Development and Significance of the Phosphorus Emission Index of Engine Oils

Abstract

This paper reports the author's effort to v e r i h some of the present assumptions regarding causes and relationships in the volatility of engine oil phosphorus. Using Selby-Noack volatility data froni 2300 engine oils collected by the Institute of Materials in three areas of the uiorld, volatilised phosphorus showed very low statistical dependence on either oil volatility or phosphorus concentration in the fresh oil. Rather, the data seeined to indicate that the chetilistries of the phosphorus-containing additives and their forniiilation ioith other additives 7uere the controlling cause of phosphorus volatility and, by extension, emission level.The study permitted the development of a phosphorus emission index that predicts the emission potential of a forniiilated oil based on the amount of phosphorus found in the volatilised oil collected in the Selby-Noack test.

Phosphorus Additive Chemistry and Its Effects on the Phosphorus Volatility of Engine Oils

“…The figures show the additives present as well as the level of phosphorus deposits and the NO x emissions for each oil. This study of field test oils resulted in three important findings on the questions raised in the earlier work [19][20][21] regarding the significance of PEI and the effects of other oil additives:…”

“…Thus, the PEI analysis of the Ford Motor Company field study resolved the previous posed question [20] of whether other additives in the oil formulation can influence the volatility of phosphorus. More specifically and importantly, it seems apparent that engine oil formulation can be tailored to control phosphorus volatility.…”

“…In a further analysis of the IOM data, it was surprisingly found that phosphorus volatility is unrelated to phosphorus concentration in the fresh oil [19,20] as shown in Fig. 4.…”

“…Considering the lack of relationship of volatilized phosphorus with either oil volatility or initial phosphorus concentration in the oil, it seemed important to have a measure of the comparative phosphorus volatility of engine oils. This led to a concept of ranking engine oils based on the volatility of their phosphorus-containing additive(s) [20]. The ranking method was called the Phosphorus Emission Index, or PEI.…”

“…PEI is defined as milligrams of phosphorus volatilized per liter of fresh oil based on results obtained in the special Noack test. Repeatability was tested and shown in past papers [20,21].…”