DE1260859B - Diesel internal combustion engine with direct fuel injection - Google Patents

Description

Diesel internal combustion engine with direct fuel injection Die The invention relates to a diesel internal combustion engine with direct fuel injection in a rotationally symmetrical, z. B. ellipsoidal or pear-shaped combustion chamber, in the compression stroke almost all of the combustion air under one to the Cylinder axis circling motion flows in and the fuel flows out to the axis of rotation of the combustion chamber and thus eccentrically arranged multi-hole nozzle to the combustion chamber opening is injected so that to localize the first auto-ignition by the fuel jet from the shortest free jet length the edge of the combustion chamber side wall of a portion of the jacket of this fuel jet against the radial movement component the combustion air flowing into the combustion chamber is sprayed over, according to the patent 1175 486.

In the known diesel internal combustion engines of this type, the nozzle axis is mostly arranged in the longitudinal axis of the combustion chamber, and the fuel jets, the axes of which lie on a cone shell have practically the same lengths. The fuel is distributed over several areas of the The combustion chamber or the combustion chamber wall, what a good mixture formation, even with relatively little air turbulence in the combustion chamber, is beneficial.

However, there is a disadvantage of such a fuel injection that in view of the symmetrical design of the fuel jets this all offer the same prerequisites for the first compression ignition; Consequently auto-ignition can start at several points in the combustion chamber at the same time.

Experience has shown that those with such a fuel injection tend to be working diesel internal combustion engines for knocking and with little air movement Immediately to smoke, so that only moderate combustion agent pressures are achieved can.

It has already been recommended to equip the multi-hole nozzle with an additional To provide an outlet hole for a "pilot jet" that enters the hot center of the Combustion chamber is directed. Apart from that, an increase in the number the nozzle bores, especially with a smaller engine displacement, the disadvantage of a slight clogging of the then correspondingly narrow nozzle bores opposes experience has shown that such a measure is in most cases insufficient, to significantly improve combustion. Above all, it does not produce that Desired effect if the combustion chamber wall has larger local temperature differences during operation having; but this is usually the case, since experience has shown the temperatures at the edge delimiting the inflow opening of the combustion chamber lie significantly higher than in the area of the combustion chamber floor.

It has also already been proposed for injection internal combustion engines those in the cylinder cover or piston crown are spherical, ellipsoidal or ring-bead-shaped Have combustion chamber that absorbs almost all of the compressed air, the multi-hole nozzle with their nozzle bores distributed symmetrically around the nozzle axis eccentrically in the To accommodate combustion chamber. The purpose of this arrangement was to sloped through If the fuel jets hit the combustion chamber wall, these jets in the circumferential direction deflect the combustion chamber and in this way a more intimate mixture of the fuel to achieve with the air than would be possible with approximately vertical impact should.

Since, according to this proposal, the fuel jets always only on the Inner wall of the combustion chamber are directed and also despite their different Lengths there are only slightly different conditions for a first spontaneous ignition, are with regard to the uncertainty about the location of the start of the ignition, the knocking and smoking as well as combustion agent pressures have the same disadvantages as with a symmetrical injection by means of one in the axis of the combustion chamber arranged nozzle. In addition, the multi-hole nozzle protrudes relatively far into the combustion chamber into it.

Newer fuel injection methods work with an injection in the direction of a strong inlet swirl flow that flows into the combustion chamber Combustion air, with several nozzle bores arranged asymmetrically to the nozzle axis at least a large proportion of the fuel under a more or less flat Angle - for example fan-like - sprayed onto part of the combustion chamber wall and then detached again from this wall in vapor form with the combustion air gets mixed up and burned away. The relatively high fuel density that occurs in the process on a limited - through, possibly fan-like division of the fuel jets only slightly expanded - area of the combustion chamber wall forces to detach the Fuel to generate very violent swirl currents of the combustion air and to to apply special additional measures for this purpose, such as the Arrangement of a spiral air inlet duct, which is used in multi-cylinder engines brings great difficulties in the design of the cylinder heads, or the placement of special deflector screens on the intake valves.

In these known injection methods, fuel jets do indeed result different length and accordingly different shape. These fuel jets however, they all hit parts of the combustion chamber wall that remain cooler during operation on, and the point of the first self-ignition is more or less random; it is not tied to a specific point in the combustion chamber. For this reason the optimal conditions cannot be achieved here either, as they are comparatively for internal combustion engines of the Otto type by a fixed location and time Ignition sparks are attainable.

