ABSTRACTThis study investigates the differences between oxycombustion and conventional air combustion through methane flame extinction measurements and calculations. We report global extinction strain rates for methane with O2/N2, O2/CO2, and O2/CO2/H2O flames for a range of calculated stoichiometric adiabatic flame temperatures. Tests were performed in a subatmospheric opposed-jet burner, with pre-vaporized water. For a given oxidant diluent, global extinction strain rates increase strongly with increasing flame temperature and with pressure. At a given temperature, the effect of oxidant composition depends on whether dissociation is included in computing the stoichiometric adiabatic flame temperature. When dissociation is included, O2/CO2 and O2/CO2/H2O flames are roughly 30% harder to extinguish than O2/N2 flames. When dissociation is not included, the oxidant composition has a minimal effect. Calculations with the CHEMKIN suite of programs yield the same ranking of extinction strain rate for the diffe...