William Stoddard

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...

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 ...

Comparative Numerical Study of RDE Injection Designs

The pressure gain of detonation has great potential to increase efficiency of cycles involving combustion. Rotating detonation engines (RDEs) have a great deal of promise as a detonation based combustor. The RDE’s advantages over current pulsed detonation cycles include needing only a single initiation, having a more uniform exhaust pressure, compact design, and capability to process high flow rates. With very few exceptions, premixed operation of an RDE has proven difficult, with the flame igniting the supply upstream of the RDE. As a consequence, much energy has been put toward the design of a mixing system that occurs near or at the inlet of the RDE. Designs utilizing many thin two dimensional (2D) slots have shown some promise, however ignition of the incoming flow due to dead zones behind the plates has occurred. This may be the cause for reversals as seen in simulations by Schwer and Kailasanath, which also may be a mode for blow-off. The current study aims to investigate more complex three dimensional RDE injection and mixing designs and to reduce the ability to flame-hold, and ensure fewer hot dead zones in the post-detonation refill. A numerical study using a Reynolds-Averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) program Fluent, by ANSYS is performed to test three dimensional (3D) configurations of RDE fuel injection and mixing. The effect of various 3D geometries are studied, including central pintel injection and side wall simple constriction injection, along with modifications to a currently viable experimental design. A simple Spalart-Allmaras turbulence model is used to better simulate mixing of hydrogen and air. Detonation of the more successful mixing designs will test for flame-holding.

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.

Simulations of Detonation Based Cycles in Tubes with Multiple Openings

Computational fluid dynamics (CFD) analysis on detonations, and the resulting exhaust dynamics are studied. Specifically the analysis seeks to quantify the relative ability of the cycles to refill with unburned air that can be mixed with fuel for pulsed detonation. The relative magnitude of the effects of ignition location, fuel location, and basic tube geometry on this self-aspiration are first investigated in smaller, more time-efficient simulations. From these, additional variables, such as ejectors, and different inlet shapes are tested with the most promising configuration of fuel ignition and overall pipe geometry. These further tests are carried out at scales more comparable to the experimental setups. The results obtained are compared with the previous pulsejet configurations and known pulse detonation data. Steps are taken toward optimizing a static thrust self-aspirating valveless pulse detonation engine (PDE). Nomenclature AEJECT = inner cross-sectional area of ejector APDE = inner cross-sectional area of pulse detonation tube CFD = computational fluid dynamics LEJECT = length of ejector LPDE = length of pulse detonation engine main tube P = pressure PDE = pulse detonation engine t = time after ignition x = longitudinal position relative to left end of pulse detonation engine

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.

Numerical Study of Obstacles in Rotating Detonation Engines

A University of Cincinnati computational fluid dynamic study is being carried out to investigate obstacles in a Rotating Detonation Engine configuration. A two-dimensional periodically bounded simulation is used to test walls and ramps in the path of a Rotating Detonation Engine, with respect to its ability to stabilize flow and prevent reversed detonation waves that can cause blowout in RDE systems. Data have shown a direct initiation of detonation near a ramp followed by a step to propagate only in the direction away from the step, if initiated next to the step. Additional characterization of this ramp is done with more realistic injector plates. In addition, walls intruding from below or in the middle of the flow are tested to see their initial effects on an RDE.

Dual Crossover Dual Shock Ignition of a Pulse Detonation Engine

A study has been done on the potential to ignite a detonation by reflected shock in a Pulse Detonation Engine (PDE) from another PDE over a wider range of crossover tube lengths with dual crossover tubes carrying the shock generated by a detonation. Frequency of firing was also varied to test viability at high frequencies and the dependence of detonation on frequency. Two main configurations of 2-crossover-tube PDE configurations were tested. One configuration was with parallel tubes, one downstream of the other. The other consisted of the same driver PDE configuration, but with a modified fitting allowing the two to converge at a single spot at the second PDE.

Experimental Study of Shock Transfer in a Multiple Pulse Detonation-Crossover System

A University of Cincinnati experimental study was carried out on a Multi-Pulse Detonation Engine (PDE) crossover system. Detonation tubes were connected through tubes of varying lengths that allow a shockwave to crossover from one PDE to another. Only the driving PDE was ignited. The current study aims to investigate the effect of crossover tube entrance locations on the operability of a driven PDE. Results suggest that shock initiated detonation is more prevalent when originating in the headwall of a detonation tube, a considerable improvement from previous results 11,14 . Furthermore, results have shown the effectiveness of igniting a subsequent driven PDE from a proceeding driven PDE, indicating the possibility of arranging a Multi-PDE Crossover System into an annular array whereby all detonation tubes will be ignited through continuous shock transfer. Finally, results have shown two distinct modes of operation whereby there is “fast” initiation or “slow” initiation.

Numerical Investigation of Centerbodiless RDE Design Variations

The pressure gain of detonation has great potential to increase efficiency of cycles involving combustion. Rotating detonation engines (RDEs) have a great deal of promise as a detonation based combustor. The RDE’s advantages over current pulsed detonation cycles include needing only a single initiation, having a more uniform exhaust pressure, compact design, and capability to process high flow rates. However, without consideration for pressure losses due to friction or shock strength, it is possible to lose the efficiency advantages RDEs have over conventional combustion. Some recent numerical studies have shown it may be 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, which may increase the total propulsive efficiency. 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 is being performed to test three dimensional (3D) configurations of centerybodyless RDE. The effect of various alterations to the design will be studied, including hydrogen injection hole size alteration, longitudinal walls, and an ejector. A simple Spalart-Allmaras turbulence model will be used to better simulate mixing of hydrogen and air. Detonation will test for steady operation for multiple cycles.