Since the start of the industrial revolution at around 1850, the temperature and the CO2 concentration in the atmosphere has risen by ~1.0°C and ~120 ppm, respectively, most likely as the result of human activity. Solving the global warming problem is thus one of the most urgent challenges facing mankind in the 21st century. Securing a breakthrough in reduced greenhouse gas emissions and global warming requires a transfer away from our current heavy dependence on fossil fuels. An essential strategy is to increase the efficiency of the energy conversion technologies, increasing the fuel flexibility to enable carbon neutral fuels, and develop new and improved efficient, carbon neutral energy conversion technologies. Numerical simulations and experiments are complementary tools for understanding, developing, and improving such technologies. The objective of this project is to support the goals of the Paris climate accord of 2015 by researching different wind and solar, thermo- and electro-chemical energy conversion technologies such as jet- and dual mode ramjet engines, heat exchangers, batteries, fuel cells, rotating detonation engines and wind turbines as well as the fuels utilized. The group applying for this project have 12 active research projects (including 2 competence centers and 4 EU projects) within the scope of energy conversion for aviation, marine, power, and electricity generation and thermal management, with a total budget of around 300 MSEK over the next four years, involving 32 researchers of which 19 are working on computational methods development and analysis. About 1/3 of the funding is related to the computational work. This research activity has been developed over the last four years with the purpose of supporting the transition from the present energy system to a more sustainable energy system by using bio-fuels, hydrogen, wind/solar and improved thermo- and electro-chemical engines as well as improved thermal management. This proposal is concerned with high-fidelity simulation of fluid mechanics and heat transfer related to wind/solar, thermo-chemical and electro-chemical energy conversion processes. This means addressing several fundamental modelling issues such as turbulence, multi-phase flow, chemical kinetics, combustion, heat transfer, thermal radiation, fluid-structure interaction and optimization. Some aspects of the research are also important for other industrial sectors such as pharmaceutical and food industry. High fidelity fluid dynamics simulations require that turbulence is modelled and treated in a proper way. The interaction of turbulence with additional physics such as heat transfer, spray and combustion necessitate the use of either large eddy simulation or direct numerical simulation. This means that proper resolution of the flow and chemical scales is of the essence, which lead to large computational meshes and long computational times, often dominated by the chemistry. The codes used will primarily be based on openFOAM but will include significant modification to the physical modeling and the numerics that will endorse more accurate and more efficient simulations, in particular on Tier-0 and Tier-1 computer systems. Previous experience with the SNIC resources shows good to excellent scaling.