FKFS Veranstaltungen

2025 Stuttgart International Symposium
on Automotive and Engine Technology

3. - 4. Juli 2025

Session: Hydrogen II | | 09:00 - 09:30

Experimental Toolchain for Evaluation of Mixture Formation and Combustion in Hydrogen Engines for Light Duty Applications

David Lejsek, Robert Bosch GmbH

The present publication focuses on the optimization of mixture formation and combustion in a low-pressure direct injection hydrogen engine for passenger cars and light commercial vehicles. In a first step, the H2 jet properties are investigated in an optical vessel. Schlieren optics are used to track the gas jet’s evolution and to identify relevant physical phenomena. To go beyond a purely descriptive analysis and understand the root causes of the observed behavior, laser induced fluorescence and particle image velocimetry are optimized to capture effects specific to gas jets such as supersonic shock structures and are used to supplement the schlieren data. High speed video endoscopy is adapted to H2 combustion in a next step, taking into account that the flame becomes visible mainly due to thermal radiation of hot water vapor. The usefulness of HSVE is highlighted by measurements in which mechanisms leading to irregular combustion events are recognized. Finally, thermodynamic analysis of the engine process concludes the investigations. The effects of late H2 injection on engine efficiency and raw exhaust emissions are discussed. When the H2 jet propagates mainly along the roof of the combustion chamber and reaches the open intake valves – an effect identified and understood due to the optical investigations – a change of exhaust gas composition is observed. Engine test bench measurements demonstrate that these changes can be taken advantage of using variable valve timings.