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Phosphorus Emission Index Studies of, and Correlation with, Taxi Fleet Engine Oils

This presentation discusses the results of studies on phosphorus emissions from taxi fleet engine oils and their correlation with the Phosphorus Emission Index (PEI). The studies show that the decomposition of ZDDP is strongly affected by oil temperature and different forms of ZDDP. The findings have implications for developing test methods that simulate engine temperature conditions. Results from taxi fleet tests conducted by Ford, Afton, and Delphi, as well as a recent study by Ford and Lubrizol, are presented.

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Phosphorus Emission Index Studies of, and Correlation with, Taxi Fleet Engine Oils

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  1. Phosphorus Emission Index Studies of, and Correlation with, Taxi Fleet Engine Oils ESCIT Meeting, GM PowerTrain Presented by: Ted Selby, Savant, Inc.

  2. Background Early PEI studies were all done at 250°C, which – while providing information on oil volatility – also was approximately the temperature of the engine ring-belt/cylinder-wall zone. A time study was made of 1. a primary alcohol ZDDP 2. a secondary alcohol ZDDP Both blended to 1,000 ppm in a GF-3 base formulation that had no prior ZDDP. The PEI data showed that the primary ZDDP had a higher PEI than the secondary ZDDP. Interestingly and important in developing a test method, the secondary ZDDP reached constant PEI value in 10 min.

  3. Primary/Secondary ZDDP Relationship Questions were raised about data showing lower PEI(250-1) values for the secondary ZDDP, since primary ZDDPs were generally found more stable than secondary ZDDPs in severe engine dynamometer tests with oil temperatures of 150+°C . These questions led to further studies of the nature of ZDDP decomposition, phosphorus volatility, and the meaning of PEI information at different temperatures regarding: 1. Taxi-fleet tests as representative of more normal (but occasionally somewhat strenuous) engine operation. 2. Severe engine dynamometer tests producing oil temperatures as high as 165°C which, while important for relatively rapid appraisal of wear rate, oxidation, and deposits formation, were representative of relatively infrequent field operation.

  4. Resolution of Primary/Secondary ZDDP Response To resolve the question of the inversion of primary/secondary ZDDP values at 250°C, two related approaches were taken: 1. Evaluation of the primary/secondary ZDDP’s PEIs at 165°C. 2. Evaluation of the phosphorus in the fresh, residual, and volatile oils from the PEI(250-1) tests using 31PNMR. PEI Protocol for Lower Temperatures At 165°C or lower temperatures, previous studies had shown that collection of sufficient volume of volatiles for PEI analysis was more difficult. Accordingly, a combination of two approaches was taken, 1. Longer volatiles collection time of 16 hours, and 2. Use of co-volatile diluent in the sample. The first approach was straightforward but the second was based on indirect evidence that phosphorus emission mass is not affected by the mass of oil also being volatilized. The following study confirmed this premise ….

  5. PEI Protocol for Lower Temperatures Two oils were run in the PEI protocol for 16 hours at 165°C both with and without dilution by 10g of 75 Solvent Neutral. No effect of the diluent was observed as shown here ….

  6. PEI Studies of Primary/Secondary ZDDPs – Applying the new PEI(165-16) protocol clearly showed reversal of the PEI values ….

  7. Volatiles Original oil Inorganic phosphates Residue oil NMR Studies of Primary/Secondary ZDDPs – 31P NMR studies showed that the secondary ZDDP had formed non-volatile, inorganic phosphates within 10 minutes. 250°C

  8. 50-minute exposure 10-minute exposure Volatiles Volatiles Original oil Original oil Residue oil Residue oil 3R.J. Bosch, et.al., “Analysis of the Volatiles Generated during the Selby-Noack Test by 31P NMR Spectroscopy”, Elemental Analysis of Fuels and Lubricants, Ed. Nadkarni, ASTM STP 1468, pp. 255-273, 2005. NMR Studies of Primary/Secondary ZDDPs – In contrast, the primary ZDDP continued to decompose during and beyond a 50-minute exposure to 250°C.

