There remains a need to improve the safe operational envelope of propulsion systems while reducing environmental impacts. This has driven a demand to understand the fundamental physics of fluid flows, heat transfer, and combustion mechanisms and to promote clean and efficient propulsion and energy systems. To provide a sustainable and flexible energy future, alternative energy conversion, energy storage, and propulsion technologies are also required. The book focuses on the development and improvement of methods and techniques for analysing and diagnosing the efficiency, operation, and maintenance of propulsion and energy systems, including fundamental research aspects of aeronautics/astronautics propulsion, power engineering, and practical applications.