Shock, Detonation, and System Dynamics in Rotating Detonation Engines
Abstract
Rotating detonation engines (RDEs) utilize pressure gain combustion, granting them significantly improved theoretical efficiency over traditional combustion engines. As their name implies, RDEs utilize detonation waves traveling azimuthally through an annular combustor to burn the fuel. This enables RDEs to release energy nearly continuously, a major advantage over pulsed detonation engines (PDEs), a more established pressure gain combustor. Despite this advantage, RDEs are less mature than PDEs; as such, several key research questions remain pertaining to their optimization. Research to this point has sufficiently established that pressure gain combustion can be achieved in RDEs through a variety of designs. In other words, the basic concept has been realized in the lab and the field. These designs different combustor geometries, injection schemes, and fuel types, among other features. Comprehensive reviews of this subject have been performed by several authors. Despite these advances, several critical factors in how these devices work, as well as their performance, require further work. This fact manifests itself in several pressing technical problems. Firstly, the performance of current RDEs lies well below their theoretical values, and the factors limiting this performance are not fully understood. Specifically, numerical and experimental studies have both shown that the performance of these devices (as quantified by thrust, specific impulse, etc.) falls short of its theoretical potential. One manifestation of this point is that the detonation wave speed in RDEs is less than the Chapman-Jouget (CJ) value. Countless authors have identified mechanisms behind these wave speed and performance deficiencies – these include inhomogeneous injection, parasitic deflagration, curvature effects, pressure drops due to overly stiff injection, and pressure feedback due to inadequately stiff injection. Next, detonations in RDEs often have unusual cellular structures and spatial structures differing markedly from that of the typical ZND detonation – it has been accordingly speculated that detonation waves in an RDE constitute a form of near-limit behavior. This non-ideal detonation structure is especially pronounced in counter-propagating detonation waves, a well-documented phenomenon whose source remains unknown. Finally, RDE performance is also known to depend on the steady wave mode (both the number and direction of waves); however, the factors governing the wave mode – how they depend on both operating conditions and the ignition procedure – is not well understood. Identifying both the optimal wave modes and how to achieve them is another requirement for optimizing performance. To summarize this paragraph, the factors governing the gains and losses of energy from both the RDEs and their constituent detonation waves have not been comprehensively identified. Understanding these gain-loss mechanisms is an imperative first step to optimizing performance and to understand the real-world factors that limit actual performance. Secondly, several questions and issues remain around computing RDE performance. Today, even the most sophisticated computational models fail to faithfully capture both the performance and wave mode of these devices. It is not clear whether this is due to improper modeling assumptions, or simply the fact that the solution is multivalued and different experimental and computational results could be converging to different, but correct, solutions.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 29, 2024
- Source ID
- FA95502310222
Entities
People
- Tim Lieuwen
Organizations
- Air Force Office of Scientific Research
- Georgia Tech Research Corporation
- United States Air Force