GB2097471A

GB2097471A - I.C. engine fuel injection nozzle

Info

Publication number: GB2097471A
Application number: GB8209402A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1981-04-23
Filing date: 1982-03-31
Publication date: 1982-11-03

Abstract

A nozzle 13 has an outlet orifice producing a jet 18 having low penetrative power and further orifices producing jets 19 having an increased penetrative power. In use the jet 18 is directed into the hottest zone of the combustion zone 14 where the air is relatively undisturbed and the jets 19 are directed into zones of the combustion chamber where the air flows is turbulent. The nozzle producing the jets may take various forms, Figs. 3 to 5 (not shown). <IMAGE>

Description

SPECIFICATION Fuel injection nozzles This invention relates to fuel injection nozzles for supplying fuel to internal combustion engines of the compression ignition type, the injection nozzle being of the kind which incorporates a valve member which is biased to a closed position and which under the action of fuel under pressure which is supplied to an inlet of the nozzle when the nozzle is in use, is moved against the action of the biasing means to an open position to allow flow of-fuel through an outlet orifice.

The fuel which flows through the orifice emerges in the form of a spray which enters the combustion chamber of the engine. A short period after the commencement of fuel supply, combustion of the fuel occurs and this period is called in the art the "ignition delay". Following the initiation of combustion, combustion spreads rapidly throughout the combustion chamber giving a rapid rise in the pressure within the combustion chamber. The rapid rise in pressure which takes place give rise to the so-called "diesel knock". It is desirable in order to maintain fuel economy whilst at the same timing reducing exhaust emissions, to reduce the period during which delivery of fuel into the combustion chamber takes place.This means that more fuel is present in the combustion chamber before combustion of the fuel starts to take place and as a result there in an even more rapid rise in the pressure.

It has been proposed to cause a small quantity of fuel to be delivered to the combustion chamber so as to ignite before the main and remaining quantity of fuel. The purpose of this is to try to form an ignitable mixture of air and fuel to ensure that combustion of fuel has started before the main sprays of fuel ignite. The rise in pressure is therefore more gradual with the result that the engine is quieter in operation. In the past this has been achieved by delivering a small quantity of fuel, known as the "pilot quantity" or by restricting the initial rate of injection of fuel which produces a similar effect. This has been effected by using various forms of valve. The performance of the known systems has proved to be difficult to predict because of the large volumes of fuel disposed between the pump supplying the fuel and the nozzle.Fuel is compressible at the pressures to which it is delivered to the injection nozzle and this can cause problems with the valve referred to above.

Moreover, arrangements incorporating valves have tended to extend the period of fuel delivery.

The object of the present invention is to provide an injection nozzle of the kind specified in a simple and convenient form.

According to the invention, a fuel injection nozzle of the kind specified is provided with at least two outlet orifices through which fuel flows at substantially the same time when the valve member is lifted, one of said outlets being designed to provide a fine spray of fuel which has a low penetration and which in use is directed into the hottest zone of the combustion chamber, the other outlet orifice or orifices being designated to provide a spray of fuel having a high penetration for the main quantity of fuel.

The invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic side elevation of a combustion chamber showing a nozzle, Figure 2 is a graph indicating the combustion characteristics, Figure 3 is a sectional side elevation of a portion of one form of nozzle, and Figure 4 is a sectional side elevation similar to Figure 3 showing another form of nozzle.

Referring to Figure 1 of the drawings there is illustrated at 10, a piston slidable within a cylinder 11 the latter being closed by a cylinder head 12. Formed in the cylinder head is a bore in which is located a fuel injection nozzle 1 3 of the type having an inwardly opening valve member that is to say in which the valve member as it is moved by fuel under pressure, moves away from the piston 10.

The piston 10 together with the cylinder 11 and the cylinder head 12 define a combustion space 14 and formed in the piston crown is a toroidal recess 1 5. As the piston moves upwardly during a compression stroke the air contained within the combustion space is forced to partake of a swirling motion within the toroidal recess 1 5.

The direction of air flow is generally indicated by the reference number 1 6.

The air during upward movement of the piston 10 becomes heated and the hottest zone of the combustion chamber is generally at the position indicated by the arrow 1 7. The reason for this is that the air in the remaining portion of the combustion chamber is in a turbulent state whereas the air in the zone 1 7 is in a relatively undisturbed state.

The nozzle 1 3 is provided with a single outlet which is so designed as to direct a fuel spray 1 8 into the zone 17, the spray 18 having a low penetrative power and a small droplet size. The nozzle 1 3 is also provided with at least one further outlet which is designed so that the fuel issuing therefrom has a high penetrative power and forms a spray indicated at 19 which is directed into the turbulent zones of the combustion chamber. As shown in Figure 1 , two of these outlets are formed but there may be others out of the plane of the paper. The fuel flow occurs through all the outlets at substantially the same time however, the fuel forming the spray 18 ignites quickly because it has a low particle size and because it is directed into the hottest zone of the combustion chamber.The combustion of fuel therefore takes place in the hottest zone slightly earlier and the flame propagates throughout the air fuel mixture with a lower rate of pressure rise than is usual. Figure 2 shows the rate of heat release plotted against time considered in terms of degrees of crank shaft rotation. Fuel delivery takes place at the origin and the chain dotted line which is referenced 20, indicates the rate of heat release obtained with a conventional form of nozzle. It will be seen that the ignition delay is substantial and that the rate of heat release is high so that the pressure rise is also high. The line 21 indicates the results which are obtained with the injection nozzle described. It will be seen that the ignition delay is considerably less and the rate of heat release is also substantially less so that the rate of rise of pressure is also reduced.

