Super adiabatic combustion of H2/Air and H2/N2O mixtures

While the impact of H ₂ chemistry on super adiabatic flame temperature (SAFT) for hydrocarbons is well understood, super adiabaticity for premixed H ₂ combustion has not been previously reported. In the present work, for the first time, premixed H ₂/air and H ₂/N ₂O combustion in 0D and 1D context have been analysed to show that the instantaneous (0D) or local (1D) temperature exceeds the equilibrium temperature at certain conditions. The open-source software Cantera with recently published mechanisms from the literature have been used for the simulations. The simulations consider varying unburnt mixture conditions, including pressure (1 atm ≤ P _u ≤ 20 atm), temperature (500 K ≤ T _u ≤ 4000 K), equivalence ratio (0.1 ≤ ϕ ≤ 4.0), and dilution by inert gases (10 vol%) to investigate their influence on super adiabatic combustion. The present study demonstrates the following: (a) H ₂/N ₂O cases show an order of magnitude higher super adiabaticity than H ₂/air mixtures, (b) the NO _x chemistry is primarily responsible for super adiabaticity in H ₂/oxidizer combustion, and (c) for H ₂/air flames, super adiabaticity is caused by the endothermic reactions in the post flame region, while for H ₂/N ₂O flames, super adiabaticity is caused by the conversion of NO into N ₂. These findings contribute towards a better understanding of the premixed combustion of hydrogen and the role of nitrogen oxidation chemistry therein. Novelty and Significance Statement The super adiabaticity of H ₂/Air and H ₂/N ₂O mixtures is investigated for the first time. A novel 0D two-regime super adiabaticity for H ₂/Air mixture was found. However, such a double regime super adiabaticity has not been observed in 1D H ₂/Air flames. N ₂O produces super adiabaticity that is an order of magnitude stronger than that of air. Our results show that H ₂/Air and H ₂/N ₂O mixtures have different chemical reasons for manifesting the super adiabatic phenomenon.