In the research project "Directly Injecting Hydrogen Diesel Engine with High Power Density and Low Emissions", the basis for the use of a large bore diesel engine fueled with hydrogen was investigated. The project partners were the MAN B&W Diesel AG , the Lehrsruhl fur Verbrennungskraftmaschinen und Kraftfahrzeuge (LVK) and the Lehrsruhl A fur Thermodynamik (LAT). The LAT investigated mixture formation, ignition and combustion processes with modern optical measurement techniques, in a newly developed rapid compression machine (RCM) and with numerical simulations. The investigations delivered a set of suitable thermodynamic parameters for the operation of the engine. In addition, optimized geometries for the nozzle design were found out. A new concept for a high pressure hydrogen injection system with variable needle lift was setup and investigated.