  9. New Studies PEI studies have clearly confirmed that decomposition of ZDDP is strongly affected by oil temperature, different forms of ZDDP, as well as the effects of other additives. This implies that bench or dynamometer test correlating with the field must simulate temperature conditions in the engine (depending on the field application). Two sets of taxi-fleet studies have been made over the last six years and these have established oils that can be used to provide bench or dynamometer correlation. The first taxi test completed in 2002 was a cooperative effort by Ford, Afton, and Delphi using five reference oils. Three of the oils contained the same ZDDP (at the same concentration) and two contained no ZDDP. Additives were used in two of the ZDDP-containing oils. Of these oils, four were made available and the PEI(250-1) protocol applied with results shown in the next slide ….

  10. Taxi Fleet Tests by Ford, Afton, and Delphi Correlation was considered promising and led to further PEI studies to determine additional field correlation.

  11. Recent Ford-Lubrizol Taxi Fleet Study Another recently completed taxi fleet test conducted through the cooperation of Ford and Lubrizol provided another set of reference oils. In this study, the two reference oils reported were made with different ZDDPs – one having low catalyst impact and the other a comparative oil formulation. These two oils were made available for PEI analyses and were subjected to three protocols of test: 1. PEI(250-1)– Analysis at 250°C for one hour. 2. PEI(165-16)– Analysis at 165°C for 16 hours. 3. PEI(120-48)– Analysis at 120°C for 48 hours. (In the development of these protocols it has been found that at low PEI values, PEI precision increases with exposure time.) Results of these three analyses are shown in the following slide ….

  12. Recent Ford-Lubrizol Taxi Fleet Study

  13. New Studies – Recent Taxi Fleet Tests Interestingly, of the three temperatures studied, 165°C produced the greatest amount of volatilized phosphorus. From previous 31P NMR studies, this was not unexpected since decomposition of ZDDP to inorganic, non-volatile phosphates happens more rapidly at 250°C. At the two temperatures at which protocols PEI(165-16)and PEI(120-48)were run without significant generation of non-volatile phosphates –– the former protocol produced much more volatile phosphorus (roughly, by a mass factor of 30). Two of the protocols, PEI(250-1) and PEI(165-16), were run in duplicate and repeatability was reasonably good. Phosphorus volatility of the comparison oil was considerably greater than the low impact blend at all three temperatures. However, the ratio of the phosphorus volatilities of these two oils remained similar at all temperatures particularly at 165° and 120°C where little conversion to inorganic (non-volatile) phosphates occurred ….

  14. New Studies – Recent Taxi Fleet Tests Phosphorus volatility of the comparative ZDDP engine oil was greater by a factor of 2 to 3 times.

  15. New Studies – Recent Taxi Fleet Tests Correlation of the PEI values at all three temperatures are plotted against the average phosphorus masses from the low impact and comparative oils tested in the taxi fleet ….

  16. New Studies and Information Several observations can be made from the data: Correlation is reasonably good particularly if it is assumed that the best lines pass through the 0,0 origin (that is: 0.0 PEI value if there were no engine-emitted phosphorus). The correlation suggests that the decomposition mechanism for each ZDDP at the three temperatures is the same and also suggests that, while the mechanisms may be different between the two ZDDPs, it is proportionately the same. It will again be noted that the high oil temperature of 165°C is most effective in producing phosphorus from the ZDDPs Question of which of these PEI temperatures best correlate with the engine zones from which the volatile phosphorus was produced, led to further efforts to extend the correlation ....

  17. New Studies – Taxi Fleet and PEI Tests PEI(250-1) data from the recent Ford-Lubrizol fleet test were co-plotted with PEI(250-1) data from four of the oils from the previous Ford-Afton-Delphi taxi fleet test.

