JP2508675B2 - Combustion chamber of direct injection diesel engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a combustion chamber of a direct injection diesel engine in which fuel is atomized and directly supplied to a combustion chamber formed at the top of a piston to spontaneously combust, and particularly, combustion is performed. by adjusting the dispersion distribution of fuel to the chamber, NO _x, it relates to a combustion chamber of a direct injection diesel engine with enhanced suppressed combustion performance emissions HC.

[Prior Art] As a combustion chamber of a diesel engine, there is generally an air-compressed fuel direct injection type internal combustion engine shown in FIG. 5 (Japanese Patent Laid-Open No. 55-49523).

As shown in the figure, this proposal forms a bowl-shaped combustion chamber a at the top of the piston by recessing it, and a part of the injected fuel is adhered to the wall surface b of this combustion chamber a as a liquid film, and this combustion is performed. The swirl S swirling in the circumferential direction of the chamber a is intended to control the separation of the liquid film and the evaporation of the fuel.

[Problems to be Solved by the Invention] The above-mentioned proposal adjusts the amount of air-fuel mixture generated in the combustion chamber by swirl and propagates the flame of the air-fuel mixture to the liquid film of another fuel to perform slow evaporative combustion. Let's say NO
_This is an attempt to reduce _x .

However, since the strength of the swirl created in the combustion chamber is uniquely determined by the helical degree of the intake port, for example, if the strength of the swirl is properly set on the low load low speed side of the engine, high load high speed There is a problem that an overswir occurs on the side. On the contrary, if the swirl is set to a strength that does not generate overswirl on the high load and high rotation side, proper spread of the spray on the low load and low rotation side and smoke due to excessive adhesion of the liquid film, and large discharge of unburned gas will occur. Not good. Separately from the above proposal, if there is one fuel injection port and this injection port is directed countercurrent to the swirl, a part of the ejected spray is pushed back by the swirl and a rich mixture is created near the injection port. There was a problem that it would end up. That is, since the penetration (= penetration force) of the spray from the injection port is also uniquely determined, it is a problem in improving the dispersion and distribution of the spray with respect to the combustion chamber together with the swirl.

[Means for Solving Problems] An object of the present invention is to solve the above problems, and the present invention forms a combustion chamber at the top of a piston by forming a depression in a bowl shape, and an upper part of an inner peripheral wall of the combustion chamber. In a combustion chamber of a direct injection type diesel engine in which a fuel injection nozzle is provided with an injection port located in the vicinity, in the fuel injection nozzle, an upper inner peripheral wall on a swirl downstream side and a lower inner peripheral wall on a swirl upstream side of the combustion injection nozzle A first injection port and a second injection port are provided to supply the fuel spray and the second injection port in the lower part of the inner peripheral wall.
A concave portion is formed in the portion facing the injection port along the radial direction, and a concave portion for distributing a part of the fuel spray supplied from the second injection port is formed in the recess.

[Operation] With the above configuration, it is possible to distribute a part of the fuel injected from the second injection port to the concave portion that is not easily affected by the swirl, and the fuel from the first injection port and the second injection port is distributed over the entire combustion chamber. It becomes possible to disperse. Therefore, an abnormally rich premixed gas is not generated in the combustion chamber, and this premixed gas is not locally distributed in the combustion chamber. A relatively rapid combustion and a slow evaporative combustion by the fuel film are normally performed. Therefore, HC, NOx, smoke,
Combustion noise is much lower than before.

[Embodiment] A preferred embodiment of a combustion chamber of a direct injection diesel engine of the present invention will be described below with reference to the accompanying drawings.

As shown in FIGS. 1 and 2, a combustion chamber 4 is formed in the piston top portion 2 of the piston 1 so as to be recessed along the axial direction with respect to the top surface 3 as a reference. The axial cross section of the piston 1 is formed in a circular upper part with a truncated shape. That is, the combustion chamber 4 is a bowl-shaped combustion chamber 4 in which a lip portion 11 which is appropriately protruded inward in the radial direction is formed in a portion along the circumferential direction of the upper opening 10 of the combustion chamber 4.

Now, the object of the present invention is that the combustion chamber 4
On the other hand, since the purpose is to improve the dispersion / distribution of fuel and improve the combustion performance, the fuel injection nozzle 7 is related to the combustion chamber 4 as follows.

