An experimental investigation of lean hydrogen flame instabilities in spark-ignition engines

This experimental study explores the pivotal role of thermodiffusive and hydrodynamic instabilities in shaping the early development of lean hydrogen flames within a spark-ignition engine. Utilizing high-speed planar laser-induced fluorescence of inert SO tracer gas, the flame front is visualized to scrutinize the lean H flame propagation in an optically accessible single-cylinder spark-ignition engine operating at 800rpm and intake pressures of 0.4bar and 0.95bar. Comparisons between H/air and CH/air flames reveal minimal disparity in the statistical distributions of flame surface density under identical initial conditions. This suggests that, within the dynamic engine environment, the influences of thermodiffusive and hydrodynamic instabilities may be counteracted by competing factors, including turbulence and dynamic volume confinement. While traditional bomb calorimeter experiments and laminar simulations provide insights into hydrogen flame evolution, their observed effects may be less pronounced in real-world applications where turbulence and flame-wall interactions play a major role. However, by significantly reducing the equivalence ratio, the observed increase in underscores that the cumulative effects of flame instabilities become notable under extremely lean conditions, even within the dynamic engine environment. This study marks a significant step in gaining new insights into the influence of flame instabilities on H-fueled spark-ignition engines. Finally, the elucidation of turbulence and flame-wall interactions in attenuating thermodiffusive instabilities presents a promising avenue for future research.