Robert Driscoll

Development of a Rotating Detonation Engine Facility at the University of Cincinnati

A new, air-breathing rotating detonation engine (RDE) facility has been constructed at the University of Cincinnati. This facility is built upon the modular designs currently in use at the AFRL, developed by Shank et al. in 2012 and was constructed as part of an ongoing research effort into air-breathing detonation engines. Operation of the facility has been achieved for hydrogen-air mixtures with the potential to expand to a variety of gaseous fuels. High speed and low speed instrumentation provide time-resolved wave speed and combustor pressure to characterize operation. The facility will be used to expand and improve RDE diagnostics, and establish and characterize operation for various injection schemes, fuel blends, and chamber pressures.

Fuel Blending as a Means to Achieve Initiation in a Rotating Detonation Engine

A fuel blending technique is proposed to achieve detonation initiation of hydrocarbon-air mixtures in a rotating detonation engine (RDE). An experimental investigation is performed at the University of Cincinnati Detonation Engine Test Facility to demonstrate the efficacy of gradual fuel transition to establish rotating detonation for less detonable hydrocarbons. Baseline ethylene operability is hindered by the existence of strong, low frequency instability, generally resulting in prompt failure of the detonation. An investigation of hydrogen-ethylene fuel blends does not exhibit an expanded lightoff range, but does yield significantly augmented detonation stability and improved recovery from extinction events related to the instability. Attempts to transition from a hydrogen-assisted state to an ethylene-air mixture are hindered by the immediate onset of instability in the absence of hydrogen. As the ZND analysis predicts a limited chemical effect for the range of hydrogen fractions explored in this study, the stabilizing mechanism of hydrogen addition may be physical rather than chemical, and is possibly due to suppression of fuel plenum feedback.

Statistical Treatment of Wave Instability in Rotating Detonation Combustors

Rotating Detonation Combustor operation is found to ensconce an inherent low frequency pulsation in addition to the dominant frequency of rotation of the Continuous Spin Detonation (CSD) waves. This low frequency oscillation of the CSD waves in a Rotating Detonation Combustor is studied by extracting the frequency, the number of detonation waves present within a period of waxing and waning, and the standard deviation of detonation wave pressure amplitudes. The experiments use a Hydrogen-Air mixture for different air flow rates and equivalence ratios and two parametric design variations: fuel injection orifice size and air injection gap width. The instability is found to be inherently linked to injection sizing, and fuel plenum pressure.

Shock Transfer and Shock-Initiated Detonation in a Dual Pulse Detonation Engine/Crossover System

An experimental investigation was carried out to study the propagation of a shock wave through a crossover tube for the purpose of causing shock-initiated detonation. A pulse detonation engine was used as a driver source to propagate a shock wave through a crossover tube into a second, adjacent detonation tube (that is, driven). Results showed a transferred shock wave achieved shock-initiated detonation, and for specific crossover tube geometries, there was a maximum effective crossover tube length for which the event was possible. This maximum effective length was strongly correlated to the strength of the transferred shock. Initiation performance in the driven detonation tube declined when the incident shock strength decreased below MS=2.0. Introducing a bend to the end of the crossover tube increased the driven detonation tube initiation performance by enhancing the strength of the transferred planar shock wave by an average of 20%. A numerical investigation on shock wave planar attenuation in a crosso...

Experimental Investigation of H2-Air Mixtures in a Rotating Detonation Combustor

The operating range and wave speed performance of a Rotating Detonation Combustor (RDC) is characterized for hydrogen-air mixtures for three fuel injection schemes and two air injection schemes. The fuel injection scheme is altered by changing the total number of injection orifices and the individual orifice area, while maintaining the same fuel mass flux across the three schemes. The operability, performance and combustion-induced pressure rise due to the addition of a back-pressurizing convergent nozzle is also characterized. While the operating range is largely unaffected by changes in the length-to-diameter ratio of the fuel injector orifices, higher length-to-diameter ratios correspond to a lower number of pop-out events. Pop-out event is defined as a transitional RDC operation where there is a sudden abatement of the continuously propagating detonation wave, once established inside the combustor. Increased air injection area diminishes the operability, while producing high stochasticity in the performance of the RDC. The length-to-diameter ratio of the fuel orifices has a significant impact on the number of detonation waves that can exist in the chamber. For the highest length-to-diameter ratio of the fuel orifices, and at the highest air flow rates, the RDC supports multiple detonation waves inside the chamber. Without the convergent nozzle attachment, 80% of Chapman-Jouguet (C-J) detonation speed is achieved for all three fuel injection schemes. C-J detonation wave speed is achieved in the annulus when the RDC is back-pressurized using the nozzle. The ratio of reactant fill-height to the detonation cell-width tapers at the lean and rich operating conditions, while peaking at an equivalence ratio of around 1.2. The detonation-induced static pressure rise produced in the RDC is found to be dependent on the air flow rate and the equivalence ratio of the reactants.Copyright

