High-Level Modeling of an RF Pulsed Quarter Wave Coaxial Resonator with Potential use as an SI Engine Ignition Source

Significant environmental and economic benefit could be obtained if spark ignited (SI) engines could be made more efficient. Engine operation using leaner fuel air mixtures at higher power densities and pressures promise higher thermal efficiencies. Mixtures required for such operation are often difficult to ignite with traditional spark plugs. In pursuit of better ignition sources, this paper presents a high-level model of an alternative microwave plasma ignition source under development. In this publication, atmospheric measurements of a pulsed microwave ignitor are used to derive an empirical model that will allow for control and increased energy delivery to the device. The model accounts for a simplistic plasma formation delay, a drop in resonance frequency as a result of plasma formation, and a subsequent change in associated microwave reflection coefficient. Using this model, it is then possible to suggest a control strategy for the device where input variables such as the excitation frequency can be adjusted. Such adjustment should result in improved energy coupling to the device.