Internal combustion engine

May 31, 1966

3,253,584

W. TRAUB ETAL

INTERNAL· COMBUSTION ENGINE

Filed Aug. 5, 1963

FIGI

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INVENTORY

WERNER TRAUB WILHELM WAGNER

BY HANS TUCHER

ATTORNEYS

United States Patent Office

3,253,584

Patented May 31, 1966

3,253,584 INTERNAL COMBUSTION ENGINE

Werner Traub, Wilhelm Wagner, and Hans Tucher, Stuttgart, Germany, assignors to Daimler-Benz Aktiengesellschaft, Stuttgart-Unterturkheim, Germany

Filed Aug. 5, 1963,- Ser. No. 299,838

Claims priority, application Germany, Aug. 7, 1962, D 39,572

Claims. (Cl. 123—32)

The present invention relates to internal combustion engines, and more particularly to air-compressing, autoignition combustion engines for multi-fuel operation.

One seeks in connection with diesel engines to keep the ignition process or ignition delay relatively small in order that the ignition sets in already at a time when only a part of the fuel has been injected. The complete ignition of the then still relatively small amount of fuel will not produce in that case an undesirable hard ignition knock or detonation.

Particularly important are measures for shortening pie ignition process or ignition delay in multi-fuel engines, i.e., in engines which are to be operated, in addition to operation with diesel oil, also with considerably less selfignition-prone fuels, such as, for example, anti-knock or anti-detonant gasolines. Since the spontaneous or selfignition temperature of gasoline is about 550° C., and that of diesel oil about 350° C., it follows that, with gasoline operation, the temperature difference between the self-ignition temperature and the compression temperature of about 650° C. is reduced, whereby the ignition process or delay is then correspondingly lengthened. However, in a multi-fuel engine, in the interest of as much as possible an equally good operational behavior with the use of the various types of fuel, the ignition processes or delays should not differ too much from each other. Consequently, particularly for such multi-fuel engines suitable measures have to be found to shorten the ignition process or ignition delay.

As is well known, such a measure consists, for example, in increasing the compression ratio and therewith the compression temperature. As is also known, a correspondingly high temperature level may be achieved also with the aid of the following measures: By preheating the drawn-in or sucked-in air, for instance by heat exchange on the side of the exhaust pipe, by supercharging, and by a partial, load-dependent exhaust-gas return into the inlet connection or manifold.

While the increased temperature level during the ignition readying process shortening the ignition delay, as intended, it has the disadvantage that long-chain molecules are decomposed into short fragments, i.e., that cracking and thermal decomposition takes place. Since molecular fragments with a small number of carbon atoms have a slower reaction velocity, the occurrence of cracking delays the course of the actual combustion process properly speaking, which signifies a deterioration with respect to the degree of quality of the combustion. The decomposition reactions can thereby go so far that carbon skeletons will finally remain, for the oxidation of which the time until opening of the outlet valves will no longer be sufficient, and a smoking combustion will result therefrom.

It may be deduced from the foregoing that attempts should be made to subject to the heating which shortens the ignition process or delay only such a small portion of the injected fuel as will be sufficient for initiating the ignition, whereas the major portion of the fuel is to be supplied to the combustion at as low as possible a temperature so that a thermal decomposition is far-reachingly eliminated.

It is the aim of the present invention to satisfy these seemingly contradictory requirements. A direct-fuelinjection engine is more suitable for this purpose than a precombustion chamber engine in which the fuel is injected into the hot charge of the pre-chamber, the temperature of which is higher than the compression temperature in the main chamber; this is so as in such pre-chamber engines a hot burner additionally heats the inflowing air, a mixing takes place with relatively hot residual gases within the chamber, and the precombustion chamber insert is usually precluded from any direct cooling action. Except at small partial loads, the course of the reaction of the combustion process in such a precombustion chamber engine, after the ignition has been effected, with relatively .short ignition delay takes place by way of the soot phase. This type of reaction is additionally favored by the fact that the precombustion chamber into which the entire amount of fuel is injected contains only approximately 30-40% of the air charge so that, accordingly, only a partial oxidation takes place therein resulting in air deficiency combustion.

In contradistinction thereto, with the direct-fuel-injection engine, the fuel jet, upon leaving the injection nozzle, enters directly into the pre-compressed air charge. The temperature of the air charge depends primarily on the structurally conditioned compression ratio and, moreover, on the position of the injection start before top dead center position. On this basis, the temperature level of the charge and thus also that of the fuel particles which have penetrated the charge during the ignition-readying period, can be determined quite accurately and may be adjusted to the “mild” temperature level which is favorable for the combustion from reaction-kinetic points of view, whereby cracking is effectively avoided.

This adjustment, however, is neither theoretically nor practically the correct one for the ignition-readying period during which the fine fuel particles along the jet surface should be under the influence of a considerably higher temperature, particularly for the purpose of shortening the ignition delay in connection with light fuels.

In order to achieve this purpose, there is proposed in accordance with the present invention for an air-compressing, self-igniting combustion engine, particularly one adapted for operation with mult-type fuels, having direct fuel injection, preferably into a piston-recess combustion chamber, to secure at the cylinder head small plates which project into the combustion chamber and which are maintained at a relatively high temperature by the combustion and/or compression heat, particularly at a temperature higher than the compression and temperature, and past which sweeps the fuel-containing combustion air. That portion of the mixture composed of air and fuel which sweeps past the hot plates having, for example, a temperature of 750° C., whereby the fuel particles may be delayed or also stopped, is effectively heated, and a shortening of the ignition process or delay is thereby imparted to such heated air-fuel mixture portion, whereas the remainder of the mixture does not become heated to that extent and is therefore not cracked but ignited by

3,253,584 first-mentioned portion of the mixture so that the main mixture portion is burnt perfectly satisfactorily without the formation of soot.

