GB2113318A - Fuel system for compression ignition engine - Google Patents

Abstract

A fuel system for a compression ignition engine includes a pump 11 operable in timed relationship with the associated engine and a nozzle 10 having a valve controlled outlet 17 through which fuel can flow to the engine. The nozzle also includes a plunger 20 in a bore 19 and an actuating piston 22 which engages the plunger. The piston is of larger diameter than the plunger and is contained within a cylinder one end of which is connected by a pipeline 14 to the pump. The bore 19 has one end connected to the outlet 17 so that when the pump operates fuel is delivered through the outlet. A non- return valve 26 connects the said one ends of the bore and cylinder to allow fuel flow into the bore when the piston is returned to the one end of the cylinder following delivery of fuel by the pump. <IMAGE>

Description

SPECIFICATION Fuel system for compression ignition engine This invention relates to a fuel system for supplying fuel to a compression ignition engine, the system comprising a fuel injection nozzle having a valve controlled fuel outlet, the nozzle in use being mounted upon an associated engine at a position in which fuel is directed from the outlet into a combustion chamber of the engine, a fuel injection pump driven in use by the engine in timed relationship therewith and a pipeline connecting an outlet of the pump with an inlet of the nozzle.

Such systems are of course well known in the art. Development of compression ignition engines has lead to the requirement to increase the injection pressure of the fuel and whilst it is possible to do this with known systems various difficulties arise in the process. Increasing the injection pressure requires an increase in the pressure at which fuel is delivered by the pump and this leads to an increase in the leakage of fuel within the pump. This introduces additional problems particularly when the associated engine is being started. A further problem arises in connection with the pipeline and it is necessary to make this more substantial so that it can cope with the increased pressure without the volume of fuel in the pipeline increasing to any substantial extent as the fuel pressure within the pipeline increases during delivery of fuel by the pump.Moreover, increasing the fuel pressure results in an increased pumping loss due to the compressibility of the fuel.

In order to minimise the aforesaid problems it is proposed to develop the required high pressure of fuel within the injection nozzle.

According to the invention in a fuel system of the kind specified said nozzle includes a bore having a plunger therein, one end of the bore being connected so that fuel displaced therefrom by movement of the plunger will flow to the valve controlled fuel outlet, a cylinder containing a piston having a larger diameter than the plunger, said piston being engageable with said plunger, one end of said cylinder being connected to the inlet of the nozzle whereby fuel under pressure supplied through the inlet will displace the piston and the plunger so that the latter displaces fuel from said one end of the bore, and a nonreturn valve connected between said one end of the bore and said one end of the cylinder, said valve being arranged to permit fuel flow from the one end of the cylinder to the one end of the bore.

An example of a fuel system in accordance with the invention will now be described with reference to the accompanying diagrammatic drawing.

Referring to the drawing the fuel system comprises a fuel injection nozzle generally indicated at 10 and a high pressure fuel pump generally indicated at 11. The fuel pump draws fuel from a supply tank 12, in a practical embodiment, a filter is provided intermediate the injection pump and the tank.

The pump is driven in timed relationship with an associated engine and it may be of the socalled rotary distributor type.

The pump is provided with a high pressure outlet 1 3 which is connected by means of a pipeline 14 to a fuel inlet 1 5 of the nozzle.

The nozzle 10 includes a conventional spring loaded valve member 1 6 which controls fuel flow through an outlet orifice 1 7 from a fuel supply passage 18. In the normal form of nozzle the passage 1 8 is connected to the inlet 1 5 but in the system forming the subject of the present application the passage 1 8 is connected to one end of a bore 1 9 which contains a plunger 20. The plunger extends into a coaxial cylinder 21 in which is slidable a piston 22 and the end of the cylinder remote from the bore 1 9 communicates with the aforesaid inlet 1 5. The piston 22 is of cup-shaped form and engages the plunger 20.In addition, the piston is biased towards the end of the cylinder communicating with the inlet 15, by means of a coiled compression spring 23. The portion of the cylinder which contains the spring 23 is connected by way of a non-return valve 24 to a drain channel 25 the latter also being connected to the spring chamber which accommodates the spring which biases the valve member 1 6. In addition, a further non-return valve 26 is provided this connecting the end of the cylinder which communicates with the inlet 15, with the end of the bore 1 9 which communicates with the supply passage 1 8.

The valve 26 is arranged to permit fuel flow in the direction from the cylinder to the bore but to prevent flow in the opposite direction.

In operation, when fuel is delivered by the injection pump to the inlet 1 5 the pressure acting on the piston 22 moves the piston against the action of the spring 23 and also effects movement of the plunger 20 to displace fuel from the bore 1 9 through the supply passage 1 8. As is well known in the art, the fuel under pressure acts on the valve member 1 6 to lift the valve member away from a seating to permit fuel flow through the outlet 17. This flow of fuel continues so long as fuel is supplied by the injection pump and so long as the piston 22 can partake of movement.

When the flow of fuel from the injection pump ceases the spring 23 acts on the piston to urge it towards the end of the cylinder which communicates with the inlet 1 5. The fuel in this end of the cylinder is therefore at a higher pressure than the fuel in the bore 1 9 causing flow by way of the non-return valve 26, into the bore 1 9 forcing the plunger 20 to follow the piston. The bore is therefore fully charged with fuel. During the return motion of the piston there will be more fuel displaced by the piston than can be taken up by movement of the plunger and the surplus fuel is returned to the outlet 1 3 of the pump.The amount of fuel returned to the pump is equal to the volume of fuel which is displaced by the piston less the amount of fuel which is supplied to the bore, this latter volume representing the amount of fuel which has been supplied to the engine. In practice there will be slight leakage of fuel along the working clearances defined between the piston and the wall of the cylinder and between the plunger and the wall of the bore. This fuel can escape to the drain channel by way of the valve 24.

The piston and plunger act as a pressure intensifier and the increase in pressure which is obtained depends upon the relative areas of the piston and plunger.

It is necessary to ensure that during the movement of the piston under the action of the spring, the differential pressure across the valve 26 is sufficient to open the valve. It will be appreciated that the displacement of the injection pump 11 will be increased as compared with the conventional form of pump however, the pressure is lower and hence the problems encountered with leakage in the pump and the construction of the pipeline are minimised.

If desired the piston and plunger can be connected together so that the spring will effect movement of the piston and the plunger.

Claims (5)

1. A fuel system for supplying fuel to a compression ignition engine, the system comprising a fuel injection nozzle having a valve controlled fuel outlet, the nozzle in use being mounted upon an associated engine at a position in which fuel is directed from the outlet into a combustion chamber of the engine, a fuel injection pump driven in use, by the engine in timed relationship therewith and a pipeline connecting an outlet of the pump with an inlet of the nozzle, said nozzle including a bore having a plunger therein, one end of the bore being connected so that fuel displaced therefrom by movement of the plunger will fl to the valve controlled fuel outlet, a cylinder containing a piston having a larger diameter than the plunger, said piston being engageable with said plunger, one end of said cylinder being connected to the inlet of the nozzle whereby fuel under pressure supplied through the inlet will displace the piston and the plunger so that the latter displaces fuel from said one end of the bore, and a nonreturn valve connected between said one end of the bore and said one end of the cylinder, said valve being arranged to permit fuel flow from the one end of the cylinder to the one end of the bore.

2. A system according to claim 1 including resilient means biasing the piston towards said one end of the cylinder.

3. A system according to claim 2 in which said resilient means comprises a coiled compression spring located in the other end of the cylinder.

4. A system according to claim 1 in which said piston and said plunger are connected together.

5. A fuel system for supplying fuel to a compression ignition engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.