Effects of partial premixing on NO production in methanol/dimethyl ether counterflow flames

In this study, the effects of partial premixing on NO production in methanol/dimethyl ether counterflow flames were investigated through the simulation of counterflow flames. Two types of partially premixed counterflow flames were computed: methanol-side premixed counterflow flames and dimethyl ether-side premixed counterflow flames. These two types of flames were both air-side partially premixed ones because the strategy of partial premixing was to add excessive air into one side of counterflow to produce the lean fuel/air mixture while remaining the fuel stream on the other side. The computation results showed that there were two flame reaction zones in these air-side partially premixed flames. For both types of flames, NO was primarily produced in the non-premixed flame zone through the formation routes of thermal and prompt NO and the destruction pathway of reburn NO. In the premixed flame zone, the reactions related to NO were not active, but the NO2 reactions could be promoted with partial premixing. For both types of flames, with the increase in the premixing equivalence ratio, the peak concentrations of NO and its peak production rates were decreased, but the integrated NO production and NO emission index showed the significantly different variations. All studied flames presented the decreased NO production when their strains increased.