Understanding of MILD Combustion Characteristics of NH3 Air Flames in N2 And H2O Steam Diluted Environment at Atmospheric Pressure

Abstract

Ammonia is becoming increasingly popular as a carbon-neutral fuel with zero carbon dioxide emissions. However, a significant hurdle lies in its combustion, which leads to substantial emissions of NOx. The current research involves conducting a chemical kinetic investigation to examine the characteristics of Intense Low oxygen Dilution (MILD) or Moderate combustion in ammonia (NH₃)/air flames. This study is carried out under specific conditions, such as oxygen concentrations ranging from 11to 23%, premixed reactant temperatures between 1300 and 1700 K, and a pressure of one atmosphere. The study focuses on investigating the combustion characteristics of MILD using dilution with H₂O and N₂.With the rise in the inlet temperature of the premixed reactant, the peak temperature of the flame also rises. Moreover, flames diluted with H₂O exhibit lower peak temperatures compared to flames diluted with N₂.Flames diluted with H₂O result in lower NOx emissions compared to flames diluted with N₂. Additionally, for N₂diluted flames, the exit NOx emissions rise as the oxygen concentration increases.Despite this, NOx emissions from H₂Odiluted flames demonstrate non-monotonic behaviour.This means that the exit NOx increases initially as the oxygen concentration reaches 21%, but then begins to decrease. In contrast to N₂and H₂Odiluted flames exhibits a wider regime of no-ignition.Moreover, the rise in peak temperature in H₂Odiluted flames is less apparent than in N₂diluted flames, corresponding to broader ranges MILD combustion ranges.Furthermore, to attain MILD combustion in H₂O diluted flames at a specific O₂ concentration, the temperature of reactant needs to be higher than that required for N₂diluted flames.