Chemiluminescence imaging of an optically accessible non-premixed rotating detonation engine

Rotating detonation combustors and their similarities to rocket instabilities

Recent accomplishments related to the performance, application, and analysis of rotating detonation engine technologies are discussed. The pioneering development of optically accessible rotating detonation engines coupled with the application of established diagnostic techniques is enabling a new research direction. In particular, OH* chemiluminescence images of detonations propagating through the annular channel of a rotating detonation engine are reported and appear remarkably similar to computational fluid dynamic results of rotating detonation engines published in the literature. Specific impulse measurements of rotating detonation engines and pulsed detonation engines are shown to be quantitatively similar for engines operating on hydrogen/air and ethylene/air mixtures. The encouraging results indicate that rotating detonation engines are capable of producing thrust with fuel efficiencies that are similar to those associated with pulsed detonation engines while operating on gaseous hydrocarbon fuels....

Overview of Performance, Application, and Analysis of Rotating Detonation Engine Technologies

A rotating detonation engine is experimentally tested with various nozzle configurations for the purpose of measuring the propulsive performance of these devices in terms of thrust and specific impulse. Particular attention is given to comparing different internal nozzle configurations, which include bluff body, aerospike, and choked aerospike arrangements. The nozzle throat exit choke present in the rotating detonation engine exhaust is analyzed to provide insight into the stagnation pressure gain nature of the device.

Experimental Study of the Performance of a Rotating Detonation Engine with Nozzle

Investigation of rotating detonation combustor operation with H2-Air mixtures

The detonation structure, pressure gain, and thrust production in a rotating detonation engine (RDE) are studied using a combination of experimental and numerical approaches. High frequency time-dependent and low frequency time-averaged static pressure and thrust measurements are acquired for a range of operating conditions and geometry configurations. Acoustic coupling between the detonation channel and air plenum is important for low air mass flow rates and large air injection slots based on analyses of the pressure measurements in the time and frequency domains. The static pressure increases across the air inlet by up to approximately 15% when utilizing a large air injection slot. The pressure increase across the air inlet demonstrates encouraging progress towards realizing pressure gain combustion in RDEs with corresponding challenges associated with isolating the inlet plenums. The time-dependent pressure measurements acquired using a semi-infinite tube arrangement and time-averaged pressure measurements acquired using a capillary tube attenuated arrangement agree to within 30% depending upon location. Quantification of the similarities and differences between the two techniques represents important progress towards acquiring quantitative time-dependent pressure measurements in the challenging environment presented by RDEs. Twodimensional simulations of the RDE capture the essential features of the flow field such as the detonation wave height and angle, trailing edge oblique shock wave, shear layer between the freshly and previously detonated products, and deflagration between the fuel fill region and expansion region containing detonated products. The presence of air purging from the plenum to the channel behind the detonation wave is suggested by the comparison of measured and simulated channel pressure distributions. The pressure, thrust, and wave speed measurements provide benchmark data that are useful for evaluating low and high fidelity simulations of RDEs and improving fundamental understanding of the critical design parameters that influence RDE operation and performance.

Experimental and Numerical Evaluation of Pressure Gain Combustion in a Rotating Detonation Engine

During the testing of a Rotating Detonation Engine coupled with an ejector, pressure measurements indicated a deficiency in the understanding of the pressure probes. The pressure histories came from an array of Infinite Tube Pressure (ITP) static probes, Capillary Tube Average Pressure (CTAP) static probes, and direct Kiel stagnation pressure probes. Upon examination of the pressure histories, the average of the Kiel probe pressure over several laps of detonation, it was revealed that the ITP static pressures measured higher than the Kiel stagnation pressures both within the mixing chamber and at the exit of the ejector. This research conducts an unsteady calibration of the different probe configurations in order to quantify the unsteady response of the probe configurations. The unsteady calibration allows the pressure at the entrance of the probes to be reconstructed from the recorded pressure histories. The unsteady calibration of the pressure probes was performed by subjecting each of the probes to a single detonation in a detonation tube. The pressure history of a planar detonation such as the one in a detonation tube is well understood, and accurately modeled by the Zeldovich-vonNeumann-Doring (ZND) model. A transfer function for each probe type was constructed from the model pressure history and the measured pressure history. The transfer function for each configuration accounts for damping and phase lag introduced by the probe configuration. Each of the probe configurations has distinct phase lag and damping and the transfer function for each will be dominated by different phenomena. The CTAP consists of a 0.0625 in (1.6 mm) diameter, 36 in (0.91 m) long tube connected to the RDE at one end and a pressure transducer at the other. In the tube, viscous dissipation results in a temporal average of the pressure. The dissipation results in strong damping of any perturbations. The length of the tube results in longer phase lag than any other configuration. In the ITP configuration, the pressure transducer is connected to the RDE by 1.5 in (3.8 cm) of 0.0625 in (1.6 mm) diameter tubing and to ambient air by 72 in (1.83 m) of 0.0625 in (1.6 mm) diameter tubing. The proximity of the transducer to the probe entrance reduces impact loading on the transducer and the open ended tube does not reflect shockwaves. The distance from the tube entrance to the transducer results in little phase lag, but the small diameter tubing significantly damps pressure perturbations. The chamber connecting the transducer

Comparison of Transient Response of Pressure Measurement Techniques with Application to Detonation Waves

Propellant Plenum Dynamics in a Two-dimensional Rotating Detonation Experiment

A quasi-two-dimensional, computational fluid dynamic (CFD) simulation of a rotating detonation engine (RDE) is described. The simulation operates in the detonation frame of reference and utilizes a relatively coarse grid such that only the essential primary flow field structure is captured. This construction and other simplifications yield rapidly converging, steady solutions. Viscous effects, and heat transfer effects are modeled using source terms. The effects of potential inlet flow reversals are modeled using boundary conditions. Results from the simulation are compared to measured data from an experimental RDE rig with a converging-diverging nozzle added. The comparison is favorable for the two operating points examined. The utility of the code as a performance optimization tool and a diagnostic tool are discussed.

https://ntrs.nasa.gov/api/citations/20150018399/downloads/20150018399.pdf

Comparison of Numerically Simulated and Experimentally Measured Performance of a Rotating Detonation Engine

Thrust stand testing is conducted on rotating detonation engines of various annular detonation channel widths and the impact of different scaling parameters on the performance of the devices is discussed. A focus is given in this work to identifying the relationship between the appropriate flow variables to facilitate comparison between geometries and the experimentally obtained specific impulses and specific thrusts, as well as an examination of stagnation pressure usage, through corrected thrust. Operation on both hydrogen and gaseous hydrocarbon fuel is presented. A comparison is made between the resulting propulsive performances found for similar rotating detonation engine geomtries.

Matthew Fotia

Papers

Experimental and Numerical Evaluation of Pressure Gain Combustion in a Rotating Detonation Engine

Comparison of Transient Response of Pressure Measurement Techniques with Application to Detonation Waves

Propellant Plenum Dynamics in a Two-dimensional Rotating Detonation Experiment

Comparison of Numerically Simulated and Experimentally Measured Performance of a Rotating Detonation Engine

Experimental Study of Performance Scaling in Rotating Detonation Engines Operated on Hydrogen and Gaseous Hydrocarbon Fuel