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Matei Radulescu (University of Ottawa)
The Detonation Structure and its Impact on Detonation Limits Predictions
All gaseous detonations take on a cellular structure with large departures from the steady 1D laminar ZND model. The present talk outlines the current understanding on how the departure from the steady model influences the dynamics of detonations with boundary losses and ultimately their limits. It is argued that there are two wide classes of detonation behavior. Detonations in which all gas reacts rapidly by auto-ignition behind the different elements of the cellular front are well predicted by the ZND model neglecting the non-steady cellular structure. We refer to these as piece-wise laminar detonations. In the second class, for more sensitive chemistry, the gas escapes auto-ignition via unsteady expansion behind the non-steady lead shocks and turbulent diffusive burning controls the burning rate. Large departures are found from the ZND model predictions for these turbulent detonations. We review the mechanisms controlling the generation of turbulence in detonations in the latter class, associated with the Mach reflections of strong shocks in low isentropic exponent gases.
Bing Wang (Tsinghua University)
Recent Research Progress on Rotating Detonation and Its Application in Different Engines
Propulsion devices based on rotating detonation have been proposed, and hot tests have been performed over the past 60 years. With a historical overview of research highlights, this presentation focuses on recent research progress on unstable combustor phenomena, the combustion mode identification and the associated physical mechanism. Research indicates that multiple factors can influence rotating detonation instability and most of them can be linked to the reactants injection condition and combustor geometry. A series of instabilities can be identified in the combustor by either changing the mass flow rates and the equivalence ratios, or adopting a different injection configuration. The mechanisms for the effects of injection conditions are investigated by means of flow visualization and flame diagnosis. With respect to the effects of the combustor geometry, the minimum combustor channel has been accepted as a key criterion for the stable rotating detonation, but other geometrical factors have also been suggested to influence the instabilities, such as, the length of combustor, the hollow combustor and the exit size of throat. Both experimental and numerical simulations have been carried out in our laboratory investigating this problem. In particular, we experimentally investigated the mechanisms and the control method of the instabilities of rotating detonation, and an explanation based on the combustor acoustic modes has been proposed to illustrate the occurrence of unstable phenomena. Future prospects for rotating detonation engines are provided.
Jiro Kasahara (Nagoya University)
Rotating and Pulse Detonation Engines System Development for the Sounding Rocket S520-31 Space Flight Experiment
A research group consisting of Nagoya University, Keio University, Japan Aerospace Exploration Agency Institute of Space and Astronautical Science (JAXA/ISAS), and Muroran Institute of Technology is developing a space flight rotating detonation engine demonstrator using the JAXA/ISAS sounding rocket S520-31. Development of the engine is ongoing with the goal of launch in the summer of 2020. The sounding rocket will be equipped with two rotating detonation engines and one pulse detonation engine as a second stage system. This flight experiment will demonstrate that a detonation engine can function as a high-performance rocket engine for space propulsion and a reaction control system engine. In this talk the recent experimental results and the total system of the second stage are presented.
Ulrich Maas (Karlsruhe Institute of Technology)
Mathematical Modelling of Ignition processes
Detailed numerical simulations of ignition processes using the complete set of time-dependent governing equations and complex chemistry have become an important research tool in the recent years. Whereas in most cases such simulations are used to optimize practical combustion systems like internal combustion engines, these simulations are also of tremendous value to explain the multiple-parameter dependence of ignition hazards.
A major problem of mathematical models is the multi-physics character of such ignition processes. Processes that have to be accounted for are: multi-phase processes (e.g., ignition of droplets), formation of ions, interaction with electrical fields (e.g., spark ignition, streamer discharges), heterogeneous reactions (e.g., ignition at hot walls or by hot particles), and very detailed chemical kinetics (e.g. auto-ignition at low temperatures). In addition interaction of the ignition process with turbulent flow conditions has to be accounted for.
In the talk we discuss the principle of these modelling strategies and their application to generic ignition scenarios like auto ignition, ignition by sparks or by hot particles. Although these ”generic” scenarios already allow a good insight into the governing processes, it is important for practical applications to characterize the overall ignition process. Therefore, we shall discuss in the second part of this work how the detailed information can be used to devise models for the overall ignition process. The problem in modelling these (typically turbulent) processes is that the description of chemically reacting systems leads to scaling problems in space and time. In particular, an oversimplification of the coupling processes between chemical reaction and turbulent flow should be avoided by all means to allow a predictive character. In the presentation it is shown how hierarchical concepts can be used to solve this problem.