JPH0763076A - Internal combustion engine - Google Patents

Abstract

PURPOSE:To improve fuel consumption so sharply by securing a stable combustion even in a high air-fuel ratio and elongating a lean limit yet longer. CONSTITUTION:This engine is provided with a carburetor 13 supplying compressed natural gas into intake air at an intake stroke and also a liquid fuel injection means 11 spraying igniting liquid fuel toward a part to lee opposed to a spark plug 10 on top of a piston 4 prior to ignition, and in this constitution, a sufficiently rich air-fuel mixture is formed in and around the spark plug 10 in time of ignition and thereby it is made so as to make up a strong flame. Differently this engine may be provided with another liquid fuel injection means supplying the liquid fuel into the intake air at the intake stroke and an injector spraying the igniting compressed natural gas toward the spark plug prior to the ignition otherwise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine, and more particularly to an internal combustion engine which uses a liquid fuel and a compressed natural gas and is capable of lean burn operation.

[0002]

2. Description of the Related Art Conventionally, there are various internal combustion engines that use gasoline as fuel to realize lean burn operation by giving a strong swirl to intake air flowing into a cylinder in order to improve fuel efficiency. Proposed.

On the other hand, natural gas is drawing attention as a fuel that replaces gasoline, and an internal combustion engine that uses compressed natural gas (hereinafter referred to as CNG) as a fuel to improve fuel consumption has also been proposed. Since natural gas contains methane gas as a main component, it cannot be stored in a liquid phase at room temperature like LPG (liquefied petroleum gas), and therefore CNG which is compressed in a gas phase and filled in a cylinder is used as a fuel.

Further, Japanese Patent Laid-Open No. 63-68728 discloses an internal combustion engine which is operated by switching and supplying liquid fuel and CNG according to the operating state.

[0005]

However, in a lean burn internal combustion engine that uses gasoline as a fuel, the limit of the leanness of fuel that can be stably burned (hereinafter, referred to as lean limit) is currently the air fuel consumption (A / F). ) It is set to about 30, and it is difficult to obtain stable combustion in a leaner region than that, and there is a limit in improving fuel efficiency and reducing CO _{2 in} exhaust gas. The reason is that since gasoline is a liquid fuel, it is not completely vaporized in the cylinder, and a portion of the intake gasoline remains in the form of liquid droplets, which plunges into the ignition / combustion process with uneven mixing. Seen according to.

On the other hand, in an internal combustion engine that uses CNG as a fuel,
Since CNG is a gas fuel, the unevenness of mixing in the cylinder is less than in the case of gasoline, and the lean limit is significantly extended, but because CNG has a slow propagation speed of combustion, CNG is fully open compared to gasoline. Since the volumetric efficiency (ηv) at the time is low, there is a problem that the output is reduced as compared with the case of gasoline fuel.

Even in the case of switching between liquid fuel and CNG, the above problems in each operating state cannot be solved.

In view of such conventional problems, it is an object of the present invention to provide an internal combustion engine capable of ensuring stable combustion even at a high air-fuel ratio, extending the lean limit, and greatly improving fuel consumption. And

[0009]

The first invention of the present application is a means for supplying CNG into the intake air in the intake stroke, and a liquid for ignition toward the portion of the upper surface of the piston facing the spark plug before ignition. Liquid fuel injection means for injecting fuel is provided.

A second aspect of the present invention is a liquid fuel injection means for injecting and supplying liquid fuel into intake air in an intake stroke,
An injector for injecting CNG for ignition toward the spark plug immediately before ignition is provided.

[0011]

According to the first invention of the present application, although CNG is used as the main fuel, a small amount of the liquid fuel for ignition is injected to the portion on the upper surface of the piston facing the ignition plug before ignition, so the ignition plug is ignited. Since a sufficiently rich air-fuel mixture is formed around and a strong flame is formed, even if CNG has the property of slow combustion propagation, the strong flame promotes smooth combustion propagation, and CNG has uneven mixing. Combined with the small amount, the mixture of intake air and CNG has an air-fuel ratio of 30 or more,
For example, even in an extremely lean state where the air-fuel ratio is 50 or more, sufficiently stable combustion is performed. Further, if the injection amount of the liquid fuel from the liquid fuel injection means is increased at the time of full opening, it is possible to prevent the output reduction due to the low volume efficiency of CNG. Moreover, CNG is further exhaust gas has a low CO ₂ in order to be lean on originally a low CO _2.

