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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.

A detailed investigation of the intake port mixing process was performed on a fired single cylinder port fuel injected research engine. The liquid fuel droplets were studied using several different methods of analysis ranging from spatially and temporally resolved to spatially and temporally averaged data. Comparisons of the port mixture preparation results were made to the combustion performance of the engine in order to develop correlations between the mixing process and resulting engine performance. It is suggested that while the nature of the fuel spray produced by the injector is important, there are several other factors that influence fuel delivery to the cylinder. Calculations are given that indicate drops must be very small to entrain in the flow and avoid wall wetting. Secondary drop formation mechanisms may ultimately determine the nature of the fuel delivery to the cylinder and have an impact on combustion performance.

We describe a method for detecting and quantifying time irreversibility in experimental engine data. We apply this method to experimental heat-release measurements from four spark-ignited engines under leaning fueling conditions. We demonstrate that the observed behavior is inconsistent with a linear Gaussian random process and is more appropriately described as a noisy nonlinear dynamical process.