The effect of dilution on the diffusive-thermal instability of the rich premixed hydrogen deflagration

The study focuses on the dynamics of rich premixed diluted hydrogen-oxygen flames. The problem of unsteady flame propagation is treated numerically within a 1D framework with a detailed model for the chemical kinetics and mixture averaged molecular diffusion. The effect of mixture dilution on the onset of the diffusive-thermal pulsating instabilities of freely propagating flames is investigated by studying the characteristics of the pulsating instabilities e.g. critical pressure of the onset, period and amplitude of pulsations. The dilution with helium, nitrogen and argon shows quantitatively a similar effect on the flame instability: namely, the critical pressure for the onset of oscillations is essentially reduced, while the period of oscillations increases. It is also shown that the neutral stability boundary is affected to a leading order through the reduction of the adiabatic flame temperature rather than by modification of the species molecular diffusion. The observed reduction of the critical pressure for the onset of oscillations and the sensitivity of the stability boundary of a steady flame propagation regime to the thermo-chemical system parameters open new perspectives for additional experimental validation of mechanisms of chemical kinetics. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.