1 Phosphorus Emission Index Studies of, and Correlation with, Taxi Fleet Engine Oils ESCIT Meeting,...

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Phosphorus Emission Index Studies of, and Correlation with,

Taxi Fleet Engine Oils

ESCIT Meeting, GM PowerTrain

Presented by: Ted Selby, Savant, Inc.

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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 of1. a primary alcohol ZDDP2. a secondary alcohol ZDDP

Background

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.

Change in PEI Values of Special ZDDPs In Time Interval Tests

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0 20 40 60

Time Interval, min.

PE

I, m

g/L

Primary ZDDP

Secondary ZDDP

250°C

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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.

Primary/Secondary ZDDP Relationship

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To resolve the question of the inversion of primary/secondary ZDDP values at 250°C, two related approaches were taken:

2. Evaluation of the phosphorus in the fresh, residual, and volatile oils from the PEI(250-1) tests using 31P NMR.

1. Evaluation of the primary/secondary ZDDP’s PEIs at 165°C.

PEI Protocol for Lower TemperaturesAt 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 ….

Resolution of Primary/Secondary ZDDP Response

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PEI Protocol for Lower TemperaturesTwo 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 ….

CD

PEI@250°C,1h, no diluent

PEI@165°C,16h, diluent in sample

PEI@165°C,16h, no diluent in sample

PEI@165°C,16h, no diluent in sample- repeat

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60

Oils

PEI values

Study of PEI(165-16), With and Without SN75 Co-Volatile

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52

28

25

8

13

5455

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

Study of PEI Values of Primary and Secondary ZDDPsAt 250° and 165°C

13.6

3.5

5.9

13.2

0.0

5.0

10.0

15.0

250°C 165°CTemperature

PE

I T, m

g/L

Primary ZDDPSecondary ZDDP

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31P NMR studies showed that the secondary ZDDP had formed non-volatile, inorganic phosphates within 10 minutes.

NMR Studies of Primary/Secondary ZDDPs –

Residue oil

Volatiles

Original oilInorganic phosphates

250°C

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In contrast, the primary ZDDP continued to decompose during and beyond a 50-minute exposure to 250°C.

NMR Studies of Primary/Secondary ZDDPs –

3 R.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.

10-minute exposure

Volatiles

Original oil

Residue oil

Volatiles

Original oil

Residue oil

50-minute exposure

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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.

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.

The first taxi test completed in 2002 was a cooperative effort by Ford, Afton, and Delphi using five reference oils.

This implies that bench or dynamometer test correlating with the field must simulate temperature conditions in the engine (depending on the field application).

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 ….

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Taxi Fleet Tests by Ford, Afton, and Delphi

Correlation was considered promising and led to further PEI studies to determine additional field correlation.

Correlation of PEI(250-1) and Taxi-Fleet OilsGenerated by Ford-Afton-Delphi Study

R2 = 0.92

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Phosphorus from Engine, grams

PE

I (2

50

-1),

mg

/L

1st samples for PEI (2003)

2nd samples for PEI (2006)

Best line

P

P,Ca,Mg,Ca

P,Ca

Mg,Caw/o P

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Another recently completed taxi fleet test conducted through the cooperation of Ford and Lubrizol provided another set of reference oils.

These two oils were made available for PEI analyses and were subjected to three protocols of test:

Results of these three analyses are shown in the following slide ….

Recent Ford-Lubrizol Taxi Fleet Study

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.

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.)

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Recent Ford-Lubrizol Taxi Fleet Study

PEIT Values of Ford-Lubrizol Taxi Fleet Engine Oils

1.6 3.3

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25

50

75

100

125

Oils and Analysis Protocol

PE

I (T

), m

g/L

Low impact ZDDP

Comparison ZDDP

250°C, 1 hr. 165°C, 16 hrs. 120°C, 48 hrs.

Repeat Tests

Repeat Tests

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Phosphorus volatility of the comparison oil was considerably greater than the low impact blend at all three temperatures.

Interestingly, of the three temperatures studied, 165°C produced the greatest amount of volatilized phosphorus.

New Studies – Recent Taxi Fleet Tests

From previous 31P NMR studies, this was not unexpected since decomposition of ZDDP to inorganic, non-volatile phosphates happens more rapidly at 250°C.

Two of the protocols, PEI(250-1) and PEI(165-16), were run in duplicate and repeatability was reasonably good.

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).

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 ….

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Phosphorus volatility of the comparative ZDDP engine oil was greater by a factor of 2 to 3 times.

New Studies – Recent Taxi Fleet Tests

PEI(T) Ratios of Two Formulations Used inFord-Lubrizol Taxi Fleet Studies

2.03

3.21

2.90

1.931.88

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2

3

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Oils and Analysis Protocol

PE

I (T

) R

atio

250°C, 1 hr. 165°C, 16 hrs. 120°C, 48 hrs.

