GB2064643A

GB2064643A - A Method of Injecting Fuel in an Air-compression Internal Combustion Engine

Info

Publication number: GB2064643A
Application number: GB8034205A
Authority: GB
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1979-11-14
Filing date: 1980-10-23
Publication date: 1981-06-17
Also published as: HU182222B; TR20890A; IT1134228B; SE8007948L; IT8025916A0; DE2945917A1; JPS5685519A; FR2469559A1; GB2064643B

Abstract

The method comprises spraying at higher loads a fuel jet (17) through an ignition chamber (9) and a connecting passage (10) onto the wall (18) of a combustion chamber (4), where it spreads as a thin film (19). The air flow in the ignition chamber (9) during the compression stroke of the piston (2) and control of fuel injection is such as to cause individual fuel particles to be separated from the fuel jet (17) to form an ignitable mixture with the air and residual gas remaining in the ignition chamber (9). This ignitable mixture is ignited in the ignition chamber (9) so that a flame penetrates through the connecting passage (10) into the combustion chamber (4) to ignite the fuel evaporating from the combustion chamber wall (18). At idling and lower loads the injector provides an atomised spray (20) and an igniter provides for starting. <IMAGE>

Description

SPECIFICATION A Method of Injecting Fuel in an Air Compression Internal Combustion Engine This invention relates to a method of injecting fuel into an air-compression internal combustion engine comprising an ignition chamber communicating with the inside of a cylinder via a connecting passage, a fuel injector projecting into the ignition chamber, a combustion chamber in the shape of a solid of revolution provided in the piston crown, and means for imparting a rotary swirling motion about the longitudinal axis of the combustion chamber to air flowing into the cylinder, the connecting passage entering the cylinder near the combustion chamber wall at top dead centre.

An internal combustion engine of this type is known from German patent publication 1,251,577, but for fuels ignited from an external source. The connecting passage is relatively long, and the combustion chamber provided in the piston crown is cup-shaped. The electrodes of the spark plug for igniting the fuel project into the ignition chamber During operation, a constant amount of fuel is injected throughout the speed range of the engine into the ignition chamber sufficient for ignition by the spark plug and to sustain idling. The piston draws a non-controlled amount of air through the air or mixture inlet passage, and an appropriate amount of fuel is added directly thereto by a second fuel injector to suit the existing speed or load of the engine.This fuel/air mixture is ignited near the combustion chamber wall by the ignition spray emitted from the ignition chamber. In other words, this internal combustion engine employs the method of direct fuel/air mixing and has two injection devices. This frequently causes physical design difficulties because the injection devices and the spark plugs cannot be accommodated in the cylinder head in the immediate vicinity of the combustion chamber.

Furthermore, self-ignition internal combustion engines are known which employ the method of wall deposition of the fuel (German Patent Specification 865,683). These engines have the fuel applied as a thin film to the combustion chamber wall from which it evaporates to mix and eventually burn with the swirling air. This method has given excellent results for several decades, the smoothness of the engine, reduction of peak pressures resulting in reduced bearing wear as well as controlled, and hence complete, combustion deserving special mention.

However, it has been found in the course of time that engines using the above-method described suffer from a drawback at idling as weli as at lower loads and speeds. This is because, in these conditions, the combustion chamber wall temperature is relatively low, so that preparation of the fuel for combustion tends to be incomplete or proceeds at too low a rate. Part of the fuel will thus fail to participate in combustion and is discharged from the cylinder in an unburnt state.

An object of the invention is to provide a fuel injection method for an internal combustion engine whereby reliable fuel preparation, and consequently combustion takes place also as idling and at lower speeds and loads, while all merits of the method of wall deposition of the fuel continue to be obtained at upper engine loads.

The invention provides a method of injecting fuel in an air-compression internal combustion engine comprising an ignition chamber communicating via a connecting passage with the inside of a cylinder, a fuel injector projecting into the ignition chamber, a combustion chamber in the shape of a solid of revolution provided in the piston crown, and means for imparting a rotary swirling motion about the longitudinal axis of the combustion chamber to air flowing into the cylinder, the connecting passage entering the cylinder near the combustion chamber wall at top dead centre, the method comprising spraying a fuel jet from the fuel injector through the ignition chamber and the connecting passage onto the wall of the combustion chamber where it spreads as a thin film, the air flow in the ignition chamber during the compression stroke of the piston and control of the fuel injection being such as to cause individual fuel particles to be separated from the fuel jet to form an ignitable mixture with the air and residual gas remaining in the ignition chamber, this ignitable mixture being ignited in the ignition chamber so that a flame penetrates through the connecting passage into the combustion chamber to ignite the fuel evaporating from the combustion chamber wall, further combustion taking place as in internal combustion engines using the method of wall deposition of the fuel.

By applying the arrangement known in sparkignition engines, physical design difficulties are overcome because the fuel injector need not be located directly adjacent the combustion chamber in the piston.

Furthermore, the method of wall deposition of the fuel is fully applicable, i.e. its advantages at upper loads can be utilized and combustion will take place completely, if only because the fuel emitted without pressure from the nozzle at the end of the injection cycle cannot penetrate into the main combustion chamber where, according to existing experience, it will undergo incomplete combustion, but instead it will be retained in the ignition chamber and completely burnt there.

