Effect of nitrous oxide on laminar burning velocity, hydrodynamic, and diffusive–thermal instability of biogas combustion

Abstract

Biogas is a potential alternative energy source with low environmental impact. However, the practical applications of biogas are relatively limited due to the existence of CO2 which acts as a dilutant that decreases the calorific value and the burning rate of biogas. Nitrous oxide (N2O) is known to be a powerful oxidizing agent for propulsion applications which can enhance the combustion rate of biogas. In the present paper, the laminar burning velocity (LBV), hydrodynamic instability, and diffusive–thermal instability of biogas/N2O oxide were experimentally studied at different equivalence ratios. The spherical propagating premixed flames for various mixtures of biogas-N2O were determined using the constant volume combustion vessel at 303 K and atmospheric pressure. Two mechanisms were used in CHEMKIN-PRO software in order to estimate the predicted combustion characteristics of biogas/N2O mixtures. The results indicate that the decline in LBVs was prominent in the fuel-rich mixtures than in the fuel-lean mixtures with CO2 dilution. It is found that the influence of curvature on the flame front is weakened at the fuel lean-to-stoichiometric mixture due to the decrease in the flame thickness; therefore, flame instability tends to increase at the lean-to-stoichiometric region. Thermal diffusivity values decline with increasing the CO2% except in the equivalence ratios of φ = 1.0 and φ = 1.4, which showed no impact on the thermal diffusivity. The thermal reaction of N2O decomposition is the most significant reaction in biogas/N2O combustion at lean mixtures of φ = 0.6 and 0.8.