GB2052624A

GB2052624A - A fuel supply system for an engine

Info

Publication number: GB2052624A
Application number: GB8010876A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1979-06-16
Filing date: 1980-04-01
Publication date: 1981-01-28
Also published as: GB2052624B

Abstract

A fuel supply system for an engine includes means defining a cavity 12 which communicates by way of an orifice 15 with a combustion chamber 10. A low- pressure fuel pump 17 supplies fuel to the cavity via a non-return valve 18 at a time when the pressure in the combustion chamber is low, e.g. towards the end of the suction stroke. Located in the cavity is an electrode 14 insulated by an insulator 13 from the wall of the cavity. With fuel in the cavity a spark discharge is caused to take place between the wall of the cavity and the electrode and the fuel and also air in the cavity expand through the orifice into the combustion chamber. <IMAGE>

Description

SPECIFICATION Fuel supply system This invention relates to a fuel supply system for delivering fuel intermittently but at a high rate through an orifice, into a combustion chamber of an internal combustion engine.

Conventional fuel supply systems of this kind comprise a source of fuel at high pressure from which fuel is supplied to a nozzle which defines an orifice. The source of fuel may be a plunger pump in which the plunger is actuated in any convenient manner, the pump delivering a limited volume of fuel. Alternatively the source of fuel may be an accumulator from which fuel flows to the nozzle under the control of a valve to assure an intermittent supply of fuel.

The nozzle is provided with a valve member which opens to allow fuel flow only when the pressure of fuel supplied to the nozzle attains a predetermined value. This ensures that the fuel is atomised during its passage through the orifice and also it closes to prevent fuel dribble through the orifice when the supply of fuel to the nozzle is halted.

Where the fuel supply system is for supplying fuel to a compression ignition engine the pump derives its motive power from the engine and this may require a complex drive arrangement. In addition the pumps have to be manufactured to close tolerances to minimise leakage and to guarantee accuracy of delivery of fuel. In addition the injection nozzles must be accurately made to assure consistent delivery of fuel. It is an object of the present invention to provide a fuel system in a simple and convenient form.

According to the invention a fuel supply system comprises means defining a cavity, the outlet orifice communicating with said cavity, a fuel inlet to said cavity, means through which fuel can be supplied to said inlet and which will prevent flow of fuel from said cavity through the fuel inlet, and an electrically insuiated electrode extending into said cavity and between which and the wall of the cavity there can be applied in use a high voltage to cause an electrical discharge in the cavity, said discharge acting to cause fuel contained within the cavity to be delivered through the orifice at high rate.

One example of the fuel supply system in accordance with the invention will now be described with reference to the accompanying diagram.

Referring to the diagram there is shown at 10 the combustion space of a compression ignition engine. This combustion space may be formed separa ely from the engine cylinder or it may be constituted by the engine cylinder.

Forming part of the wall of the combustion chamber is a housing 11 which conveniently is located within a bore formed in the cylinder head of the engine. The housing defines a chamber 12 the open end of which is closed by an electrical insulator 1 3 which mounts an electrode 14 the latter- extending into close proximity with the wall of the cavity.

Also provided in the housing 11 is an outlet orifice 1 5 through which the cavity communicates with the combustion chamber 1 0. Moreover, the housing has a fuel inlet port 1 6 which communicates with the cavity and with a fuel pump 1 7 by way of a non return valve 18.

The housing 11 is formed from electrically conductive material as of course is the electrode 14 and these two components are connected to a high voltage supply circuit indicated at 1 9. The supply of high voltage by the circuit 1 9 is under the control of a control circuit 20 which is sensitive to the position of the rotating parts of the engine. The low pressure supply pump 1 7 is also driven by the engine so that it supplies fuel to the cavity 12 as will be described.

Fuel is supplied by the pump 1 7 to the cavity 12 during the time when the pressure within the combustion space 10 is low for example towards the end of the suction stroke of the piston with which the combustion chamber 10 is associated.

The amount of fuel supplied to the cavity does not necessarily have to fill the cavity 12 and during the compression stroke of the associated piston air under pressure will be forced into the cavity 12 by way of the orifice 1 5. In addition as is conventional in compression ignition engine practice, the air within the combustion chamber 10 will have a swirling motion imparted thereto.

At the end of the compression stroke of the associated piston, the circuit 1 9 is energised and a high voltage is supplied between the electrode 14 and the housing 11. As a result of this high voltage, a spark discharge will occur between the electrode and the wall of the cavity. At the end of the compression stroke and before the discharge occurs, the air in the cavity will contain evaporated fuel and the electrical discharge which occurs when the circuit 1 9 is energised will cause a rapid expansion of the contents of the cavity 12. The fuel and fuel air mixture is delivered through the orifice 1 5 into the combustion chamber 10 to form a jet of fuel mixture which is indicated at 21.

Because of the high temperature of the air within the combustion chamber 10 as a result of the compression of the air, the fuel starts to burn in the usual manner and expansion of the air within the combustion chamber takes place.

It is thought that by virtue of the electrical discharge within the cavity 12, chemical radicals will be formed in the cavity which will assist the ignition of the fuel within the combustion chamber. As a result it is thought that fuels of a poor quality or variable ignition quality can be burned within the combustion chamber, such fuels not normally being used with a compression ignition engine. In addition it is thought thai the chemical radicals may also suppress the formtion of soot in a diffusion flame within the jet 21.

It will be understood that the shape of the housing, electrode and cavity may be varied with a view to improving the performance of the fuel system. For example the shapes may be modified to control the mixing of fuel and air in the cavity after fuel delivery and during the compression part of the engine cycle. It may be possible to provide stratification of the fuel in the cavity prior to the electrical discharge. Moreover, the shapes of the parts may be adjusted so that there is more than one path for an electrical discharge to take place between the electrode and the wall of the cavity.

A dual electrode system may be provided with one of the electrodes together with the wall of the cavity providing the main power for discharge in a part of the cavity where the fuel ratio with air is low, and another electrode being provided to create the radicals in the fuel air mixture as it passes through the orifice 1 5.

Claims

1. A fuel supply system for delivering fuel intermittently but at a high rate through an outlet orifice into a combustion chamber of an internal combustion engine, comprising a cavity, the outlet orifice communicating with said cavity, a fuel inlet to said cavity, means through which fuel can be supplied to said inlet and which will prevent flow of fuel from said cavity through the fuel inlet, and an electrically insulated electrode extending into said cavity and between which and the wall of the cavity there can be applied in use a high voltage to cause an electrical discharge in the cavity, said discharge acting to cause fuel contained within the cavity to be delivered through the orifice at a high rate.

2. A system according to claim 1 in which means comprises a non-return valve.

3. A system according to claim 2 including a pump for supplying fuel to said cavity, said pump being arranged to deliver the fuel to the cavity towards the end of the suction stroke of the piston associated with the combustion chamber.

4. A fuel supply system for delivering fuel intermittently but at a high rate through an outlet orifice into a combustion chamber of an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.