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Experimental and numerical investigation of vitiation effects on the auto-ignition of n-heptane at high temperatures

Zhang, Dexiang, Wang, Yijun, Zhang, Changhua, Li, Ping, Li, Xiangyuan
Energy 2019 v.174 pp. 922-931
air, carbon dioxide, heptane, mathematical models, temperature, water vapor
The ground test in wind-tunnel with high temperatures plays an important role in the scramjet design and refinement. To simulate supersonic flight conditions, combustion-heated approach in ground tests introduces carbon dioxide and water vapor in the test flow. Understanding of vitiation effects is crucial for extrapolating the ground test results to the actual flight conditions. The primary goal of this work is to investigate the vitiation effects of CO2 and H2O on auto-ignition of n-heptane. With 20% CO2 or H2O replacement of N2 in air, ignition delay times of n-heptane/air were investigated behind reflected shock waves at temperatures of 1050–1400 K, pressures of 2 and 10 atm, and with equivalence ratios of 1.0 and 0.5. The addition of CO2 shows slightly inhibiting effect, whereas H2O shows a promoting effect on the ignition of n-heptane. Further numerical simulations of kinetic mechanism were performed to investigate the thermal, chemical and third-body collision effects of CO2 and H2O separately. Results indicated that the thermal effect of CO2 is the dominant factor for the inhibiting effect on n-heptane ignition, and the third-body collision of H2O is the major factor promoting the ignition of n-heptane.