Prior-Cycle Effects in Lean Spark Ignition Combustion - Fuel/Air Charge Considerations

The goal of this investigation was to gain a better understanding of the effect of fuel/air charge composition on the dynamical structure of cyclic dispersion in lean-fueled spark ignition engines. Swirl and fuel injection timing were varied on a single-cylinder research engine to investigate the effects of charge motion and stratification on prior-cycle effects under lean operating conditions. Temporal patterns in the cycle-to-cycle combustion dynamics were analyzed using return maps, Shannon entropy, and symbol sequence statistics. Our results indicated a transition from stochastic behavior to noisy nonlinear determinism as equivalence ratio was decreased from near stoichiometric to very lean conditions. The equivalence ratio at which deterministic effects became important was strongly influenced by swirl and fuel injection timing. A comparison of our results and previous results from an eight-cylinder production engine showed similar trends. These trends were also consistent with a previously suggested simple model for cyclic variation. The observation of determinism under lean conditions may have important diagnostics and control implications since cyclic dispersion is not a purely random process.