Gas engines: NG operation ofSG and DF engines BN 4 -7 low ash gas engine oils are used LFO operation DP engines BN 12 - 15 samelube oils as in diesel engines with LFO are used HFO operation DF engines BGND 3e0n g- i n5e5s BBNN 4120 -5530 or samelube oils as in dieselengines with HFO are used sdaempeenrdusleos as for diesel enginelubrication are followed here, required BN n the pilot fuel quality (LFO or HFO) Figure 2: Lııbricating oil base nuıııber (BN) for gas engines. Additives Detergents Overbased system (BN) Dispersants EP/AW agents Oxidation inhibitors Antifoamants Additive carrier Baseolls Neutrals Bright stock Figure 3: Typical coıııposition of lııbricating oil. lmprovement on Engine cleanliness Cold corration Engine wear Oil oxidation Oil foaming Bleedlng prlnclples Base oils with different viscosities are used toobtain the right viscosity grade MAKALE / ARTICLE important for achieving long oil change ilniqtueirdvafulse. lWwhi en an engine is operating on th a sulphur content varying from less than 0.1 % mass up to 5.0 % mass, a higher alkali reserve is needed to prevent corrosion of the engine components. Since power plant engines are commonly equipped with a wet lubricating oil sump, with oafn hoigil hvoBluNm(e50o-f5a5b)oluutbr0ic.5a - 1 . 0 1 /kW, the use ting oils gives longer oil change intervals compared to lower BN products, especially if the fuel sulphur content is above 2 % mass. Experience has shown that when operating on heavy fuel, lubricating oils with a higher detergency level (BN) perform better when evaluating the cl eanl iness of engine components like the piston undercrown, piston ring grooves, crankcase and camshaft compartment. Though the price of lubricating oil increases when using higher base number products, these oils normally achieve the best total economy, including lubricating oil changes, disposal costs and maintenance routines. The highest BN number used so far in lubricating oils for medium-speed diesel engines is 55. However, it would seem that there is scope for using even higher BN products when operating on heavy fuel due to the low lubricating oil consumption. Many oilier properties of lubricating oil affect the performance of the engine or component besides viscosity and BN. Lubricating oils are manufactured from one or several base oil qualities depending on the required viscosity and the configuration provided by the lubricating oil refinery or blending plant. Various additives are used as well to meet· specific needs. The most important additives are detergents, dispersants, anti-foamants, anti-oxidants, anti-wear and extreme pressure agents, rust inhibitors Lubricating oils in operation and demulsifiers, ali of which are important for the performance of the lubricating oil. Figure 3 outlines the composition of typical lubricating oil. When operating on natura! gas, the fuel is typically very clean and does not contain any sulphur. This means a rather low required alkali reserve for the lubricating oil. On the other hand, properties like oxidation stability, resistance to viscosity increase and foaming characteristics are Lubricating oil ages and starts to degrade during operation and certain additives are partly consumed. For this reason condemning limits have been set for various physical and chemical properties of lubricating oil to ensure acceptable quality during the lifetime of the equipment (Figures 4 and 5). lf the condemning limit ofa property is reached, the lubricating oil batch must usually be changed. However, Property Viscosity Viscosity waıer Unit cSt cSt o/oval. /o/omass Base Number rrg KOH/g lnsciubles in n-Pentane % mass Flash pcint (PMCC) °C Flash pcint (COC) 0c Condemnlna limit Preferred test method -20%/+25% aı 100 °C ASTMD445 -25%/+45% aı 40 °C ASTMD445 max. 0.30 ASTM D95/D1744 min. 20 (HFO q:ıeratiorı) ASTM D2896 max. 50% depletiorı (LFO q:ıeraiiorı) max. 2.0 ASTM D893b rnin. 170 ASTMD93 min. 190 ASTMD92 Figure 4: Comlemning limits of ıısed lııbricating oil: mediuııı speed diesel engin es. ENERJi & KOJENERASVON OÜNYAS I 47
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