R. A. Kishore Nadkarni1
Engine Oil Volatility: Noack Evaporation Methods
ABSTRACT: The Noack evaporation loss is an important test for base oils and lubricating oils used in
internal combustion engines. The alternate test methods used for this determination are described and evaluated regarding their applicability in the field.
KEYWORDS: Noack volatility, evaporation loss, lubricating oils, engine oils
Introduction
Evaporation loss is a critical parameter of interest to automotive manufacturers, and it is included in several oil lubricant specifications. Evaporation may contribute to oil consumption in an engine and can lead to a change to the properties of an oil. The loss of volatile materials can adversely affect the original performance characteristics of a lubricant and therefore could be a significant factor in evaluating a lubricant for a specific use. Such volatiles can become contaminants in the environment in which the lubricant is to be used. Originally in Europe and later in North America and Japan some years back, maximum volatility limits were included in the crankcase lubricant specifications. Since the volatility limits may have a significant impact on the formulation and ultimate production costs, this necessitated the development of volatility test with acceptable precision limits. There are a number of engine oil volatility tests based on diverse techniques such as gas chromatography-distillation共ASTM D5480, D2887, etc.兲 or physical measurements 共thermogravimetric analysis ASTM D6375 and Noack evaporation test ASTM D5800兲.
Gas chromatographic 共GC兲 methods are widely used in the analytical laboratories for a variety of organic analysis. Among these are ASTM D2887 for boiling range distribution of petroleum fractions, and D5480 for engine oil volatility. The former was specified by the automotive industry to measure oil volatility. The method in D2887 does not have very good precise volatility and is limited to oils that have a final boiling point⬍1000°F. As an improvement over ASTM D2887, McCann et al. devised a modifi-cation using high temperature capillary GC procedure using an internal standard. The procedure could obtain a precision of 1–2 % RSD关1兴. However, the GC methods do not necessarily duplicate the engine conditions that contribute to lubricant volatility, and necessitate the use of an arbitrarily chosen volatility temperature and the use of an internal standard to correlate with overall losses during distillation.
The Noack volatility test which evolved was ultimately accepted by both the oil and automotive industries and is today considered a vitally important test in the characterization of lubricating oils and base oils. This test method is based on the principle of loss of mass at a constant temperature under a constant stream of air, a principle developed by Dr. K. Noack in Germany in 1930s关2兴. The original Noack method was designated as DIN 51-581, and later was documented by CEC as L-40-A93, by ASTM International as D5800, by IP共now EI兲 as IP 421, and in Japan as JPI 55-41-93. The ASTM method was later modified to include procedures A, B, and C. In all these methods, the evaporation loss is defined as that mass of oil lost when the sample is heated in a test crucible through which a constant flow of air is drawn. A low Noack value indicates an oil that will maintain its original protective performance qualities for a longer period of use. In all Noack procedures, the precision and accuracy of the results are dependent on a mandatory use of a certified reference standard for the verification of the instrument operation. The equipment needs to be referenced approximately every ten tests if the test is used frequently. If the testing is infrequent, the equipment should be referenced before the first sample of the day is run. If the percent
Manuscript received January 31, 2008; accepted for publication November 10, 2008; published online December 2008. 1Millennium Analytics, Inc., East Brunswick, NJ 08816.
Paper ID JAI101691 Available online at www.astm.org
Copyright © 2009 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.
evaporation loss of the reference fluid is not within the limits given, the instrument should be checked for operating precision or recalibrated before samples are tested. Often CEC reference oil RL-172, RL-223/3, or other equivalent fluid is used as the reference fluid. This oil can also be utilized as a quality control sample for statistical quality assurance of the instrument performance.
