Autoignition of heptanes; Experiments and modeling

There is much interest in determining the influence of molecular structure on the rate of combustion of hydrocarbons; the C7H16 isomers of heptane have been selected here as they exemplify all the different structural elements present in aliphatic, noncyclic hydrocarbons. With the exception of n-heptane itself, no autoignition studies have been carried out to date on the other isomers of heptane at high temperatures. Therefore, ignition delay times were measured for the oxidation of four isomers-n-heptane, 2,2-dimethylpentane, 2,3-dimethylpentane, and 2,2,3-trimethylbutane-under stoichiometric conditions at a reflected shock pressure of 2 atm, within the temperature range of 1150-1650 K. Measurements under identical conditions reveal that they all have essentially the same ignition delay time; this confirms earlier theoretical predictions based purely on detailed chemical kinetic modeling. The variation of ignition delay times for n-heptane with changing oxygen concentrations and reflected shock pressure was determined and shown to follow expected trends. (c) 2005 Wiley Periodicals, Inc.