Direct numerical simulation (DNS) and large eddy simulation (LES) approaches that employ detailed chemistry and transport properties will be used to study the mechanisms responsible for the onset of auto-ignition and the structures and dynamics of the reaction front propagation in dual-fuel reactivity-controlled compression ignition (RCCI) engines and gas turbine engines. This project is motivated by public concerns about global warming due to the greenhouse gas CO2 and the emission of pollutants (soot, NOx, CO, and unburned hydrocarbons) from fossil fuel combustion in internal combustion engines (ICE). The Swedish and international engine industry and research community have spent significant effort in developing clean combustion engines using the concept of RCCI. There are several technical challenges in applying the RCCI concept to practical engines running with an overall fuel-lean mixture and low-temperature combustion. It is not known what the optimized stratified fuel/air mixture is for a desirable ignition while at the same time maintaining low emissions. It has been noticed experimentally that the RCCI process is rather fuel dependent. Recent studies have shown that the process is rather sensitive to in-cylinder turbulence. The goals of the DNS work are (i) to achieve an improved understanding of the physical and chemical processes in the RCCI processes; (ii) to generate reliable data for validating simulation models to analyze the class of combustion problems. The LES work aims to develop and validate sub-grid-scale combustion models for internal combustion engines and biofuel and hydrogen-fueled aircraft gas turbine engines. This shall lead to the development of controllable and robust combustion in engines while maintaining high efficiency and low emissions (soot, NOx, CO, and unburned hydrocarbons). The following fundamental issues are to be investigated: a) the onset of auto-ignition under different stratification in the charge and temperatures; b) the structures and dynamics of the reaction fronts under different stratification conditions; c) the effect of turbulence, the stratifications in temperature and charge, and the loads (mean temperature and pressure in the cylinder) on the auto-ignition and reaction front propagation; d) development of predictive tools for the analysis of combustion processes in practical engines. Generic cases will be considered in the DNS study. The computational domain will be a cubic-shaped constant volume enclosure with periodic conditions at the boundaries. The fuels will be generic but also of industrial relevance, e.g., ammonia, syngas, bio-diesel, and n-heptane. Ammonia has recently attracted the attention of the marine engine industry. Real engine cases will be considered in the LES study. The LES cases will be designed based on the engine experiments carried out through collaboration within the EU projects ENGIMMONIA and MYTHOS and a new VR project on ammonia/hydrogen turbulent combustion.