Piston-ring Lubrication Issues in Large Marine Diesel Engines

Carbon dioxide and ozone emissions from marine diesel engines are contributing to global warming, whilst emissions of sulphur dioxide, nitrous oxide and particulate matter can result in increased incidences of asthma, heart disease and cancer. Marine diesel engines use a single-pass approach to cylinder lubrication, resulting in increased pollution from the combustion of oil flowing past the piston-rings. Some technological developments – such as common-rail injection systems – have been made to reduce these impacts, but the introduction of new legislation is having a marked effect on operational costs. One example of new legislation is the designation of sulphur emission control areas. These require a vessel to use fuel with sulphur content below 1.0%. Such fuels are expensive, so away from these areas a fuel with sulphur content around 3.5% is typically used. The switch between fuels complicates the lubrication of the engine since the lubricant is required to correctly balance the acidity of the fuel as well as maintain an adequate oil-film for efficient engine performance. Increased wear and corrosion can result from both too much and too little lubricant being injected. The paper examines the impact of the shipping industry on the environment and human health, and reviews the issues associated with existing lubrication methods. It is argued that there is a pressing need for feedback control systems that maintain optimum lubricating conditions of piston-rings under all fuelling conditions.