GB2087976A

GB2087976A - Direct Injection Engine With an Eccentric Combustion Chamber Recess in the Piston

Info

Publication number: GB2087976A
Application number: GB8135040A
Authority: GB
Original assignee: Bayerische Motoren Werke AG
Current assignee: Bayerische Motoren Werke AG
Priority date: 1980-11-26
Filing date: 1981-11-20
Publication date: 1982-06-03
Also published as: IT8125010A0; FR2494768A1; GB2087976B; IT1139580B; JPS57119126A; DE3044442C1

Abstract

Air is introduced into the combustion chamber 4 to swirl in the direction of the arrow a and the main fuel stream 14 is injected towards an area 13 of the side wall 15 of the eccentric piston recess 8 which is adjacent a region 11' of the recess in which squish flow b near top dead centre accelerates air swirl in the recess. The main injection at high load occurs between 20 and 5 DEG before and at low load occurs between 35 and 15 DEG before or between 8 DEG before and 5 DEG after top dead centre so that the fuel stream is less broken up at high load. <IMAGE>

Description

SPECIFICATION Combustion Process in a Reciprocating-Piston Internal Combustion Engine This invention relates to a combustion process in a reciprocating piston internal combustion engine with direct injection into a charge introduced with angular momentum into a combustion chamber, the combustion chamber comprising a combustion-chamber recess, for receiving a body of rotating fluid and arranged eccentrically in the face of the piston which bounds the chamber, as well as a compression gap, formed between that face of the piston and the wall of the cylinder head towards the end of the compression, from which compression gap a part of the charge is passed, as compression flow, to that part of the charge which is received with angular-momentum flow by the combustionchamber recess.

German Gebrauchsmuster Specification No.

66 10 078 describes a reciprocating-piston internal combustion engine with direct injection into a charge delivered or introduced with angular momentum, the object of the arrangement being to locate a combustion chamber recess, arranged eccentrically within a face of the piston which bounds the chamber, in such a position relative to the injection nozzle and the mouths of the gasexchange ducts, that one and the same piston is suitable both for an internal combustion engine in which the charge rotates in one sense and when the piston is rotated through 1 800 about its longitudinal axis for an engine in which the charge rotates in the opposite sense. The Specification also indicates that injection of fuel takes place in the direction of the angular charge momentum and tangentially of a wall of the combustion chamber recess.Since, in the introduction to the description in that Specification, reference is also made to a diesel engine as the internal combustion engine, it can be taken that there is a compression gap, which is formed between the face of the piston surrounding the recess and the wall of the cylinder head, towards the end of compression, and from which a portion of the charge, in the form of compression flow, is delivered to a portion of the charge which has already been received, with angular momentum flow, by the combustion-chamber recess.

German Offenlegungschrift 24 07 783 also discloses a reciprocating-piston internal combustion engine with direct injection into a charge introduced with angular momentum, wherein, towards the end of compression and for the purpose of achieving thorough mixing of the fuel with the rotating charge in a combustionchamber recess at the centre of the face of the piston which bounds the chamber, the turbulence present in the charge is increased by a compression flow. Further improvement of the combustion process is regarded as resulting from a further increase in turbulence by compressed flow directed oppositely to the rotating charge in the combustion chamber.

On the other hand, in the case of diesel engines with direct injection and formation of a mixture near a wall of a combustion chamber recess, efforts are generally made, particularly by mainly concentrating fuel on the wall, to achieve, in the region where mixing and combustion take place and particularly by mainly concentrating fuel on the wall, a well directed charge flow of sufficiently high velocity and involving the greatest possible quantity, so as to set up a favourable mixtureforming and combustion process while the internal combustion engine is under high load.

The object of the invention is, therefore, to improve, in a simple manner and with simple means, a combustion process for a reciprocatingpiston internal combustion engine as set forth in the opening paragraph of the present Specification so that, when the internal combustion engine is under high load, a well directed charge flow of relatively high velocity is achieved with a very large charge quantity, in the region where the formation of the mixture and combustion take place.

