Importance of Anti-Wear / Extreme Pressure Properties of Marine Cylinder Oils

Abstract

  The predominance of marine [0]fuels with sulfur levels of ≤ 0.50 wt% has significantly reduced industry-wide concern about corrosive wear: this wear stems from the formation of sulfuric acid due to combustion of high sulfur fuel in large two-stroke marine diesel engines. However, other fundamental wear mechanisms do exist and must be properly controlled to ensure hardware durability and reliable engine operation. Liner scuffing, which can be described fundamentally as adhesive wear, continues to occur in large two-stroke marine engines regardless of fuel sulfur level. In the combustion chamber of these engines, piston rings slide against cylinder liners under conditions of high pressures and temperatures. Beyond acid neutralization and deposit control, a key function of the cylinder oil [0]is to form a durable protective film between moving surfaces that mitigate metal-to-metal contact. Multiple factors such as metallurgy, operating conditions (pressure, temperature, etc.), and lubricant impact scuffing and other types of wear. However, this article focuses on the role cylinder oils play in mitigating ring and liner wear. Engine builders determine liner wall surface finish, piston ring pack design and ring coating materials and thickness, while lubricant suppliers and additive companies develop cylinder oils to provide adequate film thickness and, in some cases, dedicated anti-wear / extreme pressure additive technology to reduce friction, minimize wear, and impart high load-carrying capability to the lubricant.