It is desirable that the movement of the combustion air not be hindered by any marked resistance as a result of the plates. For that reason, the small plates should, in the longitudinal direction thereof, conform to the direction of movement of the combustion air as much as possible. Thus, in a combustion engine having a circular piston-recess combustion chamber, central injection and vortex movement of the combustion air about the axis of the piston-recess combustion chamber extending in the longitudinal direction of the cylinder, the various plates may extend in proximity to the rim of the piston recess or trough approximately parallel thereto. In particular it is proposed according to the present invention that as many radial fuel jets be discharged from the central nozzle as there are plates present, whereby the axes of the jets issuing from the nozzle and not as yet deflected by the vortexing air, aim in each instance toward a zone or region which, as viewed in the direction of movement of the air, is positioned a small distance ahead of the respective plates coordinated thereto. In this manner, the fuel particles detached from the core of the jet by the air vortex reach immediately the plates and are heated thereat. The fuel jet itself does not directly strike or infringe upon the plates, which might lead to an excessive cooling of the plates.

For reasons of structural simplification, it is advisable to support the small plates by means of a base plate, especially formed integrally with the small plates, which is secured to the cylinder head. In order to avoid that the base plate obstructs the movement of the air, the base plate should be inserted flush with the cylinder head surface facing the combustion chamber and closing the same. With combustion engines having a four-valve head, it is advantageous in the interest of a good utilization of the available space to arranged the base plate, with the rims thereof following the curvatures of the valve seats, within the space between the valve seats. It is of advantage if the base plate covers a not too small surface because the latter may also contribute to the heating of the mixture.

In order to keep the small plates sufficiently warm, the small plates and/or the base plate may be secured at the cylinder head in a heat-insulating manner, particularly by leaving an air gap.

Accordingly, it is an object of the present invention to provide an air-compressing, auto-ignition internal combustion engine capable of readily operating with different types of fuel which effectively eliminates the shortcomings and drawbacks of the prior art by simple and relatively inexpensive means.

It is another object of the present invention to provide a multi-fuel air-compressing, self-igniting internal combustion engine in which a relatively short ignition delay is assured for all fuels without danger of improper combustion.

Still another object of the present invention resides in the provision of an internal combustion engine of the type described hereinabove which is capable of operating with widely differing fuels without danger of cracking the fuel and/or of soot and smoke formation.

A further object of the present invention resides in the provision of an auto-ignition internal combustion engine suitable for multi-fuel operation which assures about the same relatively short ignition process irrespective of the type of fuel used and which precludes a combustion characterized by combusion air deficiency.

Still a further object of the present invention resides in the provision of a multi-fuel internal combustion engine of the type described hereinabove which brings about the aforementioned objects and advantages substantially without any impairment to the free vortexing movement of the combustion air,

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, one embodiment in accordance with the present invention, and wherein:

FIGURE 1 is a longitudinal cross-sectional view through the piston, combustion chamber and cylinder head structure in accordance with the present invention, and

FIGURE 2 is a cross-sectional view through the arrangement of FIGURE 1, taken along line II—Π of FIGURE 1 and viewed in the direction toward the cylinder head.

Referring now to the drawing, wherein like reference numerals are used throughout the various views to designate like parts, reference numeral 10 designates therein a piston made, for instance, of light metal which is provided with a circular, trough-shaped or recessed combustion chamber 11, The rim 12 of the combustion chamber 11 is indicated in dash and dot lines in FIGURE 2. The cylinder jacket is designated by reference numeral 13 and the cylinder head, which may consist, for example, of grey cast iron, is designated by reference numeral 14. A recess 15 of curved, star-shaped configuration is provided within the cylinder head surface facing the combustion chamber 11 into which is embedded a base plate 16 consisting preferably of a heatresistant, highly alloyed chrome-nickel steel. A heatinsulating air gap is left between the base plate 16 and the bottom of the recess 15; only the eyes or lugs 17 provided on the base plate 16 and serving for receiving the fastening screws 18 extend through this air gap. The orifice 19 of a centrally located fuel injection nozzle 20 extends through the base plate 16.

The small plates 22 which are integral with the base plate 16 extend between the valve seats 21.

During the suction stroke, a rotation in the direction of the arrow 24 is forcibly imparted to the inflowing combustion air by means of deflector valves 23 or any other known means, such as, for instance, an appropriate guide means in the inlet channels. Corresponding to the four plates 22, four fuel jets 25 are provided which aim a slight distance past the plates 22. The air rotating in the direction of the arrow 24 guides those relatively few fuel particles which are disposed at the same radial distance from the center as the plates 22 directly toward and along the hot plates 22 for heating thereof. It is from these particles which, by reason of directing the jets in front of the respective plates, are already surrounded by a sufficient amount of combustion air, that the ignition of the remaining not so dangerously highly heated mixture begins.

While we have shown and described one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of many changes and modifications within the spirit and scope of the present invention and we, therefor, do not wish to be limited to the details shown and described herein but intend to cover all such changes and modification as are encompassed by the scope of the appended claims.