An experimental study of the detailed flame transport in a SI engine using simultaneous dual-plane OH-LIF and stereoscopic PIV

Abstract Understanding the detailed flame transport in IC engines is important to accurately predict ignition and combustion phasing, rate of heat release and assess engine performance. This is particularly important for RANS and LES engine simulations, which often struggle to accurately predict flame propagation and heat release without first adjusting model parameters. Detailed measurements of flame transport in technical systems are required to guide model development and validation. This work introduces an experimental dataset designed to study the detailed flame transport and flame/flow dynamics for spark-ignition engines. Simultaneous dual-plane OH-LIF and stereoscopic PIV are used to acquire 3D measurements of unburnt gas velocity ( U ⇀ g a s ), flame displacement speed ( S D ) and overall flame front velocity ( U ⇀ F l a m e ) during the early flame development. Experiments are performed in an optical engine operating at 800 and 1500 RPM with premixed, stoichiometric isooctane-air mixtures. Analysis reveals several distinctive flame/flow configurations that yield a positive or negative flame displacement for which the flame progresses towards the reactants or products, respectively. For the operating conditions utilized, S D exhibits and inverse relationship with flame curvature and a strong correlation between negative S D and convex flame contours is observed. Trends are consistent with thermo-diffusive flames, but have not been quantified in context of IC engines. Flame wrinkling is more severe at the higher RPM, which results in a broader S D distribution towards higher positive and negative velocities. Spatially-resolved distributions of U ⇀ g a s and S D are presented to describe in-cylinder locations where either convection or thermal diffusion is the dominating mechanism contributing to flame transport. Findings are discussed in relation to common engine flow features, including flame transport near solid surfaces. Findings provide a first insight into the detailed flame transport within a technically relevant environment and are designed to support the development and validation of engine simulations.