JPH0635828B2 - Combustion chamber structure of direct injection diesel engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a combustion chamber structure of a direct injection type diesel engine, and more particularly to promoting complete combustion of injected fuel to improve engine performance and smoke. A combustion chamber structure of a direct injection diesel engine capable of

[Technical Background of the Invention and its Problems] Generally, in a direct injection diesel engine, as shown in FIG. 1, intake air introduced into a cylinder 1 is compressed by a rising piston 2 to reach high temperature and high pressure. When the piston 2 reaches the vicinity of the top dead center, the fuel is directly injected from the injection nozzle 4 provided in the piston head 3 to spontaneously ignite and burn.

In a conventional diesel engine of this type, a combustion chamber 5 is formed by recessing a substantially central portion of a piston head 2a facing a cylinder head 3.
The combustion chamber 5 functions so that the swirl swirled allows the air and the injected fuel to be sufficiently mixed and vaporized to improve the combustion efficiency.

By the way, in the prior art, immediately after the start of combustion, the flame of the fuel injected from each injection port of the injection nozzle 4 and colliding with the peripheral side wall of the combustion chamber 5 causes the head clearance (the piston 2 reaches the top dead center) from the combustion chamber 5. When it reaches, there is a problem that it spreads to a void portion (C) formed between the cylinder head 3 and the piston head 2a, and incomplete combustion causes smoke to worsen. Regarding combustion, it is desirable that the head clearance C is eliminated and combustion is achieved in the closed combustion chamber 5 of a predetermined volume. However, between the cylinder head 3 and the cylinder body 6, airtightness and liquid tightness are provided. A gasket is provided to secure the property, and a head clearance C corresponding to the thickness is formed. The combustion chamber 5 takes in sufficient intake air to improve the combustion efficiency inside the combustion chamber 5, and when the flame spreads into the narrow head clearance C with a small amount of air (oxygen amount), it causes incomplete combustion due to lack of oxygen. become.

[Object of the Invention] The present invention was devised in view of the above-mentioned problems, and an object thereof is a direct injection type which can achieve complete combustion of injected fuel to improve engine performance and smoke. Providing a combustion chamber structure for a diesel engine.

The inventor of the present application has found that most of the flame that spreads to the head clearance is injected from each of the injection holes of the injection nozzle and collides with the peripheral side wall of the combustion chamber from the adhering portion of fuel (hereinafter referred to as “fuel region”) to swirl flow. Focusing on the fact that it is formed on the downstream side in the direction of the head, the air clearance is formed only in the area where the flame spreads to secure the minimum necessary oxygen amount, and the head clearance is not significantly reduced without significantly reducing the air amount in the combustion chamber. The inventors have completed the present invention by finding that a flame that spreads to can be completely burned.

[Embodiment of the Invention] A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

As shown in FIGS. 2 and 3, 5 is a piston head 2.
The combustion chamber 5 is formed by being depressed in a, and in this embodiment, the combustion chamber 5 is shown formed relatively deep. The combustion chamber 5 is opened at the upper side facing the cylinder head 3 provided with the injection nozzle 4 in order to introduce the swirl S to swirl the chamber and take in the injected fuel F to generate a mixture. The bottom portion and the bottom portion are defined by the peripheral side wall 5a and the bottom wall 5b, respectively.

In the upper peripheral edge portion 5c of the combustion chamber 5 formed in this way,
The auxiliary combustion air chambers 7 are formed on the downstream side in the flow direction of the swirl S from the fuel region A that collides with the peripheral side wall 5a of the combustion chamber 5.
These auxiliary combustion air chambers 7 are formed in the cylinder head 3 so as to correspond to the injection ports 4a of the injection nozzle 4 for injecting the fuel F. In the present embodiment, the auxiliary combustion air chambers 7 ... It is composed of a recessed portion continuous outward in the radial direction of the combustion chamber 5 so as to give a sufficient amount of combustion air to the flame B that spreads to the downstream side of the swirl S from. The concave portion is divided into side portions 7a formed in the cylinder head 3 along the circumferential direction of the combustion chamber 5 and has a volume capable of retaining combustion air to be given to the flame B.