In this embodiment, the fuel injection nozzle 7 is arranged at an offset position with respect to the axis of the combustion chamber 4, and is housed and fixed in a cylinder head (not shown). The injection port portion 7a of the fuel injection nozzle 7 is arranged on the inner peripheral wall 4a side of the combustion chamber 4 so as to face the inside of the combustion chamber 4. In this embodiment, the fuel injection nozzle 7 has two injection ports 8a, 8b, and one injection port (first injection port) 8a is in the forward direction of the swirl S of the combustion chamber 4 and on the axis of the combustion chamber 4. On the other hand, it is exposed to the upper part of the inner peripheral wall 4a on the radially outer side. Here, the swirl S is designed to swirl in the circumferential direction of the combustion chamber 4, and is supplied from the helical-shaped swirl port 12 shown by an imaginary line. In addition, one of the nozzles 8a has a remaining portion of the fuel atomized and supplied so that a part of the fuel atomized and supplied from the nozzle 8a collides with the inner peripheral wall 4a and is further atomized and scattered. Is diffused and spread along the direction of the swirl S, and the nozzle diameter is determined so that a uniform and thin fuel film F ₁ can be formed on the inner peripheral wall 4a. The other nozzle (second nozzle) 8b
In this embodiment, is exposed to the inner peripheral wall 4a below the combustion chamber 4 that is radially outward with respect to the axial center of the combustion chamber 4 and in the direction opposite to the swirl S, and the other injection port 8b. Also has a sufficient penetrating force against the swirl S, and has a nozzle diameter capable of producing atomized fuel spray and fuel film F ₂ in the same manner as above by being collided with the inner peripheral wall 4a. In the lower portion of the inner peripheral wall 4a, the portion where the other injection port 8b is exposed is recessed along the radial direction to form the fuel spray f ₂
Recesses 9 are formed to distribute a part of the above. Further, in order to improve the low temperature startability, a heat insulating layer 6 is formed on the inner peripheral wall 4a, the top surface 3 and the recess 9 by coating with ceramics or the like as shown in FIG.

 Next, the operation will be described.

At the end of the compression stroke, one jet port (first jet port) 8a and the other jet port (second jet port) 8b are opened. Is fuel spray f ₁ was the ejected from one nozzle hole 8a, and flies toward the upper part of the inner circumferential wall 4a, collide with the inner peripheral wall 4a, the fuel spray f ₂ ejected from the other nozzle holes 8b are inner peripheral wall 4a Fly toward the bottom of. A part of the fuel spray f ₁ is finely crushed by the collision and scattered, and then evaporated by the internal atmosphere of the combustion chamber 4 and mixed with air to become a premixed gas F ₃ which flows in the swirl S direction. . The remaining portion of the fuel spray f ₁ becomes a fuel film F ₁ that flows in a liquid film along the inner peripheral wall 4 a and is evaporated by the internal atmosphere of the combustion chamber 4. This steam also flows in the swirl S direction.

The fuel spray f ₂ is further accelerated in evaporation by the countercurrent flow with the swirl S, partly becomes the premixed gas F ₄ , partly becomes the fuel film F ₂ , and the rest is affected by the swirl S. It reaches the difficult recess 9 and evaporates there. The heat insulation layer 6 prevents the temperature of the inner peripheral wall 4a from decreasing due to the heat insulation, and thus improves the low temperature startability.

Therefore, an abnormally rich premixed gas is not generated in the combustion chamber 4, and the premixed gas is not locally distributed in the combustion chamber 4 in a biased manner. The relatively rapid combustion by the premixed gas and the slow evaporative combustion by the fuel film are normally performed. For this reason, HC, NOx, smoke, and combustion noise are greatly reduced compared to the conventional case.

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

(1) HC, NOx, smoke and combustion noise can be reduced.

[Brief description of drawings]

1 is a top view showing a preferred embodiment of a combustion chamber of a direct injection type diesel engine of the present invention, FIG. 2 is a sectional view taken along line II-II of FIG. 1, and FIG. 3 is a longitudinal sectional view showing a conventional example. Is. In the figure, 1 is a piston, 2 is a piston top portion, 3 is a top surface, 4
Is a combustion chamber, 4a is an inner peripheral wall, 6 is a heat insulating layer, 7 is a fuel injection nozzle, 8a is one injection port (first injection port), 8b is the other injection port (second injection port), and 9 is a recess.

Claims (2)

(57) [Claims] 1. A combustion chamber of a direct injection type diesel engine in which a combustion chamber is formed in a bowl-like shape at the top of a piston, and a fuel injection nozzle is provided with an injection port located near the upper portion of the inner peripheral wall of the combustion chamber. The fuel injection nozzle is provided with a first injection port and a second injection port for supplying combustion spray to the upper part of the inner peripheral wall on the swirl downstream side of the fuel injection nozzle and the lower part of the inner peripheral wall on the swirl upstream side of the fuel injection nozzle. Of the above, the portion facing the second injection port is recessed in the radial direction, and a recess for distributing a part of the fuel spray supplied from the second injection port is formed in the recess. Combustion chamber of injection diesel engine. 2. A combustion chamber for a direct injection diesel engine according to claim 1, wherein at least an inner peripheral wall of the combustion chamber defining the recess is covered with a heat insulating layer.