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A propane-fueled research combustor has been designed to represent the essential features of primary zones of combustors for aircraft gas turbine engines in an investigation of lean blowouts. The atmospheric pressure test facility being used for the investigation made it difficult to approach the maximum heat release condition of the research combustor directly. High combustor loadings were achieved through simulating the effects on chemical reaction rates of subatmospheric pressures by means of a nitrogen diluent technique. A calibration procedure is described, and correlated experimental lean blowout results are compared with well-stirred reactor calculations for the research combustor to confirm the efficacy of the calibration.

The Eddy Dissipation Concept (EDC), proposed by Magnussen (1985), advances the concept that the reactants are homogeneously mixed within the fine eddy structures of turbulence and that the fine structures may therefore be regarded as perfectly stirred reactors (PSRs). To understand more fully the extent to which such a subgrid scale stirred reactor concept could be applied within the context of a computational fluid dynamics (CFD) calculation to model local or global extinction phenomena: (1) Various kinetic mechanisms are investigated with respect to CPU penalty and predictive accuracy in comparisons with stirred reactor lean blowout (LBO) data and (2) a simplified time-scale comparison, extracted from the EDC model and applied locally in a fast-chemistry CFD computation, is evaluated with respect to its capabilities to predict attached and lifted flames. Comparisons of kinetic mechanisms with PSR lean blowout data indicate severe discrepancies in the predictions with the data and with each other. Possible explanations are delineated and discussed. Comparisons of the attached and lifted flame predictions with experimental data are presented for some benchscale burner cases. The model is only moderately successful in predicting lifted flames and fails completely in the attached flame case. Possible explanations and research avenues are reviewed and discussed.

This paper presents results from an Air Force program being conducted by researchers at Brigham Young University (BYU) Wright-Patterson Air Force Base (WPAFB), and Pratt and Whitney (P&W). This study is part of a comprehensive effort being supported by the Aero Propulsion and Power Laboratory at Wright-Patterson Air Force Base, and Pratt and Whitney in which simple and complex diffusion flames are being studied to understand better the fundamentals of gas turbine combustion near lean blowout. The program's long-term goal is to improve the design methodology of gas turbine combustors. This paper focuses on four areas of investigation: (1) digitized images from still film photographs to document the observed flame structures as fuel equivalence ratio was varied, (2) sets of LDA data to quantify the velocity flow fields existing in the burner (3) CARS measurements of gas temperature to determine the temperature field in the combustion zone, and to evaluate the magnitude of peak temperature, and (4) two-dimensional images of OH radical concentrations using PLIF to document the instantaneous location of the flame reaction zones.

Measurements of the emissions from an experimental engine were analyzed to construct a design chart for the reduction of oxides of nitrogen (NOx) in conventional combustors. The design chart was used to reconfigure the stoichiometry distribution of the combustor of a production engine so as to reduce NOx while holding the emissions of carbon monoxide, unburned hydrocarbons, and smoke well below existing regulations. Combustion section pressure loss and combustor outlet temperature distributions were substantially unchanged. The modified design was refined with the aid of computational fluid dynamics calculations to optimize the emissions reduction. Worthwhile reductions in NOx were obtained with combustor modifications that are transparent to the engine user.

Experimental information is presented on the effects of back-pressure on flame-holding in a gaseous fuel research combustor. Data for wall temperatures and static pressures are used to infer behavior of the major recirculation zones, as a supplement to some velocity and temperature profile measurements using LDV and CARS systems. Observations of flame behavior are also included. Lean blowout is improved by exit blockage, with strongest sensitivity at high combustor loadings. It is concluded that exit blockage exerts its influence through effects on the jet and recirculation zone shear layers.

A propane-fueled research combustor has been designed and developed to investigate lean blowouts in a simulated primary zone of the combustors for aircraft gas turbine engines. To understand the flow development better and to ensure that the special provisions in the combustor for optical access did not introduce undue influence, measurements of the velocity fields inside the combustor were made using laser-DOppler anemometry. These measurements were made in isothermal, constant density flow to relate the combustor flow field development to known jet behavior and to backward-facing step experimental data in the literature. The major features of the flow field appear to be consistent with the expected behavior, and there is no evidence that the provision of optical access adversely affected the flows measured., A research combustor is developed to study lean blowouts in a simulated primary zone of combustors for aircraft gas turbine engines. The combuster is equipped with an optical access window to allow velocity measurements using the laser-Doppler anemometer system. Measurements are based on constant, isothermal density flow conditions. Results indicate three regions of flow development and that flow features can be computed using integration techniques for fluid dynamics. The presence of an optical window did not affect flow measurements.

A research combustor is designed and developed to simulate the recirculation patterns and lean blow-out (LBO) processes found in a real aircraft gas turbine engine combustor. The design constraints, aerothermochemical design, choice of configurations, combustor sizing, mechanical design, combustor light-off and acoustic characteristics for the research combustor are presented. Results show that the combustor provides significant data for estimating LBO in actual combustors.