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Cyclic variability has long been recognized as limiting the range of operating conditions of spark ignition engines, in particular, under loan and highly diluted operation conditions. Previous studies have shown that if cyclic variability could have been eliminated, there would be a 10% increase in the power output for the same fuel consumption. The cyclic variability results also in high levels of variation in the engine speed that is interpreted as poor driveability. At full load, some of the cycles tend to knock, while some others may not have complete combustion by the time the exhaust valve opens. The cyclic variability is usually attributed to the result of random fluctuations in equivalence ratio and flow field due to the turbulent nature of the flow in the cylinder.

Cyclic Variability has long been recognized as limiting the range of operating conditions of spark ignition engines, in particular, under lean and highly diluted operation conditions. Previous studies have shown that if cyclic variability could have been eliminated, there would be a 10% increase in the power output for the same fuel consumption. The cyclic variability results also in high level of variations in the engine speed which is interpreted as poor driveability. At full load, some of cycles tend to knock, while other may not have complete combustion by the time the exhaust valve opens. An experimental study has been performed in order to evaluate the relative contribution of several relevant parameters on the cyclic variability in spark ignition engines. The cyclic variability has been examined via five major different pressure-related identifier, i.e. Pmax, θPmax, IMEP, (dp/dθ)max and θ(dp/dθ)max.