Matthew S. Kurman

Preignition and Autoignition Chemistry of the Xylene Isomers

The relative reactivity of the xylene isomers has been compared under preignition and autoignition conditions. Preignition experiments of each isomer with n-dodecane were conducted in a flow reactor facility at 600–850 K temperatures, 0.8 MPa pressure, and 0.23–0.30 equivalence ratios. Stable intermediates identified from xylene oxidation were tolualdehyde, toluene, and cresol, and the xylenes showed similar reactivity. Autoignition experiments of each isomer with n-decane were conducted in a single-cylinder research engine, and o-xylene was the more reactive isomer. Among several proposed JP-8 surrogates containing xylene, a six-component surrogate with m- or p-xylene was found to best approximate the autoignition conditions of average JP-8. The data can be used for the improvement of xylene chemical kinetic models, and the conclusions from this study will aid in the selection of the appropriate xylene isomer for JP-8 surrogate fuels.

Oxidation of Alternative Jet Fuels and their Surrogate Components

Samples of alternative jet fuels, including a coal-derived jet fuel produced from a hydrotreating process and a natural gas-derived jet fuel produced from a Fischer-Tropsch process, were oxidized in complementary experimental facilities to explore the preignition and autoignition behavior of the fuels. Preignition experiments were conducted in a pressurized flow reactor under lean, dilute conditions in the low and intermediate temperature regimes. Autoignition experiments were conducted in a single cylinder research engine. Results were compared to an average sample of petroleum-derived jet fuel. In both facilities, the order of reactivity in descending order was Fischer-Tropsch, petroleum, and coal. The reactivity differences are attributed to composition differences. Possible surrogates and their components were also tested in the facilities to elucidate how compositional differences affect preignition and autoignition chemistry.

Preignition Oxidation Chemistry of the Major JP-8 Surrogate Component: n-Dodecane

Four experiments were conducted to study n-dodecane oxidation at 8 atm for equivalence ratios ranging from 0.23-0.88. The experiments were performed in a pressurized flow reactor under lean, dilute conditions, throughout the low and intermediate temperature regime (600-850 K) to investigate the preignition oxidation chemistry. Samples of intermediate species produced during the oxidation process were collected and analyzed utilizing gas chromatography with flame ionization detection, coupled with mass spectrometry. The identity and quantity of intermediate species produced were similar when comparing the Moderate to High equivalence ratio experiments. However, major differences were apparent when the Moderate and High Phi experiments were compared to the Low equivalence ratio experiment. Experimental results were compared to a semidetailed kinetic model representing a Moderate Phi n-dodecane experiment. The model predicted the general trends of CO and CO2, and the consumption of n-dodecane and O2, reasonably well. Quantitatively in terms of n-dodecane consumption and carbon oxides production, the model underpredicted fuel reactivity, particularly at temperatures above 700 K.