DE2407783A1 - COMBUSTION MACHINE WITH COMBUSTION CHAMBER TAP IN THE PISTON BOTTOM - Google Patents

Description

February 19, 1974 - / Jg - 1 1

Dipl.Ing.Dr.Dr.h.c. Hans LIST, in Graz (Austria)

Internal combustion engine with arranged in the piston crown

Combustion bowl

The invention relates to an internal combustion engine with a combustion bowl arranged in the piston crown, in particular Diesel engine with direct injection into the cylinder, in which the combustion air is swirled is guided into the combustion chamber with respect to the cylinder axis.

According to the latest findings in engine construction, the turbulence of the air in the combustion chamber can be increased by increasing the turbulence and the associated better mixing of the fuel with the combustion air, the combustion process be influenced in a favorable sense. In diesel engines with direct injection this influence on the combustion process in a reduction of smoke formation and an equalization the temperature of the burning charge over the entire combustion chamber. This generally leads to a reduction in the proportion of nitrogen oxide in the exhaust gases, as there are areas of small excess air and thus high combustion temperatures with strong nitrogen oxide formation can be avoided »

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In diesel engines with direct injection into the combustion chamber located in the piston, the quality of the Mixing of the fuel with the combustion air on the one hand from the macro mixture formation, i.e. the coarse Distribution of the fuel to the combustion chamber and, on the other hand, the formation of micro-mixtures, i.e. the mixture of the fuel with the air in the small and smallest sub-areas of the combustion chamber. For the macro-mixture formation is, for example, in fast-running diesel engines of the lower performance classes a distribution of the fuel in the combustion chamber from a nozzle located approximately in the middle of the combustion chamber provided with beams arranged in a star shape. The distribution of the fuel in the between the fuel jets located combustion chamber segments is done by the appropriate design of the intake duct system caused! rotation of the combustion air around the cylinder axis.

The formation of micro-mixtures is based on the presence of a certain turbulence in the rotating combustion air, which does not follow strictly circular paths around the cylinder axis, but superimposed irregular ones Performs movements which contribute to the improved mixture formation insofar as an equalization the distribution of the fuel to the combustion air is achieved.

It is now the aim of the present invention in an internal combustion engine of the type mentioned at the beginning Measures promoting the formation of micro-mixtures to intensify the turbulence in the immediate area of the combustion chamber to find, which require a relatively low structural effort and the overall structure of the Leave the machine unchanged so that a subsequent

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Slow equipping of existing engines with these turbulence-demanding means is possible. For this purpose it is provided according to the invention that in the peripheral wall of the combustion bowl and "or or recesses extending from the edge of the opening of the combustion bowl are provided in the end wall of the piston, and that the outer cross section of at least the recesses of the combustion bowl is asymmetrical, with swirl direction mag the combustion air is followed by a shorter end part on a longer flat 'cross-section, the circumferential wall of the combustion bowl, preferably cuts at an acute angle "

In this way it is possible to use a part of the flow energy of the rotating air, especially in the peripheral Areas of the combustion chamber to convert into additional turbulence and at these important points to achieve an improvement in the formation of micro-mixtures »In the area of the combustion bowl, this is stronger Turbulence is caused by the fact that the flow in the vicinity of the wall of the combustion bowl in the direction of rotation of the cylinder charge Layers of air enter the recesses in the bowl wall and are deflected there in one direction, which is directed transversely or against the main flow direction of the cylinder charge, which leads to a reduction of the "total twist of the cylinder charge simultaneous increase in their turbulence leads. The turbulent flow therefore spreads throughout Piston door room and also reaches those places where, with the usual smooth-walled shape of the combustion bowl, there is predominantly pure rotary flow.

The extent of the additional turbulence can be determined by the number and shape of the existing

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and the respective requirements be adjusted.

