Effects of vitiation and pressure on laminar flame speeds of n-decane

Air Force Research Laboratory, Wright Patterson Air Force Base, Dayton, OH, 45433 There is currently a lack of experimental data required for kinetic model validation of the effect of oxidizer vitiation on laminar flame speeds of aviation fuels. This study examines the role of vitiation through the introduction of CO₂ and H2O to the oxidizer stream at varying pressures (0.5-5.0 atm) at 450 K, conditions relevant to vitiated combustion devices, using n-decane as the model fuel. The experimental portion of this effort has acquired laminar flame speed data of n-decane in vitiated air using two separate techniques. A well-validated Bunsen Flame Technique was used to primarily examine the effect of total dilution and vitiation over a range of equivalence ratios and the Combustion Bomb Technique was used to investigate vitiation effects at various pressures and equivalence ratios. Overlap between measurement techniques has been performed as well as comparison to an analytical model to better understand the thermodynamic and chemical kinetic effects that vitiation has on hydrocarbon fuel combustion and flame structure. Experimental data shows that CO₂ has the largest effect in reducing the flame speed over the range of equivalence ratios and pressures studied. Based on a kinetic analysis, chemical kinetic effects play a major role in reducing the flame speed when CO₂ is present. The impact of chemical kinetic effects due to the diluent species on flame speed was found to have the following trend: CO₂ > H2O > N2.