Abstract: A unit injector for staged injection of fuel in an internal combustion engine is disclosed. The unit injector comprises a fuel pump and a spray nozzle combined in a single unit adapted to be mounted on the engine with the fuel pump adapted to be driven by a mechanism provided on the engine. The fuel pump of the unit injector includes a pair of cooperating plungers defining first and second fuel compression chambers for producing a plurality of discrete fuel injections during a single cycle of the internal combustion engine and with a single stroke of the driven plunger of the fuel pump.

Abstract: A method of monitoring the cylinder wall wear using ultrasonic phase comparison techniques is disclosed. The method comprises the steps of introducing ultrasonic waves in a cylinder wall so that the waves travel through the cylinder wall. A change in the traveling time of the ultrasonic waves traveling through the cylinder wall due to cylinder wall wear is determined. The amount of wear of the cylinder wall is calculated by multiplying the velocity of the ultrasonic waves in the cylinder wall by the traveling time change due to cylinder wall wear. The traveling time change due to cylinder wall wear is obtained by determining the actual change in travel time by a phase comparison of the traveling ultrasonic waves and adjusting the actual change in travel time to compensate for any change due to temperature variation of the cylinder wall. With this method, small changes in traveling time on the order of 10.sup.-11 second can be determined so that thickness changes due to wear on the order of 5.times.10.sup.