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. This project is motivated by the public concerns on global warming due to emissions of the greenhouse gas CO2, as well as 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 great 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 overall fuel-lean mixture, 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 incylinder turbulence. The goals of the DNS work are (i) to achieve improved understanding of the physical and chemical processes in the RCCI processes; (ii) to generate reliable data for validating simulation models for analysis of the class of combustion problems. The goals of the LES work are to make use of the DNS data to develop and validate sub-grid-scale combustion models for internal combustion engines, including RCCI, and to apply the models to real engine simulations. This shall lead to development of new strategies to achieve controllable low temperature combustion IC-engines, while maintaining high efficiency and low levels of 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 RCCI combustion processes. 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 is recently attracted the attention of 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 project ENGIMMONIA and the Nordic Energy Research project CAHEMA.