EFFECT OF FINE DIRECT LIFT CONTROL ON IGNITION DELAY
GPDT's first engine test adapted an available GPDT actuator to an existing diesel fuel injector. The OEM injector solenoid and servo valve were replaced by the GPDT actuator and custom hydraulic compensation chamber. The actuator, operating through the hydraulic chamber, directly lifted the injector needle. Installed on cylinder #1, the top of GPDT's test apparatus projects through the valve cover of the test engine as the photograph shows.
In the graph, the dashed red line is a stock solenoid injector for comparison. The GPDT injection profile was a pilot followed by a main charge. The difference between each run is that the pilot lift was varied by one micrometer. This cause was followed by effect: the delay after the pilot after which the main charge ignited varied linearly with pilot lift, a clear demonstration of the fine control GPDT's actuator possesses.
In addition, the rate of heat release was observed to depend upon the rate at which current changed.