The nozzle described with reference to Figure 1 is of the conventional type and its tip portion is shown in greater detail in Figure 3. The nozzle includes a valve member 22 which is shaped to co-operate with a seating 23. The spray 1 8 is produced by a small orifice 1 8A which is aligned with the axis of the valve member, and the sprays 19 by orifices 1 9A which are larger than the orifice 18A. All the orifices extend from the sac chamber 23A. In Figure 4 there is indicated a different form of nozzle which is known in the art as a "pintle" nozzle. The nozzle includes a valve member 22 which again is shaped to co-operate with the seating 23 but which also has a projection 24 which extends through an aperture in the nozzle body.In addition, at least two orifices 25 are provided through which in use and when the valve member 22 is moved away from its seating, the main flow of fuel occurs to provide the sprays 19. The projection 24 has a small clearance with the aperature in the body and through this clearance a small quantity of fuel flows which provides the spray 1 8. In this case the spray is of annular form. It should be noted that the projection 24 always lies within the aperture so that the spray 18 has a low penetrative power throughout the delivery of fuel.

In Figure 5 there is illustrated a nozzle in which the valve members opens outwardly i.e. in a direction towards the piston. The valve member has a head 26 part of which is shaped to cooperate with a seating 27. Downstream of the seating 27 there is defined an annular space from which extends orifices 28 which correspond to the orifices 25 of the nozzle shown in Figure 4.

Moreover, the valve head defines a parallel portion 29 which defines a small annular clearance with the surrounding body and it is through this clearance which is indicated at 30 that fuel flows to form the spray 1 8. As with the arrangement of Figure 4, the spray 18 produced by the nozzle shown in Figure 5, is of annular form and the portion 29 of the head always lies within the aperture in the body.

The various clearances and orifices must be carefully controlled to produce in a particular engine installation, the desired spray forms. With the nozzles described the fuel flows through the various orifices and clearances at the same time.

The reduction of ignition delay is of course achieved by the fact that one orifice of clearance produces a spray which has a small droplet size, has little penetrative power, and achieves an ignitable mixture more rapidly than the main fuel sprays. This spray is directed into the hottest zone of the combustion chamber so that combustion of the fuel starts quickly as compared with the rate of fuel/air mixing of the remaining quantity of fuel.

Claims

1. A fuel injection nozzle for supplying fuel to an internal combustion engine of the compression ignition type comprising a valve member which is biased to a closed position and which under the action of fuel under pressure supplied to an inlet of the nozzle when the nozzle is in use, is moved against the action of the biasing means to an open position, at least two outlet orifices through which fuel can flow at substantially the same time when the valve member moves against the biasing means, one of said outlet orifices being designed to provide a fine spray of fuel having a low penetrative power and which in use is directed into the hottest zone of the combustion chamber of the engine, the other outlet orifice or orifices being designed to provide a spray or sprays of fuel having a high penetration for the main quantity of fuel.

2. A nozzle according to Claim 1 including a seating and a sac chamber defined below the seating said orifices extending from said sac chamber, said valve member in use moving away from said seating to allow flow of fuel into said sac chamber.

3. A nozzle according to Claim 1 including a seating and a sac chamber defined below the seating, an opening from the chamber and a pintle carried by the valve member, said pintle extending with clearance through said opening, said clearance forming said one orifice, and the orifice or orifices extending from said seating.

4. A nozzle according to Claim 1 including a seating, the valve member having a valve head shaped for co-operation with said seating, said valve head being lifted from said seating by the action of fuel under pressure, an annular space defined by the valve head and the body of the nozzle downstream of said seating, a small annular clearance defined between the valve head and the body, said clearance defining said one orifice and the other orifice or orifices extending from said annular space.

5. A compression ignition engine incorporating a combustion chamber including a toroidal recess, a fuel injection nozzle as claimed in any one of Claims 1, 2, 3 or 4 mounted so as to direct fuel into said combustion chamber, said one orifice being positioned to direct fuel into a zone of the combustion chamber in which in use the air is in a relatively undisturbed state, the other orifice or orifices being disposed to direct fuel into a zone in which in use, the air is in a turbulent state.

6. A fuel injection nozzle for supplying fuel to an internal combustion engine of the compression ignition type comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figures 1-3 of the accompanying drawings.

7. A fuel injection nozzle for supplying fuel to an internal combustion engine of the compression ignition type comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figures 1-3 as modified by Figure 4 of the accompanying drawings.

8. A fuel injection nozzle for supplying fuel to an internal combustion engine of the compression ignition type comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figures 1-3 as modified by Figure 5 of the accompanying drawings.

9. A compression ignition engine comprising the combination and arrangement of parts substantially as hereinbefore described.