Repeat Tests

Repeat Tests

PEI(T) Ratio = Comparative ZDDP/Low-Impact ZDDP

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New Studies – Recent Taxi Fleet TestsCorrelation 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 ….

Correlation of PEI(250-1), PEI(165-16) and PEI(120-48) Comparative and Low Impact Taxi Fleet Oils

R2 = 0.996

R2 = 0.973

R2 = 1.000

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80

100

120

0 2 4 6 8 10 12


PE

I (T

), m

g/L

250°C165°C120°C

Presumed 0,0 value

Best lines

Low ImpactZDDP Comparative

ZDDP

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Several observations can be made from the data:

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 ....

It will again be noted that the high oil temperature of 165°C is most effective in producing phosphorus from the ZDDPs

New Studies and Information

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.

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New Studies – Taxi Fleet and PEI TestsPEI(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.

Correlation of PEI(250-1) and Both Ford-Afton-Delphi and Ford-Lubrizol Taxi Fleet Oils

R2 = 0.82

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PE

I (25

0-1)

, m

g/L

Ford-Lubrizol Taxi Fleet

Ford-Afton-Delphi Taxi Fleet

Replicate PEI on 2006 oils

Best line

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New Studies – Taxi Fleet and PEI Tests

Considering the number of factors that differed between the two taxi fleet tests, such as:

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.

1. Type of vehicles and engines,2. Type of catalytic system,

correlation between phosphorus deposits and PEI at 250°C in two considerably different taxi fleet tests is good.

3. ZDDP chemistries,4. Other oil additives (or their lack in one earlier fleet test oil),5. Protocols for oil change intervals, etc. …..,

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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 ….

One of these considerations was the influence of other oil additives on the ZDDP decomposition and phosphorus volatility. Fortunately information was available.

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Comparison of PEI Values at 250° and 165°C forTwo Oils from Ford-Afton-Delphi Study with Same ZDDP

0.0

20.0

40.0

60.0

80.0

Oils and Temperatures

PE

I Val

ues

, mg

/L

w/ Ca and Mgw/o Ca or Mg

250°C, 1 hr. 165°C, 16 hrs.

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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).

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.

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.

It is was of considerable interest and importance to generate the 31P NMR spectra for these two oils …..

The mass of volatile phosphorus from this decomposition of the same ZDDP at 250°C is less in the presence of additives.

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Original

Residue

Volatiles

inorganic phosphates

no remaining ZDDP

With Ca, Mg at 250°C

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Residue

Original

Volatiles

With no Ca, Mg at 250°C


no remaining ZDDP

Residue

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Original

Volatiles

With no Ca, Mg at 165°C

remaining ZDDP Residue


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Original

Residue

Volatiles


remaining ZDDP

With Ca, Mg at 165°C

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Thus, the PEI information using PEI(250-1) and PEI(165-16) protocols is amplified by the 31P NMR measurements:

Whether this effect on ZDDP decomposition applies to other ZDDPs is an interesting and (as will be shown) relevant question.

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.

Similarly, PEI measurement of effects of other additives on decomposition of ZDDPs at varied exposure temperatures in the engine should be interesting.

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.

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From this and other data from this study:

At 165°C, ZDDP produces volatile phosphorus decomposition largely unhindered by phosphate formation.

Considerations from PEI/Taxi-Fleet CorrelationIn this study, the relatively simple PEI protocol has

thus shown that phosphorus volatilization from decomposition of ZDDP in engine oil is a function of:

At 250°C, ZDDP decomposition is accompanied by marked formation of non-volatile phosphates – much more quickly in the case of some ZDDPs

At 120°C ZDDP produces volatile phosphorus decomposition much more slowly that at 160°C but the decomposition is essentially unhindered by phosphate formation.

• oil temperature,

• rate of ZDDP conversion to non-volatile phosphates.

• presence of other additives, and

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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.

Considerations from PEI/Taxi-Fleet Correlation

150+°C ~100°C

`

250+°COil Pan

Ring Belt& Cylinder

Oil Pan NormalSevere

+ +

Engine Operation

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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.

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.


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.

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.

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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.

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Conclusions

The study has shown:

• 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.

• PEI(250-1) correlation with a Ford-Afton-Delphi taxi fleet test where one ZDDP was used in three formulations at 250°C.

• A marked reduction of volatile phosphorus from the ZDDP of the low-impact oil in contrast to the comparative ZDDP.

• 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.

• Good PEI(250-1) correlation with the combined data from both taxi fleet tests.

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Conclusions (cont.)

• 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.

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.

• 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.

The study has also shown that:

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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.

Effect of Exposure Time on ZDDPs In PEI(250) Method

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Time Interval, min.

PE

I, m

g/L

250°C

2-Ethyl HexanolZDDP

2-Methyl-4-PentanolZDDP

Unstable ZDDP

Classic exponential decomposition

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1 Phosphorus Emission Index Studies of, and Correlation with, Taxi Fleet Engine Oils ESCIT Meeting,...

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