Equivalent Supply Pressure for Pressure Gain Estimation in Rotating Detonation Engines

Plaehn, Ethan W.; Gejji, Rohan; Walters, Ian V.; Slabaugh, Carson D.

doi:10.2514/1.b39009

Journal of Propulsion and Power

2023

DOI: 10.2514/1.b39009

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Equivalent Supply Pressure for Pressure Gain Estimation in Rotating Detonation Engines

Ethan W. Plaehn

Rohan Gejji

Ian V. Walters

et al.

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2024

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Cited by 6 publications

References 28 publications

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Rotating detonation combustor performance informed through a novel megahertz-rate stagnation pressure measurement

Dille,

Frederick,

Slabaugh

et al. 2024

Physics of Fluids

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An experimental stagnation pressure measurement technique is presented for a rotating detonation combustor (RDC). Schlieren imaging enables rotating detonation wave passage to be correlated with oscillations observed in the under-expanded exhaust plume. By measuring the spatiotemporal variation in exhaust plume divergence angle, stagnation pressure measurements of the RDC were acquired at a rate of 1 MHz. Combustor mass flux was varied between 202 and 783 kg/m2s, producing equivalent available pressures (EAPs) in the range of 3.42–13.5 bar. Time-averaged stagnation pressure measurements gathered using this technique were in agreement with the measured EAP within ±1.5%. Time-resolved stagnation pressure measurements allow for the pressure ratio produced across detonation wave cycles to be determined. For the conditions tested, detonation pressure ratios and wave speeds decreased while increasing the mean operating pressure of the combustor. Numerical modeling of the conditions tested indicates that the decrease in pressure ratio and wave speed is a result of elevated levels of combustion prior to the detonation wave arrival (i.e., “preburning”). Simultaneous OH* chemiluminescence measurements within the combustion chamber show an increase in preburned heat release relative to detonative heat release for increasing operating pressures of the RDC, in agreement with the results of the numerical model. Modeled chemical kinetic timescales decrease by approximately the same magnitude by which the preburning mass fraction increased in the range of operating pressures tested, suggesting that the faster reaction rates associated with higher pressure combustion may be the reason for increased preburning within the combustor.

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Rotating detonation combustor performance informed through a novel megahertz-rate stagnation pressure measurement

Dille,

Frederick,

Slabaugh

et al. 2024

Physics of Fluids

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Continuous Injector Geometry Variation to Augment Rotating Detonation Combustor Operation and Performance

Plaehn,

Gejji,

Walters

et al. 2024

Journal of Propulsion and Power

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Sensitivity of rotating detonation combustor operation and performance to oxidizer injector pressure drop was characterized using continuous variation of the injector area during combustor operation. As the oxidizer injector area was both increased and decreased, the sensitivity of the combustion process to varying injector pressure drop was characterized using high-frequency measurements of pressure and chemiluminescence intensity. Detonation wave strength and coherence were characterized using peak-to-peak intensity and power fraction calculated from point-chemiluminescence measurements. Propulsive performance of the combustor was evaluated using thrust and equivalent available pressure, relating them back to reactant supply pressures for assessment of combustor pressure gain. Pressure gain increased during a test as the oxidizer injector area was increased and the corresponding manifold pressure was decreased. At larger injector areas, pressure gain decreased as the operating mode of the combustor transitioned from detonation to deflagration, concomitant with a reduction of gross thrust. Modeling of injector recovery time revealed that the injector operated in both choked and unchoked regimes, which was used to explain detonation wave number transitions in the experiment. A broadened range of detonative operability enabled by active variation of combustor geometry resulted in higher performance with a lower injector pressure drop.

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Improving Base-Drag Corrections for Rotating Detonation Combustor Gross Thrust Measurements

Feleo,

Gamba

2024

Journal of Propulsion and Power

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One of the primary means of evaluating the total pressure ratio across a rotating detonation engine/combustor requires measuring its gross thrust output. The presence of flat aft-facing surfaces introduces base-drag forces; necessitating corrections to the measured thrust to determine the gross thrust. A finite number of static pressure measurements are taken on these surfaces, which are then numerically integrated to estimate the resulting base-drag force. This work systematically describes the methods of numerically integrating a limited number of pressure measurements at discrete locations. Sample base-drag measurements were performed on the truncated nozzle of a hydrogen/air operated rotating detonation combustor. The nozzle was instrumented with 17 pressure measurements distributed at three evenly spaced circumferential locations. An asymmetry in the pressure distribution is observed contrary to what is typically assumed in the literature. The relative impact of the edge pressure treatment is highlighted and is found to be a significant source of error in the numerical integration. The alternative means of numerical integration using a Gauss–Kronrod scheme is evaluated and compared to the standard Newton–Cotes method. Recommendations are provided to address the limitations and challenges of these types of base-drag measurements as they pertain to rotating detonation combustors.

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Equivalent Supply Pressure for Pressure Gain Estimation in Rotating Detonation Engines

Cited by 6 publications

References 28 publications

Rotating detonation combustor performance informed through a novel megahertz-rate stagnation pressure measurement

Rotating detonation combustor performance informed through a novel megahertz-rate stagnation pressure measurement

Continuous Injector Geometry Variation to Augment Rotating Detonation Combustor Operation and Performance

Improving Base-Drag Corrections for Rotating Detonation Combustor Gross Thrust Measurements

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