The Control of Piston Crownland Deposits in Diesel Engines through Oil Formulation

Newer design direct injection diesel engines show tighter top land clearances between piston and liner. An industry specification, PC-1, is being worked on to define the lubrication needs of these new tight top land direct injection engines. Multi cylinder diesel dynamometer tests show that the reduction of top land deposits in these new design engines tends to improve oil consumption and engine life. A main contributor to these deposits is the ash content in the lubricating oil. Evaluations run in a Cummins NTC 400 dynamometer test show that lower ash oils tend to form fewer crownland deposits and give lower (better) oil consumption. A field test run using Cummins NTC 400 engines on 11 oils confirmed the dynamometer data. Included in the field testing were a very low ash oil (0.5 wt%) and an ashless oil, each having carefully balanced formulations. These two oils provided the best overall control of top land deposits and showed no debits in operation compared to the other oils tested.