diffuse combustion, and is a spark ignition type engine. Compared with, it does not cause severe knocking, so it is possible to improve the thermal efficiency by increasing the compression ratio, and by reducing the fuel injection amount while suppressing pumping loss without restricting the intake passage. Since it can perform partial load operation, it is widely used as a stationary power source for cogeneration, including transportation such as large vehicles and ships where fuel economy is particularly important. In addition, the disadvantage of diesel engines that use light oil as fuel is that because light oil diffuses and burns, harmful exhaust components such as graphite, fine particles and nitrogen oxides are easily generated, and because the compression ratio is high and the maximum combustion pressure is high. It may be necessary to make the members such as the piston and the cylinder strong.

Natural gas containing methane as a main component and liquefied petroleum gas containing propane and butane as a main component (liquefied petr)
oleum gas, hereinafter referred to as LP gas. ) Is used not only in households but also as a combustion fuel for industrial use, and is also used as a fuel for engines for cogeneration or heat pumps. Further, recently, from the viewpoint of environmental protection and the like, the use of natural gas in automobiles has been promoted.

Since such natural gas has a wide combustible range and can realize lean combustion, it can lower the combustion temperature and greatly reduce NOx emissions, and further, CO ₂ emissions per calorific value. It is also advantageous in terms of exhaust gas purification because it has less harmful emission components such as less gas. Further, hydrogen gas, like natural gas, can also reduce NOx emissions due to lean combustion, has very few harmful emission components, and is also advantageous in terms of exhaust gas purification.

Therefore, if such natural gas, LPG, or hydrogen gas can be used as a fuel for a diesel engine, an engine with high thermal efficiency and less harmful emissions can be realized. Compared with, the self-ignition temperature is high, for example, the self-ignition temperature of light oil is about 350 ℃ ~ 400 ℃, whereas the self-ignition temperature of natural gas city gas 13A is about 550 ℃,
Since the self-ignition temperature of LPG is about 450 ° C. and the self-ignition temperature of hydrogen gas is about 570 ° C., even if the compression ratio is set to a high value, for example, about 22 purely, the fuel cannot be self-ignited for diesel combustion.

Therefore, in recent years, in diesel engines, as a method for burning diesel fuels such as natural gas having a high self-ignition temperature, a method of adding a cetane number improver to the fuel or a glow plug of a combustion chamber is used. Methods have been devised, such as a method of raising the temperature of the fuel to a temperature capable of self-ignition by an external heat source and a method of heating fresh air drawn into the combustion chamber.

[0007]

However, the method of adding a cetaneation improving agent to a fuel having a high self-ignition temperature as described above is an advantage of a diesel engine because the cetaneation improving agent is expensive. The economy is impaired, and the engine itself becomes expensive because a tank for storing the cetaneation improving agent and a device for adding the tank are required for the engine.

Further, the method of raising the temperature of the combustion chamber to a temperature at which the fuel can be self-ignited by an external heat source and the method of heating the fresh air drawn into the combustion chamber require an external heat source, so that thermal efficiency is improved. In addition, the temperature of the fresh air sucked into the combustion chamber rises, and the density of the fresh air sucked into the combustion chamber decreases, so that the efficiency of filling the fresh air into the combustion chamber decreases and the output and The thermal efficiency is reduced, and the high efficiency advantage of diesel engines is impeded. Therefore, in view of the above circumstances, an object of the present invention is to provide a diesel engine that is simple and low-cost and that can perform diesel combustion even with fuel having a high self-ignition temperature.

[0009]

The first characteristic structure of the diesel engine according to the present invention for achieving this object is as follows.
As described in claim 1 of the scope of claims, a spark that forms a rich mixture capable of spark ignition in a predetermined spark ignition region of the combustion chamber by injecting fuel into fresh air sucked into the combustion chamber. Ignition fuel injection means, spark ignition means for generating sparks in the spark ignition region to perform spark ignition combustion of the rich mixture, and diesel combustion for injecting fuel directly into the combustion chamber after the spark ignition to perform diesel combustion And fuel injection means for use.

The second characteristic constitution is, in addition to the first characteristic constitution, as described in claim 2 of the scope of claims,
The fuel is natural gas, liquefied petroleum gas, or hydrogen gas.

