Cyclic Variability Correlations to Operating Conditions for Spark-Ignition Engines

Variations of successive combustion cycles are associated with power losses, vibration and fluctuations in the engine speed, torque and work done. Previous studies declared that the elimination of cycle-to-cycle variation (CCV) could improve the engine power by 10 %. This work aims at correlating cyclic variability to engine operating conditions to determine the relevant operating conditions that affect the CCV and help designers to predict it. Experimental work was carried out on spark ignition, 4-stroke, 4-cylinder, 2.2 liters, with an 8.85:1 compression ratio and a maximum power of 85 kW at 5,000 rpm. The cyclic variability of many indicators is calculated from the measured in-cylinder pressure data. Results have been used to introduce new correlations considering the effect of normalized speed and load on cyclic variability with acceptable fit. These correlations could be a useful tool in early design calculations, CCV modeling and control.