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Highlighted Research Results

Below is a selection of recently published and ongoing research results.

An empirical model for predicting pressure gain for rotating detonation combustors

Bach, E., Paschereit, C.O., Stathopoulos, P., Bohon, M.D., "An empirical model for stagnation pressure gain in rotating detonation combustors," Proceedings of the Combustion Institute, Vol. 38 (3), 2021: pp. 3807-3814. [link]

This work investigates the stagnation pressure gain in rotating detonation combustors (RDC) and its dependency on the geometry and mass flux of the combustor. Using a Kiel probe to directly measure stagnation pressure in the high-enthalpy exhaust stream, results are presented for a systematic variation of these parameters. The best-performing configuration achieved a pressure gain of −8%. A comparison with thrust-based equivalent available pressure data from literature shows that the Kiel probe measurements are in good agreement. It is observed that pressure gain increases with increasing air injector area, decreasing outlet throat area, increasing combustor mass flux, and is seen to be dependent on the operating mode. The data are then used to obtain an empirical model that describes pressure gain as a function of the three variables of injector area ratio, outlet area ratio, and combustor mass flux. The model is compared with measurements in this combustor and others, and is used to predict the pressure gain boundaries and to assess design corridors that potentially achieve positive pressure gain. 

(left) Comparison of pressure gain measurements, (right) Pressure gain model prediction
 

Pressure gain measurements using Kiel probes

Bach, E., Stathopoulos, P., Paschereit, C.O., Bohon, M.D., "Performance analysis of a rotating detonation combustor based on stagnation pressure measurements," Combustion and Flame 217 (2020): pp. 21-36. [link]

As a first in PGC research, we publish stagnation pressure data obtained  with a Kiel probe directly from the product gas stream of a rotating detonation combustor. These data allow a detailed look into the flow conditions in the combustion chamber, the pressure rise due to the detonation process, as well as the average Mach number of the flow. Combined with information about the wave mode, this allows an assessment of the performance of various RDC configurations

(left) Experimentally determined stagnation pressure gain, (right) RDC setup and detail view of Kiel probe
 

Autoignition in Stratified Mixtures for Pressure Gain Combustion

 
Yücel, F.C., Habicht, F., Bohon, M.D., Paschereit, C.O. "Autoignition in Stratified Mixtures for Pressure Gain Combustion," Proceedings of the Combustion Institute, Vol. 38 (3), 2021: pp. 3815-3823. [link]

In this work a new concept for pressure gain combustion, the Shockless Explosion Combustion, is investigated. The goal is to trigger different modes of autoignition by injecting a well-defined fuel trajectory into a continuous air flow. By this, a gradient in ignition delay time is induced that lead to multiple ignition fronts. This quasi-homogeneous autoignition results in an aerodynamic confinement similar to a constant volume combustion and thus, induces an increase in pressure inside the combustor.

A robust injection strategy is developed to enable a precise injection of a defined fuel profile. Non-reactive measurements are implemented that reveal a presevation of the injected fuel profile throughout the measurement section. Pressure sensors, ionization probes and optical measurements of the emitted OH* chemiluminescence reveal the successful initiation of different modes in flame propagation by fuel stratification. Although there is  visible cycle-to-cycle variability, results reveal that a shift towards higher pressures is very well controllable with the injected profiles.

(top) SEC experimental apparatus, (bottom-left) Fuel injection trajectories and stratification, (bottom-right) OH* chemiluminescence and pressure histories during ignition
 

Detonation Initiation by Shock Focusing at Elevated Pressure Conditions in a Pulse Detonation Combustor

Habicht, F. E., Yücel, F. C., Gray, J. A., & Paschereit, C. O., "Detonation initiation by shock focusing at elevated pressure conditions in a pulse detonation combustor," International Journal of Spray and Combustion Dynamics 12 (2020): pp. 1-12. [link]

Experimental investigations on the detonation initiation process via a shock-focusing device are conducted for various initial pressures and mass flow rates. A pulse detonation combustor is operated with stoichiometric hydrogen–air–oxygen mixtures in single cycle operation. Three main statements can be drawn from the results. (1) An increase in the mean flow velocity induces higher velocity fluctuations which result in a stronger leading shock ahead of the accelerating deflagration front. (2) An increase in the initial static pressure reduces the critical shock strength that must be exceeded to ensure successful detonation initiation by shock focusing. (3) Since the initial pressure is directly linked to the mass flow rate, these contrary trends can cancel each other out, which could be observed for 40% vol. of oxygen in the oxidizer.

(Left) Shock pressure ratio over the initial pressure for 40% vol. in the oxidizer. The color represents the success rate. (Right) Success rate as a function of the Reynolds number.
 

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