A diesel engine according to the present invention for attaining this object is preferably implemented by the diesel engine of the first characteristic structure, which is characterized by injecting fuel into fresh air sucked into a combustion chamber. Spark injection fuel injection step for forming a rich mixture capable of spark ignition in a predetermined spark ignition region of the combustion chamber, and spark ignition for spark ignition combustion of the rich mixture by generating a spark in the spark ignition region. The point is that the step and the fuel injection step for diesel combustion in which the fuel is directly injected into the combustion chamber after the spark ignition to perform diesel combustion are sequentially executed.

That is, according to the diesel engine and the method of operating the same of the present invention, in the fuel injection process for spark ignition, the combustible range equivalence ratio is formed in the predetermined spark ignition region of the combustion chamber by the fuel injection means for spark ignition. In the spark ignition process, a spark ignition means is used to form a rich mixture capable of spark ignition at a predetermined ignition timing immediately before, for example, the TDC timing (the timing at which the piston position is the top dead center) at the latter stage of the compression stroke. By spark-igniting the rich air-fuel mixture formed in the combustion chamber, the temperature of the combustion chamber near the TDC time reaches a temperature at which self-ignition is possible even for fuels with relatively high self-ignition temperatures such as natural gas, LP gas and hydrogen gas. The temperature can be raised. Therefore, in the fuel injection process for diesel combustion, the fuel injection means for diesel combustion injects fuel such as natural gas or LP gas or hydrogen gas having a relatively high self-ignition temperature into the combustion chamber thus heated. The fuel can then be burned in diesel. Therefore, it is possible to realize a diesel engine capable of performing diesel combustion even with fuel having a high self-ignition temperature, without using a cetaneation improving agent or an external heat source, and without requiring a very high compression ratio. it can.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a diesel engine according to the present invention will be described with reference to FIGS. A diesel engine of the present embodiment (hereinafter abbreviated as the present engine) shown in FIG. 1 is rotationally driven by burning a fuel, which is LP gas, in a combustion chamber 1 formed by a top surface of a piston 3, an inner surface of a cylinder 2, and the like. It is an engine that obtains power, and specifically, diesel combustion is performed from a fuel injection valve 4 (an example of a fuel injection unit for diesel combustion) in hot air (an example of fresh air) that is sucked into the combustion chamber 1 and compressed. It is configured to perform so-called diesel combustion in which the fuel fd for high pressure is injected at high pressure, self-ignited, and diffused and burned.

Further, this engine has a compression ratio of 17 (maximum combustion chamber volume / minimum combustion chamber volume), which is about the same as that of a diesel engine that uses ordinary light oil as fuel. Since LP gas having a high self-ignition temperature of about 100 ° C. is used, as indicated by a chain line in the graph showing the relationship between the cylinder internal pressure (pressure in the combustion chamber 1) and the crank angle shown in FIG. Only by compressing the air sucked into the combustion chamber 1, does the pressure and temperature in the cylinder become high until the LP gas is self-ignited.

Therefore, in addition to the fuel injection valve 4, the present engine has the same L level as the diesel combustion fuel fd.
A fuel injection valve 5 (an example of a fuel injection unit for spark ignition) capable of injecting a spark ignition fuel fs that is P gas into a recess 1a (an example of a spark ignition region) formed above the combustion chamber 1;
A spark plug 7 (an example of spark ignition means) capable of generating a spark is provided in the recess 1a of the combustion chamber 1, and the detailed configuration thereof will be described below together with the operating method of the present engine. The solid line portion in FIG. 2 shows the relationship between the cylinder internal pressure (pressure in the combustion chamber 1) and the crank angle in the present engine. Further, in FIGS. 1 and 2, the operating method of the present engine is shown. The states of each process are shown in order by adding the symbols (a) to (e).

First, in the present engine, as shown in FIG. 1A, in the initial or middle stage of the compression stroke in which the piston 3 is raised to compress the air sucked into the combustion chamber 1, as shown in FIG. The spark ignition fuel injection step of injecting a small amount of spark ignition fuel fs into the recessed portion 1a of step 1 is executed.

Then, as shown in FIG. 1B, the spark ignition fuel fs injected in this spark ignition fuel injection step.
Is vaporized in the recessed portion 1a in the subsequent compression stroke and diffused into the air in the recessed portion 1a, and at the end of the compression stroke (specifically, when sparks are generated by the ignition plug 7 described later), the recessed portion is The fuel f for spark ignition is shown in 1a.
By s, a rich air-fuel mixture having an equivalence ratio within the combustible range of LP gas and capable of spark ignition is formed.

