Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/601893
phorus and sulfur. In the first analyses of volatiles collected from the bench test, it was apparent that the phosphorus additives in the engine oils were also producing phosphorus through additive decomposition. On the basis of these findings, a parameter related to the amount of phosphorus released during the test was devel- oped called the phosphorus emission index (PEI). Figure 5 shows the change in PEI over the last eight years. It is evident that considerable progress has been made in reducing the phosphorus decomposition and/or volatility of these two multi- grade SAE classifications. The reduction of the PEI to 6 to 10 milligrams per liter of engine oil is a significant change in protecting the catalytic converter from the effects of phosphorus. With the trend toward smaller, fuel-efficient and turbocharg- er-equipped engines generating higher temperatures during operation, a bench test that can reveal an oil formulation's phos- phorus emission tendencies would be useful in designing lubricants best suited to the engine and the environment. Phosphorus Content and Volatility How much influence the phosphorus in an engine oil has on the amount of phosphorus volatilized during engine operation is an important question affecting the choice of additives in oil formula- tion. Figure 6 shows the phosphorus content in a number of SAE 0W-20 and 5W-30 engine oils vs. the PEI values obtained. The data reveals that phosphorus volatility generated by the Selby-Noack test is virtually unrelated to the amount of phosphorus present in the oil as an additive. The lack of correlation between the phosphorus in the engine oil and the amount of phosphorus volatilized is evident in the low correlation coefficient (R²) values. This parameter would be near a value of one if phosphorus concentration affected its volatility. As shown in Figure 6, the values obtained from the data are much lower, with R² at 0.05 for SAE 0W-20 and 0.17 for SAE 5W-30 engine oils. The PEI data are primarily clustered at values from 2 milligrams per liter to about 30 milligrams per liter. However, a small number of PEI values exceed 40 milligrams per liter. These engine oils are likely to be more harmful to the exhaust catalyst. However, as has been shown in Figure 5, PEI levels have been decreasing markedly over the last few years. Without question, the quality of engine oils will play a much greater role in the smaller, more powerful turbocharged engines that are entering the automotive market. However, it is essentially impossible to establish the quality of an engine oil by appearance. This determination can only be made by using the oil or pre-testing it. Obviously, the latter is the much preferred option for automo- bile owners, who have a significant investment in and need for a well-functioning and durable engine.