The focus of this project is on a revolutionary power cycle that converts energy from renewable fuels into power, with substantially enhanced efficiency by using argon as working fluid. The efficiency of a thermal power cycle is limited by the specific heat ratio of its working fluid. By using argon instead of air the cycle efficiency can be increased by about 25% reaching values above 80%! A new internal combustion cycle that circulates argon will be explored in this project. Such a closed-loop argon power cycle (APC) would most conveniently burn hydrogen and oxygen, leading to an exhaust stream that is emissions-free and effectively contains only water and argon, which allows for easy separation by condensation. Furthermore, the closed-loop nature of APC makes carbon capture affordable, which enables the use of carbonaceous fuels without greenhouse gas emission. Although combustion in air is more convenient, APC will be preferred when efficiency is critically important. Current concerns about climate change and increasing amounts of intermittent renewable energy sources, make hydrogen energy storage and power generation applications of keen interest. A major hurdle to take in the development of APC technology is the control of the combustion process. Since both fuel and oxidizer are to be injected, new injection and combustion strategies of fuel and oxidizer in argon will be investigated. The aim to develop and validate an advanced numerical model that will be used to find the optimal combustion strategy. The project encompasses a multi-scale approach that includes an exploration of the fundamental processes in unsteady igniting gas jets by using high-fidelity numerical models and detailed optical diagnostics. This fundamental knowledge is then translated via experimental and numerical studies of lab-scale setups into design tools for APC technologies. Finally, the injection strategies will be investigated on full-scale research engines.