Program Summary: High Pressure Ring Contraction of Cyclic Hydrocarbons

.    The behaviors of cyclic hydrocarbons in the supercritical fluid phase and in the gas phase at high pressures and temperatures are of interest because their chemical breakdowns will affect their performance in future combustion engines. These fuels undergo increasing amounts of ring contraction under these conditions instead of fragmentation into smaller molecules leading to increased soot and coke formation. Ring contraction has been attributed to molecular caging effects on the fuel by the solvent, but more plausible hypotheses for ring contracted products can also be explored. We are examining these hypotheses directly through pyrolysis studies of selected radicals in a high pressure shock tube, where the use of an argon bath will rule out any additional solvent effects.

.    The research work consists of shock tube pyrolysis studies of dilute quantities of  radical precursors, and of  stable cyclic molecules at high temperatures, 1000-1300K, pressures from atmospheric to 1000 bar, in argon, with hydrocarbon pyrolysis product species sampling to identify fuel fragment species. Studies will be performed with the high pressure single pulse shock tube at the University of Illinois at Chicago (UIC) up to 1000 bar and in the low pressure single pulse shock tube below 15 bar.





Program Summary: Pyrolysis and Oxidation Studies of Real Propulsion Fuels

.    The aim of this program is to provide experimentally determined concentrations of intermediate chemical products of the pyrolysis and oxidation of currently used military jet fuels as a function of temperature and pressure. These values are expected to serves as inputs into emerging models for fuel combustion that have taken advantage of the observation that within a given combustion reaction, there is a separation in time, temperature, and position within a combustion chamber between the pyrolysis process pathways—which can be lumped together for kinetics modeling—and the onset of oxidation. This two-stage or hybrid approach allows the modeling of both pyrolysis and oxidation to be simplified, which can then lead to greater applicability of these predictive models for actual fuels. The chemical kinetics of real military fuels will be studied in the context of the hybrid model of lumped pyrolysis and detailed (foundational) oxidation chemistry over a wider range of propulsion fuels, pressures, and intermediate species than in previous studies. Such new studies are made possible by the well-established and proven UIC Single Pulse Shock Tubes. Experiments will be conducted over the pressure range of 15-100 bar, a temperature range of 1100-1400K, and a nominal reaction time of 2-6 milliseconds.