An experimental study on CH4–H2–NH3 fuel blends: flame stability and emission reduction in a combustor

As zero-carbon emission combustion and energy production activities accelerate today, ammonia energy is attracting attention. Ammonia serves as an important hydrogen carrier and a potential alternative fuel because it contains a large amount of hydrogen. In this study, the addition of ammonia (NH 3 ) and hydrogen (H 2 ) fuels to a methane (CH 4 ) flame at different ratios was tested. The experiments were conducted at constant thermal power (5 kW) and an equivalence ratio (ϕ = 0.7). A swirl-assisted combustor was used as the burner, and the number of swirl generators (1.2) was kept constant. The aim of this study is to model a realistic transition strategy representing the transition process from natural gas-fired systems to zero-carbon systems by simultaneously mixing NH 3 , H 2 , and CH 4 , and to evaluate the combustion stability and emission behavior. The findings indicated that increasing the ammonia fraction led to a reduction in flame temperature. However, adding hydrogen raised the lower heating value, which in turn caused the flame temperature to rise. In this burner, when NH 3 is added to pure methane, the maximum allowable NH 3 fraction is limited to 30% by volume, beyond which flame blowoff occurs. In contrast, hydrogen-enriched flames can tolerate higher NH 3 volumetric fractions. By increasing the H 2 content in the mixture, stable combustion was achieved with mixtures containing up to 50% H 2 and 50% NH 3 . Thus, the zero-carbon fuel target was achieved. Due to the decreasing methane content, CO emissions decreased to almost zero at 4,100 ppm. Furthermore, increasing H 2 content caused an increase in NO X emissions due to thermal effects, while adding NH 3 at the same hydrogen ratio offset the impact of H 2 and reduced NO X emissions. However, at very high NH 3 ratios, the fuel’s nitrogen atoms increased NO X emissions to 4,781 ppm. Due to the low heating value of the ammonia fuel, it acted as a diluent, reducing the thermoacoustic response of the flame. However, as ammonia addition reached high levels, the flame approached the blowoff limit and became unstable again.