Accordingly, in the present invention, a piston with a combustion-chamber recess of such eccentricity is used that the angular-momentum flow in the combustion chamber recess is accelerated in a region which is adjacent to a side wall of the recess by the compression flow, and, when the internal combustion engine is under relatively high load, the main quantity injected is discharged into an area close to the side wall of the recess and at least adjacent to the said region in the direction of angular-momentum flow, the injected stream entering this area with a component of velocity which is tangential to the side wall of the combustion chamber recess.

The present invention is also directed to a reciprocating-piston internal combustion engine comprising means for introducing a charge with angular momentum into a combustion chamber, an eccentrically positioned combustion-chamber recess in the face of the piston which bounds the chamber, and direct injection means, the direct injection means being so constructed and arranged, and the combustion-chamber recess being of such eccentricity, that when the internal combustion engine is under relatively high load, discharge is effected of a main injected quantity into an area which is close to a side wall of the recess and at least adjacent to a region where the angular momentum flow in the combustionchamber recess is accelerated by compression flow in the chamber, the injected stream entering this area with a component of velocity which is tangential to the side wall of the combustionchamber recess.

With the combustion-chamber recess or depression arranged off-centre to a relatively great extent, the initial angular-momentum flow, that is the rotating charge flow in the combustionchamber recess, is accelerated by superposing the compression flow directed mainly towards the middle of the combustionchamber recess, in a region close to the wall of this recess, with the advantage of a relatively strong and well-directed charge flow in this region.

Since this region of accelerated angularmomentum flow or charge flow moves in the direction of the angular-momentum flow, the feature whereby, when the internal combustion engine is under relatively high load, the injected quantity is discharged into an area near the wail and adjacent to the afore-mentioned region in the direction of angular-momentum flow, achieves the advantage that the region of accelerated annular-momentum flow or charge flow moves past the fuel, concentrated on the wall when the internal combustion engine is under high load, so that an intensive and systematic mixture-forming and combustion process can be achieved.

The mixture-forming and combustion process is further improved by the feature whereby an injection stream or jet enters the area near the wall with a component tangential of the wall of the combustion-chamber recess, since this results in accumulation on the wall over a large area.

If, when the internal combustion engine is under relatively high load, the main quantity injected is discharged when the crank-shaft is between 200 and 50 forward of top dead centre, the time at which fuel is injected coincides substantially with the period or phase during which compression flow is great. This results in the velocity of the fuel stream or jet being low relative to the region of accelerated angular momentum flow or charge flow, so that, advantageously, the fuel stream or jet is broken up to a lesser extent and is therefore mainly concentrated on the wall. Thus, in the full-load range, the method of the invention results in injection being distributed over the wall with the known advantages of a favourable increase in pressure, a low maximum pressure and a short combustion period.

If, on the other hand, when the internal combustion engine is under a low load, the main quantity injected, which is lower than that for a full-load operation, is introduced when the crankshaft is between 350 and 150 forward of top dead centre of between 80 forward of and 50 beyond top dead centre, the time at which fuel is injected corresponds substantially to the period or phase during which compression flow is small.

Since the angular-momentum flow is now only slightly accelerated in the acceleration region, the velocity of the fuel stream or jet is now relatively great compared with that of the angularmomentum flow in the region, so that the fuel stream or jet is broken up. The fuel therefore has much air distributed in it, and is burnt with the advantage of low hydrocarbon emission.

The invention thus provides the further advantage of load-dependent control of the ratio of fuel with air distributed in it to fuel accumulating on the wall. Rotation of the charge in the cylinder or in the combustion-chamber recess is achieved, in the known manner, mainly by means of an intake angular-momentum duct or tangential duct during the inflow phase. Since, in the present invention, the flow velocity of the charge may be particularly high, during full-load operation, in the region of combustion and at the moment when it takes place, the angular momentum imparted to the charge when it is introduced, brought about by an angular charging duct or a tangential duct, may be considerably reduced. In addition to a form of inflow duct that is of simple design and requires reduced space, this results in the further advantage of reduced gas-exchange work.Furthermore, an improved delivery rate and a higher mean pressure at the smoke boudary in diesel engines can be achieved, as well as reduced fuel consumption.

