Evaluation of Combustion Characteristics of Methane/Hydrogen Mixture by Counterflow Flames

Abstract

Combustion characteristics of methane/hydrogen mixture are evaluated focusing on the NOx production by using numerical analysis of counterflow flames with evaluation parameters: molar ratio of hydrogen to methane “a”, combustion air temperature “T_air”, equivalence ratio ”er” and velocity gradient of counterflow “k”. As the increase in “a”, flame temperature becomes high, heat release rate becomes large, and eventually EI_NOxQ becomes larger in counterflows with a diffusion flame, a double flame, a twin flame, and a triple flame. With a larger “k”, strong flame stretch effect is obtained offsetting the EI_NOxQ increase even if with a large “a”. The counterflow with a diffusion flame for a lower air temperature shows larger fuel consumption rate, higher heat release rate, and lower flame temperature, resulting in lower emission index EI_NOxQ. The EI_NOxQ of counterflow with a double flame and a triple flame show local maximum values between 1 and 2 of “a”, being dominated by a result of the balance of total heat release rate “Q”, total fuel consumption rate and total NOx production rate. Among all the configurations of counterflow flames including planer one dimensional premixed flame, planer one dimensional premixed flame without flame stretch effect (er=1) shows the largest EI_NOxQ. The counterflow with a triple flame (er=1.2/0.8, k=666.7 s^-1) with small “a”, the counterflow with a double flame (er=1.5, T_air = 500 K, k=666.7 s^-1) and planer one dimensional premixed flame (er=1.5) with large “a” show the smallest EI_NOxQ. The counterflow with a diffusion flame (T_air =300 K, 500 K, k=666.7 s^-1) shows the smallest Q and second largest EI_NOxQ. The planer one dimensional premixed flame (er=1) and the counterflow with a triple flame (er=1.2/0.8, k=666.7 s^-1) show large Q.