The correlation between intake fluctuation and combustion CCV (cycle-to-cycle variations) on a high speed gasoline engine: A wide range operating condition study

•The CCV in engine thoroughly estimated under various operating and controlling parameters.•A residual method was proposed to assess the CCV data’s accuracy versus cycle numbers.•A time-surface value was proposed to estimate intake charge ability.•The contribution of the intake fluctuation on CCV was assessed under wide operating conditions.•The CCV of thermal efficiency was much gentler than that of apparent performances. In this work, the cycle-to-cycle variations (CCV) and their correlations to intake charge fluctuation of a motorcycle engine under wide operating conditions were investigated by experiment. Several key engine operating parameters (engine speed/load, air/fuel ratio, compression ratio and ignition mode) were considered and analyzed thoroughly. A new concept of intake charge time-pressure value (TPV) was proposed to estimate its charge capacity, and its fluctuation’s contribution to CCV was also assessed. Some important findings include: 1) the CCV goes up with engine speed. Engine speed is also the most important factor to affect intake charge fluctuation, coefficient of variation (COV) of TPV is only 3.38% at 3000 rpm under 60% load, but it rises up to 13.41% at 5000 rpm; 2) the contribution of charge cyclic fluctuation to CCV decreases with engine speed. At 3000 rpm, over 80% of CCV are caused by TPV’s fluctuation for all engine loads, but its contribution drops to about 30% at 5000 rpm under medium to full load; 3) engine load has moderate impact on intake charge fluctuation’s contribution to engine CCV within test range. This depends on the competition between intake pressure loss and trapped ability of residual gas; 4) the three factors of air/fuel ratio, compression ratio and ignition mode do not affect much the air exchange process, but largely influence the combustion process. The more they improve combustion process, the larger degree of participation in engine CCV by intake charge fluctuation.