Test Method ASTM D5800 Procedure A
In this as well as in its equivalent DIN 51-581 and CEC L 40-A93 methods, a measured amount of the sample is placed in an evaporating crucible which is then heated to 250° C with a constant flow of air drawn through it for 60 min. The loss in the mass of the oil is then determined. The method uses Wood’s metal as a heating medium. Safety Considerations. There are two safety concerns in utilizing the above procedure A method: volatilization of the heated oil, and release of toxic metals from the Wood’s metal heating block at 250° C during testing. Wood’s metal is made up of lead 共25 %兲, tin 共12.5 %兲, bismuth 共50 %兲, and cadmium 共12.5 %兲, all toxic materials and chronic poisons. Although the method calls for operation in a draft-free area, the exhaust fumes from the evaporating oil must be ventilated to an outside source. Thus, the analyzers must be operated in well-ventilated hoods. Further specific precautions may be necessary to prevent exposure to these toxic metal fumes and heated oil vapors. At least two vendors are selling instruments 共procedures B and C兲 which do not use Wood’s metal as a heating medium.
A second concern is the exposure to heated oil fumes in the vicinity of the apparatus. Although the test method calls for a draft-free area, the exhaust fumes from the evaporating oil must be ventilated to an outside source. For safety reasons, some laboratories place the Noack apparatus in a hood. Others place it on a bench-top with an elephant trunk to draw the fumes. Higher volatility results have been observed when the apparatus is used in a hood, because the airflow will sweep the fumes from the top of the crucible. ExxonMobil Research and Engineering Company proposed a shield for creating a draft-free environment and greater safety in operation关3兴. This device isolates the instrument’s heater block envi-ronment using a metal box, thus greatly reducing the air flow immediately around the sample while allowing sufficient thermal exchange. The accessory can be made from a 14GA aluminum sheet for a box fitted to the top of the heating block with its length and width somewhat larger than the dimensions of the top of the heating block. The box has slots in the sides to allow for protruding outlet tubes and temperature sensor wires and a hole in the top to allow heat escape. This device is described in Appendix X3 of D5800-05 standard, and is now commercially available from the vendor ISL. The use of this draft deflector significantly improves the accuracy and the precision of Noack testing as shown by ExxonMobil 关3兴. Given overall safety concerns and the declining use of this particular instrument, CEC has deleted this procedure from its L-40 standard as of 2007. However, it remains as procedure A in the ASTM D5800 standard.
Test Method ASTM D5800 Procedure B
An alternative to the use of Wood’s metal as a heating medium was developed by French instrument manufacturer ISL共later part of PAC Instruments兲 in 1998. The method uses the same principle and the same crucible of the original Noack test method, but does not use the Wood’s metal as a heating medium, and the sample temperature is directly monitored. At present, this is probably the most widely used technique for Noack volatility measurements.
Test Method ASTM D5800 Procedure C
A second alternative to using Wood’s metal heating medium was developed by Savant Laboratories, Inc. It uses the so-called Selby-Noack volatility test equipment and uses a special noble metal sheathing bonded to the volatility chamber. It relates to one set of operating conditions, but may be readily adapted to other conditions when required. The Selby-Noack procedure correlates well with the Noack procedure A. Since then the Selby-Noack procedure has been modified to also run procedure B. The data showed no significant bias against the procedure B results.
The instrument also permits collection of the volatile oil vapors for the determination of their physical and chemical properties, by using a specially designed coalescing system placed just ahead of the
tion flask which is cooled in dry ice. At all levels of volatilization the recovery is essentially complete 共about 99.5 %兲. The details of the early development of this technique can be found in several publications by Selby et al.关4–7兴. Elemental analysis of the collected volatiles may be helpful in identifying compo-nents such as phosphorus, which has been linked to premature degradation of the automotive emission system catalysts. It appears that some phosphorus compounds in the fresh engine oils decompose and are found in the volatiles. The amount of phosphorus in the volatiles is independent of the volume of the volatile products. Selby coined a term Phosphorus Emission Index to quantify the amount of volatile phosphorus species released during the Noack-Selby test关8兴. He has shown that the phosphorus volatility is not related to engine oil volatility or to the phosphorus content of the oil. This lack of correlation could be due to the effects of other engine oil additives and/or variations in the phosphorus additive chemistry. Marked differences were found depending on whether primary or secondary alcohols were used in the ZDDP.