Further, according to the second invention of the present application, the liquid fuel is used as the main fuel, but since CNG which is easily ignited is injected toward the spark plug immediately before ignition, the CNG is the same as the liquid fuel. A mixture of CNG suitable for ignition is formed around the spark plug without wetting the electrode, and this CNG is first burned to form a flame, and C
Since NG is lighter than air and has good followability to intake air, this flame propagates smoothly into the mixture of intake air and liquid fuel, and is therefore sufficiently stable even when the mixture of intake air and liquid fuel is super lean. Burning takes place. Further, since CNG has a high pressure, it can be directly injected from the injector into the combustion chamber, and an in-cylinder injector as in the case of liquid fuel is unnecessary.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, 1 is a cylinder block of an internal combustion engine, 2 is a cylinder head, and 3 is a cylinder block 1.
Cylinders 4 formed in 1 are pistons that move up and down in the cylinder 3, and 5 is a combustion chamber formed on the cylinder 3 below the cylinder head 2.

Intake ports 6 are provided on both sides of the ceiling of the combustion chamber 5.
The exhaust port 7 is opened, and the intake valve 8 and the exhaust valve 9 are opened and closed at predetermined timings. An ignition plug 10 is provided near the top of the ceiling of the combustion chamber 5.

Liquid fuel injection means 11 for injecting gasoline for ignition is arranged near the ignition plug 10. A cavity 12 is formed in an upper surface of the piston 4 at a portion facing the spark plug 10, and the liquid fuel injection means 1 is provided.
1 is configured to inject a small amount of gasoline for ignition toward the cavity 12.

On the other hand, a carburetor 13 for supplying and mixing CNG to the intake air is connected to the intake port 6. The carburetor 13 is not provided with a throttle valve, and output control is performed by the supply amount of CNG.

In the above structure, during the intake stroke, the carburetor 13 mixes CNG with intake air so as to have a desired air-fuel ratio, and then flows into the combustion chamber 5. Next, a small amount of gasoline for ignition is injected from the liquid fuel injection means 11 into the cavity 12 on the upper surface of the piston 4 so that the injection ends at about 300 ° ATDC at the end of the compression stroke, and is injected into the cavity 12. Fuel drops are scattered. Then, 330 ° to 3
At about 40 ° ATDC, the fuel droplets start to vaporize, a rich mixture is formed in the cavity 12, and the cavity 12 comes close to the spark plug 10. Therefore, at this time (20 ° to 30 ° BTDC), ignition is performed. When ignited by the plug 10, the rich air-fuel mixture in the cavity 12 ignites and burns violently, developing a strong flame and forming a strong flame.

The flame of this kind of flame propagates to the surrounding CNG mixture, so that the inside of the combustion chamber 5 burns quickly. That is, since CNG easily ignites in the form of a gas and has little mixing unevenness, CNG has a property that combustion propagation is slow, but combustion propagation can be smoothly performed by making the ignition point sufficiently strong. As a result, even in an extremely lean state where the air-fuel ratio is 30 or more, for example, the air-fuel ratio is 50 or more, it is possible to perform combustion in a sufficiently stable manner. In addition, gasoline and CNG
The ratio is preferably about 1:10 by weight.

According to the present embodiment, since stable combustion can be performed in a super lean manner as described above, output control can be performed by the supply amount of CNG, output control by a throttle valve is unnecessary, pumping loss is reduced, and Since it is super lean, it is close to an air cycle with a large specific heat ratio, and a low fuel consumption internal combustion engine can be realized. Further, since CNG is originally low in CO ₂ and lean, the exhaust gas is further reduced in CO ₂ , and an economical and clean internal combustion engine can be obtained.

If there is a concern that the output will decrease due to the low volumetric efficiency of CNG when fully opened, the output decrease can be prevented by increasing the injection amount of the liquid fuel from the liquid fuel injection means 11. it can.

Next, a second embodiment of the present invention will be described with reference to FIG. The same components as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 2, liquid fuel injection means 14 for injecting liquid fuel into the intake air is arranged in the intake port 6, and an injector 15 for injecting CNG for ignition toward the spark plug 10 is provided in the combustion chamber 5. Is disposed on one side of the lower part of the.

