Investigation of unsteady premixed micro/macro counterflow flames for lean to rich methane/air mixture

In the current work, an unsteady analysis of methane/air premixed counterflow flame is carried out for different flame conditions and stability parameters considering different strain rate values. The results are presented at unsteady and final steady conditions, and the impact of time-dependent regimes and variations in equivalence ratio, from lean flame to rich one, are analyzed. The governing equations including continuity, momentum, energy, and species are numerically solved with a coupled simple and Piso algorithm. It is also found that when the strain rate value is 1000 s−1, for flame stability, the hydraulic distance of the microchannel must be at least 0.05 mm. Increasing the strain rate results in decreasing the time of stabilizing temperature distribution with a faster quasi-steady equilibrium. The necessity of time-dependent analysis is to comprehend the variations in the main factors of flame structure before reaching the finalized steady-state condition. Therefore, by designing an intermittent automatic valve, if the flow stops in time period of 0.0025 s and starts again, the formation of NO2 and CO2 will be reduced about 50% and 9%, respectively, in a case with a = 100 s−

The time dependent investigation of methane-air counterflow diffusion flames with detailed kinetic and pollutant effects into a micro/macro open channel

In the present study, time-dependent numerical analysis of methane-air counterflow diffusion flame into a selected macro/micro open channel is investigated. The flame is simulated by multi and single-step reaction approaches into an open channel with a constant distance of 15 mm between air and the fuel inlet, and a hydraulic distance at the order of 0.1 mm. To solve the unsteady problem, a coupled pressure-velocity implicit division method is considered. The results show an acceptable agreement between numerical and experimental data that confirm the accuracy of the model. The results also revealed that the variation of the residence time to the inlet velocity is more sensitive than the inlet temperature. It is also found that at the larger inlet velocities, the flame is stabilized at a smaller value of hydraulic distance. This is a result of increasing the possibility of reactions between species. The generation rates of CO2, CO and H2O species are found to be nearly constant at t > 0.009s while for NO and NO2 species the rates remain unchanged at t > 0.013s and t > 0.016s, respectively