Carbon-free fuels present a potential solution for achieving climate-neutral
operation of marine engines. However, their availability is minimal at the
moment, though a steady increase can be expected in the coming years. During
this transition phase, engine concepts that offer conventional diesel operation
and a partial blending of alternative fuels to substitute diesel become
interesting. This can be achieved, for example, by blending hydrogen in the
intake air of a diesel engine, known as hydrogen fuel-share. Due to the high
reactivity of hydrogen, its use in engines is limited by abnormal combustion
phenomena (e.g., pre-ignition, knocking combustion), which current research on
pure gas engines has shown to be strongly promoted by lube oil reactivity.
Building on these fundamental investigations, this paper examines the influence
of lubricating oil on the combustion characteristics of a H2
fuel-share medium-speed diesel engine and quantifies the potential to increase
the hydrogen share using a less reactive engine oil. For this purpose,
single-cylinder engine tests were conducted and supported by 0D/1D simulations
with GT-Power and Cantera. The engine was configured as a conventional
medium-speed marine diesel, equipped with a hydrogen port fuel injection (PFI)
system on the cylinder head. A thermally stable ester-based gas engine oil was
used for reducing reactivity compared to a state-of-the-art mineral diesel
engine oil. The results show reduced auto-ignition tendency during compression
and a mitigation of backfire. An increase in average effective CO2
reduction of up to 17 percentage points is demonstrated, resulting in a total
CO2 reduction of 39% on a standard load profile for main
propulsion engines. These findings highlight that the choice of lubricating oil
can play a key role in increasing the hydrogen share in H2 fuel-share
diesel engines, thereby supporting the transition toward climate-neutral
propulsion concepts.