JPH0110411Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a combustion chamber structure for a diesel engine.

The combustion chamber structure of a conventional diesel engine is as shown in Fig. 1, in which a recess b serving as a combustion chamber is formed in the upper end surface of a piston a that reciprocates within the cylinder of a diesel engine. A multi-hole nozzle c is disposed in the cylinder head portion corresponding to the substantially central position of the recess b.

However, in such a conventional combustion chamber structure, since the multi-hole nozzle c is used, the particle size of the injected fuel tends to be small, and this reduces the amount of premixing (fuel and air are mixed in advance). NOx
There are problems in that it causes an increase in noise and increases noise.

Therefore, it is conceivable to inject fuel into half of the recess b using a small-hole nozzle such as a single-hole nozzle, but with the combustion chamber structure shown in Fig. 1,
Since the half of recess b where fuel is injected and the remaining half where fuel is not injected are set to have approximately the same capacity, it is not possible to achieve an appropriate distribution of fuel and air, resulting in lower fuel efficiency. There is a problem that it gets bulky.

The present invention aims to solve these problems by creating a combustion chamber structure for diesel engines that achieves an appropriate distribution of fuel and air while reducing the amount of premixing. The purpose is to provide

For this reason, the combustion chamber structure of the present invention is used in a diesel engine in which a toroidal combustion chamber is recessed in the upper end surface of a piston that reciprocates within a cylinder. By being tilted with respect to the central axis, a first recessed portion that is deep and has a large capacity and a second recessed portion that is shallow and has a small capacity are formed, and is located at a position offset from the center of the combustion chamber. A small injection hole type fuel injection nozzle is provided, and the injection hole of the fuel injection nozzle is directed only toward the first recessed portion, so that the direction in which the injection hole is directed is directed toward the fuel injected from the injection hole. It is characterized by being set in an oblique direction so that the swirl flow can be blown from the upstream side to the downstream side against the wall surface of the first recess portion.

The combustion chamber structure of a diesel engine as an embodiment of the present invention will be explained below with reference to the drawings. Fig. 2 is a partial vertical sectional view schematically showing the main parts thereof, and Fig. 3 is a direction in the direction of the arrow in Fig. 2. FIG.

As shown in FIGS. 2 and 3, a combustion chamber 2 as a toroidal recess is formed in the upper end surface of a piston 1 that reciprocates within a cylinder of a diesel engine.

Further, a small-hole fuel injection nozzle 3 is disposed in the cylinder head above the combustion chamber 2 and injects fuel into the combustion chamber 2 from a position offset from the center of the combustion chamber 2.

The combustion chamber 2 has a first recess portion 2a which is deep and has a large capacity by tilting the center axis 2c of the toroidal recess with respect to the cylinder center axis A.
and a second recessed portion 2b which is shallow and has a small amount of melt.

The nozzle hole of the fuel injection nozzle 3 is directed only toward the first recessed portion 2a, and the direction in which the nozzle hole is directed directs the fuel injected from the nozzle to the first recessed portion 2a. Swirl flow S against wall surface 4 at
It is set in an oblique direction so that the air can be sprayed from the upstream side to the downstream side.

Note that θ in FIG. 2 indicates the angle formed by the first recessed portion 2a and the second recessed portion 2b.

With the above configuration, the fuel F is supplied to the fuel injection nozzle 3.
When the fuel F is injected from the nozzle hole toward the first recessed portion 2a of the combustion chamber 2, the fuel F is blown obliquely against the wall surface 4 of the first recessed portion 2a and forms a film along the same wall surface. become. A strong swirl of air is then introduced as shown by the arrow in Figure 3, and combustion occurs.

At this time, the first recessed part 2a into which the fuel is blown has a deep and large-capacity space and contains a large amount of air, so it is difficult to make the distribution of fuel and air uniform in the combustion chamber 2. This allows combustion to be carried out quickly and efficiently. As a result, lower fuel consumption can be achieved.

In addition, a small injection hole type fuel injection nozzle 3 is used,
This fuel injection nozzle 3 is provided at a position offset from the center of the combustion chamber 2, and from this offset position, a swirl flow S is directed against the wall surface 4 of the first recess portion 2a.
Since the fuel is injected from the upstream side to the downstream side, the fuel F can be formed in the form of a film on the wall surface 4 of the first recessed part 2a while reducing the amount of premixing. , this results in NOx
and noise can be reduced.

Note that the number of holes in the fuel injection nozzle 3 is set to one or more, and even if two or more injection holes are provided, the fuel from each injection hole is
As shown in FIG. 3, the liquid is injected only into the first recessed portion 2a.

As detailed above, according to the combustion chamber structure of the diesel engine of the present invention, the upper end surface of the piston reciprocating within the cylinder of the diesel engine,
In a diesel engine having a recessed toroidal combustion chamber, the central axis of the combustion chamber is tilted with respect to the central axis of the cylinder, so that the first recessed part is deep and has a large capacity, and the first recessed part is shallow and has a large capacity. A small-volume fuel injection nozzle is provided at a position offset from the center of the combustion chamber, and the nozzle hole of the fuel injection nozzle is located at a position offset from the center of the combustion chamber. The fuel injected from the nozzle hole is directed only toward the recessed portion of the first recessed portion, and the fuel injected from the nozzle hole is directed from the upstream side to the downstream side of the swirl flow toward the wall surface in the first recessed portion. Since it is set in a diagonal direction, the following effects or advantages can be obtained.

(1) The amount of premixing can be reduced, which allows
It can contribute to reducing NOx and noise.

(2) Since the mixing state of fuel and air can be made uniform and an appropriate distribution state of these can be achieved, combustion can be performed quickly and efficiently, which can contribute to lower fuel consumption.

[Brief explanation of the drawing]

Fig. 1 is a partial vertical sectional view schematically showing the main part of the combustion chamber structure of a conventional diesel engine, and Figs. 2 and 3 show the combustion chamber structure of a diesel engine as an embodiment of the present invention. FIG. 2 is a partial vertical sectional view schematically showing the main parts thereof, and FIG. 3 is a plan view seen from the direction of the arrow in FIG. 2. 1... Piston, 2... Combustion chamber, 2a... First
recessed portion, 2b... second recessed portion, 2c...
Central axis of the combustion chamber, 3...Fuel injection nozzle, 4...
...Wall surface of the first recess portion, A...Cylinder center axis, S...Swirl flow.

Claims (1)

[Scope of utility model registration request] On the upper end surface of the piston that reciprocates inside the cylinder,
In a diesel engine having a recessed toroidal combustion chamber, the central axis of the combustion chamber is tilted with respect to the central axis of the cylinder, so that the first recessed part is deep and has a large capacity, and the first recessed part is shallow and has a large capacity. A small-volume fuel injection nozzle is provided at a position offset from the center of the combustion chamber, and the nozzle hole of the fuel injection nozzle is located at a position offset from the center of the combustion chamber. The fuel injected from the nozzle hole is directed only toward the recessed portion of the first recessed portion, and the fuel injected from the nozzle hole is directed from the upstream side to the downstream side of the swirl flow toward the wall surface in the first recessed portion. The combustion chamber structure of a diesel engine is characterized by being set in a diagonal direction.