Effects of Initial Temperature on the Deflagration Characteristics and Flame Propagation Behaviors of CH₄ and Its Blends with C₂H₆, C₂H₄, CO, and H₂

Abstract

An experimental study was performed on pressure evolution and flame propagation for CH4 and its blends with C2H6, C2H4, CO, and H2 over its entire flammable range for systems with various concentrations (0.4–2.0 %) and initial temperatures (298–373 K) of closed-vessel deflagration. The peak explosion pressure (Pmax) and the maximum pressure rise rate (dp/dt)max were observed and analyzed. In the outwardly spherically propagating flame method, the unstretched laminar burning velocity (Ul) was obtained from the flame radius with time. Within the range of the experiments, the results show that Pmax decreases linearly and that (dp/dt)max first increases and then decreases with increasing initial temperature at a constant initial concentration. When a gas mixture is added to a 9.5 % CH4–air mixture, Pmax and (dp/dt)max exhibit decreasing trends at a constant initial temperature. A nonlinear regression formula was obtained, and this formula can be used to predict Pmax at different temperatures and concentrations. The kinetic model using two detailed mechanisms (GRI-Mech 3.0, FFCM-1) is compared with the experimental results using linear and nonlinear models of stretch extrapolation. The laminar burning velocities (LBVs) measured by FFCM-1 are closer to the experimental value than those measured by GRI-Mech 3.0. The Ul values of CH4 and its blends with C2H6, C2H4, CO, and H2 increase with an increase in the initial temperature. Based on the analysis of experimental values, the temperature exponent (α) is derived to predict the LBVs of the mixture at an elevated temperature under atmospheric pressure.