An internal combustion engine of the type mentioned is already known in which two to eight niches are incorporated into the toroidal peripheral wall of the combustion bowl, the number of which corresponds to the number of nozzle jet openings. The individual niches are separated from one another by projections protruding towards the center of the cylinder. The known design also aims at a certain deflection of the air flow parallel to the wall towards the central area of the combustion chamber, but this measure proves to be used for the formation and maintenance of increased turbulence before and during the combustion because of the strong constriction of the inlet opening of the toroidal piston combustion chamber as ineffective. In addition, the symmetrically formed in the known case, extending according to an arc combustion chamber recesses permit only a slight deflection of the air against the combustion chamber center, in no way, however, a pronounced transverse or counter-flow of the cylinder charge of the niches exiting air layers be train to the rotating in the combustion chamber core .

In the internal combustion engine according to the invention, however, additional turbulence can also be caused by the recesses the piston end wall are generated. This phenomenon is based on the following principle: When the As is well known, a squeezing flow occurs from the edge of the piston into the piston before the top dead center is reached A combustion chamber, which increases the turbulence on the outer periphery of the combustion chamber. With the usual Smooth execution of the piston face is due to the displacement of the rotating air above it into the piston combustion chamber, its contents in the same sense

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rotates, according to the radial velocity component of the displaced air in the combustion bowl additional Caused turbulence. This additional turbulence is, however, caused by the design according to the invention significantly increased, since the squeezed air through the recesses in the piston end wall in the radial direction or is steered in a direction of movement which has a tangential component opposite to the direction of rotation which has circulating air in the combustion bowl. Here, too, there is the possibility, through the number, shape and direction of the recesses of the piston end wall any adaptation to desired! turbulence and To make twist ratios.

Are recesses according to the invention both in the peripheral wall of the combustion bowl and on the piston face provided, it is ensured that the desired turbulent flow conditions up to far are maintained into the combustion period, with shortly before reaching top dead center the piston shows a renewed increase in turbulence due to the described squeeze flow.

Since the measures according to the invention exclusively on the area of the piston itself are limited, any internal combustion engine can be replaced by a simple exchange the piston can be redesigned without any other structural change in accordance with the principle of the invention. This is especially important because it is then possible to use older engines as well Design to meet the stricter provisions of environmental protection with regard to exhaust gas decontamination without significant Having to accept conversion costs.

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According to a preferred embodiment of the invention, the recesses of the combustion bowl are essentially Shaped according to a general cylinder surface and each form with the peripheral wall of the combustion bowl a sharp, preferably approximately straight edge. In this way arise at the intersections of the short Cross-sectional end parts of the recesses with the bowl wall pronounced, continuous up to the piston face Tear-off edges, which distribute the turbulent flow conditions over the height of the combustion bowl cause.

In a further development of the inventive concept, the two cross-sectional parts of the recesses are advantageous the combustion bowl is formed by tangentially adjoining circular cylinder surfaces with different radii, of which the circular cylindrical surface, which has the larger radius and which forms the flat cross-sectional part, is tangential adjoins the peripheral wall of the combustion bowl. These The formation of the recesses is, on the one hand, from processing favorable for technical reasons, because the precision work is limited to the production of circular cylindrical surfaces, on the other hand, however, there are also fluidic advantages, which consist in the fact that the near-wall parts of the air rotating in the combustion bowl enter the recesses without changing direction and within the same dead spaces, which from Airflow cannot be met, cannot form.

In a further embodiment of the invention, the recesses of the combustion bowl can also be located above the bottom surface the trough end and the lower beveling edge of each recess can move from one to the trough bottom sloping, in the development approximately straight section and an adjoining, arcuate section

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section rising to the edge of the opening of the combustion bowl exist. This edge formation promotes the desired turbulent flow condition by the an additional air entering the recesses, the distribution of the eddies over the height of the Trough combustion chamber favoring transverse movement granted will.

According to the invention, it can also be advantageous if the circumferential wall of the combustion bowl is made up of a large number narrower, more directly adjacent in the circumferential direction Recesses is formed. Such recesses act like a rough roughening of the bowl wall from which the rotary movement of the air around the cylinder axis in favor of increased turbulence generation decelerates.

Advantageously, the directly adjacent recesses sawtooth-shaped cross-section may according to a further feature of the invention comprise ₀ This manufacturing technology without difficulty to be realized wall structure makes it possible to take with the appropriate inclination of the planks of the sawtooth-shaped recesses largely on the degree of addition the resulting turbulence influence.

