Experimental and modeling study on the oxidation of Jet A and the n-dodecane/iso-octane/n-propylbenzene/1,3,5-trimethylbenzene surrogate fuel

Abstract

Jet A POSF 4658 and n-dodecane/iso-octane/n-propylbenzene/1,3,5-trimethylbenzene (2nd generation surrogate) oxidation experiments were conducted in a shock tube at high pressures and at fuel lean and rich conditions to verify if the formulated surrogate fuel emulates the combustion characteristics of the jet fuel. A model was developed for the 2nd generation surrogate using an existing 1st generation surrogate model (consisting of n-decane/iso-octane/toluene) as the base model and sub-models for n-propylbenzene and 1,3,5-trimethylbenzene were included from the literature. The experimental work on both the Jet A and 2nd generation surrogate was performed in a heated high-pressure single pulse shock tube at equivalence ratios of 0.46, 1.86 and 0.47, 1.85, respectively. Experimental data were obtained over the temperature range of 879–1733K, a pressure range of 16–27atm, and reaction times from 1.34 to 3.36ms. The mole fractions of the stable species were determined using gas chromatography and mass spectroscopy. Comparing the Jet A and the 2nd generation surrogate experiments showed that the surrogate fuel emulates the decay of O2, and the formation of CO, CO2, and C1–C3 intermediate species within experimental errors. The modeling results of the 2nd generation surrogate model compared against the experimental data showed good agreement with the mole fractions of CO, CO2, C1–C3 intermediate species and the decay of the surrogate fuel and oxygen. Comparison of the modeling results for O2 decay to the 2nd generation surrogate experiments and pure 1,3,5-trimethylbenzene oxidation experiments revealed that the surrogate fuel model is capable of predicting O2 decay with a greater degree of accuracy in the 2nd generation surrogate experiments than in that of pure 1,3,5-trimethylbenzene experiments. This suggests that the radical pool formed due to the non-aromatics species during the consumption of 2nd generation surrogate fuel components prior to the formation of CO and CO2 could contribute to the initial decay of O2 at lower temperatures and thereby results in better prediction by the model, which includes both non-aromatics and aromatics chemistry, of O2 decay and formation of CO and CO2. Flow reactor simulations of the 2nd generation surrogate fuel experiments showed the surrogate model captures the overall trends of the decay of O2 and the formation of CO, CO2, and H2O. Additionally, simulated shock tube ignition delay times above 750K were within a factor of two when compared to experimental ignition delay times.