Research on ion current signal based on wavelet threshold de-noising method

On a spark ignition engine, ion current signals across two electrodes of spark plug were measured. Filtered and de-noised by wavelet threshold shrinkage de-noising method, the measured ion current signals can clearly distinguish ignition, flame front and post-flame zones, furthermore, the peak originated from ignition pulse is at 5~6°CA BTDC, the position of flame front zone peak is near TDC, and the position of post-flame zone peak is close to the position of pressure peak (differs less than 1°CA). When relative air-fuel ratio varies between 0.9 and 1.2, both the flame front zone peak and post-flame zone peak of de-noised ion current decrease as the air-fuel ratio increasing.