Comparison of ring-liner oil film thickness resulting from different injector designs in a diesel marine engine using an ultrasound measurement method

The global drive to combat climate change is a primary driving force towards producing greener and cleaner marine diesel engines to meet emission legislations. The main cause of an engine’s parasitic frictional loss is the interaction between piston rings and the cylinder liner. Therefore, the piston ring lubricating oil film has been the focus of much prior research, chiefly focusing on small-scale automotive engines. This work employs the ultrasonic reflectometry technique to evaluate the oil film formation resulting from different lubricant injector arrangements on a large two-stroke marine diesel engine. A series of piezoelectric transducers close to the top dead center (TDC) have quantified the oil film thickness (OFT) across three engine loading levels and three injector configurations. The injector configurations compare a more traditional pulse-jet (PJ) injector to a needle lift-type (NLT) injector, which reduces the rate of lubricant atomization. The results gathered show that the OFT increases with decreased engine load for all injector systems. The needle lift injector has been shown to increase the minimum OFT for the first ring at the TDC, reducing the likelihood of boundary lubrication for this ring while also reducing the amount of lubricant present in the exhaust manifold.