Time-resolved carbon monoxide measurements during the low- to intermediate-temperature oxidation of n-heptane, n-decane, and n-dodecane

Time-resolved mid-infrared laser absorption measurements of carbon monoxide were carried out during the low- and intermediate-temperature oxidation of n-heptane, n-decane, and n-dodecane in a shock tube. Dilute mixtures of n-alkane/O2/Ar were shock heated, initiating oxidation and resulting in CO formation and heat release with time scales of 1 to 10 ms. Experiments are reported in two temperature and oxygen concentration ranges, 686-797 K at 5% O2 and 1121-1290 K at 0.5% O2, for pressures around 10 atm. For measurements in the lower temperature range, first-stage ignition was observed and found to exhibit negative-temperature-coefficient behavior. The low-temperature reactivity was found to increase with increasing n-alkane chain length and first-stage ignition delay to be well correlated with literature derived cetane numbers. The time-resolved CO measurements and first-stage ignition delay times provide quantitative targets for kinetic models that are sensitive to important low-temperature ignition chemistry; comparisons are made with n-alkane kinetic models from the literature.