Investigations on particle emissions of large-bore engines powered by natural gas and hydrogen†

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.