Shock Tube Study of Ignition Delay Characteristics of n‑Nonane and n‑Undecane in Argon

Ignition delay times of n-nonane and n-undecane in 4% oxygen/argon have been measured behind reflected shock waves in a heated shock tube at temperatures of 1168–1600 K, pressures of 2, 10, and 20 atm, and equivalence ratios of 0.5, 1.0, and 2.0. Ignition delay times are determined by using CH* emission and pressure signals monitored at the sidewall. Results show that ignition delay times of two fuels decrease as the temperature or pressure increases, and a decrease in equivalence ratio results in a shorter ignition delay time. For fuel-lean and stoichiometric mixtures, n-nonane has ∼25%–35% longer ignition delay times than n-undecane. For fuel-rich mixtures, ignition delay times of two fuels are very close. Correlations for ignition delay times of two fuels as a function of temperature, pressure, and equivalence ratio are formulated through regression analysis. The experimental data are in good agreement with shock tube data available, and the trends of experimental data were captured well by the predictions from the LLNL and JetSurF mechanisms under conditions studied. Comparison of ignition delay times for nine n-alkanes from propane to n-undecane reveals that the n-alkanes have the similar ignition delay behavior and their ignition delay times are close to each other. Reaction path analyses and sensitivity analyses are performed to investigate the consumption of fuels and identify the important reactions in the ignition process. To our knowledge, we provide the first ignition delay time data for n-undecane at elevated pressures, and our measurements for n-nonane are at a broader range of conditions than previous studies. Current results contribute toward understanding the ignition characteristics of n-nonane and n-undecane, and they provide validation targets for corresponding kinetic mechanisms.