If, on the other hand, the previous form of angular-momentum duct or tangential duct is substantially retained in a reciprocating-piston cylinder internal combustion engine which operates in accordance with this invention, then in the case of diesel engines, the fuel can be injected at a relatively late stage, in relation to the end of the compression stroke, without resulting in disadvantage as regards exhaust gas blackening and fuel consumption. The composition of the exhaust gas is thus favourably influenced. On commencement of injection for achieving optimum consumption, a higher load can be used at the smoke boundary. This invention can also be used with advantage in the case of engines using external auto-ignition.

Examples of a combustion process and an engine in accordance with the present invention are illustrated in the accompanyingdrawings, in which: Figure 1 shows a perspective, partly axialsectional diagram of a combustion chamber with an angular-momentum intake duct, Figure 2 shows a diagrammatic plan view of a piston shown in Figure 1, with an eccentric recess, and with different velocity vectors of the rotating charge at diametraliy opposite points; and Figure 3 shows a further diagrammatic plan view of the piston shown in Figure 1, with a region adjacent to a side wall of the recess where angular-momentum flow is accelerated, and an area adjacent to that side wall in which a mixture is formed in the recess.

In a reciprocating-piston internal combustion engine (not illustrated in detail), a piston 1, in the zone of top dead center, delimits a combustion chamber 4 in a cylinder 2 having a head 3. An angular-momentum intake duct 5 is formed in the cylinder head 3, whereby angular momentum is imparted to the inflowing combustion air or charge about the axis 6 of the cylinder and piston, as indicated, for example, by the arrow "a".

The piston 1 has a flat face 7 bounding the chamber 4. A combustion-chamber recess 8 is formed in that face 7. The recess 8 is in the form of a swirl chamber in that it receives a body of rotating fluid, possibly enhancing its rotation as it does so. The recess 8 is considerably off-centre from, or is eccentric in relation to, the axis 6 of the cylinder and piston. Shortly before completion of the compression stroke of the piston 1, a compression gap is defined between the face 7 of the piston (surrounding the recess 8) and a flat cylinder-head wall 9. From this gap a part of the charge is delivered in the form of compression flow to the recess 8 which has already received a part of the charge with angular-momentum flow.

The compression flow, in the direction of the arrows "b", is very intensive just before top dead centre of the piston 1 and is directed towards the central axis 10 of the combustion-chamber recess 8. Because of the relatively pronounced eccentricity or off-centre position of this recess 8, a region 11 which is adjacent to a side wall 1 5 of the recess, as indicated in Figure 3, is created in the recess 8 when the rotary direction indicated by the arrow "a" is selected for the charge, in which region the rotating charge is accelerated by substantially unidirectional velocity components of the compression flow "b".Figure 2 illustrates, in the case of a particle of the charge in the walladjacent region 11, the increased circumferential velocity component VUR, resulting from vectoral addition of the circumferential velocity component VUD from the angular-momentum flow and the local circumferential velocity component VUQ from the compression flow. On the other hand, in a region 12 of the combustion-chamber recess 8 that lies beyond the plane bounded by the axes 6 and 10, the initial angular-momentum flow "a" is retarded, since the above-mentioned individual components are directed opposite to each other in the circumferential direction.

A fuel-injection nozzle (not illustrated) is so arranged in the cylinder-head 3 that, when the internal combustion engine is under relatively high load, the main quantity injected is delivered or dispersed into an area 13, as shown in Figure 3, that is near the wall 1 5 and is adjacent to the region 11, in the direction "a" of angularmomentum flow. Thus an injection stream or jet 14 enters the area 13 with a component tangential to the wall 15 of the combustion chamber recess 8, and in this area 13 a mixture forms and combustion takes place.

