Craig Neuroth

Temperature Measurements in a Gas-Turbine-Combustor Sector Rig Using Swept-Wavelength Absorption Spectroscopy

Gas-temperature measurements in the combustion zone of a high-pressure gas-turbine-combustor sector rig were made with a Fourier-domain mode-locked laser using wavelength-agile absorption-spectroscopy techniques. These measurements are among the first employing broadband high-resolution absorption spectroscopy in gas-turbine-engine environments. Compared with previous measurements in reciprocating engines and shock tubes, signal contamination from thermal emission was stronger in this combustor rig; methods for managing emission during experimental planning and postprocessing are discussed. H 2 O spectra spanning 1330―1380 nm (which includes the ν 1 + ν 3 and 2ν 1 overtone bands) are presented along with a method for calculating gas temperatures from the spectra. The resulting temperatures are reported for a variety of combustor conditions. These tests show promise for simple gas-turbine sensors and potential for more detailed experiments involving tomographic reconstruction or multispecies concentration measurements.

Experimental and Computational Studies of an Ultra-Compact Combustor

Reducing the weight and decreasing pressure losses of aviation gas turbine engines improves the thrust-to-weight ratio and improves efficiency. In ultra-compact combustors (UCCs), engine length is reduced and pressure losses are decreased by merging a combustor with adjacent components using a systems engineering approach. High-pressure turbine inlet vanes can be placed in a combustor to form a UCC. Eliminating the compressor outlet guide vanes (OGVs) and maintaining swirl through the diffuser can result in further reduction in engine length and weight. Cycle analysis indicates that a 2.4% improvement in engine weight and a 0.8% increase in thrust-specific fuel consumption are possible when a UCC is used. Experiments and analysis were performed in an effort to understand key physical and chemical processes within a trapped-vortex UCC. Experiments were performed using a combustor operating at pressures in the range of 520–1030 kPa (75–150 psi) and inlet temperature of 480–620 K (865–1120 °R). The primary reaction zone is in a single trapped-vortex cavity where the equivalence ratio was varied from 0.7 to 1.8. Combustion efficiencies and NOx emissions were measured and exit temperature profiles obtained, for various air loadings, cavity equivalence ratios, and configurations with and without turbine inlet vanes. A combined diffuser-flameholder (CDF) was used in configurations without vanes to study the interaction of cavity and core flows. Higher combustion efficiency was achieved when the forward-to-aft momentum ratios of the air jets in the cavity were near unity or higher. Discrete jets of air immediately above the cavity result in the highest combustion efficiency. The air jets reinforce the vortex structure within the cavity, as confirmed through coherent structure velocimetry of high-speed images. A more uniform temperature profile was observed at the combustor exit when a CDF is used instead of vanes. This is the result of increased mass transport along the face of the flame holder. Emission indices of NOx were between 3.5 and 6.5 g/kgfuel for all test conditions. Ultra-compact combustors (with a single cavity) can be run with higher air loadings than those employed in previous testing with a trapped-vortex combustor (two cavities) with similar combustion efficiencies being maintained. The results of this study suggest that the length of combustors and adjacent components can be reduced by employing a systems level approach.Copyright

High -Pressure Tests of a High -g, Ultra -Compact Combustor

The Ultra-Compact Combustor (UCC) is part of evolving technology in the development of near-constant-temperature-cycle gas turbine engines. This technology can provide a significant reduction in engine weight and size while providing large amounts of power. The UCC uses high swirl in a circumferential cavity to enhance reaction rates via high cavity gloading on the order of 3000 g’s. Increase in reaction rates translates to a reduced combustor volume. Axial flame lengths are extremely short, at about 50% those of conventional systems. High-pressure UCC tests conducted in the Air Force Research Laboratory (AFRL) High Pressure Combustor Research Facility (HPCRF) have demonstrated the feasibility of using UCC technology in advanced main combustor and Inter-Turbine Burner (ITB) systems. The UCC design integrates compressor and turbine features which will enable a shorter and less complex gas turbine engine. Experimental results from UCC testing at elevated pressure indicated that the combustion system operates at 95-99 percent efficiency over an increased operating range compared to conventional gas turbine combustion systems burning JP-8+100 fuels. This paper will describe experimental results from one UCC configuration.