Using 31P NMR technique, different oils formulated with different ZDDPs and other additives were found to have different volatile components. The composition of the volatile phosphorus containing com-ponents depended on the specific ZDDP关9兴.
Test Method ASTM D6375–05
As an easier alternative to the Noack method, Ford Motor Company researchers developed a thermogravi-metric共TGA兲 method which was faster, safer, and employed no hazardous chemicals 关10兴. Rico de Paz of Texaco developed the crosscheck based on above TGA principle which resulted in the ASTM D6375 test method 关11兴. This method is also equivalent to EI methods IP 393 and IP 418. The TGA method is applicable to base stocks and fully formulated lubricating oils having a Noack evaporative loss from 0 to 30 m %. The procedure requires much smaller size sample than in the Noack procedure. A lubricant sample is placed in an appropriate TGA specimen pan that is placed on the TGS pan holder and quickly heated to between 247° C and 249° C under a stream of air, and then held isothermal for an appropriate time. Throughout the process, the TGA monitors and records the mass loss experienced by the specimen due to evaporation. The Noack evaporation loss is subsequently determined from the specimen’s TG curve versus the Noack reference time determined under the same TGA conditions.
Noack Test Methods Precision
Table 1 summarizes the precision obtained in the interlaboratory studies for the five main Noack tests. This precision obtained in the original crosschecks is also borne out by the continuing Interlaboratory Cross-check Proficiency programs conducted by D02.CS 92 as shown in Table 2 comprising of lube oil and base oil data from the cross checks conducted in 2002 through 2007.
Test Method Biases
On an absolute basis there is no bias for the Noack methods since it is an empirical method and there are no certified standard reference materials available. However, there are subtle differences between the alternate approaches to the Noack evaporation determination procedures, in spite of apparent agreement between the results by three procedures shown in Table 2. The Noack values in Table 2 cover a wide range of Noack values each with its own reproducibility that can mask any differences; higher repeatability for procedure C is in part because of fewer laboratories making the analyses. To determine the differences
TABLE 1—Precision of noack volatility test methods.
Procedure Repeatability Reproducibility
CEC L40-A93 0.18+共0.031 X兲 0.40+共0.069 X兲
ASTM D5800 A 5.8 % X 18.3 % X
ASTM D5800 B 0.095X0.5 0.26X0.5
ASTM D5800 C 0.81 % 1.62 %
ASTM D6375 0.31X0.60 0.39X0.60
X is the m % evaporation loss.
between Procedures A and B, many measurements were made by a number of laboratories on the same reference materials and thus, the difference between procedures A and B was determined.
Noack results using ASTM procedures D5800 A and B show consistent differences. Procedure A gives slightly lower results versus procedure B on formulated engine oils, while procedure A gives higher results versus procedure B on basestocks. Interlaboratory tests have shown that procedures A, B, and C yield essentially equivalent results, with a correlation coefficient of R2= 0.996 共see Table 2兲. The data in Table 2 represent the results obtained through ASTM D02 Committee’s CS 92 Interlaboratory Proficiency Test-ing program from 2002 through 2008 conducted three times a year on a worldwide basis.
A test result obtained using one of the procedures can be transformed to an estimated result on the basis of the other procedures as follows.
共a兲 For formulated engine oils in the volatilities range of 10.5 to 21.5 m % Noack, Result by D5800 B = 1.030 X result by D5800 A, and Result by D5800 A = 0.970 X Result by D5800 B.
The 95 % confidence limits for the regression coefficients for these equations are 1.025 to 1.036, and 0.965 to 0.976, respectively.
共b兲 For basestocks in the volatility range of 4 to 25 m % Noack, Result by D5800 B=0.962 X Result by D5800 A, and Result by D5800 A = 1.039 X Result by D5800 B. The 95 % confidence limits for the regression coefficients for these equations are 0.956 to 0.969, and 1.032 to 1.046, respectively.
