It has been proposed in the past to utilise the build up of pressure within the cylinder of an internal combustion engine during the compression stroke to provide the motive force to compress fuel within the injector body. For example, there has been proposed a fuel injector which has a body, and a piston which is movable within the body under the action of cylinder pressure. The movement of the piston in the injector body causes an increase in pressure of a fuel charge introduced into the body to a point where the pressure enables a non-return valve associated with the injector nozzle to open and allow the fuel to be injected under pressure into the engine cylinder. Problems with this device include difficulty and uncertainty in closing of the valve leading to fuel continuing to dribble from the injector after the desired cut off point, and also a general lack of control over the operation of the injector.

U.S. Pat. No. 2,516,690 in the name of French shows a fuel injector which utilises the associated engine cylinder pressure to develop the pressure to inject the fuel. The French apparatus has a simple spring biased non-return valve at the injection nozzle so that the opening and closing of the injection nozzle is solely controlled by pressure differential and spring force. Some control of pressure developed is provided by a non-return valve in an outlet from the pumping chamber and an adjustable flow restrictor downstream of the non-return valve. The French apparatus has very limited ability to enable control of the injector operation including timing, injection pressure, volume of fluid injected, and degree of positiveness in action.