According to the invention it has proved to be particularly advantageous if the recesses in the piston end wall than from the opening edge of the combustion bowl radiate diverging grooves, N _u th or the like. are formed »The squeezing flow that forms before the piston reaches the top dead center position is then guided by the grooves or hats mentioned in a defined direction from the periphery of the piston to the combustion bowl.

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According to a further embodiment of the invention, the recesses of the piston end wall should be approximately radial or opposite to the radial direction against the direction of rotation of the combustion air at an acute angle be arranged offset. During the upward movement of the piston within the recesses of the piston end wall Air flowing to the hand of the combustion bowl then collides with the rotating layers of air at the edge " the combustion bowl together at any angle so that a strong turbulence is formed can. The greater the ßtrömungsicomponente opposite to the direction of rotation of the cylinder charge the air currents guided inwards in the recesses of the piston end face, the greater it also becomes the resulting turbulence in the contents of the combustion chamber with a corresponding reduction in the resulting swirl be.

According to the invention, the depth of the recesses in the piston end wall to the opening edge of the combustion bowl can also be adjusted to increase. The most appropriate cross-sectional shape of the recesses can at best be empirical be determined.

If the recesses of the piston end wall are designed as grooves, it is finally after another Feature of the invention of particular advantage when each with respect to the swirl direction of the combustion air The groove flank at the front is flattened and the other groove flank rises in an arc shape towards the piston face is trained. The purpose of this arrangement is to prevent the piston entering the piston combustion chamber through the grooves Increase airflow. The air rotating above the piston front wall then hits a groove flank,

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is deflected there and then flows in the longitudinal direction of the groove into the combustion bowl, Αμοη in this Execution is depending on the direction of the grooves and the intensity of the collision of the stream achieved displaced air with the rotating contents of the combustion bowl produces more or less turbulence.

The invention is explained in more detail below with reference to exemplary embodiments shown in the drawing. It lines Pig. 1 shows an axial section of the cylinder and Zyliriderkopfbereiches an internal combustion engine according to the Invention according to the section line I-I in Fig. 2, Jig. 2 a top view of the piston from Pig. 1, Fig. 3 shows the axial section of a modified embodiment of the Piston of an internal combustion engine according to the invention, FIGS. 4 to 6 show further designs of pistons of the type according to the invention in plan view, Figo 7 a Axial section of a further embodiment according to the invention, Fig. 8 is a plan view of the piston 7, 9 a modified variant of the piston according to FIG. 8 in plan view, FIG. 10 a further design example of a piston according to the invention in plan view, FIG. 11 shows a development of the peripheral edge of a Piston according to FIGS. 10 and 12, a further embodiment variant of the invention in axial section.

The internal combustion engines shown are consist of diesel engines with direct injection into the trough-shaped combustion chamber in the piston crown. The cylinder 1, the piston 2 and the cylinder head 3 are only partially shown in the drawing. In Fig. 1, the inlet channel 4, the inlet valve 5 and the injection nozzle 6 are also shown. In the Exemplary embodiments are four-hole injection nozzles shown, the nozzle jets of which are denoted by 7.

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In the context of the invention, of course, injection nozzles with a different number of nozzle ' Openings and are provided in a position deviating from the arrangement shown.

As already mentioned, each of the pistons 2 shown has a combustion bowl 8, the bottom 9 of which According to FIG. 1, it can be curved or else flat, as can be seen in FIGS. 3, 7 and 12 is. The peripheral wall 10 of the combustion bowl 8 theoretically has in the illustrated embodiments the shape of a circular cylinder, for example, but it can also deviate from this, depending on the type of machine Have shapes. The edge of the opening of the combustion bowl 8, i.e. the cut contour with the piston face 11, is denoted by 12

