Acoustic Emission of Thermodiffusive Unstable Premixed Lean Hydrogen-Air Slit Flames

Combustion noise is linked to fluctuations in flow field variables. Heat release fluctuations are a direct noise source caused by perturbations of the flame surface generated by velocity fluctuations, which also arise from the flow field. Intrinsic stability phenomena like hydrodynamic and preferential diffusion effects either damp or amplify flame front perturbations. In this study two-dimensional lean premixed hydrogen-air slit flames are investigated. The impact of varying the fuel-to-air-equivalence ratios on flame dynamics are investigated. For each case, notable intrinsic instabilities of the non-excited flame result in prominent cellular structures along the flame front leading to persistent pocket shedding and intense pressure fluctuations at the flame tip. Markstein-length related effects reveal intrinsic disparities when compared to methane-air premixed flames. A more in-depth analysis of thermoacoustics can be achieved by solving the acoustic perturbation equations, the source terms of which are determined by the flow field. This will enhance our understanding of the distinct acoustic sources which contribute to the hydrogen-air flame's acoustic field when compared to that of methane-air flames.