In an effort to mitigate the impact of climate change, e.g., by reducing the emission of greenhouse gases, hydrogen is becoming an increasingly attractive alternative energy source, replacing conventional long-chain hydrocarbon fuels in the energy and transport sector. While there is a shift in individual transport towards battery-electric applications, the maritime and energy production sectors rely on a high energy density and time- and location-independent availability of the energy carrier. Therefore, large-bore engines powered by renewable fuels have the potential to shift the industry towards a climate-neutral operation. Besides the emission of greenhouse gases, internal combustion engines are known for emitting pollutant emissions, harming human health and the environment. Research on particle emissions of natural gas and hydrogen engines has mainly focused on automotive and heavy-duty applications. Hence, this study investigates particle emissions of a large-bore single-cylinder research engine powered by hydrogen, compared to natural gas, for the first time. Investigations on particles with a diameter as low as 10 nm showed particle numbers of 10⁴ to 10⁵ # cm⁻³, unexpectedly achieving slightly higher particle numbers in hydrogen than in natural gas operations. This is due to particles from lubricant oil and a stronger fuel interaction with the liner oil film in hydrogen operation, demonstrated within a 3D-CFD simulation. The concentrations are still lower by several orders of magnitude than in long-chain hydrocarbon fuel operations of identical engines. An extended emissions analysis based on the gaseous components THC, CO, and CO₂ shows the negligible carbonaceous emissions induced by these oil-based particles.

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.