TABLE 2—Comparative Analysis of Oils by Alternative Noack Procedures.
Sample D 5800 A D 5800 B D 5800 C Lube oils LU 0201 7.63⫾0.38共20兲 7.74⫾0.26共17兲 7.46⫾0.78共5兲 LU 0205 22.32⫾1.39共24兲 23.06⫾0.71共19兲 23.85⫾2.44共4兲 LU 0209 14.54⫾0.95共22兲 14.78⫾0.50共19兲 14.78⫾0.25共4兲 LU 0301 14.77⫾0.63共20兲 15.05⫾0.41共18兲 15.30⫾0.34共3兲 LU 0305 14.92⫾0.74共21兲 15.31⫾0.54共21兲 14.25⫾1.43共3兲 LU 0309 12.60⫾0.59共20兲 12.83⫾0.30共22兲 12.43⫾0.34共4兲 LU 0401 13.84⫾0.97共21兲 14.04⫾0.55共23兲 13.57⫾0.49共4兲 LU 0405 16.02⫾1.28共19兲 16.35⫾0.42共26兲 16.85⫾1.17共4兲 LU 0409 12.12⫾0.56共19兲 12.57⫾0.25共19兲 12.60⫾0.21共4兲 LU 0505 10.69⫾0.59共19兲 11.21⫾0.54共35兲 10.99⫾0.95共7兲 LU 0509 14.61⫾0.77共24兲 14.55⫾0.56共33兲 14.54⫾0.95共5兲 LU 0601 9.51⫾0.53共19兲 10.10⫾0.34共31兲 10.68⫾0.53共5兲 LU 0605 14.20⫾0.89共15兲 14.60⫾0.57共39兲 14.83⫾0.65共4兲 LU 0609 13.87⫾0.71共19兲 14.50⫾0.54共36兲 14.29⫾0.34共5兲 LU 0701 6.40⫾0.58共15兲 6.66⫾0.21共36兲 6.40⫾0.32共4兲 LU 0705 13.85⫾1.58共16兲 14.49⫾0.58共32兲 13.72⫾1.43共5兲 LU 0709 10.83⫾0.46共15兲 10.81⫾0.33共34兲 11.10⫾0.83共5兲 LU 0801 13.42⫾0.91共16兲 13.93⫾0.61共27兲 14.30⫾0.32共2兲 LU 0805 9.94⫾0.86共18兲 10.36⫾0.26共30兲 10.34⫾1.40共5兲 LU 0809 10.18⫾0.50共14兲 10.34⫾0.32共33兲 10.05⫾0.54共4兲 Base oils BO 0206 27.60⫾3.43共7兲 27.54⫾0.90共9兲 BO 0212 24.08⫾1.81共6兲 23.96⫾0.46共12兲 BO 0312 26.44⫾1.35共7兲 25.04⫾0.76共13兲 BO 0406 25.93⫾0.82共7兲 14.91⫾0.38共16兲 BO 0412 2.66⫾0.27共8兲 2.55⫾0.12共16兲 BO 0506 1.05⫾0.14共8兲 1.04⫾0.14共17兲 BO 0512 5.51⫾0.63共5兲 5.16⫾0.32共18兲 BO 0606 6.76⫾0.27共8兲 6.75⫾0.40共16兲 BO 0612 16.59⫾0.68共6兲 16.86⫾0.63共13兲 BO 0704 20.28⫾0.51共7兲 20.04⫾0.72共21兲 BO 0708 19.62⫾1.26共8兲 19.19⫾1.02共19兲 BO 0712 2.56⫾0.15共5兲 2.54⫾0.12共21兲 BO 0804 14.34⫾0.79共8兲 14.35⫾0.54共20兲 14.1共1兲 BO 0808 14.22⫾1.02共7兲 14.14⫾0.39共21兲 14.63⫾0.58共3兲
Only if the nature of the test specimen is known with certainty, i.e., whether it is a basestock or a formulated oil, above equations may be used to convert results on the basis of procedure A or B. If the nature of the test specimen is not definitively known, i.e., whether it is a basestock or a formulated oil, these conversion equations should not be used to obtain results from one procedure to the other.
