JPH0768902B2 - Internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention comprises at least one reciprocating piston and a combustion chamber arranged in the piston, the combustion chamber comprising at least two narrow chambers which extend to the bottom of the combustion chamber. The combustion chamber is subdivided into partial combustion chambers, which are formed asymmetrically in plan view and are arranged rotationally symmetrically with respect to the combustion chamber axis, which passes through the center of the combustion chamber and is parallel to the piston longitudinal axis. Starting from the combustion chamber axis in the cutting plane lying just below the piston head, the measurements are made with a minimum spacing in the region of the narrow section of the combustion chamber wall and a maximum in the region of the concavely formed combustion chamber wall. The invention relates to an internal combustion engine which is arranged at intervals and in which the ratio of the minimum distance to the maximum distance is greater than or equal to 0.2.

In the case of a gas internal combustion engine, in the case of an extremely lean air-fuel mixture operation, as in the case of stoichiometric operation in a three-way catalytic converter, the low emission of nitric oxide is certainly compared with a relatively high internal efficiency. This can be achieved with a relatively low heat load of components.

However, lean mixtures burn at relatively low velocities, which is thermodynamically disadvantageous and results in varying combustion pressures during the cycle. An effective means to increase the burning rate is to increase the turbulent portion of the flow inside the cylinder.

[0004]

2. Description of the Related Art Papers submitted at the NGV meeting in Geteborg, Sweden, September 21-25, 1992 34
From pages 303 to 315 of "Development of a medium, turbocharged, lean-burn natural gas engine", for example, the so-called Nebula combustion chamber of an internal combustion engine of the kind mentioned at the beginning of the Ricardo Company is known. A high charge air turbulence can be generated in the chamber up to the moment of ignition and during combustion. Turbulence is created in the combustion chamber by two flows directed in the same direction towards the ignition center in the Nebula combustion chamber. Satisfactory lean air-fuel mixture operation is possible up to the air ratio λ = 1.6. As the mixture becomes even thinner, the burning rate is no longer sufficient for reliable combustion of the mixture. However, turbulence can no longer be significantly improved with the effective main flow directed towards the center of the combustion chamber in the Nebula combustion chamber.

Even in the case of direct-injection diesel engines, it has been found that the turbulent part has a substantial effect on the soot emission. So far, in order to reduce the soot emission, it has been attempted mainly to reduce the soot generation during the first phase of combustion by optimizing the torque level and injection in the rotor-like combustion chamber. Yet another substantial factor in achieving low soot emissions is the oxidation of soot generated in the further course of the expansion stroke. High charge air turbulence is advantageous in order to achieve a satisfactory soot post-oxidation.

Even in direct injection engines for the fuel to be spark ignited, the high turbulence of the charge air in the cylinder is effective in the emission of exhaust gas.

[0007]

An object of the present invention is to further increase the turbulence level of the internal cylinder flow relative to the turbulence level of the Nebula combustion chamber.

[0008]

According to the invention, the object is to ensure that the ratio of the minimum distance of the region of the narrow section to the piston radius is less than or equal to 0.5, the area of the narrow section being less than 0.5. This is achieved by forming the walls of the combustion chamber in a convex shape and by having the ratio of the maximum distance to the piston radius be greater than or equal to 0.7.

By thus specially forming the combustion chambers present in the piston head, the turbulent flow motions of the Nebula combustion chambers are directed substantially towards each other as a compressed flow. The additional charge movement formed is added, which further increases the turbulence level. Thereby, on the one hand, the flow velocity near the center of the combustion chamber is kept very low, so that the initial flame generation is by extinguishing the sparks of the spark plugs attached to it or extinguishing the flame front. It will not be harmed. On the other hand, during the downward movement of the piston, the flame propagation is clearly enhanced by the intensified flow directed towards the cylinder wall. In the case of a direct-injection diesel engine, high turbulence levels result in a particularly good soot post-oxidation, which has a very favorable effect on the soot emission. In direct injection engines for the fuel to be spark ignited, the high turbulence in the cylinder wall results in the advantage of the gas engine on the combustion process of the mixture, as well as the fuel accumulated in film form on the combustion chamber wall. Vaporization is promoted.

