Study on cycle-by-cycle variations of ion current integral and pressure in spark ignition engine

The investigation of correlations of ion current integral, cylinder peak pressure and indicated mean effective pressure at different operating conditions were carried out on a spark ignition (SI) engine fueled by compressed natural gas (CNG) with 20%(in volume) Nitrogen enrichment. Then influencing factors of cycle-to-cycle combustion variations (CCV) in SI engine, such as throttle opening and engine speed were discussed. The results show that, at the same operating condition, the CCV of cylinder peak pressure and indicated mean effective pressure are smaller than the variations of ion current integral; the correlations of ion current integral, cylinder peak pressure and indicated mean effective pressure increase with the decrease of CCV; the CCV of ion current integral, cylinder peak pressure and indicated mean effective pressure decrease with the throttle opening increases or engine speed decreases.