If, while the internal combustion engine is under relatively high load, the main quantity injected is delivered when the crankshaft is between 200 and 50 forward of top dead centre, the time at which the fuel is injected corresponds to the phase in which compression flow is great.

Consequently, the difference between the velocity of the fuel stream or jet 14 and the region 1 1 t of accelerated charge flow is small, with the result that the fuel stream or jet 14 is broken up only to a slight extent. Thus, a combustion process involving fuel that is mainly concentrated by the wall 1 5 is achieved for the full-load range.

If, on the other hand, when the internal combustion engine is under a low or partial load, the main quantity injected, which is small compared with fuil-load operation, is introduced when the crank-shaft is between 350 and 150 forward of top dead centre or between 80 forward of and 50 beyond top dead centre, the time at which fuel injection occurs coincides with that of a period or phase of small compression flow "b".

Since the velocity of the fuel stream or jet 14 relative to that of the slightly accelerated charge flow in the region 11' is therefore relatively high, the fuel stream or jet 14 is broken up. Thus, in the partial load range, a combustion process involving fuel in which a considerable amount of air is distributed is obtained.

In order to achieve the greatest possible acceleration of the angular-momentum flow "a" in the wall-adjacent region 11 with the aid of the compression flow "b", the region at which the wall 1 5 of the combustion-chamber recess 8 merges with the face 7 of the piston is rounded and has a radius of curvature of approximately 1 to 2 mm.

Claims

1. A combustion process in a reciprocatingpiston internal combustion engine with direct injection into a charge introduced with angular momentum into a combustion chamber, the combustion chamber comprising a combustionchamber recess, for receiving a body of rotating fluid and arranged eccentrically in the face of the piston which bounds the chamber, as well as a compression gap, formed between that face of the piston and the wall of the cylinder head towards the end of compression, from which compression gap a part of the charge is passed, as compression flow, to that part of the charge which is received with angular-momentum flow by the combustion-chamber recess, in which process a piston with a combustion-chamber recess of such eccentricity is used that the angular-momentum flow in the combustion chamber recess is accelerated in a region which is adjacent to a side wall of the recess by the compression flow, and, when the internal combustion engine is under relatively high load, the main quantity injected is discharged into an area close to the side wall of the recess and at least adjacent to the said region in the direction of angular-momentum flow, the injected stream entering this area with a component of velocity which is tangential to the side wall of the combustion-chamber recess.

2. A combustion process according to claim 1, in which, at relatively high load, the main quantity injected is discharged into the area close to the side wall of the recess when the crankshaft is between 200 and 50 forward of top dead centre.

3. A combustion process according to claim 1 or claim 2, in which, for a low load, the main quantity injected is discharged into the area close to the side wall of the recess when the crankshaft is between 350 and 150 forward of top dead centre or between 80 forward of top dead centre and 50 beyond top dead centre.

4. A combustion chamber process is a reciprocating-piston internal combustion engine with direct injection into a charge introduced with angular momentum into a combustion chamber, substantially as described herein with reference to the accompanying drawings.

5. A reciprocating-piston internal combustion engine comprising means for introducing a charge with angular momentum into a combustion chamber, an eccentrically positioned combustion chamber recess in the face of the piston which bounds the chamber, and direct injection means, the direct injection means being so constructed and arranged, and the combustion-chamber recess being of such eccentricity, that, when the internal combustion engine is under relatively high load, discharge is effected of a main injected quantity into an area which is close to a side wall of the recess and at least adjacent to a region where the angular momentum flow in the combustion-chamber recess is accelerated by compression flow in the chamber, the injected -stream entering this area with a component of velocity which is tangential to the side wall of the combustion-chamber recess.

6. A reciprocating-piston internal combustion engine substantially as described herein with reference to the accompanying drawings.