Limited amount of data available shows that procedures A and C give similar results for formulated engine oils. However, no comparative data is available for the basestocks. Further work is necessary to quantitate the relationship.
Values in Table 2 are expressed in m % as robust mean⫾robust standard deviation 共number of valid results兲. For this set of base oil samples, laboratories did not submit results by procedure C. As can be seen from this table, while the use of procedure A has remained relatively static, the use of procedure B has significantly increased, while procedure C is used in a much smaller number of laboratories. Recently, CEC has decided to omit procedure A from its protocol because of the hazards associated with the Wood’s metal as well as declining number of labs using that procedure. Thus, at least at present procedure B seems to be the dominant means of determining the engine volatility in automotive and oil industries.
Quality Management in Noack Analysis
Noack volatility is an empirical test. That means, per se, there is no calibration or standardization step involved in the analysis. Hence, to obtain best accuracy and consistency of results it is important to follow the test method instructions correctly. Additionally, special attention should be given to the following points:
共a兲 A reference oil with certified value must be analyzed in the beginning of each test cycle. If the percent evaporation loss is not within the limits given, the instrument should be checked for operating parameters, and reverified with the reference fluid.
共b兲 A quality control sample representative of the samples being routinely tested should be included in the analysis sequence. Any out of control data should trigger investigation for root cause共s兲. 共c兲 Strong air drafts or turbulence around the instrument may adversely affect the test results. The instrument should not be placed in a draft area; however, the exhaust fumes from the evaporat-ing oil should be ventilated to an outside source. An alternative means for preventevaporat-ing air drafts described in the ASTM D5800 test method has proven effective in experience.
In summary, the ASTM D5800 Noack volatility test is an important and crucial test for characterizing the performance of engine lubricants for both automotive and oil industries. Its importance will surely increase with newer oil classification grades on the way, which further restrict the engine oil volatility limits. An equally intriguing aspect is perhaps the volatility of phosphorus compounds in these oils, and characterization of the phosphorus species present in the volatiles, which can cast light on further refining of these products to make them less harmful to automotive engine parts such as pollution prevention catalysts.
References
关1兴 McCormack, A. J., Mc Cann, J. M., and Bohler, R. J., LC-GC, Vol. 9, No. 1, 1990, pp. 28–32. 关2兴 Noack, K., Angew. Chem., 1936, Vol. 49, p. 385.
关3兴 DiSanto, F., Presentation at the ASTM D02 Meeting, Salt Lake City, UT, June 2004.
关4兴 Selby, T. W., Reichenbach, E. A., and Hall, R. H., Proceed. 9th International Colloq. On Tribology, 1994, Esslingen, Germany Bartz, W. J., Ed., 5.5, pp. 1–11.
关5兴 ibid-Amer. Chem. Soc. Publication, 1994.
关6兴 Selby, T. W. and Reichenbach, E. A., Proceed. International Tribology Conf., Yokohoma, Japan, 1995, pp 1–4.
关7兴 Cluff, B. J., McMahon, D., and Selby, T. W., SAE Technical Paper, 961227, pp. 57–60. 关8兴 Selby, T. W., Bosch, R. J., and Fee, D. C., J. ASTM Int., Vol. 2, No. 9, 2005, pp. 239–254. 关9兴 Bosch, R. J., Fee, D. C., and Selby, T. W., J. ASTM Int., Vol. 2, No. 9, 2005, pp. 255–273. 关10兴 Zinbo, M., and Skewes, L. M., Thermochim. Acta, Vol. 154, 1989, pp. 367–376.
关11兴 de Paz, E. F., and Sneyd, C. B., SAE Technical Paper 962035 1996.