Characterization of Shock Wave Transfer in a Pulse Detonation Engine–Crossover System

Shock wave propagation within a pulse detonation engine–crossover system is investigated, examining the properties and mechanisms of the transfer process. A shock wave is transferred through a crossover tube that connects a spark-ignited driver pulse detonation engine to a secondary, driven pulse detonation engine. Detonations in the driven pulse detonation engine develop from shock-initiated combustion, as strong shock wave reflection can cause ignition within a reactive mixture. A pulse detonation engine–crossover system can decrease deflagration-to-detonation transition length while employing a single spark source to initiate a system consisting of multiple detonation engines. Visualization of a shock wave propagating through a clear channel reveals a complex shock train behind the leading shock wave. Transverse waves connect with the leading shock wave to form a triple point that oscillates through the leading shock wave. The shock wave Mach number and decay rate remain constant for varying crossover ...

Starting Transients and Detonation Onset Behavior in a Rotating Detonation Combustor

The onset phase between combustor initiation and the appearance of a stable, periodic operating state is studied for four combustor conditions. The onset behavior and duration is assessed for varying air flow rate and equivalence ratio for cases with and without a converging nozzle at the combustor exit. The median duration and scatter of the onset phase is a function of flow rate and the combustor exit geometry, with higher air flow rate or the presence of a converging nozzle yielding rapid onset of a stable operating mode. The duration of the onset phase is very stochastic and varies by a factor of two for cases without a converging nozzle. However, the combustor behavior during this transitory period is very repeatable between subsequent tests.

The Design and Validation of a Pulse Detonation Engine Facility with and without Axial Turbine Integration

A new air-breathing ethylene-burning Pulse Detonation Engine (PDE) facility has been constructed at the University of Cincinnati (UC). This facility supports up to six twoinch or three-inch detonation tubes driven by an automotive-derived valving and ignition system and Shchelkin-type spirals for deflagration to detonation transition (DDT). The new PDE is also mated to an axial-flow power turbine with each PDE tube supplying a one-sixth sector of the turbine inlet so that turbine efficiency may be studied under the partial admission and pulsing flow or detonating flow that the PDEs subject it to. The interface between each PDE and its inlet sector is closely coupled in order to maximize the effects of pulsation and partial admission. This paper documents the particular details of this new facility, provides sample data for a few representative cases and provides enough information on the system’s geometry and initial conditions to support numerical simulation of its operation. The presented sample data should allow validation of these numerical simulations.

Experimental Comparison of Axial Turbine Performance Under Steady and Pulsating Flows

The performance of an axial turbine is studied under close-coupled, out-of-phase, multiple-admission pulsed air flow to approximate turbine behavior under pulsed detonation inflow. The operating range has been mapped for four frequencies and compared using multiple averaging approaches and five formulations of efficiency. Steady performance data for full and partial admission are presented as a basis for comparison to the pulsed flow cases. While time-averaged methods are found to be unsuitable, mass-averaged, work-averaged, and integrated instantaneous methods yield physically meaningful values and comparable trends for all frequencies. Peak work-averaged efficiency for pulsed flow cases is within 5% of the peak steady, full admission values for all frequencies, in contrast to the roughly 15–20% performance deficit experienced under steady, 50% partial admission conditions. Turbine efficiency is found to be a strong function of corrected flow rate and mass-averaged rotor incidence angle, but only weakly dependent on frequency.Copyright

Experimental Validation of Expanded Centerbodiless RDE Design

Rotating Detonation Engines (RDE’s) or Rotating Detonation Combustors (RDCs) are a detonation based combustion method that shows potential capability of high efficiency, compact geometry, and continuous operation. Pressure losses due to friction, flow turning, or shock strength could cause a loss to the efficiency advantages RDEs have over conventional combustion. Some recent numerical studies have shown it is possible to ignite an RDE that has only the outer wall, with air going through the center instead of a centerbody. These centerbodiless RDE Designs may entrain flow and impart momentum to more air if driven only from the outer annulus, which may increase the total propulsive efficiency. They may also be a good afterburner design. In addition, their unique design with fewer walls for reflection may result in fewer reversals and blow-outs of the RDE. This may expand the range of operation for certain applications. A numerical study using a Reynolds-Averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) program Fluent, by ANSYS has been performed to test three dimensional (3D) configurations of centerybodyless RDE. A physical model of the most successful design has been tested experimentally using air and hydrogen as a proof of concept. This represents the first experimental test of this design, and the first 3D printed RDE at the University of Cincinnati.