Self-Oscillating Resonance Tracking Ignition System Design Using the Method of Describing Function

Reducing emissions and increasing efficiency of modern spark ignited internal combustion engines are crucial for the future of the environment and the global economy. This paper presents a plasma ignition system with self-oscillating resonance tracking capability to promote these objectives. The proposed ignition system is composed of a high quality factor series RLC circuit driven by a radio frequency (RF) generator to start and sustain a plasma torch for a prescribed duration inside the combustion chamber. Resonant frequency tracking is achieved using an integrated self-oscillating feedback topology. A phase-lead compensator is used to compensate for the propagation delay in the RF generator and a signum type nonlinearity is used to achieve the amplitude limitation for sustained oscillation. The describing function method is employed for analysis and design of the self-oscillating resonance tracking system. Simulation and experimental results are presented to illustrate the performance of the proposed ignition system and to demonstrate its feasibility in practical applications.