A similar well-known suggestion for better distribution and ignition of the injected fuel in a swirl chamber designed asymmetrically designed combustion chamber, which is arranged very eccentrically in the piston and in which the combustion air flowing in over an overflow edge during the compression stroke creates a powerful vortex of air that goes into most of the fuel by means of one or more bores at a large angle to the cylinder axis inclined and arranged in the vicinity of the outer cylinder edge with their nozzle head Injection nozzle on an inclined surface of the combustion chamber opposite the overflow edge to be sprayed in the same direction as the air vortex, while at the same time through a special nozzle hole intended to supply the remaining parts of the combustion chamber Fuel jet against the most violent eddy in the area of the overflow edge in the Combustion chamber is injected. The first self-ignition takes place in this fuel jet of the fuel, in whose flame then that of the inclined surface of the combustion chamber fuel detached or distributed over the air space of the chamber by the air vortex is introduced so that the main combustion at the Ab = detachment eddy of the overflow edge he follows.

In this internal combustion engine, too, the local and temporal Use of the ignition is not determined because the self-ignition occurs on one or more Place the relatively long pilot jet inside the combustion chamber space can and not only from the formation of the pilot jet itself, but also from depends on the intensity of the air movement or turbulence. In addition, the Nozzle bores in the nozzle head be distributed asymmetrically, which is known to be a disadvantage consists.

The present invention is based on the object described above Disadvantages of known diesel internal combustion engines with direct fuel injection to be eliminated by means of a multi-hole nozzle; it relates to a special diesel internal combustion engine with direct fuel injection in a rotationally symmetrical, z. B. ellipsoid or pear-shaped combustion chamber, in which almost all of the combustion air flows during the compression stroke flows in with a circular motion around the cylinder axis, while the multi-hole nozzle through their outlet bores symmetrically distributed around the nozzle axis These bores exiting fuel jets approximately perpendicular to the circumferential Air flow in the combustion chamber essentially on its side wall below the The edge of the combustion chamber.

While maintaining the advantage of that to be achieved with this type of injection very favorable distribution of the fuel on the circumference of the combustion chamber at the same time a locally precisely defined first self-ignition can be achieved, from which the ignition of the mixture formed in the meantime proceeds, so that the adverse knocking and smoking of the engine is practically completely avoided and high combustion medium pressures can be achieved.

The invention is based on that already disclosed in patent 1175,486 general knowledge that a very precise local definition of the auto-ignition point and at the same time a safe onset of this self-ignition at a point in time is reached at which no ignitions occur at other points in the combustion chamber can if a shorter pilot jet compared to other fuel jets the Edge of the combustion chamber in which it enters the piston or cylinder cover surface a more or less pronounced edge passes over at which the highest temperatures occur, partially oversprayed. The portion of the splashing over this edge The pilot jet has one of the direction of flow of the combustion air into the combustion chamber oppositely directed propagation component and is consequently at the Splash point ignited quickly while in prolonged jets on the The fuel hitting the cooler combustion chamber wall only ignites later.

In a diesel engine with direct fuel injection in a rotationally symmetrical, z. B. ellipsoidal or pear-shaped combustion chamber, in which almost all of the combustion air flows in with a circular motion around the cylinder axis during the compression stroke and the fuel is injected from a multi-hole nozzle that is off-center to the axis of rotation of the combustion chamber and thus to the combustion chamber opening in such a way that the first self-ignition is injected through the fuel jet from the shortest free beam length of the edge of the Brennraumseitenwandung from a portion of the jacket of this fuel jet, against the radial movement component of the overflowing into the combustion chamber combustion air, according to Patent 1175 486, the solution of the invention is that the multi-hole nozzle with nozzle bores evenly distributed on the circumference of its head and inclined at an angle to the combustion chamber axis in such a way that the fuel jet emerging from the nozzle bore closest to the combustion chamber edge partially covers the combustion chamber edge overmolded, while the fuel jets exiting from the other nozzle bores of greater free jet length are directed against combustion chamber wall locations which have a lower temperature than the edge of the combustion chamber, the temperature decreasing in inverse proportion to the free jet lengths.

Such a design of the internal combustion engine not only the advantages of the perfect with the symmetrical distribution of the nozzle bores Distribution of the fuel to the individual jets and the favorable distribution of the fuel achieved in the combustion chamber or on its walls, but the The pilot jet having the smallest free length always reaches the precisely determined one first Ignition point at the edge of the combustion chamber before the other rays, which are directed deeper into Points of the combustion chamber wall located near the combustion chamber are directed to reach them, so that the ignition always starts at the same point. Next can be special Measures to achieve a particularly strong swirl flow of the combustion air can be omitted in the combustion chamber, so that the technical effort for special Measures and those associated with their application, especially in the case of higher There is no need for a reduction in performance and efficiency that would affect the number of revolutions.

