Experimental and kinetic study on laminar burning velocities of ammonia/ethylene/air premixed flames under high temperature and elevated pressure

Abstract

The laminar burning velocities (LBVs) of ammonia (NH3) blended with ethylene (C2H4) were measured at different blending ratios (α = 0–1), initial temperatures (Tu = 300–440 K), and initial pressures (Pu = 1–5 atm). The flame morphology showed that the NH3/C2H4/air flames suffer from cellular instability under elevated pressures (Pu = 5 atm). The Lewis number (Le) was used to evaluate the thermal diffusion instability. Le was insensitive to the initial pressure and positively correlated with the blending ratio. The hydrodynamic instabilities were investigated under various initial conditions, which were exacerbated by elevated initial pressures and large blending ratios. The LBVs and hydrodynamic instabilities of NH3 were enhanced by adding C2H4. The existing kinetic models can only accurately predict measured data within a narrow range. Based on Konnov Mech (2021), a new detailed kinetic model with 119 species and 1,365 reactions was developed, which could satisfactorily predict the LBVs of NH3/C2H4/air flames under current conditions. The analysis of reaction flux, sensitivity, and radical concentration in the pure and blended fuels provided deep kinetic insights. The consumption pathways of NH3 and C2H4 were diversified after blending. NH2, an important precursor of ammonia oxidation, adds a consumption channel with HO2, whereas HCCO, an important intermediate of ethylene oxidation, adds new channels with NO. H + O2 = OH + O, a chain branching reaction, significantly contributes to the LBVs of NH3/C2H4/air flames. The peak concentrations of H, O, and OH radicals increased as the C2H4 percentages increased. The relationship between the H radical concentration and blending ratio was virtually the same as that for the LBVs.