GB1576384A - Mixture-compressing internal conbustion engine - Google Patents

Description

(54) MIXTURE-COMPRESSING INTERNAL COMBUSTION ENGINE (71) We, DAIMLER-BENZ AKTIEN GESELLSCHAFT, of Stuttgart-Unterttirkheim, Germany, a Company organised under the laws of the Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a mixturecompressing internal combustion engine, particularly but not necessarily a reciprocating-piston engine having an auxiliary chamber opening by way of a transfer duct into a main combustion space.

In known engines of the aforesaid kind, which operate with stratified charges in order to satisfy exhaust-gas regulations, part of the fuel is introduced or injected directly into the auxiliary chamber so that, with a mixture which as a whole is weak in relation to the total charge, a richer, readily ignitable, mixture is obtained in the said chamber and, starting from the latter, good combustion of a mixture which in itself is poorly ignitable is achieved. Consequently with its relatively small volume, the auxiliary chamber has to be supplied with very small amounts of fuel or mixture, which necessitates sensitive and, consequently, expensive additional metering Oï mixture-preparing devices.In contrast, the invention seeks to provide an internal combustion engine of the aforesaid kind such that, even with mixtures which are weak as a whole, it is possible to operate with excellent ignition without expensive additional devices.

It has been found that, in a mixturecompressing internal combustion engine comprising a precombustion or swirl chamber opening into a main combustion space by way of a transfer duct, and an ignition source open to the said chamber, effective operation can be achieved by a combination of features, namely by providing a high-energy plasma-jet ignition source and introducing all of the fuel into the main combustion space.

The introduction of the whole amount of the fuel into the main combustion space has the result that the mixture will be of the same composition in the said space and chamber. For weak mixtures, this means that, in principle, equally unfavourable prerequisites for combustion will prevail in the said space and chamber. Despite the unfavourable conditions in the main combustion space because of the introduction of all the fuel into it, the invention nevertheless results in reliable ignition and good combustion of the whole mixture, even with a weak, not readily ignitable, mixture.

Disposed in the auxiliary chamber, the plasma-jet ignition source, which results in high ignition energy and good conditions for ignition, is utilised at a point which, when all the fuel is introduced into the main combustion chamber, unexpectedly also results in even better conditions for combustion. Firstly, this may be due to the fact that, during compression and subsequent transfer of part of the mixture from the main combustion space into the auxiliary chamber, the transferred portion of the mixture is better mixed and therefore, as a whole, more homogeneous because of the high speeds of flow in the duct. Secondly, it may be an important point that the transferred part of the mixture is heated more intensively because of conditions in the duct and auxiliary chamber, so that increased fuel evaporation is achieved.This may also have a positive influence on the homogenisation and dilutability of the mixture.

Turbulence in the peripheral region of the chamber makes it possible to achieve local enrichment of the mixture which can also contribute to improved ignitability.

The invention may be applied advantageously to engines which have an un scavenged auxiliary chamber, with which not only fuel-metering devices but also other control means associated with the chamber are avoided.

Two embodiments of the invention by way of example will now be more fully described with reference to the accompanying diagrammatic drawing, which represents a section through the cylinder head of an internal combustion engine with an auxiliary chamber in the form of a precombustion chamber.

The drawing Illustrates the cylinderhead region of a four-stroke reciprocatingpiston internal combustion engine for operation with low-boiling fuels. Some features, in respect of which the engine can he constructed in basically conventional manner for single- or multi-cylinder engines, are not shown.

A composite combustion space above the piston 1 is divided into a main combustion space 2, formed substantially by a recess or trough in the piston head, and an auxiliary chamber 3, in this case a conventional precombustion chamber. Through a transfer duct 4, the auxiliary chamber 3 communicates with the main combustion space 2, into which also open valve passages (not shown) and a fuel-injection nozzle 5 disposed in the cylinder head 6 beside the chamber 3. The nozzle 5 injects the fuel approximately centrally into the recess 2 which constitutes a substantial portion of the main combustion space, the amount injected being controlled in dependence on load in customary manner.

The entire amount of fuel is injected by the nozzle 5 directly into the main combustion space. No fuel is supplied directly to the chamber 3, but, during the compression stroke of the engine, a part of the fuel-air mixture formed in the main combustion space is simply compressed into the chamber 3. This part of the mixture is thus subjected to additional mixing or preparation, in the sense of a higher degree of homogenisation, which is achieved particularly because of the additional swirling and heating of this part of the mixture when it is forced through the duct 4 into the chamber 3. Heating can be further intensified by additionally insulating the chamber 3 against the cylinder head, al through this is not illustrated.Despite the fact that a weak mixture, corresponding in weakness to the mixture as a whole, is present also in the chamber 3, the additional mixing and improved homogenisation ensure such good ignitability of the said part of the mixture that it can be reliably ignited by a high-energy ignition source in the form of a plasma-jet spark device 7 open to the chamber 3.

