Time Irreversibility of Cycle-by-Cycle Engine Combustion Variations

Spark-ignition engines exhibit patterns of increasing instability as engine fueling goes from stoichiometric to lean. The observation of time irreversibility in cycleresolved combustion measurements indicates that this combustion instability is inherently nonlinear. Using time return maps and symbolic time-series analysis, we demonstrate the presence of strong time irreversibility in experimental data from production and laboratory sparkignition engines under lean fueling. We propose that the time-irreversible patterns can be explained as the result of nonlinear coupling between successive cycles combined with the effects of dynamic noise. This model is inherently distinct from models which attempt to explain cyclic variations as arising from linear Gaussian random processes.