Experimental and modeling study of the auto-ignition of n-heptane/n-butanol mixtures

Ignition delay times of n-heptane/n-butanol mixtures (neat n-heptane, 80/20, 50/50, 20/80 and neat n-butanol in mole) diluted with argon were measured behind reflected shock waves. The experiments were performed in the temperature range of 1200–1500 K, at pressures of 2 and 10 atm and equivalence ratios of 0.5 and 1.0. Kinetic modeling was conducted for interpreting the oxidation of the fuel mixtures. The computed ignition delay times was then validated against the present measurements as well as the low-temperature data from literatures. It was found that the new blend model can give fairly good prediction on the ignition delay times. Particularly, it well captures the weakened negative-temperature-coefficient (NTC) behavior of the binary mixtures compared to neat n-heptane. Analysis on the effect of chemical structure of n-butanol shows that only a very limited part of n-butanol participates in the low-temperature branching due to the influence of OH group, leading to an increased ignition delay times at low temperature. The competition between n-heptane and n-butanol for OH radicals inhibits the consumption of n-heptane and promotes the consumption of n-butanol. Sensitivity analysis on ignition delay times was conducted and the dominant reactions in the oxidation of binary mixtures at high and low temperatures were identified respectively.