A similar arrangement may be employed in an engine having a conventional swirl chamber instead of a precombustion chamber. The main combustion space is again formed to a substantial extent by a recess in the piston. The swirl chamber opens by way of an oblique transfer duct into the main combustion space, and is open in it upper region to a plasma-jet device serving as high-energy ignition source. The fuel is again injected directly into the main combustion space, no fuel being supplied directly to the swirl chamber. Mixture is simply compressed into the chamber, through the transfer duct, from the main combustion space during the compression stroke, improved mixing and homogenisation of the mixture being achieved due to the turbulence occurring during the flow through and the heating occurring in the said duct and in the chamber.In addition to the homogenisation, a certain stratification will occur in the swirl chamber, which leads to improved ignitability in the region of the spark device.

In neither of the above-described embodiments of the invention is there provision for scavenging the precombustion or swirl chamber WHAT WE CLAIM IS: 1. A mixture-compressing internal combustion engine having a divided combustion space with a precombustion or swirl chamber opening by way of a transfer duct into a main combustion space and an ignition source open to the said chamber, the ignition source being a highenergy plasma-jet spark device and the whole of the fuel being introduced into the main combustion space.

2. An engine according to claim 1, wherein the auxiliary chamber is unscavenged.

3. A mixture-compressing internal combustion engine substantially as hereinbefore described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. also contribute to improved ignitability. The invention may be applied advantageously to engines which have an un scavenged auxiliary chamber, with which not only fuel-metering devices but also other control means associated with the chamber are avoided. Two embodiments of the invention by way of example will now be more fully described with reference to the accompanying diagrammatic drawing, which represents a section through the cylinder head of an internal combustion engine with an auxiliary chamber in the form of a precombustion chamber. The drawing Illustrates the cylinderhead region of a four-stroke reciprocatingpiston internal combustion engine for operation with low-boiling fuels. Some features, in respect of which the engine can he constructed in basically conventional manner for single- or multi-cylinder engines, are not shown. A composite combustion space above the piston 1 is divided into a main combustion space 2, formed substantially by a recess or trough in the piston head, and an auxiliary chamber 3, in this case a conventional precombustion chamber. Through a transfer duct 4, the auxiliary chamber 3 communicates with the main combustion space 2, into which also open valve passages (not shown) and a fuel-injection nozzle 5 disposed in the cylinder head 6 beside the chamber 3. The nozzle 5 injects the fuel approximately centrally into the recess 2 which constitutes a substantial portion of the main combustion space, the amount injected being controlled in dependence on load in customary manner. The entire amount of fuel is injected by the nozzle 5 directly into the main combustion space. No fuel is supplied directly to the chamber 3, but, during the compression stroke of the engine, a part of the fuel-air mixture formed in the main combustion space is simply compressed into the chamber 3. This part of the mixture is thus subjected to additional mixing or preparation, in the sense of a higher degree of homogenisation, which is achieved particularly because of the additional swirling and heating of this part of the mixture when it is forced through the duct 4 into the chamber 3. Heating can be further intensified by additionally insulating the chamber 3 against the cylinder head, al through this is not illustrated.Despite the fact that a weak mixture, corresponding in weakness to the mixture as a whole, is present also in the chamber 3, the additional mixing and improved homogenisation ensure such good ignitability of the said part of the mixture that it can be reliably ignited by a high-energy ignition source in the form of a plasma-jet spark device 7 open to the chamber 3. A similar arrangement may be employed in an engine having a conventional swirl chamber instead of a precombustion chamber. The main combustion space is again formed to a substantial extent by a recess in the piston. The swirl chamber opens by way of an oblique transfer duct into the main combustion space, and is open in it upper region to a plasma-jet device serving as high-energy ignition source. The fuel is again injected directly into the main combustion space, no fuel being supplied directly to the swirl chamber. Mixture is simply compressed into the chamber, through the transfer duct, from the main combustion space during the compression stroke, improved mixing and homogenisation of the mixture being achieved due to the turbulence occurring during the flow through and the heating occurring in the said duct and in the chamber.In addition to the homogenisation, a certain stratification will occur in the swirl chamber, which leads to improved ignitability in the region of the spark device. In neither of the above-described embodiments of the invention is there provision for scavenging the precombustion or swirl chamber WHAT WE CLAIM IS:

1. A mixture-compressing internal combustion engine having a divided combustion space with a precombustion or swirl chamber opening by way of a transfer duct into a main combustion space and an ignition source open to the said chamber, the ignition source being a highenergy plasma-jet spark device and the whole of the fuel being introduced into the main combustion space.

2. An engine according to claim 1, wherein the auxiliary chamber is unscavenged.

3. A mixture-compressing internal combustion engine substantially as hereinbefore described with reference to the accompanying drawing.