Experimental study on the thermoacoustic instability and bifurcation phenomenon of ammonia-methane premixed swirl-stabilized combustor

Abstract

The combustion characteristics of ammonia-methane composite fuel in a premixed swirl-stabilized combustor are experimentally investigated in the study. The combustion instability bifurcation phenomenon induced by the variation of ammonia-fuel ratio and equivalence ratio is observed and analyzed. It is found that, under fixed equivalence ratio (Φ) and inlet flow rate, when the ammonia-fuel ratio (X_NH3) is gradually increased, the flame heat release rate fluctuation is weakened, the phase difference between the pressure oscillation and heat release rate fluctuation is increased, and three distinct modes of limit are formed successively in the combustor. It is shown that when X_NH3 or the equivalence ratio is varied independently, subcritical bifurcation and supercritical bifurcation occur when the combustion mode is changed between limit-cycle oscillation and quasi-periodic oscillation. The equivalence ratio is an important parameter for determining the type of bifurcation in the stability of ammonia-methane swirl-stabilized combustor. Subcritical bifurcation occurs only under lean fuel conditions, and particularly, as X_NH3 is changed, its influence on the flame length and heat release fluctuations intensifies with increasing equivalence ratio, resulting in a progressive reduction in the hysteresis interval. When rich fuel conditions are reached, the hysteresis interval disappears and the combustor exhibits supercritical bifurcation.