A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

Empirical Study of the Stability of 

Biodiesel and Biodiesel Blends 

Milestone Report 

R.L. McCormick 

National Renewable Energy Laboratory 

Golden, Colorado 

S.R. Westbrook 

Southwest Research Institute 

San Antonio, Texas 

Milestone Report 

NREL/TP-540-41619 

May 2007 

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 
National Renewable Energy Laboratory

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Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337

Milestone Report 

NREL/TP-540-41619 

May 2007 

Empirical Study of the Stability of 

Biodiesel and Biodiesel Blends 

Milestone Report 

R.L. McCormick 

National Renewable Energy Laboratory 

Golden, Colorado 

S.R. Westbrook 

Southwest Research Institute 

San Antonio, Texas 

Prepared under Task No. FC079400 
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Acknowledgments 

This study is the result of a collaborative program between the National Renewable Energy 

Laboratory (NREL) and the National Biodiesel Board (NBB), with technical direction from 

the ASTM Biodiesel Stability Task Force. The authors acknowledge financial support from 

NBB and technical assistance from NBB technical director Steve Howell. Additionally the 

authors thank Teresa Alleman, Stu Porter, and Melissa Williams for their assistance in 

completing this project. 

 i
Executive Summary

In support of the U.S. Department of Energy Fuels Technologies Program Multiyear Program Plan 

goal of identifying fuels that can displace 5% of petroleum diesel by 2010, the National Renewable 

Energy Laboratory (NREL), in collaboration with the National Biodiesel Board (NBB) and with 

subcontractor Southwest Research Institute, performed a study of biodiesel oxidation stability. The 

objective of this work was to develop a database that supports specific proposals for a stability test and 

specification for biodiesel and biodiesel blends. B100 samples from 19 biodiesel producers were 

obtained in December of 2005 and January of 2006 and tested for stability. Eight of these samples 

were then selected for additional study, including long-term storage tests and blending at 5% and 20% 

with a number of ultra-low sulfur diesel (ULSD) fuels. These blends were also tested for stability. The 

study used accelerated tests as well as tests that were intended to simulate three real-world aging 

scenarios: (1) storage and handling, (2) vehicle fuel tank, and (3) high-temperature engine fuel system. 

Several tests were also performed with two commercial antioxidant additives to determine whether 

these additives improve stability. This report documents completion of NREL’s Fiscal Year 2007 

Annual Operating Plan Milestone 10.1. 

The B100 samples examined show a broad distribution of stability on accelerated tests, with oil 

stability index (OSI) or Rancimat induction time results ranging from less than 1 hour to more than 9 

hours and ASTM D2274 total insolubles ranging from less than 2 mg/100 ml to nearly 18 mg/100 ml. 

The accelerated test data indicate that if the B100 stability is above roughly a 3-hour induction time, 

blends prepared from that B100 appear to be stable on the OSI and D2274 tests. 

The D4625 long-term storage results for B100 indicate that most biodiesel samples, regardless of 

initial induction time, will begin to oxidize immediately during storage. If induction time is near or 

below the 3-hour limit, the B100 will most likely go out of specification for either stability or acid 

value within 4 months. Even B100 with induction times longer than 7 hours will be out of 

specification for oxidation stability at only 4 months, although these samples may not have shown a 

significant increase in acidity or in deposit formation. The 3-hour B100 induction time limit appears 

to be adequate to prevent oxidative degradation for both B5 and B20 blends in storage for up to 12 

months. 

For tests that simulated fuel tank aging and high temperature stability, we conclude that stable B100 

(longer than 3 hours induction time) leads to stable B5 blends. For B20, the results are less definitive, 

but provide considerable evidence that B100 with induction time of at least 3 hours produces stable 

B20 blends, but the test cannot differentiate between intermediate and highly stable samples for acid 

number increase or sediment formation under these worst-case test conditions. Additional work is 

required to confirm this finding and to determine whether an additional stability test for the B20 blend 

is required. 

These results indicate that B100 stability is the main factor that affects the stability of B5 and B20 

blends, independent of diesel fuel aromatic content, sulfur level, or stability. An antagonism between 

unstable B100 and diesel fuel was observed. For B100 with an induction time lower than 3-hours, the 

level of deposits formed on the D2274 stability test was well above what would be expected based on 

the B100 deposit level and the percentage of biodiesel in the fuel. This antagonistic effect was 

significantly greater for B20 than for B5. The hindered phenolic antioxidants tested here prevented 

oxidative degradation of B100 in the storage simulation, and prevented degradation of biodiesel blends 

in the storage, fuel tank, and high-temperature simulations. 

