Extinction and NO formation of ammonia-hydrogen and air non-premixed counterflow flames

Green ammonia, produced using renewable energy, is a promising carbon-free energy vector and fuel. This work studies combustion of ammonia-hydrogen fuel mixtures with air in counterflow diffusion flame ex-periments and provides an improved kinetic mechanism for modeling ammonia combustion. The extinction strain rate is measured for a range of 0 to 15% hydrogen in the fuel blend. The flame structure is also inves-tigated with quantitative laser-induced fluorescence (LIF) measurements of nitric oxide (NO) for the same hydrogen concentrations and strain rate range from 26 to 134 s -1. For these conditions, NO concentration in-creases with both strain rate and fuel hydrogen content. The previously published kinetic model developed by the authors is used to perform one-dimensional flame simulations of the experimental setup and conditions, and results are compared to three other recently published ammonia mechanisms. None of the selected mod -els satisfactorily predict both the measured extinction strain rate and flame NO concentration. The models mainly fail to predict extinction strain rate at higher H2 fraction and NO formation at the highest experimen-tal strain rates and H2 fraction. The reaction rate parameters for some of the key reactions in the published model developed by authors were updated to improve agreement with experimental results. The updated model results are closely aligned with extinction strain rate measurements, and have improved prediction of flame NO concentration. The model reveals that the reactions from the NH2 and NH sub-mechanism are sensitive in predicting the extinction strain rate as well as NO. In particular, the reaction NH+NO = N2O+H had significant impact on NO predictions.& COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This study investigates the combustion of ammonia-hydrogen fuel mixtures and provides an improved kinetic mechanism for modeling ammonia combustion. The measured extinction strain rate and flame NO concentration are compared to various models, and it is found that the previously published models do not accurately predict the experimental results. By updating the reaction rate parameters, the improved model shows better agreement with the experimental data, especially in predicting NO concentration.