Monte Carlo Simulation of Cycle by Cycle Variability

One of the characteristics of nominally homogeneous charge spark ignition engines is a pronounced variation in the combustion rate from cycle to cycle. Many theories have been advanced which attempt to explain the fundamental origin for differences on a cyclic basis. In the present work, some of the suspected causes or their manifestations have been incorporated into Ford's engine combustion model with the intention of determining if their impact on the combustion rate is as theorized. It has been found that initial spark kernel burn rate, the displacement of the spark kernel from the spark plug gap, and the turbulence intensity must all be perturbed simultaneously on a cycle-by-cycle basis to cause the cycle simulation program to mimic the experimentally determined burn parameters with respect to their averages and distributions.