Influence of CF3I and CBrF3 on Methanol–Air and Methane–Air Premixed Flames

Abstract

The suppression of CH4 and CH3OH premixed flames with CBrF3 and CF3I is examined, using computational techniques. By combining sensitivity analysis, reaction pathway analysis (based on carbon, hydrogen, bromine and iodine atom fluxes) and heat release estimation, we develop an explanation for the difference of suppression efficiencies which is qualitatively consistent with experimental cup burner data. The key reaction steps and channels responsible for the (apparent) higher inhibition efficiency of CF3I compared to CBrF3 in CH3OH premixed flames are disclosed, by combining reaction pathway and heat release contribution analysis. The reaction of bromine atom dominates the decomposition channel for CH3OH but plays a relatively minor role in the activation of CH4, while I atom plays a minor role in CH3OH or CH4 activation. Accordingly, the rate of production of flame propagating radicals CH2O and OH is higher in a CH3OH–air–CBrF3 system than in a CH3OH–air–CF3I system. The overall conclusion is that CBrF3 contributes significantly to flame propagation for CH3OH fuel reactions and consequently more CBrF3 is required to extinguish a CH3OH flame than CF3I. Finally the explanation is validated by applying the reaction “switching-off” test.