Terrence R. Meyer

Experimental Study of Deflagration-to-Detonation Enhancement Techniques in a H2/Air Pulsed-Detonation Engine

Abstract : Experiments are performed on a number of deflagration-to-detonation (DDT) enhancement techniques for use in a H2/Air pulsed-detonation engine (PDE). The mechanism, speed and location of DDT for three configurations are considered, including a Shehelkin spiral, an extended cavity/spiral and a co-annulus. High speed digital imaging is used to track flame propagation. and simultaneous time-correlated pressure traces are used to record progress of the shock structure. It is found that DDT is initiated primarily through local explosions that are highly dependent on the particular geometry. In addition to various geometries. The effect of equivalence ratio and spark timing are also investigated.

CHEMILUMINESCENCE AS A MEASUREMENT OF LOCAL EQUIVALENCE RATIO

Measurements of the chemiluminescence of OH*, CH*, and C2* in laminar laboratory propane/air flames and a liquid-fueled model combustor are presented. Ratios of the emission intensity for the three species are a strong function of equivalence ratio. Results of the laboratory measurements are used to infer conditions within the model combustor. Discussion of the measurements and their utility is made in the context of previous studies.

Optical Diagnostics for Characterizing Advanced Combustors and Pulsed-Detonation Engines (Invited)

While optical diagnostic techniques have been applied with great success to the fundamental study of combustion chemistry and physics in the laboratory, the challenges afforded by real-world propulsion systems demand continuing innovation if such techniques are to be adapted and transitioned for use in engineering tests and on-board monitoring and control applications. This paper documents continuing efforts to transition aerodynamic measurement technologies from diagnostics-development laboratories to combustor test- and-evaluation facilities in the Propulsion Directorates Combustion Science Branch (Turbine Engine Division). Applications of various optical diagnostic techniques for visualizing flowfields and quantifying temperatures and key species concentrations in several advanced combustors are described. A number of next- generation diagnostics targeted for laboratory-to-facility transition in the near future are highlighted as well.

STUDIES ON SOOT FORMATION IN A MODEL GAS-TURBINE COMBUSTOR

Residence time and thermo-chemical environment are important elements in the soot-formation processes in combustors, especially which use swirl for flame stabilization. For understanding the chemical and physical structure of the soot formed in these combustors knowledge on flow dynamics and formation of polycyclic aromatic hydrocarbons (PAHs) is required. A time-dependent, detailed-chemistry computational-fluid-dynamic (CFD) model is developed for the simulation of the reacting flows in a model swirl-stabilized combustor. While commercial JP-8 fuel was used in the experiments, a 6-component surrogate mixture was used in the calculations for mimicking the JP-8-fuel combustion. Detailed chemical kinetics were used for the simulation of combustion as well as formation of PAH species. Several calculations were made for different equivalence ratios obtained by varying the fuel jet velocity and by keeping the airflow unaltered. Turbulent-flow simulations revealed that two recirculation zones that are separated by the air jet establish in the swirlstabilized combustor. Stabilization of flames between the air jets and the recirculation zones depends on the equivalence ratio. For the highly fuel-lean cases (φ = 0.65) flame is stabilized between the air jet and the central recirculation zone and for the fuel-rich cases flame is stabilized between the air jets and the corner recirculation zone. However, both flames seem coexist for slightly fuellean cases (φ = 0.85). Predicted OH concentration fields are compared with the OH images obtained using planar-laserinduced-fluorescence (PLIF) technique. Probe measurements made in the exhaust products are also compared.

Vortex-induced flame extinction in two-phase counterflow diffusion flames with CH planar laser-induced fluorescence and particle-image velocimetry

Here the interaction between a laminar two-phase, non-pre-mixed counterflow flame and a vortex is examined. Special emphasis is given to the influence of different flame and vortex parameters on the extinction behavior of the flame. Simultaneous planar laser-induced fluorescence of the CH radical layer produced by the flame and particle-image velocimetry measurements of the flowfield are used to characterize the flame-vortex interaction. These simultaneous diagnostics are used for the first time in this configuration. The extinction processes occurring during the flame-vortex interaction can be analyzed by this method, especially the influence of strain at the flame surface. The influence of the droplets on the extinction behavior appears clearly compared with a fully gaseous flame. The spray flame is weaker and extinguishes earlier than does a gaseous flame. In the measurements an additional broadband signal in the vicinity of the CH layer is probably due to the induced fluorescence of polycyclic aromatic hydrocarbons, excited at the same wavelength.

Numerical Studies on Soot Mitigation in a Model Gas- Turbine Combustor

A time-dependent, detailed-chemistry, computational-fluid-dynamics (CFD) model is developed for the evaluation of the performance of a soot-reducing additive in a model swirl- stabilized combustor. While commercial JP-8 fuel was used in the experiments, a 6- component surrogate mixture was used in the calculations for mimicking the JP-8-fuel combustion. Di-teritiary-butyle-peroxide (DTBP) additive, which is known for improving the ignition characteristics of hydrocarbon fuels, was tested for its ability in reducing the soot. Detailed chemical kinetics were used for the simulation of JP-8+DTBP combustion and the consequent formation of PAH species. Calculations were made for different equivalence ratios obtained through varying the fuel jet velocity while keeping the airflow unaltered. Turbulent-flow simulations with the base JP-8 fuel revealed that significant amount of soot is formed for fuel-rich conditions while no or negligible soot is formed for equivalence ratios less than 0.8. Addition of DTBP for the fuel-rich operating conditions resulted in only a marginal decrease in the amount of soot formed. Its effect on fuel-lean operation of the combustor is also found to be negligible. However, DTBP seems to be more effective in reducing the soot when the combustor is operating in the neighborhood of stoichiometric conditions. Consistent with these results, calculations made for a simple jet diffusion flame also revealed that DTBP has no effect on soot formation when it was added to the fuel jet.

OH PLIF and Soot Volume Fraction Imaging in the Reaction Zone of a Liquid-Fueled Model Gas-Turbine Combustor

Simultaneous measurements of OH planar laser-induced fluorescence (PLIF) and laser-induced incandescence (LII) are used to characterize the flame structure and soot formation process in the reaction zone of a swirl-stabilized, JP-8-fueled model gas-turbine combustor. Studies are performed at atmospheric pressure with heated inlet air and primary-zone equivalence ratios from 0.55 to 1.3. At low equivalence ratios (φ < 0.9), large-scale structures entrain rich pockets of fuel and air deep into the flame layer; at higher equivalence ratios, these pockets grow in size and prominence, escape the OH-oxidation zone, and serve as sites for soot inception. Data are used to visualize soot development as well as to qualitatively track changes in overall soot volume fraction as a function of fuel-air ratio and fuel composition. The utility of the OH-PLIF and LII measurement system for test rig diagnostics is further demonstrated for the study of soot-mitigating additives.© 2004 ASME