An experimental investigation into the effect of spark gap and duration on minimum ignition energy of partially dissociated NH3 in air

This paper presents an experimental investigation into the effect of spark gap and spark duration on the minimum ignition energy (MIE) of partially dissociated NH3 in air at 295 K and 1 atm. The measurements were carried out using a Hartmann bomb apparatus with the degree of NH3 dissociation varying from 0 to 10%, corresponding to 0 to 7.5%v/v H-2 in the fuel mixture with a fixed H-2/N-2 ratio of 3, and equivalence ratio varying from 0.7 to 1.2, assuming complete oxidation. Axisymmetric two-dimensional CFD modelling was performed using Ansys Fluent incorporating the Okafor mechanism to predict MIE. At a given equivalence ratio, both measured and predicted MIE values decreased significantly with increasing the degree of NH3 dissociation, due to increased presence of H-2 in the mixture. There were optimum spark gap and spark duration for a given degree of NH3 dissociation and equivalence ratio at which the MIE was the lowest. The increased presence of H-2 due to rising degree of NH3 dissociation enhances the mixture's oxidation reactivity and combustion intensity, which in turn increases the flame kernel temperature and size, the rate of production of key radicals (OH, NH2, H, and O) and rate of heat generation, leading to a more self-sustaining flame and significantly reduced MIE. (c) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This paper investigates the effect of spark gap and spark duration on the minimum ignition energy (MIE) of partially dissociated NH3 in air. The results show that increasing the degree of NH3 dissociation significantly reduces the MIE. Moreover, there are optimal spark gap and spark duration for achieving the lowest ignition energy, considering the specific degree of NH3 dissociation and equivalence ratio.