Effects of diluents on the ignition of premixed H₂/air at micro-gravity conditions

A computational study was performed to investigate the effects of diluents (He, Ar, or CO₂) on the ignition of premixed H₂/air mixtures. The objective of this study was to assess and explain the change of the minimum ignition energies (MIE) with the dilution ratio. It was found that, at the same dilution ratio, the MIE of He dilution was always higher than that of Ar dilution. The MIE of CO₂ dilution was between those for He and Ar dilution at a low value of the dilution ratio, while it was higher than those for He and Ar dilution at a high value of the dilution ratio. The thermal and flame-dynamic effects of dilution were discussed to explain the change of the MIE with the dilution ratio.