Study on counterflow premixed flames using high concentration ammonia mixed with methane

In the present study, combustion characteristics of ammonia/methane were evaluated computationally utilizing counterflow premixed ammonia/methane/air flames at normal temperature and pressure conditions. Investigations were carried out over a wide range of flame strain rates, fuel blend compositions and equivalence ratios. Extinction characteristic results show that methane addition and equivalence ratio have significant impact on the extinction limits of the stretched flames. With more methane in the ammonia/methane fuel blends, the flame sustainability to high stretch rate substantially increases. Flame structures of the stretched flames were then investigated to have a deep insight into the combustion process of the ammonia/methane premixed combustion. Results show that temperature, heat release rate and important intermediate radicals of the flames are enhanced. However, the considerably increased carbon oxides and nitrogen oxides emissions suggest emission reduction is a key issue in the ammonia/methane combustion process. Pathway and sensitivity analyses reveal the chemistry of NOx emission characteristics of different ammonia/methane flames.