It has proven to be advantageous if by appropriate arrangement of the multi-hole nozzle the free length of the fuel jets in such a ratio is set to each other that the free jet length of the longest fuel jet about 2.5 times the jet length of the shortest free fuel jet (pilot jet) which, as experience shows, in the case of conventional combustion chamber arrangements - result in the most favorable burn-through ratios.

Is it a diesel internal combustion engine with in the cylinder head arranged combustion chamber - in particular a two-stroke engine of this type - in the the combustion air flows in with a relatively weak circular movement, so the position of the multi-hole nozzle is expediently determined so that the shortest fuel jet about half of its jet jacket is sprayed over the edge of the combustion chamber. In this In the case, the other fuel jets can also hit the edge of the combustion chamber with one of them increasing length roughly proportionally decreasing. considerably smaller proportion of the radiation cladding overspray without significantly disturbing the situation. In particular the onset of self-ignition remains at the point of over-injection of the shortest Beam (pilot beam) unimpaired.

The invention is illustrated in the drawing. It shows F i g. 1 the piston and the cylinder head of a diesel internal combustion engine with in the piston horizontal combustion chamber in section.

F i g. 2 the piston in a view directed towards the piston crown, F i g. 3 the piston and the cylinder with a combustion chamber in the cylinder head other diesel internal combustion engine in section, F i g. 4 this cylinder head in one towards the combustion chamber opening directed view.

In the case of the internal combustion engine corresponding to a first exemplary embodiment, according to FIG. 1 and 2, the piston 1. is shown in a position before its top dead center position (dashed line 2), in which the shortest fuel jet 3 with its jet tip has just reached the edge 4 of the combustion chamber 5 located in the piston 1 and this edge with a very small one Part of its jet jacket is sprayed over at the point 6, while the main part of the fuel of this jet strikes the side wall of the combustion chamber 5.

The axis of the combustion chamber 5 lies opposite the axis of the cylinder laterally offset by a small amount e and is (Fig. 1) designed pear-shaped, d. H. its bottom is provided with a kind of cone point in the middle, that of the inflowing Combustion air is to straighten up from the side wall to the center. Instead of this the combustion chamber could also have the approximate shape of an ellipsoid of revolution, by its bottom running along the broken line 7. The degree of displacement e of the combustion chamber 5 is limited by the requirement that the displacement by the Even circular inflow of the combustion air into the combustion chamber 5 is not is significantly disturbed.

The upper edge 4 of the combustion chamber 5 is sharp-edged into the piston crown 8 over, it should be noted that the temperature at this edge of the combustion chamber is not on its shape, but above all on the ratio of the largest combustion chamber diameter to the diameter 2 r of the connection opening between the combustion chamber 5 and the cylinder chamber depends. For the safe first self-ignition at point 6 on piston crown 8 is also essential that the combustion air flowing into the combustion chamber 5 on the point 6 a sufficiently large, the fuel jet 3 substantially opposite, having radially inwardly directed flow component. However, since this is just in the case of weaker swirl flows of the combustion air flowing into the combustion chamber 5 is the case, the preconditions for a reliable first self-ignition can be found at point 6 with certainty.

As shown in FIG. 1 also shows, the axis 11 of the multi-hole nozzle 9 held in the cylinder head 13 is inclined with respect to the axis of the combustion chamber by an angle e, the size of which results from the condition that the remaining fuel jets 10 adjacent to the fuel jet 3 serving as the pilot jet exclusively focus on parts of the Combustion chamber wall should hit, the temperature of which is significantly lower than the temperature of the combustion chamber edge 4 . From this it follows that the angle .x is primarily dependent on the design of the combustion chamber and in its other shape - z. B. with flat combustion chambers - can also have a different value and a different direction. In the case of such inclined arrangements of injection nozzles with several nozzle outlet openings, it is of course necessary for the nozzle to be fixed in its angular position within the associated nozzle holder (not shown).

The optimum number, position and size of the bores in the nozzle head 9 'results from the dimensions of the combustion chamber 5, the intensity of the air flow and finally also from the mode of operation of the injection system used. When the pilot jet or fuel jet 3 has reached the combustion chamber wall and the point 6 of the piston head 8, the remaining fuel jets 10 are still removed from this wall by distances that correspond to the different free path lengths of the different fuel jets, the time differences between the impact of the different Of course, fuel jets also depend on the jet speed in the compressed combustion air. Before the fuel jets 10 hit the combustion chamber wall, the pilot jet has already led to a first self-ignition at point 6 of the piston crown 8, whereupon the pilot flame spreads from there through the air flow in the direction of the remaining fuel jets 10 . The circular flow movement of the combustion air into the combustion chamber is shown in FIG. 1 and 2 indicated by a helically wound arrow 12.