In order to further strengthen the problematic compressive flow, and thus even greater turbulence, in a further configuration of the invention, the combustion chamber wall is designed to overhang at least in the region of the narrow section, thereby compressing. We propose to achieve a surface enlargement.

In an embodiment variant, it is proposed that the bottom of the combustion chamber is designed to be convex, the ratio of the minimum combustion chamber depth in the region of the center of the combustion chamber to the maximum combustion chamber depth being at least 0.3. To do. Thereby, otherwise the cylinder charge present there is displaced into the region of relatively large turbulence.

To achieve the asymmetry of the individual partial combustion chambers, it is provided according to the invention, for example, that the individual partial combustion chambers have respective circular depressions arranged rotationally symmetrically with respect to the combustion chamber axis. Good. The circular depression is created by forming the walls of the individual partial combustion chambers by a combination curve that largely redirects the inlet swirl flow from the vicinity of the cylinder wall into a partial flow directed towards the center of the combustion chamber, said partial flow being From the region of the narrow section is directed into the compressed flow.

The invention is also applicable to combustion chambers which consist of three partial combustion chambers and which have a three-part symmetry in plan view.

[0014]

The present invention will be described in detail below with reference to the embodiments shown in the drawings. 1 and 2, a combustion chamber 2 is formed in the piston head 1 ′ of the piston 1, which combustion chamber 2 lies in a cutting plane 4 which lies perpendicular to the piston longitudinal axis 3. Immediately below the ′ is substantially defined by its combustion chamber longitudinal axis 5 and its combustion chamber transverse axis 6. In the region 6 ′, the combustion chamber 2 has a clearly defined narrow section 7, which divides the combustion chamber into two partial combustion chambers T. In the region 5'of the combustion chamber longitudinal axis 5, a combustion chamber wall 2'is formed concave in the direction of the piston axis, the combustion chamber wall 2'having a maximum radius of curvature 8 in this region. The combustion chamber wall 2'is formed point-symmetrically with respect to the combustion chamber center 10 in this embodiment.
The narrowed portion 7 of the region 6 ′ is formed in a convex shape toward the center 10 of the combustion chamber and has a radius of curvature 11. The two transition regions 24, which are point-symmetrically opposite to each other with respect to the center 10 of the combustion chamber, from the concave regions 5 ′ to the convex regions 6 ′, are formed substantially flat. The combustion chamber longitudinal axis 5 and the combustion chamber transverse axis 6 are inclined with respect to each other at an angle 25 between 35 ° and 145 °. 9'and 9 "show the position of the curve center 9a with respect to the combustion chamber center 10. The combustion chamber contour can consist of one or more arcs or general combination curves. In the example, combustion chamber center 1
0 lies at a distance 10 'from the longitudinal axis 3 of the piston. The inlet valve 12 and the outlet valve 13 are shown by dotted lines.

Each of the partial combustion chambers T has a combustion chamber axis 10a.
Each having one circular symmetry b arranged with respect to. Due to the special design of the combustion chamber, the charge flow 14 from the region of the compression surface 16 is supplemented by another charge flow according to arrow 17 which is still formed as a compression flow.

What is important for forming a satisfactory turbulence is the minimum distance 1 between the combustion chamber walls 2'in the region of the narrow section 7.
8 and the maximum distance 19 between the combustion chamber walls 2 ′, measured respectively from the combustion chamber axis 10 a, and the ratio to the piston radius 22. In that case, the ratio of the minimum distance 18 to the piston radius 22 must be less than or equal to 0.5 and the ratio of the maximum distance 19 to the piston radius 22 must be greater than 0.7. In the design according to FIGS. 1 and 2, in which the combustion chamber bottom 2 ′ is convexly shaped, the maximum combustion chamber depth 20 is compared with the minimum combustion chamber depth 2
The ratio of 1 must also be at least 0.3. The compression surface 16 thus formed, which is relatively large with respect to the piston cross section 15, produces an additional compression flow 17. Here, the convexly formed piston head 2 ″ pushes the cylinder charge into a relatively large turbulent flow region.

