Numerical investigation of laminar flame speed and NO emission of hydrogen-enriched ammonia at elevated pressures or temperatures

Ammonia is gaining recognition as a promising renewable energy source. This study investigates numerically the potential of hydrogen-enriched ammonia under elevated pressure and temperature conditions. Within the considered equivalence ratio range Φ from 0.7 to 1.4, the elevation in both the hydrogen enrichment and initial temperature promotes the laminar flame speed of the mixtures. But the molar fraction of NO in the mixture also increases accordingly. The increase in initial pressure reduces laminar flame speed. However, due to the significantly enhanced sensitivity of reaction R5: H + O2 = O + OH to hydrogen under high-pressure conditions, the addition of more hydrogen into the mixture can counteract the decrease in laminar flame speed caused by the increase in initial pressure. Furthermore, the molar fraction of NO decreases with rising initial pressure. The analysis indicates that it is advisable to utilize the energy from hydrogen-enriched ammonia under conditions of lower initial pressure and higher initial temperature. Additionally, ammonia plays a dominant role in the laminar flame speed of ammonia-hydrogen mixtures when using γ_H, α(Φ), and β(Φ) to characterize hydrogen enrichment, temperature, and pressure respectively.