Shock tube study of n-nonane/air ignition over a wide range of temperatures

Ignition delay experiments for gas phase n-nonane/air mixtures have been performed behind reflected shock waves over a wide temperature range of 684-1448 K, pressures of 2.0-15.0 atm, and equivalence ratios of 0.5, 1.0, and 2.0. Ignition delay times were determined using electronically excited CH emission and reflected shock pressure signals monitored at the sidewall of the shock tube. A negative-temperature-coefficient (NTC) behavior of n-nonane/air ignition was observed at temperatures of 800-950 K. Dependence of ignition delay time upon temperature, pressure, and equivalence ratio was investigated systematically. High temperature (T > 1000 K) results show that the effect of equivalence ratio on ignition delay times is different at low and high pressures. In the NTC region, ignition delay times are highly sensitive to equivalence ratio and pressure. The present ignition data are in satisfactory agreement with predictions of two widely used chemical kinetic mechanisms. Sensitivity and reaction pathway analyses reveal that the dominating reactions affecting ignition delay times and reaction pathways during ignition process for n-nonane/air are quite different at high and low temperatures. Comparison of n-nonane/air ignition delay times with those of other larger n-alkanes (n-heptane, n-octane, n-decane, n-dodecane, and n-tetradecane) indicates that the length of n-alkanes chain influences little on ignition delay times of n-alkanes. The present results are useful for understanding ignition characteristics of n-nonane and providing experimental data to validate chemical kinetic mechanisms for n-nonane.