In the case of the FIGS. 3 and 4 shown, another embodiment corresponding internal combustion engine, the combustion chamber 5 'is housed in the cylinder head 13', and the multi-hole nozzle 9 is located with its nozzle head 9 'on one in the vicinity the location of the combustion chamber floor located along the axis of the combustion chamber. The essential one The difference compared to the injection according to the first exemplary embodiment is in that all fuel jets 3 ', 10' are in a very specific constant position to the combustion chamber 5 'and in particular also to the edge of the combustion chamber 4' whereupon when choosing the angle ä the nozzle inclination relative to the combustion chamber axis Is to be taken into consideration.

In the case of the injection according to FIGS. 3 and 4 are oversprayed by the pilot jet 3 'the edge 4' of the combustion chamber - 5 'at 6' - with a small portion of its jet jacket, that on the piston head 8 'of the piston 1' of the diesel internal combustion engine is approximately straight in the position shown shortly before top dead center (dashed line 2 ') of the piston 1' strikes. It is the second embodiment a two-stroke internal combustion engine in which the combustion chamber is arranged in the piston itself easily overheating due to the two-stroke working process anyway heavily loaded piston could result. The piston 1 'has a smooth one here Bottom area 8 ', by overheating as a result of their relatively small area of the piston 1 'is bent forward. Of course, the piston head 8 'shows in his middle area has such a high temperature that the against such a point impacting portion of the fuel jet 3 'with a noticeable time advantage ignites in front of the remaining fuel jets 10 '. While the rest of the fuel jets 10 'according to the F i -g. 3 and 4 only hit the combustion chamber wall, it can be in cases where the combustion air in the combustion chamber 5 'is only below a relatively weak circular movement flows in and the axis of the combustion chamber is laterally offset from the cylinder axis by a small amount, expedient be, the remaining fuel jets 10 'the combustion chamber edge with a considerable to have a smaller portion of the jet sprayed over. In such circumstances it is then permissible, the oversprayed fuel portion of the fuel jet 3 'approximately to half of the fuel injected at this point, so this "pilot jet" with its overmolded portion is much larger than the overmolded Shares of the other fuel jets 10 'remains. The angle a 'becomes the The nozzle axis 11 'with respect to the combustion chamber axis is determined according to roughly the same guidelines, as mentioned above, although it may be useful for one only weakly circling air movement to provide a greater number of fuel jets from however, the beam with the shortest free length goes first and the one with the longest free jet length should be the last to ignite.

If the aforementioned design of the injection system in a two-stroke engine also no such favorable running properties - especially with regard to what is achievable Knock-free combustion medium pressure at the smoke limit and with regard to combustion quality - As with an injection into the piston combustion chamber of a four-stroke internal combustion engine with intensive circles of the combustion air flowing into the combustion chamber around the Can arise combustion chamber axis, so is already with such a design of the combustion system a noticeably softer gear of the machine and a remarkable one at the smoke limit favorable combustion medium pressure with low fuel consumption at the same time accessible.

The invention is not limited to the details of the exemplary embodiments described bound. So it is z. B. not necessary that the combustion chamber edge from F i g. 1 has emerging sharp edge. The passage opening from the combustion chamber the cylinder space can also be cylindrical or conical in the usual way or finally with a rounded neck in the surface of the piston crown pass over.

Claims (2)

Claims: 1. Diesel internal combustion engine with direct fuel injection in a rotationally symmetrical, z. B. ellipsoidal or pear-shaped combustion chamber, in the compression stroke almost all of the combustion air under one to the Cylinder axis circling motion flows in and the fuel flows out to the axis of rotation of the combustion chamber and thus eccentrically arranged multi-hole nozzle to the combustion chamber opening is injected so that to localize the first auto-ignition by the fuel jet from the shortest free jet length the edge of the combustion chamber side wall of a portion of the jacket of this fuel jet against the radial movement component the combustion gas flowing into the combustion chamber Air splattered is, according to patent 1175 486, characterized in that the multi-hole nozzle (9) with on the circumference of their head (9 ') evenly distributed nozzle holes and under one Angle (a) is inclined to the combustion chamber axis in such a way that the from the Combustion chamber edge (4) next to the nozzle hole exiting fuel jet (3) the edge of the combustion chamber (4) is partially overmolded, while that from the remaining nozzle bores Exiting fuel jets with a greater free jet length against the combustion chamber wall (5) are directed, which have a lower temperature than the edge of the combustion chamber (4), where the temperature decreases in inverse proportion to the free jet lengths. 2. Diesel internal combustion engine according to claim 1, characterized in that the free The jet length of the longest fuel jet is about 2.5 times the jet length of the shortest fuel jet (3 or 3 '). Considered publications: German patent application k 4124 I a / 46 a2 (published on March 13, 1952); British U.S. Patent No. 509,838.