Numerical Investigation of the Minimum Ignition Energy in Ammonia/Hydrogen/Air Mixtures Considering Radiative Heat Loss

This study investigates the minimum ignition energy (MIE) of ammonia/air and ammonia/hydrogen/air mixtures through numerical simulations. The effect of radiative heat loss on the ignition process is examined by employing the optically thin approximation model (OTM). Two different reaction mechanisms, proposed by Glarborg and Otomo are utilized to simulate ignition and no ignition events close to the MIE across varying equivalence ratios (ϕ) until flammability limits are determined. Hydrogen is included at 0% and 10% by volume to examine its impact on ignition characteristics and for capturing the effect of radiation on the MIE and flammability limits, simulations are performed both with and without OTM.
An analysis of radiative species is conducted to identify the most dominant contributors to radiative heat loss dependent of the time during the ignition process. The in-house code INSFLA is used for the simulations with a detailed chemical kinetic model and a detailed molecular transport model, including differential diffusion and soret effect. Results indicate that the addition of hydrogen significantly lowers the MIE, and that including radiative heat loss in the model leads to better match with experimental data. ... mehrThe numerical trends agree qualitatively with experimental observations, slight deviations are observed. This work provides insights into the role of radiation, equivalence ratio, and hydrogen addition in influencing ammonia ignition for reaction kinetics based on Glarborg and on Otomo. Furthermore, the analysis reveals that H2O is the primary contributor to radiative heat loss once a self-sustaining flame is formed, while other species dominate during the initial flame kernel formation phase.