Measurement of time histories of stable intermediates during first stage ignition of n-heptane and its two isomers in a shock tube

The first shock tube measurements of formaldehyde during the first stage ignition of n-heptane, 2-methylhexane, and 3,3-dimethylpentane were performed in highly diluted fuel/oxygen mixtures in the pressure range of 7–10 atm and temperature range of 700–880 K. Combined time histories of all carbonyl (–C = O) species, CO, and fuel were also measured simultaneously to study the impact of fuel structure on the concentration and the rate of evolution of first stage ignition products. Of the three isomers considered, n-heptane was the fastest, while 3,3-dimethylpentane was the slowest. The differences in the time scale of formation, and plateau concentration of the intermediates between the isomers across the entire range of test conditions suggested a strong dependency of the measured time histories to fuel structure. These species act as markers of the Negative Temperature Coefficient behavior of fuels and could be used as targets for developing semi-empirical, hybrid chemistry models of complex, multi-component petroleum derived gasoline, and jet fuels.