The use of alternative/synthetic fuels in jet engines requires improved understanding and prediction of the performance envelopes and emissions characteristics relative to the behavior of conventional fuels. In this study, experiments in a toroidal well-stirred reactor (TWSR) are used to study lean premixed combustion temperature and extinction behavior for several fuels including simple alkanes, synthetic jet fuels, and conventional JP8. A perfectly stirred reactor (PSR) model is used to interpret the observed behavior.

The first portion of the study deals with jet fuels and synthetic jet fuels with varying concentrations of added aromatic compounds. Synthetic fuels contain little or no natural aromatic species, so aromatic compounds are added to the fuel because fuel system seals require these species to function properly. The liquid fuels are prevaporized and premixed before being burned in the TWSR. Air flow is held constant to keep the reactor loading roughly constant. Temperature is monitored inside the reactor as the fuel flow rate is slowly lowered until extinction occurs. The extinction point is defined by both its equivalence ratio and temperature. The measured blowout point is very similar for all four synthetic fuels and the baseline JP8 at aromatic concentrations of up to 20% by volume. Since blowout is essentially the same for all the base fuels at low aromatic concentrations, a single fuel was used to test the effect of aromatic concentrations from 0 to 100%. PSR models of these complex fuels show the expected result that behavior diverges from an ideal, perfectly premixed model as the combustion approaches extinction.

The second portion of this study deals with lean premixed combustion of simple gaseous alkanes (methane, ethane, and propane) in the same TWSR. These simpler fuels were tested for extinction in a similar manner to the complex fuels, and behavior was characterized similarly. Once again, PSR models show that the TWSR behaves similar to a PSR during stable combustion far from blowout, but as it approaches blowout and becomes less stable a single PSR no longer accurately describes the TWSR.

This work is a step towards developing chemical reactor networks (CRNs) based on computational fluid dynamics (CFD) of the simple gaseous fuels in the TWSR. Ultimately, CRNs are the only realistic way to accurately perform detailed chemical modeling of the combustion of complex liquid fuels.

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