We recommend that additional tests be performed with real equipment to validate these conclusions. 

 ii
Acronyms and Abbreviations 

ASTM ASTM International, a standards setting organization 

Bxx designation of biodiesel or biodiesel blend (B100 is pure biodiesel, B20 is a 

20% blend, for example) 

EN European Normalisation 

ISO International Standards Organization 

KOH potassium hydroxide 

NBB National Biodiesel Board 

NREL National Renewable Energy Laboratory 

OSI oil stability index (also called Rancimat induction time) 

PV peroxide value 

RME rapeseed methyl ester 

T90 90% boiling temperature 

ULSD ultra-low sulfur diesel

 iii
Contents 

Acknowledgments....................................................................................................................... i 

Executive Summary ................................................................................................................... ii 

Acronyms and Abbreviations....................................................................................................iii 

Tables........................................................................................................................................ vi 

Figures...................................................................................................................................... vii 

Introduction................................................................................................................................ 1 

Background ................................................................................................................................ 2 

Methods...................................................................................................................................... 5 

B100 and Diesel Fuel Properties............................................................................................ 5 

Accelerated Stability Tests..................................................................................................... 6 

Simulation of Real-World Aging Scenarios .......................................................................... 7 

Results: Stability of B100 ........................................................................................................ 10 

Accelerated Testing and Characterization ........................................................................... 10 

Storage Stability of B100..................................................................................................... 18 

B100 Antioxidant Testing.................................................................................................... 20 

Results: Stability of Biodiesel Blends...................................................................................... 23 

Diesel Fuel Properties and Stability..................................................................................... 23 

Stability of B5 Blends.......................................................................................................... 25 

Accelerated Tests............................................................................................................. 25 

Storage Stability............................................................................................................... 29 

Simulated Vehicle Fuel Tank Aging................................................................................ 32 

Simulated Vehicle Tank Aging Followed by High Temperature Testing ....................... 34 

Stability of B20 Blends........................................................................................................ 36 

Accelerated Tests............................................................................................................. 36 

Storage Stability............................................................................................................... 39 

Simulated Vehicle Fuel Tank Aging................................................................................ 42 

Simulated Vehicle Tank Aging Followed by High-Temperature Testing....................... 44 

Discussion ................................................................................................................................ 46 

Do Accelerated Tests Predict B100 Storage Stability?........................................................ 46 

Is B100 Stability a Predictor of Blend Stability? ................................................................. 48 

Accelerated Tests............................................................................................................. 48 

Aging and In-Use Scenario Tests (Storage, Vehicle Tanks, High-Temperature 

Environment)............................................................................................................. 52 

How Do Diesel Fuel Properties Effect Stability? ................................................................ 53 

How Do Antioxidant Additives Affect Stability?................................................................ 58 

Is a 3-Hour B100 Induction Time Adequate? ...................................................................... 58 

Storage Stability............................................................................................................... 58 

Stability in Simulated Vehicle Fuel Tank and High-Temperature Environments........... 59 

Conclusions and Recommendations ........................................................................................ 60 

References................................................................................................................................ 62 

 iv
Appendix A: B100 Characterization and Stability Test Data .................................................. 64 

Appendix B: D4625 Results for B100 Samples....................................................................... 68 

Appendix C: D4625 Results for Petroleum-Derived Diesel Fuels .......................................... 71 

Appendix D: Accelerated Test Results for B5 Blends............................................................. 72 

Appendix E: B5 Blend Storage, Fuel Tank, and High-Temperature Stability Results............ 75 

Appendix F: Accelerated Test Results for B20 Blends ........................................................... 80 

Appendix G: B20 Blend Storage, Fuel Tank, and High-Temperature Stability Results ......... 83 

 v
Tables 

Table 1. Results of D6468 Ullage Purge Scoping Tests............................................................ 7 

Table 2. Results of D4625 (6-Day, 80oC Modification) Ullage Purge Scoping Tests............... 8 

Table 3. Biodiesel Samples Obtained and Preliminary Characterization ................................ 10 

Table 4. Results of ASTM D6468 Performed on B100 Samples at 150°C/180 Minutes and 

Modified for Gravimetric Determination of Deposits .............................................. 15 

Table 5. B100 Samples Selected for Long-Term Storage and Blending Studies .................... 16 

Table 6. Characterization Results for B100 Samples Downselected for Further Study and 

Blending*................................................................................................................... 17 

Table 7. Results of Accelerated Stability Tests for Biodiesel Treated with Antioxidant 

Additives................................................................................................................... 21 

Table 8. Characterization Results for Petroleum Diesel Samples To Be Used in Preparation of 

B5 and B20 Blends ................................................................................................... 24 

Table 9. B5 Samples Downselected for More Detailed Study................................................. 28 

Table 10. Accelerated Test Results for B5 Samples Treated with Antioxidant ...................... 29 

Table 11. B20 Samples Downselected for More Detailed Study............................................. 38 

Table 12. Accelerated Test Results for B20 Samples Treated with Antioxidant..................... 39 

 vi
Figures 

Figure 1. Glass vessel used for D4625 stability test .................................................................. 7 

