Analysis of the Piston-Bore Interface with Regard to Friction, Combustion Anomalies and Oil Consumption on a Hydrogen Engine

The significantly changed mechanical and thermal boundary conditions of a hydrogen engine require an adaptation of the “piston-bore interface” (liner honing, ring and piston design). Due to the higher risk of oil-induced pre-ignition in the H2 engine, the interaction of friction, blowby and oil entry into the combustion chamber was investigated in detail on both a single-cylinder (“floating liner”) and a multi-cylinder engine. In addition to a baseline measurement with gasoline, four different liner honing variants were tested with hydrogen. Crank angle-resolved friction force and lube oil consumption were evaluated. The frictional force was measured using piezoelectric sensors, while oil consumption was determined by balancing all carbon-containing components in the intake air and exhaust gas, which is only possible when using a carbon-free fuel. The basis for the optimisation was a honing system used in series production gasoline engines. Three other liners with different surfaces were tested: a smooth honed liner with low roughness and low lubricant retention volume, a spiral glide honed liner with modified honing angle and roughness depths for increased lubricant retention, and a liner with a strip honed variant derived from this. This special strip honing combined low friction losses with sufficient lubricant supply in the top dead center area to ensure wear protection and optimum tribological properties. The investigations provided valuable insights into the tribological optimisation of the piston-bore interface and oil-induced combustion anomalies in hydrogen operation.