In this engine, as shown in FIG. 1 (c), the spark plug 7 is actuated at the spark ignition timing immediately before the TDC timing to generate sparks in the recess 1a and form in the recess 1a. A spark ignition step is performed to ignite and burn the rich air-fuel mixture thus generated. Then, in the combustion chamber 1, as shown in FIG. 2, the high pressure and the high temperature at which the LP gas can self-ignite due to the combustion of the rich mixture near the TDC timing.

Therefore, in this engine, as shown in FIG. 1 (d), immediately after the TDC timing, the fuel injection valve 4 to L
A diesel combustion fuel injection process of injecting the diesel combustion fuel fd into the combustion chamber 1 in which the P gas is capable of self-ignition is executed.

Then, the diesel combustion fuel fd injected from the fuel injection valve 4 is swirl of high temperature gas generated near the top surface of the piston 3 of the combustion chamber 1 as shown in FIG. 1 (e). A so-called diesel combustion is realized in which it diffuses into the flow, self-ignites, and diffuses and burns well. Then, due to such diesel combustion, the piston 3 is pushed down, and rotational power can be obtained on the crankshaft (not shown).

As described above, the present diesel engine uses, for example, the LP gas having a relatively high self-ignition temperature as the fuel, but heats the air taken into the combustion chamber 1 to generate the air. Since the LP gas and the like can be diesel-combusted with a simple structure in which the fuel injection valve 5 and the ignition plug 7 are properly operated without lowering the charging efficiency, the thermal efficiency due to the high compression ratio is improved. Further, the advantages of the diesel engine, such as the partial load operation, can be sufficiently exhibited by reducing the injection amount of the diesel combustion fuel fd without narrowing the intake passage.

In the present embodiment, the diesel engine using LP gas, which is a fuel that is difficult to be diesel-combusted in the conventional diesel engine, has been described. However, the diesel engine according to the present invention is used as a fuel. For example, natural gas, hydrogen gas, or the like having an auto-ignition temperature higher than that of light oil, like LP gas, can also be used.

Further, the fuel injection valve 5 for injecting the spark ignition fuel fs to form a rich air-fuel mixture in the recess 1 of the combustion chamber 1,
It is advantageous to inject the fuel fs directly into the combustion chamber 1 in order to form a rich air-fuel mixture in the depression 1a, but by devising the shape of the combustion chamber 1 and the top surface of the piston 3, etc. The fuel injection valve 5 may be provided at the intake port when a rich mixture can be formed in the recess by the injected spark ignition fuel.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a diesel engine of the present embodiment.

FIG. 2 is a graph showing the relationship between cylinder pressure and crank angle of the diesel engine shown in FIG.

[Explanation of symbols]

1: Combustion chamber 1a: depression (spark ignition region) 2: Cylinder 3: Piston 4: Fuel injection valve (fuel injection means for diesel combustion) 5: Fuel injection valve (fuel injection means for spark ignition) 7: Spark plug (spark ignition means) fs, fd: fuel

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02M 21/02 F02M 21/02 LF term (reference) 3G023 AA08 AB06 AC01 AC07 AG05 3G092 AA01 AA02 AB07 AB08 AB09 BB06 BB13 DE02S DE03S EA12 FA01 FA24 HB01X HB02X

Claims (3)

[Claims] 1. A fuel injection device for spark ignition for injecting fuel into fresh air drawn into a combustion chamber to form a rich mixture capable of spark ignition in a predetermined spark ignition region of the combustion chamber, and the spark ignition. An engine comprising: spark ignition means for generating sparks in a region to spark-ignite and burn the rich mixture; and diesel combustion fuel injection means for directly injecting fuel into the combustion chamber after the spark ignition to perform diesel combustion. 2. The engine according to claim 1, wherein the fuel is natural gas, liquefied petroleum gas, or hydrogen gas. 3. A fuel injection process for spark ignition for injecting fuel into fresh air drawn into a combustion chamber to form a rich mixture capable of spark ignition in a predetermined spark ignition region of the combustion chamber, and the spark ignition. An engine that sequentially executes a spark ignition step of generating sparks in a region and performing spark ignition combustion of the rich mixture, and a diesel combustion fuel injection step of injecting fuel directly into the combustion chamber and performing diesel combustion after the spark ignition. Driving method.