Exploration on laminar flame propagation of ammonia and syngas mixtures up to 10 atm

Abstract

Reactivity enhancement is crucial for the potential applications of ammonia (NH3) as a gas turbine fuel. Doping more reactive fuels like H2, methane and syngas is a widely adopted strategy in this field, however fundamental combustion studies of NH3/reactive fuel mixtures under gas turbine-relevant high pressure conditions are still very limited. This work reports an effort to study laminar flame propagation of NH3/syngas mixtures up to 10 atm. Laminar burning velocities (LBVs) of NH3/syngas/air mixtures were measured at 298 K, various syngas contents in fuel mixtures (α) and H2 contents in syngas (β), and equivalence ratios of 0.7–1.5 in a high-pressure constant-volume cylindrical combustion vessel. A kinetic model was developed for NH3/syngas combustion based on our recent NH3 model and a recent syngas model in literature. It shows reasonable predictions on the present NH3/syngas LBVs at 1–10 atm, as well as previous data including NH3/syngas LBVs at 1 atm, NH3/syngas ignition delay times at various pressures and pure NH3 LBVs at various pressures. Modeling analysis including the sensitivity analysis and rate of production analysis provides kinetic interpretation for the effects of fuel composition (α and β), equivalence ratio and pressure on NH3/syngas LBVs. It is found that the addition of syngas shifts the chemistry from NH3 sub-mechanism to syngas sub-mechanism. A modified fictitious diluent gas method was proposed to separate the chemical and thermal effects of syngas addition, which shows that the chemical effect is more responsible for the enhanced laminar flame propagation. NH3/syngas/air flames have similar reaction networks but different preferred pathways under lean and rich conditions. Compared with pure NH3 flames, the addition of syngas also improves the importance of H + O2 (+ M) = HO2 (+ M) and consequently leads to strong pressure dependency of NH3/syngas/air flames.