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HANSA 02-2017

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Schiffstechnik | Ship

Schiffstechnik | Ship Technology A whirlwind of change Cylinder oil lubrication is becoming an increasingly complex part of engine operations. ExxonMobil and Fathom Maritime Intelligence have conducted a study to evaluate the impact of regulations and changing vessel operational profiles It is important for ship operators to understand the factors that impact cylinder oil lubrication, how they need to plan for these and how to optimise lubricant use to deliver the best results, according to the study »The Impact of Regulation on Cylinder Oil Lubrication«. The introduction of emissions and effciency-based regulations has catalysed a change in the way ships are operated, fuel types that are used and the technologies installed on-board ships. A range of different fuels are now being used to power ships alongside traditional HFO such as heavy fuel oil (HFO). Engine designs are evolving to satisfy effciency demands, which in turn is impacting operating conditions within the engine cylinders’ machinery. Key changes in ship operation, fuel use and engine development are lower-load operations (slow steaming), fuels alternative to heavy fuel oil (HFO) that have a wider variation of sulphur content as well as new engine designs. All of these factors influence the selection of suitable cylinder oil lubricants. According to the study it is vital that different specifications of cylinder oils designed for specific operating conditions and fuel types are matched with ship fuel and engine operating requirements. Failure to do so can have severe cost implications. The impact of legislation The emission of sulphur oxides (SOx) from ships is regulated internationally by the International Maritime Organization (IMO) and on a regional level by attendant regulatory bodies. SOx emissions are formed in the combustion chamber of the engines due to the sulphur present in fuel. The concentration of the SOx gases formed is directly linked to the fuel sulphur content. It is the reduction in the sulphur content of marine fuels upon which regulatory requirements for SOx emission reduction are based. The legislation also allows operators to comply with regulation by installing appropriate abatement technology. Not utilising the correct cylinder oil lubricant in two-stroke engines with an optimised feed rate has financial implications for ship operators, ExxonMobil and Fathom explain. Cylinder oil lubricants are a single use product. If feed rates are not optimised, there can be unnecessary oil consumption. Many vessels have the feed rate set higher than necessary by up to 50% or more which means that a significant volume of cylinder oil is wasted. On a single large vessel this over lubrication can cost as much as an additional 100,000 $ in a year. Incorrect use of lubricant and mismatch to the type of fuel used can have serious mechanical consequences including excessive wear of engine components. This can cause shortened life spans of engine components and costly replacements through to engine failure. In order to stay competitive in a challenging market it is critical ship operators utilise the correct lubricants as well optimising the quantities utilised for each vessel. During combustion the sulphur in the fuel is subject to oxidation and SOx (sulphur dioxide and sulphur trioxide) formation. The SOx compounds react with the water created from combustion to sulphurous and sulphuric acids. These corrosive compounds, if not neutralised, will corrode the cylinder liner wall. One of the principal functions of the cylinder oil lubricant is to act as a neutralising agent. The BN (Base Number) of a lubricant represents its »neutralising power«. A BN too low means that corrosive sulphuric by-products of combustion remain un-neutralised. These create excessive corrosion of the cylinder liner leading to metal-to-metal contact and scuffng as oil control is lost. A BN too high means there is more base (calcium carbonate, CaCO3) than is required. This starts to form hard deposits that can cause fouling of the piston crown which in turn can lead to bore polishing as well as deposition of ash in the combustion chamber, exhaust vales and turbocharger. Again, loss of oil control results in metal-to-metal contact and adhesive wear. The BN is what is often referred to as the »alkalinity« or »base« of a lubricant, however it is actually the quantity of acid, expressed Iain White, Global Marketing Manager, Marine Fuels and Lubricants for ExxonMobil, presented the study at the 2016’s SMM in Hamburg, where he told HANSA: »We are almost in the middle of a whirlwind of change. New regulations and effciency measures also impact engine designs. From a lubricants point of view we have to look at every single engine.« in terms of the equivalent number of milligrams of alkaline potassium hydroxide, that is required to neutralise all alkaline constituents in one gram of sample. The higher the sulphur content of the fuel, the more acidic compounds form and the higher the BN of the lubricant that is required for effective neutralisation. Therefore, a careful balance is required. Fuel Switching As the BN of a lubricant must be carefully matched to the sulphur content of the fuel and the operating conditions of the engine, switching between fuels of differing sulphur contents causes a mismatch. The risk depends on the length of time a vessel operates with a lubricant that is not matched to fuel sulphur content. Since the introduction of switching between fuels with varying sulphur content there has been no »safe period« that has been established by OEMs. Vessels have been found to be particularly at risk when leaving ECAs. Therefore, the advice is to switch lubricants when 74 HANSA International Maritime Journal – 154. Jahrgang – 2017 – Nr. 2

