Malte Jaensch

The transition of large-bore internal combustion engines to hydrogen offers a pathway for decarbonizing stationary power generation. However, achieving competitive power densities with port fuel injection requires high charging pressures due to intake air displacement and lean-burn combustion. The combination of high charging requirements and low exhaust gas enthalpies constrains conventional single-stage turbocharging, necessitating alternative concepts such as multi-stage or assisted systems. Because the charging architecture directly influences in-cylinder thermodynamics, this study experimentally quantifies the impacts of exhaust backpressure on a single-cylinder large-bore hydrogen engine by comparing an unrestricted exhaust baseline with configurations emulating the backpressure of single-stage and assisted turbocharging concepts. Results indicate that applying a realistic single-stage turbocharger efficiency decreases the indicated engine efficiency by 3.7 percentage points compared to an unrestricted baseline. Emulating an electrically or mechanically assisted turbocharger setup restricted the stable operating map, reduced the maximum indicated mean effective pressure from 19.7 to 18.7 bar, and caused an indicated efficiency penalty of up to 3.1 percentage points. This highlights the fundamental trade-off: achieving the necessary boost pressure either induces a thermodynamic penalty via high exhaust backpressure or requires additional power to drive the compressor. Regarding emissions, the elevated backpressure substantially reduces nitrogen oxides at medium loads with less lean mixtures compared to the unrestricted baseline due to the increased trapping of residual gas, while causing a slight increase at low loads. At high engine loads, however, both nitrogen oxides and unburned hydrogen emissions remain unaffected by the increased backpressure. These findings demonstrate the necessity of advanced charging architectures, such as multi-stage or externally assisted systems, to optimize the efficiency of stationary hydrogen engines.

Understanding and mitigating limiting combustion phenomena, such as pre-ignition and knocking (termed combustion anomalies), is essential for establishing hydrogen as a viable fuel or blend component. Optically accessible engines are commonly used to gain spatially and temporally resolved insights into such abnormal events. However, the hydrogen flame spectrum is primarily in the ultraviolet (UV) range, which necessitates the use of costly and bulky UV-optimized hardware. Furthermore, the stochastic nature of these events limits the use of targeted excitation sources for conventional optical diagnostics. This study investigates ammonia as a potential gaseous dye at low concentrations (0.5 and 2 vol.-%) in preliminary non-engine experiments. The objective is to enable detection in the visible spectrum through the expected visible flame emissions from the amino radical (NH ₂ *). Hydrogen-ammonia flames with 0–2 vol. − % ammonia were analyzed using high- and low-speed optical recordings in the visible and ultraviolet (Hydroxyl radicals (OH*)) ranges, alongside spectroscopic measurements in a turbulent burner. The OH* signal remained largely unaffected by ammonia addition, while NH ₂ * effectively localized the flame, offering a visible alternative to UV-based detection. The impact of ammonia addition on key combustion parameters and the flame stability of the original hydrogen flame was analyzed using 0D-reactor and 1D-flame simulations. The NH ₂ * radical, produced during ammonia combustion, proved to be a reliable flame marker due to its heat release dependence and position within the reaction zone. For the lean operating range relevant to hydrogen combustion, the deviations observed were comparable to commonly used tracers. For a 1 vol. − % ammonia fraction, the maximum deviation in laminar flame speed was 6 %. The ignition delay time showed negligible differences at pressures exceeding 15 bar. In this study, preliminary optical and simulative investigations demonstrate that small ammonia additions of 1 vol. − % are effective for dyeing hydrogen flames for localization purposes without significantly affecting combustion characteristics. These findings support future applications in engine-side operations.

Hydrogen combustion in internal combustion engines is a strongly awaited technology on the way to carbon neutrality, but still with major challenges to takle. There are plenty of combustion anomalies like preignition, backfire, knock and lube oil ignition that come along with the technology, hence not yet controllable. To gain more knowledge about their origin, optical engines and CFD simulations are well established methods to investigate and develop knew combustion processes. Hydrogen’s wide flammability range and its short quenching distance bring new challenges. However, optical engines give the best insight into the real combustion behavior. Therefore, their understanding and proper modeling in the simulation is of great importance to calibrate the simulation models accurately. For optical engines there are diverging opinions on how to deal with their blow-by losses. Due to their lack of oil different sealing mechanisms exist and those seem to be crucial for the question on how or wether the blow-by has to be modelled. proposed a numerical multi-zone blow-by model whereas the opinion at is to neglect those losses.