Blow-Off Limits, Flame Structure, and Emission Characteristics of Lean Partially Premixed Swirl-Stabilized Flames with NH3/CH4

Recently, ammonia/methane mixtures have been considered as potential alternative fuels. The present study experimentally investigates the blow-off limits, flame structure, and pollutant emission of ammonia/methane mixtures in a partially premixed swirl-stabilized burner. The effects of fuel composition and the equivalence ratio are also studied. The results show that the NH3/CH4flame can be stabilized at an equivalence ratio of 0.55. The addition of methane has a positive effect on the blow-off limits. For the chemiluminescence profile, the OH* distribution and CH* distribution of NH3/CH4flames show a similar tendency under various conditions. The peak OH* and CH* radiances monotonically decrease with increasing ENH3, while the maximum NH2* shows an opposite trend. The influence of the equivalence ratio on OH* and CH* in the NH3/CH4flames is negligible. However, when ENH3is 60%, the equivalence ratio has a significant effect on NH2*. In terms of pollutant emissions, the peaks of NO and NO2emissions are all found around an ENH3of 20%. When the equivalence ratio reaches 1.0, NO and NO2emissions are as low as 15 and 10 mg/m3, respectively. At the same time, both CO and unburned NH3emissions increase. Therefore, further studies on the application of secondary air or improvement of the fuel injection method to improve the combustion efficiency and reduce the pollutant emissions for ammonia combustion are still needed.