Experimental Characterization of the Reaction Zone in an Ultra-Compact Combustor

Significant benefits can be obtained with respect to engine thrust-to-weight ratio and specific fuel consumption if the length, weight, and pressure drop of the combustor can be reduced. The ultra-compact combustor (UCC) has the potential to aid the realization of these benefits by integrating neighboring components such as the compressor exit diffuser and the turbine inlet guide vanes (IGV) within the combustor using a systems-level engineering approach. The UCC presented here utilizes a trapped-vortex cavity. This combustor design has been shown to exhibit larger turn-down ratios, higher flame stability, shorter flame lengths, and acceptable NOx emissions when compared to conventional richburn, quick-quench, lean-burn combustors. The axial distance required to complete combustion within the mainstream dictates a minimum combustor length for obtaining acceptable levels of combustion efficiency. Hence, characterization of the reaction zone within a UCC is required to optimize the length. In this study OH* chemiluminescence imaging is used to assess the characteristics of the reaction zone via windows in the side and top of the combustor. CO, NOx, and total hydrocarbon (THC) emissions indices obtained with gas-sample probes at the exit of the combustor as well as computed combustion efficiencies are provided as a reference for the OH* chemiluminescence. Configurations with no turning vanes (CDF and CDF-2), with standard vanes (CDF-2SV), and with radialvane-cavity (RVC) vanes (CDF-2RV) were used. The first study shows that the CDF-2 configuration has similar combustion efficiencies compared to that of the previously studied CDF configuration between 0.6 1.1 but has a higher peak OH* intensity and higher window exit intensity than that of the CDF configuration. The second study shows that the addition of standard vanes to the UCC decreases the peak and exit OH* intensities and lowers the exit temperature peak to 30% height, while the addition of the RVC vane tends to increase the peak and exit OH* intensities and raise the exit temperature peak to 50% height. Combustion efficiencies are similar for the CDF-2, CDF-2SV, and CDF-2RV configurations up to = 1.1. Combustion efficiency remains above 99% for the CDF2SV configuration up to = 2.0. The third study shows that OH* intensity increases

Numerical-Experimental Research of Ultra Compact Combustors containing Film and Effusion Cooling

A novel Ultra-Compact Combustor (UCC) that operates as a main combustor in a gas turbine engine is modeled with the Trapped Vortex Combustor (TVC) incorporating three inlet guide vanes (IGVs), containing no radial vane cavities (RVC), and three deswirler vanes located further downstream (Configuration 1). This geometry is compared with another configuration containing three IGVs with a full-through RVC (Configuration 2e). The steady threedimensional equations of continuity, momentum, turbulence, total enthalpy (H), C-progress variable (C), Favre mixture fraction (f), and Favre mixture fraction variance (f ` ) in Eulerian reference frame as well as the n-dodecane liquid-fuel droplet trajectory, and heat and mass exchange with the continuum phase in a Lagrangian frame are solved using FLUENT. This combustion model is referred as a partially premixed combustion (PPC) model. The PPC flamelets are calculated by solving the laminar n-dodecane/air counterflow non-premixed flame equations in a mixture fraction (f) space using the JetSurf-ls-1.0 chemical reaction mechanism containing 100 species and 856 Arrhenius reactions. A -shape probability density function (PDF) table containing density (ρ), species (Y ), and temperature (T) as function of f, f ` , H,  , and C is generated. Turbulence is modeled using the Realizable k- RANS governing equations. Liquid fuel is injected through the TVC (which contains air driver jets and effusion and film cooling jets) with a local TVC equivalence ratio of TVC1.39 (excluding cooling air) and TVC0.84 (including cooling air). The global equivalence ratio is Global= 0.066 (without cooling air), or Global= 0.059 (with cooling air). The jets involved in film cooling are resolved, whereas the effusion cooling jets are modeled as source terms because there are thousands of tiny injections with geometrical sizes comparable to that of the cells near the boundary conditions. Therefore, meshing these tiny design features would be prohibitive. Nevertheless, accurate numerical predictions call for inclusion of these effusion cooling jets in the simulated approached adopted here because their total air mass flow rate constitutes a substantial fraction of the total overall mass flow rate. Consequently, the effusion cooling jets are introduced in the model as volumetric mass flow rate and momentum source terms in the cells adjacent to the relevant boundary conditions. Simulations are compared with measurements conducted at the High Pressure Combustor Research Facility (HPCRF) located at Wright-Patterson AFB (WPAFB). This paper presents flow/flame structure, exit temperature profiles, and global performance parameters of the two UCC-TVC-IGV configurations operating at 514,762.6 Pa. Numerical results indicate that liquid fuel that is injected in the TVC as a conical spray of droplets evaporates and boils almost immediately after injection within the TVC cavity. A turbulent triple flame containing multiple reaction zones, viz., rich premixed (RPRZ), nonpremixed (NPRZ), and lean premixed (LPRZ), is attached to the TVC. Both UCC-TVC-IGV configurations show a single dominating vortex in the TVC cavity rotating in opposite direction to the mainstream flow. Generally, hightemperature regions correspond to near-stoichiometric fuel/air mixtures, whereas low temperature regions are associated with off-stoichiometric fuel/air mixtures. Increasing scalar dissipation ( ), enhancing heat losses, and flame front regions (0.0<C<1.0) reduce the temperature (T) below its corresponding adiabatic equilibrium temperature. Configuration 1 shows a more uniform temperature flow field in comparison with Configuration 2e. For the former the temperature is more equally distributed in the spanwise direction within the TVC cavity than for the latter configuration. In addition, for Configuration 1 the temperature decreases in the normal direction whereas for Configuration 2e the temperature increases in the normal direction away from the TVC cavity. However, in both configurations the Mach number does not exceed 0.5, and it is maximum downstream the TVC cavity along the IGV suction sides, and peaks at the deswirler vane leading edges. Good comparison between the measured IGV heat signature and the predicted temperature contours on the IGV was achieved. The model predicts good effusion cooling. However, where film cooling is used there is a temperature distribution such as in the aft wall of the TVC 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 07 10 January 2013, Grapevine (Dallas/Ft. Worth Region), Texas AIAA 2013-1045

