Numerical investigation and optimization on laminar burning velocity of ammonia-based fuels based on GRI3.0 mechanism

As a carbon-free fuel, ammonia is an ideal fuel for future clean fuels, but the low combustion intensity limits the application of ammonia. The combustion performance of ammonia fuels can be effectively improved by mixing hydrogen and methane, but the mechanisms involved are different. In this study, three typical ammonia-based fuels, ammonia, ammonia-hydrogen and ammonia-methane, are numerically simulated for laminar burning velocity, and the applicability of different ammonia-based fuels mechanisms is examined and analyzed. The important reactions in the mechanisms are analyzed by sensitivity. The results show that both hydrogen and methane have a significant enhancement on ammonia fuel combustion, with hydrogen being more obvious, and the maximum laminar combustion velocity is achieved around an equivalence ratio of 1.1 for all three fuels. The reaction H + O₂<=>O + OH, which is directly related to the OH radical concentration and combustion intensity, is the most sensitive reaction, while the lack of other sub-reaction mechanisms or the variation in the relative importance of the sub-reactions are the main reasons for the differences between the mechanisms. The best choice of mechanism is given with the combustion conditions. A new mechanism for laminar combustion velocity prediction of all three fuels was optimized based on the GRI3.0 mechanism, and the average error was within 10%.