On cycle-to-cycle heat release variations in a simulated spark ignition heat engine

The cycle-by-cycle variations in heat release for a simulated spark-ignited engine are analyzed within a turbulent combustion model in terms of some basic parameters: the characteristic length of the unburned eddies entrained within the flame front, a characteristic turbulent speed, and the location of the ignition kernel. The evolution of the simulated time series with the fuel-air equivalence ratio, phi, from lean mixtures to over stoichiometric conditions, is examined and compared with previous experiments. Fluctuations on the characteristic length of unburned eddies are found to be essential to simulate heat release cycle-to-cycle variations and recover experimental results. Relative to the non-linear analysis of the system, it is remarkable that at fuel ratios around phi=0.65, embedding and surrogate procedures show that the dimensionality of the system is small.