Overcoming today’s energy and environmental problems necessitates various efforts by many parties involved in enhancing the potentials of various fuels and the conversion of energies. Concurrently, how the energy is utilized must also be considered holistically. Nonetheless, awareness of the need to improve energy efficiency and protect the environment still lacks in many parts of the world. This book aims to look at some of the numerous efforts on energy research. The book first delves into thermal energy, which involves works such as air-conditioning systems.  This is followed by works on fuel technology and light energy. The final section looks into the use of numerical methods to solve energy-related problems.