The following configuration is based on the following considerations. That is, the nozzle 4a ...
The sprayed fuel f, which has been injected from and is mixed and vaporized by the swirl S until it reaches the peripheral side wall 5a, is exposed to sufficient air in the combustion chamber 5, so that complete combustion is easy. However, in the fuel region A formed by the fuel that has collided with the peripheral side wall 5a, the fuel density is high when viewed from the entire combustion chamber 5, and the amount of air in the vicinity thereof is excessive, and the fuel region A is formed. Flame B ... tends to incompletely burn. Therefore, it is necessary to supply a sufficient amount of air to the flame B formed in the fuel region A ... Spreading in the head clearance C on the downstream side in the flow direction of the swirl S, and it is not particularly necessary in other portions. . On the contrary, if the auxiliary combustion air chambers 7 are formed more than necessary, the combustion ratio in the combustion chamber 5 may be reduced, the average cylinder effective pressure (hereinafter referred to as "Pme") may be reduced, and the smoke may be aggravated. There is

Next, the operation of the present invention will be described.

As shown in the figure, the swirl S is swirled into the combustion chamber 5 and the fuel F is injected. In the center of the combustion chamber 5,
The fuel injection f toward the side wall 5a side is mixed and vaporized by the swirl S.

On the other hand, on the peripheral side wall 5a of the combustion chamber 5, a portion of the fuel that has collided without being vaporized adheres and accumulates to form a fuel row A ....
After that, as a flame kernel is generated in the air-fuel mixture and the flame propagates, flame B ... Is generated even in the fuel region A .... These flames B ... Are blown by the swirl S and the head clearance C on the downstream side is generated.
It spreads to. In this regard, in the present invention, the flame B ... Can be completely burned as much as possible by the air retained in the auxiliary combustion air chambers 7 ... Formed at the positions where the flames B ... Spread in the compression stroke. Therefore, it is possible to improve Pme and also improve smoke.

Further, since the auxiliary combustion air chamber 7 is formed in the cylinder head 3, it is not necessary to change the shape of the combustion chamber of the piston head 2a.
No turbulence is generated in the squish flow that enters inside, and part of the fuel that has collided with the combustion chamber wall does not flow into the auxiliary combustion air chamber 7 ... Absent.

In order to form the auxiliary combustion air chambers 7 ... For all the injection ports 4a ..., four auxiliary combustion air chambers 7 ...
Will be formed. In this case, the auxiliary combustion air chambers 7 are formed in the intake valve 8 and the exhaust valve 9, respectively,
The strength of these valves 8 and 9 will be increased.

[Effects of the Invention] In summary, according to the present invention, the following excellent effects are exhibited.

(1) Since the auxiliary combustion air chamber for supplying air to the flame that spreads to the head clearance for complete combustion is formed,
It is possible to improve the engine performance and smoke by promoting complete combustion of the injected fuel.

(2) The structure is simple and can be easily adopted.

(3) Since the auxiliary combustion air chamber is formed in the cylinder head, it is not necessary to change the shape of the combustion chamber formed in the piston head, so that the squish flow that occurs when the piston moves up is not disturbed, and Since a part of the fuel that has collided with the combustion chamber wall does not flow into the auxiliary combustion air chamber, the combustion is not deteriorated.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a direct injection diesel engine, FIG. 2 is a plan view showing a preferred embodiment of the present invention, and FIG. 3 is a sectional view taken along the line III-III in FIG. In the figure, 2a is a piston head, 3 is a cylinder head, 4
Is an injection nozzle, 4a is its injection port, 5 is a combustion chamber, 5a is a peripheral side wall which is an inner wall thereof, 5c is an upper peripheral portion thereof, 7 is an auxiliary combustion air chamber, A is a fuel region, and S is a swirl.

Claims (1)

[Claims] 1. In a combustion chamber structure of a direct injection diesel engine, a cylinder head facing a piston head is positioned downstream of a fuel region colliding with a combustion chamber inner wall formed in the piston head in a swirl direction to provide auxiliary combustion air. A combustion chamber structure of a direct injection diesel engine characterized by forming a chamber.