Title: Loss analysis of a direct-injection hydrogen combustion engine In the discussion on the avoidance of CO2 emissions and other pollutants in the transport sector, hydrogen, as a carbon-free fuel, is a useful alternative to conventional fuels. The use of hydrogen in modern internal combustion engines provides a quick and cost-effective way of sustainable decarbonisation of the transport sector. In comparison with conventional fuels, the efficiency of the internal combustion engine can increase by the use of hydrogen. The Chair of Energy Conversion Systems for Mobile Applications works in cooperation with some industrial partners on the use of hydrogen in internal combustion engines. To exploit the entire efficiency potential of a hydrogen internal combustion engine, it is expedient that the injection takes place directly into the combustion chamber of the engine. With direct-injection hydrogen combustion engine (H2-DI engine), the injection timing and injection strategy are of very high importance. The main goal for an efficient H2-DI engine is the development of a sensible strategy for controlling the injection timing. For this, the influence of the single losses on the indicated efficiency as a function of the injection timing has to be investigated. For this purpose, a one-dimensional simulation model was created. which based on measurement data of a hydrogen-converted diesel engine. With the help of this model for the thermodynamic loss analysis, it is possible to make predictions for the optimized design of the fuel mixture system (injector, rail and pressure accumulator) and the basic combustion process. Thus, a strategy of the hydrogen injection timing should be realized, which presents the optimum efficiency over the entire operation map.