Dedicated Piston Bore Interface Layout for H2-ICEs

The significantly changed framework conditions of a hydrogen-fuelled engine in terms of mechani-cal and thermal loads require a review and refinement of the design of the 'piston bore interface' (liner honing, ring and piston design). Since the influence of oil entry into the combustion chamber is much more important in hydrogen engines than in engines running on conventional fuels due to the risk of oil-induced pre-ignition, the interaction between friction, blowby and oil transfer into the combustion chamber was investigated in detail. Experimental tests were carried out on both a sin-gle cylinder engine ('floating liner') and a multi-cylinder engine.
In addition to a baseline measurement on gasoline, four different liner honing variants were evalu-ated on hydrogen. The main measurement and evaluation parameters were the crank angle-resolved frictional force and the oil consumption. The frictional force was determined by measuring the force on a liner attached to four triaxial piezo force sensors. A special sealing solution is used to decouple the cylinder head sealing function.
Oil consumption was determined by balancing all carbon-containing components in the intake air and exhaust gas, which is obviously only possible when using a carbon-free fuel. Due to the very low concentrations of CO, HC and CO2 (which, apart from the intake air, come 100 % from the engine oil), the demands on the measurement system are very high.
The starting point for the honing optimisation was a liner honing system currently used in a series-production gasoline engine. From this basic variant, three other honing variants were analysed, each with different objectives. Starting with a very low roughness solution with a small lubricant holding volume, a variant with a modified honing angle and thus a different lubricant interaction in terms of friction behaviour and oil consumption was also tested. The individual variants were ana-lysed in detail with a resolution of the crank angle in the sub-areas in order to gain insight into the influences on friction losses in the individual phases of the working cycle.
In order to analyse further optimisation possibilities, a variant with low roughness in the area of hydrodynamic lubrication of the piston ring assembly and a standard honing structure in the area of mixed friction of the top dead centres was finally tested. This strip honing is intended to support the objective of low friction losses and at the same time provide sufficient lubricant supply to protect against wear in the area of the top ring reversal points. The aim is to analyse a solution that is ad-vantageous for hydrogen propulsion both in tribological terms and in terms of the tendency for oil-induced combustion anomalies.
These investigations on single and multi-cylinder engines will provide valuable insights into the in-teraction of combustion development and engine mechanics in hydrogen operation.