Controlling Transcritical Thermoacoustic Interactions for Space Propulsion and Novel Energy Systems

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Rocket science can provide us with novel solutions to some of our modernday energy concerns. Combustion instabilities in liquid rocket engines are one of the most important and challenging problems in space propulsion. These instabilities occur as the unsteady heat release of combustion couples with the acoustic modes in the combustion chamber; the complexity of this interaction is compounded by the highly non-linear, transcritical thermodynamic base state of the cryogenic propellants. The self-excited thermoacoustic coupling needs to be identified, as energetic build-up in the acoustic mode is the most important cause of catastrophic engine failure. However, this very serious challenge in the rocket propulsion community may actually prove to be a novel solution to some of our energy concerns, particularly in industrial settings. By carefully controlling the entropic-acoustic coupling, the energy created through this non-linear interaction may be harvested in a thermoacoustic heat engine to produce useful mechanical power, thus, permitting the efficient re-use of industrial waste heat. The research program will build upon the research of the applicant on liquid rocket engine to extend the knowledge and expertise related to the fundamental mechanisms of thermoacoustic coupling in high-pressure, transcritical systems. This understanding is gleaned from first-principal-based, high-quality numerical simulations of canonical flow setups of the interaction between acoustics, thermodynamics and fluid mechanics. This expertise will be applied to two seemingly distinct, yet surprisingly tangential fields of science and engineering. 1) We will seek to identify intrinsic instability modes in transcritical diffusion flames as a means to explain the onset of high-frequency, self-excited instability modes in rocket engines. 2) We will then transpose our expertise in thermoacoustic coupling in rocket propulsion systems towards the development of a transcritical thermoacoustic heat engine for the conversion of industrial waste heat to mechanical energy. Up to 50% of the total energy consumed in industrial settings is lost through hot exhaust gases and liquids. The recuperation of industrial waste heat by means of a thermoacoustic heat engine increases overall efficiency, saves money and reduces emissions. Additionally, the acquired knowledge of combustion instabilities in high-pressure systems will have direct relevance to gas turbine, premixed automotive injection systems and air-breathing propulsive technology.