Frederick R. Schauer

Measurements of multiple gas parameters in a pulsed-detonation combustor using time-division-multiplexed Fourier-domain mode-locked lasers

Hyperspectral absorption spectroscopy is being used to monitor gas temperature, velocity, pressure, and H(2)O mole fraction in a research-grade pulsed-detonation combustor (PDC) at the Air Force Research Laboratory. The hyperspectral source employed is termed the TDM 3-FDML because it consists of three time-division-multiplexed (TDM) Fourier-domain mode-locked (FDML) lasers. This optical-fiber-based source monitors sufficient spectral information in the H(2)O absorption spectrum near 1350 nm to permit measurements over the wide range of conditions encountered throughout the PDC cycle. Doppler velocimetry based on absorption features is accomplished using a counterpropagating beam approach that is designed to minimize common-mode flow noise. The PDC in this study is operated in two configurations: one in which the combustion tube exhausts directly to the ambient environment and another in which it feeds an automotive-style turbocharger to assess the performance of a detonation-driven turbine. Because the enthalpy flow [kilojoule/second] is important in assessing the performance of the PDC in various configurations, it is calculated from the measured gas properties.

Performance of a Turbine Driven by a Pulsed Detonation Combustor

There is longstanding government and industry interest in pressure-gain combustion for use in Brayton cycle-based engines. Theoretically, pressure-gain combustion allows heat addition with reduced entropy loss. The pulsed detonation combustor (PDC) is a device that can provide such pressure-gain combustion and possibly replace the typical steady deflagration combustor. The PDC is inherently unsteady, however, and comparisons with steady deflagration combustors must be based upon time-integrated performance variables. In this study, the radial turbine of a Garrett automotive turbocharger was coupled directly to and driven, full admission, by a hydrogen-fueled PDC fueled. Data included pulsed-cycle time histories of turbine inlet and exit temperature, pressure, velocity, mass flow, and enthalpy. The unsteady inlet flowfield showed momentary reverse flow, and thus unsteady accumulation and expulsion of mass and enthalpy within the device. The coupled turbine-driven compressor provided a time-resolved measure of turbine power. Duty cycle increased with PDC frequency. Power and cycle-average specific work increased with PDC frequency and fill fraction.Copyright

Performance Evaluation of an Unsteady Turbine Driven by a Pulsed Detonation Combustor

Replacing a Brayton cycle near constant-pressure combustor with a pulsed detonation combustor (PDC) may take advantage of potential performance improvements from low-entropy, pressure-gain heat addition. In this paper, the radial turbine of a Garrett automotive turbocharger is coupled to a hydrogen fueled PDC. Unsteady turbine power is obtained with a conventional dynamometer technique. Sampling frequencies greater than 10 kHz resolve rapid flowfield transients of confined detonations which occur in less than a millisecond and include peak gas pressures exceeding 4 MPa and peak gas temperatures greater than 2,400 K. Results include 6 ms time histories of turbine inlet and exit temperature, pressure, mass flow, and enthalpy during blowdown of a PDC. The unsteady inlet flowfield included momentary reverse flow, which was not observed at the turbine exit. Full pulsed detonation cycle time histories of turbine power, rotor speed, rotational energy and net shaft torque are included to describe the turbine response to detonations. Rotor speed is periodic and net shaft torque oscillates in response to a detonation. Results are shown for fill fractions ranging from 0.5 to 1.0 with a 0.5 purge fraction. PDC operating frequencies in this study range from 10 Hz to 25 Hz.© 2011 ASME

Performance of Rotating Detonation Engines for Air Breathing Applications

The performance of air breathing rotating detonation engines is presented through the use of experimental measurements made at the Air Force Research Laboratory’s Detonation Engine Research Facility. The performance scaling characteristics observed between various physical device configurations is discussed; included is the influence of mass flow rate, air injection area ratio and nozzle area ratio. The impact of geometry on the unsteady nature of rotating detonation engines and the combustors’ efficient production of thrust is presented, along with an analysis of the pressure-gain properties of rotating detonation engines. Finally, the impact of transitioning from hydrogen fueled to hydrocarbon fueled devices is examined through the direct comparison of experimental measurements of operation on both gaseous hydrogen and ethylene fuels. Previous pulsed detonation engine work is used to provide a reference for this comparison.