Plasma-Jet Ignition of Fuel Sprays in a Rapid Compression Machine

Plasma-jet ignition of fuel sprays for direct-injection engine application was evaluated in two phases. In the first phase, data on the penetration characteristics of the plasma puff were obtained as a function of the input electrical energy to the igniter and the igniter cavity dimensions over a range of ambient density conditions. The jet-penetration data were used to evaluate existing plasma-jet models published in the literature. In the next phase, the three-dimensional arrangement of the combustion bowl, injector and spark plug in an engine was simulated by a simplified two-dimensional arrangement in a rapid compression machine. High-speed schlieren photography and pressure-time data were used to compare fuel-spray ignition with plasma jets and results obtained by conventional high-energy ignition (HEI) with a spark plug.

The performance of plasma-jet igniters for the ignition of fuel sprays was found to be comparable to that of a conventional spark-plug/HEI system optimised with respect to spark-plug electrode-tip location. For one plasma-jet igniter cavity dimension, at least three times the input energy of an HEI system was required. The rate of penetration of the plasma jet increased with input electrical energy and characteristic length of the igniter cavity. However, changes in these parameters over a wide range did not significantly affect the spray-ignition process.