At idling and at lower speeds and/or loads, reliable ignition and complete combustion are also ensured because the free fuel trajectory is relatively long, so that more fuel mixes with the air for combustion directly and produces an ignitable mixture quickly. Moreover, the fuel jet penetrates the ignition chamber in which there is a higher temperature than in the combustion chamber, because a certain amount of residual gas is always retained there, and because heat radiation is less.

Preferably, at idling and at lower engine loads all the fuel injected is sprayed by appropriate atomization, and if necessary by deflection of the fuel jet, exclusively into the ignition chamber to mix with the inflowing air there.

The changeover to this method of injection is solely by means of the injection nozzle and, in fact, a number of nozzles are known which can be applied to this end. For example, a controllable two-hole nozzle or a variable-geometry nozzle may be used.

As a result of this embodiment, the fuel air mixture is concentrated in the least space whereby the occurrence of lean and, consequently, difficult to ignite, mixture zones is prevented. Furthermore, the wall temperature of the ignition chamber, because of the far greater energy density, is higher than the wall temperature of the combustion chamber.

Preferably, the combustion chamber is spherical and has a constricted throat.

Preferably, starting especially cold starting is effected by a glow plug projecting into the ignition chamber to ignite the ignitable mixture present in the ignition chamber.

The invention will now be described with reference to embodiments shown, in the accompanying drawings, in which: Figure 1 is a cross-section through part of the cylinder and the cylinder head of an internal combustion engine suitable for the method according to the invention, and Figures 2 and 3 show the internal combustion engine according to Figure 1 but with glow plugs arranged differently.

In the drawings, a piston 2 is slideably movable within a cylinder 1 (only partly shown). A spherical combustion chamber 4 having a constricted throat 5 is formed in the crown 3 of the piston 2. The inside 8 of the cylinder 1 is sealed at the top of the cylinder by means of a gasket 6 and a cylinder head 7. An injection chamber 9 is formed in the cylinder head 7 and communicates via a connecting passage 10 with the interior space 8 of the cylinder 1. A heat protection plate 11, and a fuel nozzle 1 3 fitted in a nozzle holder 12 communicate with the ignition chamber 9.The nozzle holder 12, the fuel nozzle 13, the ignition chamber 9 and the connecting passage 10 have the same longitudinal axis "x" which is arranged obliquely to the longitudinal axis of the combustion chamber 4, so that when the piston 2 is at top dead centre the connecting passage 10 enters the inner space of the cylinder 8 in the direction of an air swirl 14.

Fuel is sprayed by means of a solid jet 1 7 through the ignition chamber 9 and the connecting passage 10 directly onto the wall 18 of the combustion chamber 4 where it spreads in the form of a thin film 1 9 and is subsequently removed in vapour form by the rotating air and is mixed therewith. For idling and lower engine loads, the spray pattern and/or spray orientation can be changed so that an atomizing fuel spray 20 (shown by broken lines) is formed so that the fuel is distributed only in the ignition chamber 9, mixes within the chamber 9 and is finally burnt.

As shown in Figures 2 and 3, a glow plug 15 with a glow pin 1 6 penetrating into the ignition chamber 9 is arranged in the cylinder head 7 at an acute angle to the longitudinal axis "x", the magnitude of which depends on the actual construction. The glow plug 15 only serves for starting the engine and, after this, it is immediately switched off.

Claims

1. A method of injecting fuel in an aircompression internal combustion engine comprising an ignition chamber communicating via a connecting passage with the inside of a cylinder, a fuel injector projecting into the ignition chamber, a combustion chamber in the shape of a solid of revolution provided in the piston crown, and means for imparting a rotary swirling motion about the longitudinal axis of the combustion chamber to air flowing into the cylinder, the connecting passage entering the cylinder near the combustion chamber wall at top dead centre, the method comprising spraying a fuel jet from the fuel injector through the ignition chamber and the connecting passage onto the wall of the combustion chamber where it spreads as a thin film, the air flow in the ignition chamber during the compression stroke of the piston and control of the fuel injection being such as to cause individual fuel particles to be separated from the fuel jet to form an ignitable mixture with the air and residual gas remaining in the ignition chamber, this ignitable mixture being ignited in the ignition chamber so that a flame penetrates through the connecting passage into the combustion chamber to ignite the fuel evaporating from the combustion chamber wall, further combustion taking place as in internal combustion engines using the method of wall deposition of the fuel.

2. A method as claimed in claim 1, wherein at idling and at lower engine loads all the fuel injected is sprayed exclusively into the ignition chamber by appropriate atomization, and if necessary jet deflection, to mix in the ignition chamber with the inflowing air.

3. A method as claimed in claim 1 or 2, wherein the combustion chamber is spherical with a constricted throat.

4. A method as in claims 1, 2 or 3, wherein the ignitable mixture in the ignition chamber is ignited by a flow plug projecting into the ignition chamber for starting the engine.

5. A method of injecting fuel in an internal combustion engine substantially as herein described with reference to the accompanying drawings.