Investigation on detection of misfire and knock of spark ignition engine using ionic current method

By adding a bias voltage, constant ionic current is formed between the two electrodes of a spark plug. Engine operating parameters can be detected by monitoring ionic current signals. Misfire can occur by adjusting spark plug gap or adding carbon deposits on the electrodes. By detecting the difference between misfire ionic current signals and non-misfire signals in the shape and amplitude, misfire detection can be realized. High frequency signals are superimposed on the ionic current signals when knocking happens, which can be detected by picking up these signals, and the knock frequency is about 10-11 kHz. The comparison of wave shape, FFT analysis and knock intensity value between the knock and non-knock signals is made. The experiments prove that the spark plug used as a sensor to detect misfire and knock is simple, visible and cheap and exhibits a large market potential.