Ignition delay times of low-vapor-pressure fuels measured using an aerosol shock tube

Abstract

Gas-phase ignition delay times were measured behind reflected shock waves for a wide variety of low-vapor-pressure fuels. These gas-phase measurements, without the added convolution with evaporation times, were made possible by using an aerosol shock tube. The fuels studied include three large normal alkanes, n-decane, n-dodecane and n-hexadecane; one large methyl ester, methyl decanoate; and several diesel fuels, DF-2, with a range of cetane indices from 42 to 55. The reflected shock conditions of the experiments covered temperatures from 838 to 1381 K, pressures from 1.71 to 8.63 atm, oxygen concentrations from 1 to 21%, and equivalence ratios from 0.1 to 2. Ignition delay times were measured using sidewall pressure, IR laser absorption by fuel at 3.39 μm, and CH * and OH * emission. Measurements are compared to previous studies using heated shock tubes and current models. Model simulations show similar trends to the current measurement except in the case of n-dodecane/21% O 2/argon experiments. At higher temperatures, e.g. 1250 K, the measured ignition delay times for these mixtures are significantly longer in lean mixtures than in rich mixtures; current models predict the opposite trend. As well, the current measurements show significantly shorter ignition delay times for rich mixtures than the model predictions.