If the combustion chamber wall 2'is designed to project at an angle 23 of about 10 ° with respect to the piston longitudinal axis 3,
The charge streams 14 and 17 can still be increased. The embodiment variant according to FIGS. 3 and 4 shows a simplified combustion chamber configuration similar to the design according to FIGS. In this design,
The combustion chamber bottom 2 "is designed flat and the combustion chamber wall 2'is not overhanging at all.

In the embodiment variant according to FIGS. 5 and 6, the combustion chamber has a total of three subchambers T, which are arranged symmetrically in three parts. Here, too, three symmetrically arranged circular depressions b are formed, by means of which a charge air flow 14 and a compression flow 17 are formed in the context of the narrow section 7, which meet at the combustion chamber center 10. With respect to the ratio of the minimum distance 18 or the maximum distance 19 to the piston radius 22, the above-mentioned conditions apply.

[0019]

By specially designing the combustion chambers present in the piston head as claimed in claim 1, the turbulent flow movements of the Nebula combustion chambers are substantially directed towards each other. As a result, a further charge air movement formed as a compressed flow is added, which further increases the turbulence level.

[Brief description of drawings]

1 is a plan view of the piston 1 according to the invention as viewed in the direction I of FIG.

2 is a cross section of the piston head taken along the line II in FIG.

FIG. 3 is a plan view corresponding to FIG. 1, showing an embodiment modification of the present invention.

FIG. 4 shows an embodiment variant of FIG. 3 in a section corresponding to FIG.

FIG. 5 is a plan view similar to FIG. 1, showing still another embodiment modification of the present invention.

6 shows a modification of FIG. 5 in a section similar to that of FIG.

[Explanation of symbols]

 1 piston 1'piston head 2 combustion chamber 2'combustion chamber wall 2 "combustion chamber bottom 3 piston combustion chamber axis 4 cutting plane 7 narrow section 10 combustion chamber center 10a combustion chamber axis 18 minimum interval 19 maximum interval 20 maximum combustion Chamber depth 21 Minimum combustion chamber depth 22 Piston radius T Partial combustion chamber b Circle hollow

Continuation of the front page (72) Inventor Franz Himera Austria, Graz, Am Lindenhof, 36/21 (56) Reference JP-A-2-256823 (JP, A) JP-A-58-117316 (JP, A)

Claims (5)

[Claims] 1. At least one reciprocating piston.
(1) and a combustion chamber (2) located on the piston (1), the combustion chamber having at least two partial combustions due to a narrow section (7) reaching the bottom (2 ″) of the combustion chamber. It is subdivided into chambers (T), the partial combustion chamber (T) is formed asymmetrically in plan view and passes through the center of the combustion chamber (10) to the piston longitudinal axis.
Starting from the combustion chamber axis (10a) at the cutting plane (4), which is arranged rotationally symmetrical to the combustion chamber axis (10a) which is parallel to (3), and which is located just below the piston head (1 '). In the area of the narrow section (7) of the combustion chamber wall (2 '), the combustion chamber wall formed with a concave shape with a minimum interval (18).
In the area of (2 ′), they are arranged at the maximum interval (19),
In internal combustion engines where the ratio of the minimum distance (18) to the maximum distance (19) is greater than or equal to 0.2, the ratio of the minimum distance (18) in the region of the constriction (7) to the piston radius (22). Is less than or equal to 0.5, the combustion chamber wall (2 ') in the region of the narrow section (7) being convex, and the ratio of the maximum spacing (19) to the piston radius (22) being 0.
Internal combustion engine characterized by being greater than or equal to 7. 2. The combustion chamber wall (2 ') is at least a narrow section (7).
The internal combustion engine of claim 1, wherein the internal combustion engine is designed to overhang in the region of. 3. The combustion chamber bottom (2 ″) is designed to be convex, wherein the ratio of the minimum combustion chamber depth (21) in the region of the combustion chamber center (10) to the maximum combustion chamber depth (20) is Internal combustion engine according to claim 1 or 2, characterized in that it is at least 0.3. 4. Each of the partial combustion chambers (T) has a combustion chamber axis (10).
Internal combustion engine according to any one of claims 1 to 3, characterized in that it has a circular depression (b) which is arranged rotationally symmetrically with respect to a). 5. Internal combustion engine according to claim 1, characterized in that it is provided with three partial chambers (T) having a symmetry of three parts in plan view. .