  18. New Studies – Taxi Fleet and PEI Tests Considering the number of factors that differed between the two taxi fleet tests, such as: 1. Type of vehicles and engines, 2. Type of catalytic system, 3. ZDDP chemistries, 4. Other oil additives (or their lack in one earlier fleet test oil), 5. Protocols for oil change intervals, etc. ….., correlation between phosphorus deposits and PEI at 250°C in two considerably different taxi fleet tests is good. Engine oil bulk temperatures in taxi fleet tests would be expected to be moderate rather than severe – less than 120°C – and, thus, similar to normal engine temperatures. The fact that the correlation uses the PEI(250-1) protocol and the taxi fleet oil temperature would not be expected to be much above 100-120°C led to further considerations.

  19. New Studies – Taxi Fleet and PEI Tests One of these considerations was the influence of other oil additives on the ZDDP decomposition and phosphorus volatility. Fortunately information was available. Additional samples of the ZDDP-containing blends from the first taxi fleet study by Ford-Afton-Delphi were made available for analysis and PEI(165-16) protocol tests were then run on them. As mentioned, all of these oils that contained phosphorus were blended with the same ZDDP at the same concentration and in the same base oil. Two of these oils differed only in that one oil was formulated with calcium and magnesium additives and the other was not. PEI(250-1) and PEI(165-16)values are compared in the next slide ….

  20. New Studies – Taxi Fleet and PEI Tests

  21. New Studies – Taxi Fleet and PEI Tests It is evident that a significant difference in the response of these two oils occurs when the PEI protocol is changed from PEI(250-1) to PEI(165-16). The mass of volatile phosphorus from this decomposition of the same ZDDP at 250°C is less in the presence of additives. Even more interesting: no difference in mass of volatilized phosphorus is shown at the temperature of 165°C – the two oils now have essentially identical PEI responses. And again, the mass of volatile phosphorus from this ZDDP decomposition is considerably higher at 165° than at 250°C. Apparently, influence of calcium and magnesium additives on the nature of ZDDP decomposition seems to be virtually eliminated at 165°C and this has interesting implications. It is was of considerable interest and importance to generate the 31P NMR spectra for these two oils …..

  22. With Ca, Mg at 250°C Volatiles Original inorganic phosphates no remaining ZDDP Residue

  23. With no Ca, Mg at 250°C Volatiles Original inorganic phosphates no remaining ZDDP Residue Residue

  24. With no Ca, Mg at 165°C Volatiles Original inorganic phosphates remaining ZDDP Residue inorganic phosphates

  25. With Ca, Mg at 165°C Volatiles Original inorganic phosphates remaining ZDDP Residue

  26. New Studies – Taxi Fleet and PEI Tests Thus, the PEI information using PEI(250-1) and PEI(165-16)protocols is amplified by the 31P NMR measurements: 1. Considerably more phosphorus is volatilized at 250°C when the calcium and magnesium additives are absent. 2. At 165°C, the ZDDP decomposes in the same way with or without calcium and magnesium additives. Whether this effect on ZDDP decomposition applies to other ZDDPs is an interesting and (as will be shown) relevant question. Similarly, PEI measurement of effects of other additives on decomposition of ZDDPs at varied exposure temperatures in the engine should be interesting. The relationship between this ZDDP and the calcium and magnesium additives used does suggest that whatever effects other additives may have on ZDDP decomposition, those effects may only be found at temperatures well above 165°C.

  27. Considerations from PEI/Taxi-Fleet Correlation In this study, the relatively simple PEI protocol has thus shown that phosphorus volatilization from decomposition of ZDDP in engine oil is a function of: • oil temperature, • presence of other additives, and • rate of ZDDP conversion to non-volatile phosphates. From this and other data from this study: At 250°C, ZDDP decomposition is accompanied by marked formation of non-volatile phosphates – much more quickly in the case of some ZDDPs At 165°C, ZDDP produces volatile phosphorus decomposition largely unhindered by phosphate formation. At 120°C ZDDP produces volatile phosphorus decomposition much more slowly that at 160°C but the decomposition is essentially unhindered by phosphate formation.

