Plasma assisted combustion: Dynamics and chemistry

Rotating detonation engines (RDEs), also known as continuous detonation engines, have gained much worldwide interest lately. Such engines have huge potential benefits arising from their simplicity of design and manufacture, lack of moving parts, high thermodynamic efficiency and high rate of energy conversion that may be even more superior than pulse detonation engines, themselves the subject of great interest. However, due to the novelty of the concept, substantial work remains to demonstrate feasibility and bring the RDE to reality. An assessment of the challenges, ranging from understanding basic physics through utilizing rotating detonations in aerospace platforms, is provided.

https://arc.uta.edu/publications/cp_files/AIAA%202011-6043%20Rotating%20detonation%20wave%20propulsion%20experimental%20challenges,%20modeling,%20and%20engine%20concepts%20(invited).pdf

Rotating detonation wave propulsion: Experimental challenges, modeling, and engine concepts

Infrared laser-absorption sensing for combustion gases

This article gives an overview of the back- ground-oriented schlieren (BOS) technique, typical appli- cations and literature in the field. BOS is an optical den- sity visualization technique, belonging to the same family as schlieren photography, shadowgraphy or interferometry. In contrast to these older techniques, BOS uses correlation techniques on a background dot pattern to quantitatively characterize compressible and thermal flows with good spatial and temporal resolution. The main advantages of this technique, the experimental simplicity and the robust- ness of correlation-based digital analysis, mean that it is widely used, and variant versions are reviewed in the arti- cle. The advantages of each variant are reviewed, and fur- ther literature is provided for the reader. List of symbols

/pdf/background-oriented-schlieren-bos-techniques-3m41owd4oz.pdf

Background-oriented schlieren (BOS) techniques

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

A study of the influence of orifice diameter on a turbulent jet ignition system through combustion visualization and performance characterization in a rapid compression machine

The detonation propagating through the annular channel of an optically accessible nonpremixed rotating detonation engine (RDE) is visualized in this work using OH* chemiluminescence imaging. The fuel and air are injected from separate streams and partially premix in the channel in front of the detonation wave. The OH* chemiluminescence images allow observation of the size and shape of the detonation structure, trailing edge oblique shock wave, and possible presence of deflagration between the fuel fill region and expansion region containing detonated products. The OH* chemiluminescence images are useful for evaluating the effects of the air mass flow rate, equivalence ratio, air injection area, and fuel injection scheme on the detonation structure and its corresponding impact on RDE operation and performance. The detonation increases in height as the air mass flow rate is increased for low flow rates, experiences subtle changes in size and shape for intermediate flow rates, and transitions from one-wave to two-waves as the flow rate is further increased. For fuel lean conditions, the high OH* emissions from the detonation are distributed more broadly in space. For stoichiometric and fuel rich conditions, the high OH* emissions typically are confined to a more narrow region near the detonation wave front. The wave front is more concave with respect to the fuel fill region in front of the detonation as the air injection slot is increased from low to intermediate values. The angle between the wave front and fuel injection surface in front of the detonation becomes more acute as the air injection slot is further increased. Reducing the number of fuel injection holes has significant effects on the detonation structure including transition from one-wave to two-waves. The waves typically co-rotate with the detonations propagating in the same azimuthal direction for most conditions in which two-waves are established in the channel. Counter-rotating waves with the detonations propagating in the opposite azimuthal direction are observed for some conditions. The observation of two counter-rotating detonation waves demonstrates one occasional effect of non-ideal mixing between the fuel and air in a nonpremixed RDE. The OH* chemiluminescence images are useful for evaluating RDE models and simulations, improving fundamental understanding of the detonation structure in nonpremixed RDEs, and identifying critical design parameters that influence RDE operation and performance.

Imaging of OH* Chemiluminescence in an Optically Accessible Nonpremixed Rotating Detonation Engine

Development and Testing of a Modular Rotating Detonation Engine

A rotating detonation engine (RDE) at the Air Force Research Lab (AFRL) has been modified to allow optical access to the annulus while in operation. High speed video of chemiluminescence was taken for three operating conditions to characterize the RDE flowfield. Two-dimensional representations of the entire RDE are presented to show basic flow structure. Detonation height, detonation angle, oblique shock wave angle, shear layer angle, and contact surface angle were measured. Average value for each of these measurements did not change drastically over the range tested, but large deviations of the values were observed. These considerable deviations of the flowfield point toward device variation as a major factor to be understood.

Flowfield Characterization of a Rotating Detonation Engine

A Rotating Detonation Engine engineered and manufactured by Pratt and Whitney Seattle Aerosciences Center was loaned to the Air Force Research Laboratory at WrightPatterson Air Force Base for further testing and development. The engine was originally designed for ethylene and oxygen, but was altered in order to use hydrogen and air. The engine was tested at a wide range of flow rates and equivalence ratios with hydrogen-air in order to obtain a matrix of the operating space. Although a considerable portion of the test matrix contained successful detonations, all of the detonations that occurred for the tested configuration were in the fuel rich operating regime. In the pursuit of greater thrust output and a wider range of operability, the air was slightly enriched with additional oxygen. The addition of extra oxygen not only increased the range of thrust output and operability, it also allowed the engine to detonate at high enough air mass flows that two detonation waves were established in the engine. The detonation wave activity during the approach and through the transition from one detonation wave to two detonation waves was analyzed in order to gain a deeper understanding of the transition phenomenon.

John Hoke

Papers

A study of the influence of orifice diameter on a turbulent jet ignition system through combustion visualization and performance characterization in a rapid compression machine

Imaging of OH* Chemiluminescence in an Optically Accessible Nonpremixed Rotating Detonation Engine

Development and Testing of a Modular Rotating Detonation Engine

Flowfield Characterization of a Rotating Detonation Engine

Rotating Detonation Engine Operation