Piston Ring Cylinder Liner Scuffing Phenomenon: Investigation, Simulation and Prevention

In spite of being a popular topic in technical publications, scuffing between piston ring face and cylinder liner is an extremely unpredictable and hard-to-reproduce phenomenon that significantly decreases engine performance. This paper will discuss results of metallurgical and metrological (post-mortem) examinations of the scuffing between hard and soft cylinder liners and different piston ring coatings after field, engine and bench testing. Detailed metallurgical analysis describes the lubricity mechanism between various piston ring coatings and iron cylinder liner at different temperatures with and without oil. The paper will explain the origin of the scuffing through lack of or inadequate lubrication at top dead center, particularly for hardened iron heavy-duty diesel cylinder liners. The mechanism of the scuffing origin and subsequent catastrophic seizure during lab testing with Falex and LS9 machines were evaluated through coefficient of friction and acoustic emission measurements. To simulate the same scuffing mechanism between piston ring and cylinder liner after field usage and accelerated lab testing, special testing methodology and measurement techniques were developed. The paper will provide the data from tribological testing of the conventional and new piston ring coatings against hard and soft cylinder liners at different temperatures with and without oil. A new type of piston ring coating will be described that decreases the scuffing phenomenon appearance.