  28. Considerations from PEI/Taxi-Fleet Correlation A sketch made from the foregoing facts and observations may clarify the relationship just discussed …. The sketch shows the relative level of volatile phosphorus anticipated from each area at temperatures indicated on the basis of the PEI studies presented here and before.

  29. Considerations from PEI/Taxi-Fleet Correlation From all the information collected, a reasonable explanation for the fairly good correlation of PEI(250-1) with the taxi fleet data is that volatile phosphorus collected over the period of the fleet test was produced primarily from the ring-belt area. That is, at taxi fleet operating temperatures, relatively little volatile phosphorus would be expected from the circulating oil at 120°C or less while the ring-belt would be comparatively productive over the thousands of miles of operation generated. In contrast, with an engine operating under severe conditions, (either in dynamometer tests or on the road), the circulating engine oil at 150°C or more would be expected to be much more productive of volatile phosphorus than the ring-belt. Development of good PEI correlation with phosphorus volatility from severe engine operation will require moderately repeatable engine or field data but, with this, should also be possible.

  30. Considerations from PEI/Taxi-Fleet Correlation Moreover, as shown by the ZDDP used in the Ford-Afton-Delphi taxi fleet, a ZDDP may not respond in the same way to temperature or the presence of other additives at high engine oil operating temperatures as in a taxi fleet test. This latter relationship may also indicate something about the mechanism by which the presence of other additives can influence ZDDP decomposition …. Influence of other additives may be more evident when ZDDP decomposition is occurring in the ring-belt/cylinder wall area where, in some way, the presence of these additives may inhibit the decomposition rate of some or most ZDDPs. On the basis of the information generated in this study, it is possible that taxi fleet results may only correlate with severe dynamometer or field tests when the ZDDPs tested are shown to be relatively free of the influence of other additives.

  31. Conclusions The study has shown: • PEI(250-1) correlation with a Ford-Afton-Delphi taxi fleet test where one ZDDP was used in three formulations at 250°C. • PEI correlation at 250°, 165° and 120°C with a Ford-Lubrizol taxi fleet test using two forms of ZDDP, one a so-called ‘low-impact’ ZDDP and the other a comparative ZDDP. • A marked reduction of volatile phosphorus from the ZDDP of the low-impact oil in contrast to the comparative ZDDP. • Good PEI(250-1) correlation with the combined data from both taxi fleet tests. • PEI data at 250° and 165°C on two of the oils from the Ford-Afton-Delphi study indicated that additive effects inhibited phosphorus volatility occurred in the ring-belt zone.

  32. Conclusions (cont.) The study has also shown that: • Correlation of PEI(250-1) with the taxi fleet studies can be attributed to higher phosphorus volatility from the ring-belt zone than from the 100°-120°C circulating oil. • PEI data at 250° and 165°C and 31P NMR analyses of the resulting samples show that secondary ZDDP can be less stable than primary ZDDP. • Comparatively unstable ZDDP showed rapid formation of inorganic and non-volatile phosphates at 250°C. • Severe forms of engine tests with oil temperatures of 150+°C may not correlate with the decomposition mechanism of some ZDDPs in engine oils operating at taxi fleet temperatures. In summation, the PEI(250-1) protocol has shown promise in predicting phosphorus volatility from vehicles having more common operating temperatures of 120°C or less.

  33. Proposed Test Method A proposed PEI protocol for correlation with the more normally driven automotive engine is to run the PEI(250-1) protocol with small samples of volatiles taken each 15 minutes. These and the end-of-test sample would be analyzed for their PEI(250) values for both determination of phosphorus volatility and ZDDP stability. This test protocol will be applied to other oils and their ZDDPs for the ongoing studies in ESCIT.

  34. Thanks for listening Any questions?

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