Low temperature oxidation of n-butylcyclohexane

Abstract

n-Butylcyclohexane, a possible surrogate component for petroleum- and coal-derived jet fuels, was oxidized in a flow reactor through the low temperature region from 600 to 820 K while other inlet conditions were held constant (0.8 MPa pressure, 0.120 s residence time, and 0.38 equivalence ratio). CO, CO 2, and O 2 were measured over the entire range of temperatures and stable intermediate species were collected at five temperatures and analyzed using a gas chromatograph/flame ionization detector/mass spectrometer. The measured species indicated that the n-butyl chain and the cyclohexane ring interact at low temperatures and result in low temperature reactivity similar to linear alkanes. At similar inlet conditions (0.8 MPa pressure, 0.120 s residence time, and 0.30 equivalence ratio), methylcyclohexane and n-butylbenzene, each neat, were oxidized in the reactor from 600 to 800 K and no reactivity was observed. This indicated the importance of the alkyl chain in low temperature oxidation of alkylcyclohexanes. To confirm that current understanding of low temperature oxidation chemistry of alkanes applies for n-butylcyclohexane, a preliminary reaction set, composed of 80 reactions and 42 species, was developed and incorporated into an existing high temperature jet fuel surrogate model. The new reaction scheme required calculation of thermochemistry for several compounds. The combined model predicts the overall low temperature reactivity of n-butylcyclohexane oxidation at the experimental conditions.