In the above structure, when gasoline is injected from the liquid fuel injection means 14 into the intake air so as to have a desired air-fuel ratio during the intake stroke, the air-fuel mixture flows into the combustion chamber 5. Next, at the end of the compression stroke, 330 ° to 340 ° AT
CNG for ignition is injected from the injector 15 toward the ignition plug 10 so that the injection ends at DC (10 ° CA before ignition). Then, CNG does not wet the electrode of the spark plug 10 unlike liquid fuel, and the spark plug 1
A mixture of CNG suitable for ignition is formed around 0.
Therefore, when the ignition plug 10 is ignited at about 20 ° to 30 ° BTDC, this CNG first burns to form a flame, and since CNG is lighter than air and has good followability to intake air, this flame burns. The air-fuel mixture in the chamber 5 smoothly propagates in the air-fuel mixture, and therefore, even if the air-fuel mixture in the intake air is extremely lean, the combustion is sufficiently stable.

According to the present embodiment, since the combustion is super lean and stable, the output can be controlled by the amount of gasoline supplied, and the output control by the throttle valve becomes unnecessary.
The pumping loss is small, and because it is super lean, it is close to an air cycle with a large specific heat ratio, so that a fuel-efficient internal combustion engine can be realized. Further, since it is lean, the exhaust gas becomes low CO ₂ , and an economy and clean internal combustion engine can be obtained. Further, since CNG has a high pressure of 200 kg / cm ^2, it can be injected from the injector 15 into the combustion chamber 15, and an in-cylinder injector as in the case of liquid fuel is unnecessary.

[0026]

According to the internal combustion engine of the first invention of the present application, although CNG is used as the main fuel as described above, a small amount of liquid fuel for ignition prior to ignition faces the ignition plug on the upper surface of the piston. Since a sufficiently rich air-fuel mixture is formed around the spark plug at the time of ignition and a strong spark is formed by injecting into the CNG, the CNG is smoothly propagated even though it has the property of slow combustion propagation. In addition, CNG has a small amount of unevenness of mixing, so that sufficiently stable combustion is performed even in an ultra lean state with an air-fuel ratio of 50 or more. Further, for this reason, the output can be controlled by the supply amount of CNG, the output control by the throttle valve is not necessary, the pumping loss is reduced, and since it is super lean, it is close to an air cycle with a large specific heat ratio, which results in low fuel consumption. An internal combustion engine can be realized.

Since CNG is also used as the exhaust gas, it is originally low in CO ₂ and lean, so that the CO is further reduced.
_2, and it is possible to obtain a clean internal combustion engine thus Economy.

Further, according to the second invention of the present application, the liquid fuel is used as the main fuel, but by injecting CNG which is easy to ignite toward the ignition plug immediately before ignition, it is suitable for ignition around the ignition plug. A mixture of CNG is formed and this C
NG burns first to form a flame, and this flame propagates to the mixture of intake air and liquid fuel, so that sufficiently stable combustion is achieved even when the mixture of intake air and liquid fuel is super lean. Done. Therefore, the output can be controlled by the supply amount of the liquid fuel, the output control by the throttle valve is not required, the pumping loss is small, and the super lean fuel cycle is close to the air cycle with a large specific heat ratio, resulting in low fuel consumption. The internal combustion engine can be realized.
Also, because it burns super lean and stable, the emission gas is low CO _2.
Therefore, an economical and clean internal combustion engine can be obtained. Further, since CNG has a high pressure, it can be directly injected from the injector into the combustion chamber, and the in-cylinder injection device as in the case of liquid fuel can be eliminated.
Unlike the internal combustion engine that uses the fuel, the output does not decrease, and the performance equivalent to that of the liquid fuel can be secured.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a schematic configuration of an internal combustion engine in a first embodiment of the present invention.

FIG. 2 is a vertical sectional view showing a schematic configuration of an internal combustion engine in a second embodiment of the present invention.

[Explanation of symbols]

 3 Cylinder 4 Piston 5 Combustion Chamber 10 Spark Plug 11 Liquid Fuel Injecting Means 12 Cavity 13 Carburetor 14 Liquid Fuel Injecting Means 15 Injector

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location F02M 69/04 R

Claims (2)

[Claims] 1. A means for supplying compressed natural gas into intake air in an intake stroke, and a liquid fuel injection means for injecting a liquid fuel for ignition toward a portion of a piston upper surface facing an ignition plug before ignition. An internal combustion engine comprising: 2. A liquid fuel injection means for injecting and supplying liquid fuel into intake air in an intake stroke, and an injector for injecting compressed natural gas for ignition toward a spark plug immediately before ignition. Internal combustion engine.