Methane-unconventional oxidant flames. Laminar burning velocities of nitrogen-diluted methane–N 2 O mixtures

Abstract

Abstract The flame propagation in nitrogen-diluted CH4–N2O mixtures was monitored by pressure measurements during explosions in a spherical vessel with central ignition. The burning velocities were obtained from experimental measurements of pressure variation during closed vessel explosions and from the detailed modelling of free laminar premixed flames. Lean- and stoichiometric methane–nitrous oxide mixtures (equivalence ratios: 0.8 and 1.0) diluted by various amounts of nitrogen between 40 and 60 vol% were studied at various initial pressures between 0.3 and 1.8 bar and ambient initial temperature. Nitrogen addition to each CH4–N2O mixture results in the decrease of laminar burning velocity and flame temperature, along with the increase of flame width. Examination of burning velocity variation against average flame temperature in experiments at constant initial pressure and various inert concentrations allowed the determination of the overall activation energy; examination of burning velocity dependence on pressure, at constant inert concentration, allowed the determination of the overall reaction orders. For all CH4–N2O–N2 mixtures, the temperature, volumetric rate of heat release and reactive species concentration profiles across the flame front were examined versus similar data characteristic to stoichiometric methane–air mixtures. The most important elementary reactions in CH4–N2O–N2 and CH4–air mixtures were identified by means of sensitivity analysis.