Origins of Cyclic Dispersion Patterns in Spark Ignition Engines

The focus of this study was to experimentally investigate the development of nonlinear cyclic dispersion patterns in spark ignition engines. The results indicated a transition from stochastic behavior to noisy nonlinear determinism as equivalence ratio was decreased to very lean conditions. The transition to nonlinear deterministic behavior appeared to occur via a period-doubling bifurcation sequence. The structure of the bifurcation sequence and the level of communication between successive cycles were strongly affected by the level of residual fuel in the cylinder. Experimentally observed patterns were compared with patterns predicted by a recently proposed engine model. The comparison supported the hypothesis that the combustion instability develops as a noisy period-doubling bifurcation. The observation of nonlinear determinism under lean conditions may have important implications for engine diagnostics and control since cyclic dispersion is not a purely random process.