Abstract
Ammonia (NH3) is a promising carbon-free fuel. However, modifying its high ignition temperature and low flame speed remains challenging. In this study, NH3 combustion was numerically investigated using hydrogen peroxide (H2O2) of different concentrations as the oxidizer to overcome these limitations. Adiabatic, free-propagating laminar burning velocities for NH3/H2O2/H2O mixtures were examined using a detailed chemical model. The maximum flame temperature between equivalence ratios is not considerably different at high concentrations of H2O2 (>80%), because the heat release is dominated by H2O2 decomposition. The equivalence ratio does not significantly affect the flame speed when the H2O2 concentration is less than 50%. The impact of H2O2 on the burning velocity at low concentrations is mainly attributed to the chemical effect. The chemical effect gradually decreases and the thermal effect increases because of the high heat release at high H2O2 concentrations. Moreover, the different concentrations of H2O2 consequently divide the flame into two sections. The first section is dominated by H2O2 reactions and the second by NH3 reactions. However, when the H2O2 concentration is 90 or 100%, flames do not appear in both sections. Finally, a quasilinear relationship between the flame speed and (NH2+OH)max mole fraction is identified.
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