With increasingly stringent emissions legislation it is clear that during on-road (RDE) vehicle testing and during the new WLTC cycle the engine emissions need to be controlled at any operating condition. A specific challenge is the need to meet the emission requirements under extreme environmental conditions caused by altitude (pressure) and temperature. So far, limited work has been performed on this problem that can be found in public literature. Another major challenge is the need to reduce the NOx emission, for high load operation, potentially with EGR, which to date has not been necessary for light duty diesel engines. This project is dedicated to address above mentioned challenges with a number of experimental and CFD investigations. Investigations include characterisation of the influence of extreme intake conditions on combustion and emission performance, exploration of the potential of using extreme high injection pressure, innovative nozzle and piston-bowl geometry for high-load low-NOx operations, and the corresponding engine calibration. For this, analysis of experimental data will be undertaken to provide an understanding and interpretation on how to optimise the combustion system under the aforementioned conditions. Then simulation methodology to improve fundamental understanding on the influence of above mentioned parameters affecting fuel-air mixing, combustion and emission (NOx and PM) formation and oxidation rate by properly resolving the mixing and combustion with sufficiently complex transport and chemistry will be conducted. Fundamental experiments for the characterization of mixture formation, ignition, flame propagation, and soot formation are also planned to support the project. The expected outcome of the project is to develop fundamental understanding and correlation between extreme injection pressures, innovative nozzle designs, innovative piston-bowl designs and the mixing/combustion characteristics at high-load low-NOx engine conditions and for extreme temperature and pressure boundary conditions. With the findings, guidelines for combustion system optimisation for high-load low NOx operations will be proposed.