Direct numerical simulation (DNS) and large eddy simulation (LES) approaches, incorporating detailed chemistry and transport properties, will be used to study the mechanisms responsible for the onset of auto-ignition, as well as the structures and dynamics of reaction front propagation of green fuels in dual-fuel reactivity-controlled compression ignition (RCCI) engines and gas turbine engines (GTE). This project is motivated by public concerns about global warming due to greenhouse gas (CO₂) emissions and the release of pollutants (soot, NOx, CO, and unburned hydrocarbons) from fossil fuel combustion in internal combustion engines (ICE) and GTE. The objective is to investigate the combustion and emission characteristics of green fuels (hydrogen, ammonia, and methanol) in ICE and GTE to facilitate the green transition in the transport and power production sectors. Several technical challenges arise when applying green fuels in ICE and GTE. Hydrogen faces issues related to low volumetric energy density and storage difficulties. Ammonia and methanol exhibit ignition challenges, slow flame propagation speeds, and poor combustion efficiency. Additionally, ammonia combustion produces high NOx emissions due to the nitrogen content in the fuel molecule. These challenges can be mitigated through co-combustion with high-reactivity fuels such as diesel (or biodiesel) and biogas (methane). The goals of the DNS work are: (i) To improve the understanding of the physical and chemical processes in ammonia/methanol/biodiesel RCCI combustion. (ii) To generate reliable data for validating simulation models used to analyze combustion processes. The LES work aims to develop and validate sub-grid-scale combustion models for numerical simulations of combustion in ICE and GTE. This will contribute to the development of controllable and robust combustion in engines while maintaining high efficiency and reducing emissions (NOx, CO, and unburned hydrocarbons). The following fundamental issues will be investigated: a) The onset of auto-ignition under varying charge stratification and temperature conditions. b) The structures and dynamics of reaction fronts under different stratification conditions. c) The effects of turbulence, temperature and charge stratifications, and engine load (mean temperature and pressure in the cylinder) on auto-ignition and reaction front propagation. d) The development of predictive tools for analyzing combustion processes in practical engines. For the DNS study, generic cases will be considered. The computational domain will consist of a cubic-shaped constant volume enclosure with periodic boundary conditions. The LES study will focus on real engine cases, with LES simulations designed based on engine experiments conducted through collaborations within the EU project ENGIMMONIA and the new Nordic Energy Research (NER) project Hi-EFECTS.