Experimental Studies of a High-g Ultra-Compact Combustor at Elevated Pressures and Temperatures

Volatile fuel costs have initiated a global sprint for technologies that will increase fuel efficiency in gas turbine engines, which continue to be a primary propulsion system for commercial and military aircraft. The Ultra-Compact Combustor (UCC) is an advanced gas turbine combustor which integrates the high pressure turbine inlet guide vanes into the combustor. In comparison to conventional combustor systems, the UCC has the potential to shorten engine length, decrease engine weight, and reduce pressure losses entering the high pressure turbine rotor, all of which contribute subtantially to improving engine efficiency. The UCC has been studied in two forms in the literature – the Trapped-Vortex concept (TV) and the High-g concept (HG); the current study focuses on the latter. The HG-UCC utilizes a rectangular cavity wrapped around the outside circumference of the combustor where fuel and air are injected in a manner that generates a highly swirling flow within the circumferential cavity. The flow within the cavity experiences a centripetal acceleration (“g-load”) which varies with tangential velocity and radius from the combustor axis. This “high-g” effect has the potential to increase flame speeds and volumetric heating rates, as well as enhance fuel air mixing and spreading providing the potential to reduce fuel injector count without compromising performance. Experiments were performed on the HG-UCC combustor at higher operating pressures, temperatures, and equivalence ratios than previous high-g experiments conducted in a similar uncooled inter-turbine burner (ITB). Results show that the HG-UCC has high combustion efficiencies for the entire range of data considered. The effects of pressure and temperature, cavity driver angle, centripetal acceleration (g-load), and equivalence ratio are studied for their impacts on combustion efficiency and nitrogen oxide (NOx) emissions. An important result of this work is the construction of NOx correlations for the HG-UCC. Test data performance results and correlations are compared to previous trapped vortex and high-g UCC experiments.

Heating and Efficiency Comparison of a Fischer-Tropsch (FT) Fuel, JP-8+100, and Blends in a Three-Cup Combustor Sector

In order to realize alternative fueling for military and commercial use, industry guidelines be met. These aviation fueling requirements are outlined in MIL-DTL-83133F(2008) or ASTM D 7566-Annex standards and are classified as “drop-in” fuel replacements. This paper provides combustor performance data for synthetic-paraffinic-kerosene- (SPK-) type (Fisher-Tropsch (FT)) fuel and blends with JP8

Application of Optical Measurement Techniques in Combustion Test-Cell Environments

Optical measurement techniques are required to determine flow-field parameters for the development and evaluation of advanced combustion systems. Parameters include but are not limited to velocity, temperature, and species concentrations. There are many challenges to implementing diagnostic techniques in practical combustion rigs, including temperature/pressure effects, vibration, flow perturbation, limited optical access, as well as optical engineering and alignment. Current implementation options discussed here include incorporating in-situ launching assemblies and integrating fiber-based methods. First, a novel laser launching system is described for high-temperature, high-pressure combustion applications in the High-Pressure Combustion Research Facility (HPCRF) at Wright-Patterson AFB. This insitu, optical-based assembly is placed upstream in the plenum section of a combustor sector rig and used to launch double-pulsed laser light for particle-image velocimetry (PIV). Design and implementation challenges will be discussed and representative data shown. In addition to launching capability, this assembly provides the means for light collection. Optical designs will be discussed for coupling scattered light or fluorescence photons from sheet-based techniques such as PIV or planar laser-induced fluorescence (PLIF) to double-frame, high-speed, intensified cameras. Investigations into the use of this assembly for PLIF in reacting flows will be presented. Second, fiber-based approaches involving a novel imaging fiber and associated purged, watercooled probe for high-speed imaging of practical combusting flows in the HPCRF with CMOSbased cameras will be discussed. Together these two approaches represent a powerful methodology for bringing the advantages of nonintrusive, optical combustion diagnostics to practical hardware in large-scale combustion test facilities.

Multi-Hole Film Cooling With Integrally Woven SiC-SiC Ceramic Wall Panels

This paper presents numerical analyses of coupled heat transfer for multi-hole cooling of an integrally woven ceramic matrix composite, suitable for use in a combustor liner. The results indicate potential benefit in expanding the current design space for the combustor liners to include shallow film injection angles, very small diameter film holes, and a film injection scheme that features opposing cooling jets. These features can be conveniently produced in integrally woven SiC-SiC ceramic composite panels to yield film effectivenesses that are significantly higher than the current technology that is based on super alloy panels. This has the potential for significant cooling air saving that can be re-introduced in the combustor dome region and result in lower NOx emissions.Copyright