Schiffstechnik | Ship Technology switching fuels, always taking care to align the timing of fuel change with lubricant change. For dual-fuel operations, two very different types of fuel are utilised interchangeably. ExxonMobil and Fathom recommend that operators either switch between two types of cylinder oil lubricant – one for gas and one for liquid fuel operation. Alternatively, depending on the predominant operating profile of the vessel, it is possible to utilise a single lubricant for their dual-fuel engines designed to match main operating condition. NO x regulation Tier II NO x regulations (combined with Energy Effciency Design Index (EEDI) guidelines) have led to the development of new engine types to meet the requirements. By utilising longer piston strokes these newer engine designs achieve improved fuel oil consumption. To achieve this the cylinders are operating under increased peak pressures and reduced operating temperatures. This creates conditions below the dew point meaning that water may condense on the cylinder liner walls leading to significant sulphuric acid formation as compared to traditional engine designs. If the excessive sulphuric acid is not neutralised by the cylinder lubricant it accelerates cylinder liner wear. The phenomenon is known as cold corrosion. If cold corrosion is suspected it is important to identify how serious the problem is. OEMs recommended that cylinder scrape down monitoring is done to understand what is happening in the engine. MAN Diesel recommends the use of a »Sweep Test« and Wärtsilä recommends its »Quick Test«. These tests should be done as part of an established condition monitoring programme. They ensure that the performance of the engine is known so that the feed rate can be set appropriately, and the tests should be repeated whenever parameters change, such as a new fuel in use. Not only will it enable the correct cylinder oil to be selected but it will enable the feed rate to be optimised to suit the engine, operating conditions and cylinder oil in use. The impact on cylinder oil lubrication will depend on the NO x abatement technologies fitted: Selective Catalytic Reduction (SCR) Technology SCR is post combustion technique. Cylinder oil lubricant selection therefore should be based upon matching the BN to the fuel sulphur content of the marine fuel used. The possible effect of cold corrosion must also be considered. Cylinder oil lubricant additives can have an impact on the long term performance of SCR catalysts, therefore the suitability of the cylinder oil lubrication match with the technology is a key factor to consider. New Generation Engines In order to comply with NO x Tier II regulations, there is the new generation of engines. Engine operating profiles are also changing to increase low-load and partload operation. The new generation of engines are particularly susceptible to the issue of cold corrosion that can also be an issue or further exacerbated when the ship operates at low load for long periods of time as the engine is operating at lower temperatures in this state. OEMs’ recommendations will vary and the OEMs must be consulted for each specific engine type for optimal lubricant selection under different load conditions but a cylinder oil scrape down monitoring programme is always recommended. In newer engines a number of design changes are being implemented including changes to the liner cooling systems and cylinder oil injection points to address cold corrosion. Engine model, engine modification, engine load and fuel sulphur content must be taken into account when selecting a cylinder oil lubricant. Challenges ahead As legislation around the fuel-related emissions from shipping operations continues to evolve, coupled with the drive for effciency, the role of cylinder oil lubricants and their requirement to perform under varying engine conditions will become more challenging. The global sulphur cap in 2020 or 2025 will impact marine fuel use across the global fleet and this in turn will mean that ship operators will need to reconsider the cylinder oil lubricants used on a vessel-by-vessel basis. In addition, the need for a monitoring programme to ensure the safe and effcient operation of the engine will become increasingly more important (the full report can be downloaded at ED Source/Photo: ExxonMobil HANSA International Maritime Journal – 154. Jahrgang – 2017 – Nr. 2 75

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