In the designs of the internal combustion engine according to FIGS. To 6, the combustion chamber bowl is in the peripheral wall 10 starting from the opening edge 12, beyond the scope of the Combustion bowl 8 evenly distributed recesses 13 are provided which have an asymmetrical cross section have, illustrated in you by the arrows 14 Swirl direction of the combustion air in the combustion chamber on a longer flat cross-sectional part 15 a short one The end part 16 follows, which intersects the peripheral wall 10 of the combustion chamber trough 8, preferably at an acute angle. At the The interface is a sharp edge 17 as a tear-off edge for the "near the wall" emerging from the recesses 13 Air layers formed. When the recesses 13 are shaped according to a general cylindrical surface and go through essentially to the bottom 9 of the combustion bowl 8, a straight line to the piston axis is formed 18 approximately parallel tear-off edge 17 from. The air layers close to the wall become through the recesses 13

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deflected towards the center of the combustion chamber and therefore collide with the air core rotating in the combustion chamber bowl 8 together, whereby part of the flow energy is converted into turbulence and the swirl of the cylinder charge accordingly is reduced. The stronger the deflection of the air flowing through the recesses 13, the stronger is also the turbulence that occurs when it collides with the rotating air core. If the. Cross-sectional end part 16 of the recesses 13 occurs As FIG. 4 shows, for the formation of an embossed counterflow according to the arrow 19. This occurs a very strong turbulence with a considerable weakening of the resulting swirl of the combustion air "

In Fig. 5 there are various cross-sectional shapes of the recesses 13 can be seen, in which the cross-sectional end part 16, 16 ', or 16 "different degrees of curvature owns. The edge shape 16 leads to higher, the edge shape 16 · to medium and the edge shape 16 ″ to relative less turbulence formation in the area of the combustion bowl 8. It proves to be advantageous if the flat Cross-sectional part 15 is tangent to the base circle of the peripheral wall 10, for example as a circular arc larger radius than the base circle of the peripheral wall 10 is executed. This ensures that the Recesses 13 entering air fills the recesses and nowhere dead spaces arise from the air flow not be hit.

As FIG. 6 shows, a plurality can also be relative narrow, directly adjoining recesses 13 are provided, which are connected to the peripheral wall 10 of the Combustion bowl 8 form a plurality of tear-off edges 17. The recesses 13 act like a rough roughening the bowl wall and lead to a strong deceleration

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the resulting swirl of the combustion air in favor increased turbulence. The cross-section of these narrow recesses can, as in Pig. 6 top left shown, with increasing curvature in the direction of twist or, as shown at the bottom right in FIG. 6 at 20, sawtooth-like be trained. With the shape of the tooth flanks, the degree of additional turbulence can also be arbitrary can be varied.

The cross-sectional shape of the recesses is not the only factor determining the flow state that arises in the combustion bowl 8 13, but also their course in the direction of the bottom 9 of the combustion bowl 8 is decisive. As shown in Fig. 3, for example, the recesses in the combustion bowl 8 can already be above the bottom surface 9 the trough end, the lower boundary edge 21 of each recess 13 from a sloping towards the bottom 9, in the development approximately straight section and an adjoining, arcuate section towards the opening edge 12 ascending section can exist. The course of the Edge 21 is also decisive for the distribution of the turbulent flow zones over the height of the combustion chamber hollow 8 ο

Another possibility of generating additional turbulence according to the invention consists in a special design the piston end wall 11, in diesel engines of the usual design is between the periphery of the piston 2 and the opening edge 12 of the combustion bowl 8 formed annular end face of the piston executed smooth. if now the piston 2 moves towards the top dead center, arises between the piston face 11 and the Cylinder head bottom a squeezing flow, whereby by the displacement of the air located above in the combustion chamber hollow 8, the content of which rotates in the same sense, due to the radial velocity component of the

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If air is forced into the combustion bowl 8, additional turbulence is created. According to the invention, this is additional Turbulence is significantly increased in that recesses 22 are also provided on the piston end face 11 be, which the squeezed air in the radial or opposite the radial .Rrichtung opposite to the direction of rotation Direct air at an acute angle offset direction. It then comes in the area of the opening edge 12 of the combustion chamber trough 8 by the collision of the through the recesses 22 partial air flows entering the combustion bowl 8 with the rotating air core in the combustion chamber to create increased turbulence,

