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Effects of Composition on the Flame Stabilization of Alternative Aviation Fuels in a Toroidal Well Stirred Reactor

[+] Author Affiliations
Shazib Z. Vijlee

University of Portland, Portland, OR

Igor V. Novosselov, John C. Kramlich

University of Washington, Seattle, WA

Paper No. GT2015-43014, pp. V003T03A007; 12 pages
doi:10.1115/GT2015-43014
From:
  • ASME Turbo Expo 2015: Turbine Technical Conference and Exposition
  • Volume 3: Coal, Biomass and Alternative Fuels; Cycle Innovations; Electric Power; Industrial and Cogeneration
  • Montreal, Quebec, Canada, June 15–19, 2015
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-5667-3
  • Copyright © 2015 by ASME

abstract

The use of alternative/synthetic fuels in jet engines requires improved understanding and prediction of flame stabilization envelopes relative to the behavior of conventional fuels. Previous studies using the Toroidal Well Stirred Reactor (TWSR) found that synthetic alternatives to JP8 behave similarly in terms of lean flameout, but there is significant difference in the flameout behavior of a highly aliphatic fuel versus that of a highly aromatic fuel. Detailed computational fluid dynamics (CFD) and chemical reactor modeling (CRM) is necessary to understand differences in flame stabilization.

The first portion of this study employs CFD models of the TWSR with reduced methane combustion chemistry. The models provide insight into the mechanism of flame stabilization inside the reactor as equivalence ratio is decreased to flameout. The CFD domain is expanded over earlier published TWSR CFD studies to capture previously unknown asymmetrical flame behavior. The Reynolds Stress Model (RSM) is used for turbulence closure, and the Eddy Dissipation Concept (EDC) model is used to include turbulence-chemistry interaction. The CFD results show that radical species (specifically OH) are transported around the reactor to interact with the incoming premixed fuel-air jet and initiate chain branching reactions. As the equivalence ratio decreases, and flameout is approached, the species concentration in the reactor becomes less homogenous. Radical production is delayed and eventually insufficient radical concentrations are available to ignite the incoming jet. The production and transport of radical species throughout the reactor are, thus, responsible for stabilizing the flame. CFD and PSR studies with methane agree that the radical behavior dictates blowout.

The second portion of this study focuses on the importance of radical species in flame stabilization, but now employs a single perfectly stirred reactor (PSR) model, which allows the study of detailed chemistry for individual components of jet fuel. An aliphatic compound (iso-octane) and an aromatic compound (toluene) are used as investigative fuels to compare the differences in the chemical kinetic behavior of blowout for aliphatic versus aromatic fuel classes. The models show that the rates at which radical species (O, H, and OH) destroy the original fuel molecule are significantly different for iso-octane and toluene. During combustion, the radical destruction of toluene is much slower than for iso-octane at a constant temperature. In PSR systems, the toluene flame blows out at a higher temperature because a higher temperature is needed to provide sufficient radical concentrations and reaction rates to maintain a stable flame.

Copyright © 2015 by ASME
Topics: Fuels , Flames , Aviation

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