Pre-ignition (PI) is a common issue in internal combustion engines (ICE) with
spark ignition. While the various causes have been identified with conventional
fuels (such as gasoline or gasoline blends), the causes with hydrogen in ICE are
not yet fully understood.
This article presents the results of investigations into the influence of seven
different lubricating oils on PI in a single-cylinder hydrogen research engine.
The variation of two different parameters at two engine speeds were
investigated: load and air/fuel mixture. For both variations, the tests start at
the same conditions and run until the operating limit of the engine is reached
(peak firing pressure, or maximum intake manifold pressure).
The PI and knocking PI are investigated, while classifying them according to the
peak cylinder pressure. It has been observed that enleanment above λ = 2.4 can
lead to higher PI rates, while simultaneously reducing the knocking PI. During
the load sweep at 2000 1/min, the highest achievable load among all the oils
ranged from IMEP = 19–21 bar, while at 4000 1/min, it ranged from IMEP = 12–15
bar. The performance of the oils showed significantly more disparity at the
elevated engine speed.
While the impact of different lubricating oils on gasoline engines is rather
limited, the outcome of this experiment indicates that in the case of hydrogen
engines, oils can have a significant impact on PI. In addition to the oil
formulation, different viscosities were also investigated. A lower relative
calcium content leads to a much higher PI rate, a lower relative calcium content
combined with a higher viscosity did not impact the PI rate. The base oil
composition came second in terms of PI influence. The sulfated ash content did
not show differences in terms of PI rate. In contrast to gasoline engines, the
PI tendency increases with increasing engine speed.
