Evolution of ammonia/air premixed flame and explosion pressure in a square closed duct: Effects of equivalence ratio and initial pressure

Abstract

This work explores the flame propagation features and pressure evolution law of ammonia-air mixtures within square closed duct under varying initial pressures and equivalence ratios. Experimental findings indicate that ammonia/air flames are influenced by buoyancy, causing the flame core to move upward, resulting in a distinctive 'jellyfish' shaped flame. As the equivalence ratio increases, the flame-wall contact time and the time required to reach the top of the combustion chamber initially decrease before increasing. Maximum explosion overpressure and maximum pressure rise rate first increased and then decreased. The calculations of flame instability parameters reveal that thinner flames exhibit higher thermal expansion ratios. The increase in initial pressure notably affects flame stability, primarily driven by fluid dynamic instability and buoyancy. As the equivalence ratio increases, adiabatic flame temperature and maximum net heat release of ammonia/air combustion first increase and then decrease.