Low emission high temperature air combustion technology (HTAC)-numerical analysis of methane ignition phenomenon

Ignition delay is an important parameter in the most modern and advanced combustor concepts designed for low-NOx emission. This work presents the results of a modeling study of the ignition process of methane under High Temperature Air Combustion (HTAC) conditions. This technology is a promising solution for energy saving, flame stability enhancement and decreasing of harmful substances emission (NO_x, CO, C_nH_n). A mathematical model was formulated to predict the dependence of the equivalence ratio and temperature of oxidizer on the temperature increment. The mathematical model incorporates the basic principles of the energy and mass balance. The theoretical predictions were correlated with the experimental data. The increment of temperature (δT = T_max - T) was assumed as parameter characterizing the process of ignition. The influence of initial temperature of oxidizer (t = 687-961°C) and equivalence ratio is analyzed and discussed. The results of calculation were compared with the experimental ones which have been done on Constant Volume Bomb (CVB) reactor. It is shown that in order to achieve the effective reaction of ignition (taking into account the maximal value of increment of temperature δT), it is not necessary to maximize the oxidizer temperature. There are optimal values of temperature oxidizer (t ≈ 830°C) in which parameters mentioned above reaches its extreme values.