Propagation indices of methane-nitrous oxide flames in the presence of inert additives

The propagation indices (explosion pressures, rates of pressure rise, severity factors and explosion times) of CH4-N2O flames in the presence of inert gases (He, Ar, N2 and CO2) were determined by experiments performed in a spherical vessel with central ignition. Lean-and stoichiometric mixtures (φ = 0.8 and 1.0) with a variable inert gas concentration between 40 and 60% were studied, at variable initial pressures within 0.50 and 1.75 bar. Inert gas addition to each of the studied CH4−N2O mixtures results in the decrease of both experimental and adiabatic explosion pressure and of the maximum rate of pressure rise, along with the increase of the explosion time. CO2 was found to be the most efficient inert additive, followed by N2, Ar and He. The measured and computed propagation properties are examined as functions of the total initial pressure and the inert gas concentration. The correlation of peak explosion pressures with the initial pressures, derived from the heat balance of the isochoric combustion of a fuel-oxidizer mixture under non-adiabatic conditions, is used to evaluate the heat losses during the closed vessel combustion, dependent on the initial CH4/N2O ratio and on inert concentration of the flammable mixtures.