Effect of fuel type on the extinction of fuel and air stream diluted partially premixed flames

Previous investigations have demonstrated that the roles of fuel stream dilution (FSD) and air stream dilution (ASD) in suppressing CO2-diluted methane flames are strongly influenced by the level of partial premixing. Herein, we compare this influence for both counterflow and coflow laminar non-premixed and partially premixed flames (PPFs) established with various fuels, including methane, ethylene and acetylene. We find that ethylene and acetylene flames are more difficult to extinguish than those burning methane. For methane, FSD is more effective in suppressing PPFs while ASD suppression is more effective for non-premixed flames (NFs). In contrast, FSD suppression is typically more effective than with ASD for the corresponding ethylene and acetylene flames irrespective of the level of partial premixing. ASD is ineffective in suppressing the investigated coflow ethylene and acetylene flames. For counterflow flames, FSD is more effective in suppressing PPFs while ASD is more effective in suppressing NFs irrespective of the fuel burned but the range of equivalence ratios for the relative effectiveness of FSD and ASD depends strongly on the fuel. There is a linear correlation between the transition equivalence ratio at which the effectiveness switches from FSD to ASD, and the rich flammability limit for all three fuels.