Optical Investigation of the Influence of In-cylinder Flow and Mixture Inhomogeneity on Cyclic Variability in a Direct-Injection Spark Ignition Engine

Abstract In this study, a single-cylinder direct-injection spark-ignition research engine with full optical access was used to investigate the influence of flow field and fuel/air mixing on cyclic variability, in particular early flame propagation. The operated under lean-burn conditions at 1500 rpm. Two different injection strategies were compared, port-fuel (PFI) direct (DI), latter late split about 2:1 fuel mass. High-speed particle image velocimetry captured tumble plane compression stroke. velocity fields movement vortex are analyzed. Simultaneously, second camera detected chemiluminescence flame, projected area line-of-sight-integrated luminosity extracted through morphological processing. By combining pressure-based combustion analysis high-speed diagnostics, propagation correlated. separate experiments equivalence ratio imaged for DI selected crank angles correlated CA10 learn mixture inhomogeneity With PFI, near spark plug just before ignition is closely related subsequent speed combustion. combustion-relevant features can be traced back time –90 °CA. contrast, chosen scheme results decorrelation distribution becomes more important. For both fields, regions high correlation early-combustion metrics typically associated gradients multi-cycle average fields.