Experimental study on effect of cycle-to-cycle variability on HC emission in a SI engine

To improve the spark ignition (SI) engine performance, the study of the cycle-to-cycle variation is one the main concerns. The cyclic variations dependent on the fuel type, the equivalence ratio, the speed, the engine load and geometrical properties of the engine. The variations may cause fluctuations of the output power and the unburned hydrocarbon. Previous works presented effects of the fuel type, the equivalence ratio, the speed and the engine load on the cyclic variation, but no study has been reported yet on the effect of the cycle-to-cycle variation on unburned hydrocarbons. In this paper, an experimental study on a single-cylinder SI engine has been conducted to collect consecutive cycle variations and their statistical analyses. To reduce experimental errors, all controlling parameters were continuously monitored to prevent changes in engine operating conditions and that caused the inconsistent data collection. Results showed that although the cyclic variation due to the reduction of the output power was not a good phenomenon, but an increase in the cyclic variation reduced unburned hydrocarbons.