Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/601893
18 November - December 2015 | www.machinerylubrication.com The quality of engine oils will play a much greater role in the smaller, more powerful turbocharged engines that are entering the automotive market. viscosity would be expected to have important benefits in fuel efficiency but only in engines designed for their use. Viscosity-dependent Fuel Efficiency Index Given the influence that oil viscosity has on the engine, a technique was devel- oped to calculate the effects of engine oils on fuel efficiency. To be meaningful, the viscosity values had to be obtained at the high shear rates associated with oper- ation in specific sections of the engine. Earlier dynamometer work had identified the percentage of friction and operating temperature of the five main lubricating sites in a recipro- cating gas-fueled engine responsible for nearly all efficiency loss. This infor- mation was used to develop the viscous fuel efficiency index (V-FEI) parameter. With this value, which ranges from 0 to 100, the higher the V-FEI of a given engine oil, the less energy is lost to viscosity, and consequently, the more fuel efficient the engine is. Although different engine designs may have different levels of friction in the essential lubricating areas, use of this friction data provides a comparative value for engine oils. Figure 3 shows the average value of SAE 0W-20 and 5W-30 engine oils from the North and South American markets from 2008 to 2014. For comparison, the average V-FEI for SAE 0W-20 and 5W-30 in an earlier study was 46 and 47 respectively. As expected, it was determined that the yearly averaged multigrade SAE 0W-20 oils contributed more fuel efficiency to the engine than did the averaged multigrade SAE 5W-30 oils because of the viscosity differences shown in Figure 2. With the exception of 2012, the increase in V-FEI is equivalent to nearly 7 to 8 percent in viscosity-dependent fuel efficiency. The decrease shown in the average fuel effi- ciency of SAE 0W-20 engine oils collected in 2012 may indicate the development of formulations meeting automakers' concerns that the benefits of hydrody- namic lubrication will not be lost in efforts to improve fuel efficiency. Engine Oil Volatility Another aspect to consider when reducing the viscosity in engine oil formula- tions is that such a reduction is most frequently obtained by using base oils with higher volatility. Volatized oil reduces the amount of lubricant serving the engine and may carry exhaust catalyst-contaminating components, negatively affecting the cata- lyst's smog-reducing ability. The oil remaining after the loss of the more volatile components will also be more viscous and energy-absorbing. Figure 4 shows the response of two of the most volatile multigrade engine oil classifica- tions. Also shown is the specified maximum volatility set by the International Lubricant Standard- ization and Approval Committee (ILSAC). In the last few years, it is evident that the SAE 0W-20 and 5W-30 classification categories were designed to meet the ILSAC volatility specification by a comfortable margin. These results suggest that volatility control may be less demanding with the more recently classi- fied multigrade oils identified as SAE 0W-16, 0W-12 and 0W-8. Phosphorus Emissions and Volatility Soluble phosphorus compounds such as zinc dialkyldithiophosphate (ZDDP) have been used in formulating engine oils for many years. These anti-wear and antioxida- tion compounds have provided considerable support to the design of modern engines. In the mid-1900s, the reciprocating engine was identif ied as a major contrib- utor of air pollution. Unburned or partially burned hydrocarbons from the engine exhaust were modif ied by sunlight into noxious gaseous hydrocarbons, which produced smog in some large cities. As a consequence, exhaust cata- lytic converters were developed in the 1970s to treat the exhaust gas and convert it into carbon dioxide and water. Unfor- tunately, in the years following the catalytic converter's development, it was discovered that certain elements in gaso- line or engine oil, including phosphorus and sulfur, would deactivate the catalyst by coating it. This ultimately led to restrictions on the quantity of these chemicals in engine oil and fuel. Phosphorus Emission Index The Selby-Noack volatility test was devel- oped in the early 1990s as a better and safer approach for determining engine oil vola- tility. It collected the volatile component of the volatility test for further analysis, which was helpful in detecting phos-