The recesses 22 may, as the shape of grooves or slots have in FIGS. 7 to be seen _f 8,9 and 12, which may have optionally a increasing toward the combustion chamber recess depth x 8 (see. Fig. 12). However, a further increase in the additional turbulence can be achieved by designing the recesses 22 as shown in FIGS. In this embodiment, the groove flank 23 located at the front with respect to the jjrallrichtung 14 is flattened, whereas the other mutant flank 24 is designed to rise in an arc shape towards the piston end face 11. Special flow conditions then arise in the area of the recesses 22, as illustrated by the arrows 25 in FIG. 10. The air rotating above the column 2 is deflected by the groove flank 24 towards the combustion bowl 8 and there is again in the area of the opening edge 12 of the combustion bowl 8 a collision with the air rotating in the bowl with the formation of additional turbulence.

You can increase the displacement effect when the piston approaches the upper ^lj -'otpunkt and the turbulence generated by the grooves 22 by the fact that

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According to FIG. 12, a central extension on the cylinder head 3 26 provides, which penetrates into the isrennraumulde 8 shortly before reaching the top dead center position of the piston O

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Claims (1)

Claims; (1.! Internal combustion engine with • ■ J arranged in the piston crown Combustion bowl, especially diesel engine with direct Injection into the cylinder, "in which the combustion air swirls" with respect to the cylinder axis in the combustion chamber is guided, characterized in that the Combustion bowl (8) and / or in the end wall (11) of the piston (2) from the opening edge (12) of the combustion bowl (8) outgoing recesses (13; 22) are provided, and that the cross section of at least the recesses (13) the combustion bowl is asymmetrical, with the combustion air extending over a longer period in the swirl direction (H) flat cross-sectional part (15) a shorter end part (16, 16 ', 16 ") follows the peripheral wall (10) of the Firing chamber trough (8), preferably at an acute angle, cuts » 2. Internal combustion engine according to claim 1, characterized in that the recesses (13) of the combustion bowl (8) are essentially shaped according to a general cylindrical surface and with the peripheral wall (10) of the combustion bowl (8) each form a sharp, preferably approximately straight edge (17). 3. Internal combustion engine according to claim 1 or 2, characterized in that the two cross-sectional parts (15,16) of the recesses (13) of the combustion bowl (8) are formed by tangentially adjoining circular cylinder surfaces with different radii, of which the larger radius having the The circular cylinder surface forming a flat cross-sectional part (15) is tangentially connected to the peripheral wall (10) of the combustion bowl (8) ₀ 4. Internal combustion engine according to one of claims 1 to 3, characterized in that the recesses (13) of the Combustion chamber trough (8) above the bottom surface (9) of the End of the trough and the lower boundary edge (21) 409837/0726 ordered each recess (13) from a ^{sloping towards the bowl bottom (c} j), in the development approximately straight section and an adjoining, arcuate section rising to the opening edge (12) of the combustion bowl (8) 5. Internal combustion engine according to one of the preceding claims, characterized in that the peripheral wall (1O) of the combustion chamber trough (8) from a multiplicity of narrow, directly adjoining recesses (13) is formed. 6. Internal combustion engine according to claim 5 »characterized in that the immediately adjacent Have recesses (13) sawtooth-shaped cross-section (20). 7 «internal combustion engine according to one of the preceding claims, characterized in that the recesses (22) of the piston end wall (11) as from the opening edge (12) the combustion bowl (8) radially diverging Grooves, grooves or the like. are trained 8. Internal combustion engine according to one of the preceding claims, characterized in that the recesses (22) of the piston end wall (11) with respect to the piston axis (18) tung approximately radially, or with respect to the radial iilcAi contrary to the direction of rotation (H) of the combustion air at an acute angle are staggered _o 9. Internal combustion engine according to one of the preceding claims, characterized in that the depth of the recesses (22) of the piston end wall (11) to the opening edge (12) of the combustion bowl (8) increases _o 10 «internal combustion engine according to one of claims 7 to 9, (!. '■ -.by characterized in that when the recesses of the piston end wall are formed as grooves (22), the respective with respect to the direction of swirl (Η) of the combustion air, the angry flank (23) at the front is flattened and the other Groove flank (24) towards the piston face (11) Is formed so as to rise in an arc. February 15, 1974 409837/0726 eerseite