Figure 2. Histogram for B100 OSI or Rancimat induction time.............................................. 11 

Figure 3. Relationship between B100 OSI or Rancimat induction time and ASTM D525 

results. Circled data points indicate that no oxidation was observed after 780 minutes 

and the results are simply plotted as 780 minutes..................................................... 11 

Figure 4. Histogram for B100 ASTM D2274 total insolubles................................................. 12 

Figure 5. Relationship between B100 OSI or Rancimat induction time and D2274 total 

insolubles .................................................................................................................. 13 

Figure 6. Relationship between B100 D2274 total insoluble and iso-octane insoluble........... 13 

Figure 7. Change in total acid number on D2274 versus D2274 total insolubles for B100 

samples...................................................................................................................... 14 

Figure 8. Change in total acid number on D2274 versus OSI or Rancimat induction time for 

B100 samples............................................................................................................ 14 

Figure 9. Change in OSI or Rancimat for B100 samples over 4 weeks in D4625 test............ 18 

Figure 10. Peroxide value measured for B100 samples over the D4625 test .......................... 19 

Figure 11. Change in acid value for B100 samples on the D4625 test .................................... 19 

Figure 12. Total insoluble measured for B100 samples over the D4625 test .......................... 20 

Figure 13. Total acid number results for D4625 long-term storage testing of antioxidanttreated B100 samples ................................................................................................ 21 

Figure 14. Total insoluble results of ASTM D4625 long-term storage test for antioxidanttreated B100 samples ................................................................................................ 22 

Figure 15. Total insolubles for petroleum diesel fuels on the D4625 test ............................... 25 

Figure 16. Histogram of OSI or Rancimat induction times for B5 samples............................ 26 

Figure 17. Histogram of D2274 (biodiesel modification) total insolubles results for B5 

samples................................................................................................................... 26 

Figure 18. Histogram of D6468 percent reflectance results for B5 samples........................... 27 

Figure 19. Histogram of D6468 gravimetric insoluble results for B5 samples ....................... 27 

Figure 20. Peroxide value over the D4625 test for B5 samples............................................... 30 

Figure 21. Acid value for B5 blends over the D4625 test........................................................ 30 

Figure 22. Total insolubles formation for B5 blends in the D4625 test................................... 31 

Figure 23. Total insolubles formation for B5 samples treated with antioxidant additives on the 

D4625 test .............................................................................................................. 31 

Figure 24. Peroxide value for B5 blends after 1 week aging at 80oC, as a function of B100 

OSI or Rancimat induction time ............................................................................ 32 

Figure 25. Acid value for B5 blends after 1 week aging at 80oC, as a function of B100 OSI or 

Rancimat induction time ........................................................................................ 33 

Figure 26. Total insoluble for B5 blends after 1 week aging at 80oC, as a function of B100 

OSI or Rancimat induction time ............................................................................ 33 

Figure 27. Filter reflectance and gravimetric insolubles formation for B5 samples aged for 1 

week at 80oC and tested with the D6468 thermal stability test as a function of 

B100 OSI or Rancimat induction time................................................................... 35 

Figure 28. Histogram of OSI or Rancimat induction times for B20 samples.......................... 36 

 vii
Figure 29. Histogram of D2274 (biodiesel modification) total insolubles results for B20 

samples................................................................................................................... 37 

Figure 30. Histogram of D6468 percent reflectance results for B20 samples......................... 37 

Figure 31. Histogram of D6468 gravimetric insoluble results for B20 samples ..................... 38 

Figure 32. Peroxide value for B20 samples tested on D4625 test ........................................... 40 

Figure 33. Acid value for B20 samples tested on the D4625 test............................................ 40 

Figure 34. Total insolubles formed from B20 samples tested on the D4625 test.................... 41 

Figure 35. Total insolubles formation for B20 samples treated with antioxidant additives on 

the D4625 test. ....................................................................................................... 41 

Figure 36. Peroxide value for B20 blends after 1 week aging at 80oC, as a function of B100 

OSI or Rancimat induction time ............................................................................ 42 

Figure 37. Acid value for B20 blends after 1 week aging at 80oC, as a function of B100 OSI 

or Rancimat induction time.................................................................................... 43 

Figure 38. Acid value for B20 blends after 1 week aging at 80oC, as a function of B20 OSI 

induction time ........................................................................................................ 43 

Figure 39. Total insolubles for B20 blends after 1 week aging at 80oC, as a function of B100 

OSI induction time ................................................................................................. 44 

Figure 40. Filter reflectance and gravimetric insoluble formation for B20 samples aged for 1 

week at 80oC and tested in the D6468 thermal stability test.................................. 45 

Figure 41. B100 OSI or Rancimat induction period at 4 weeks on the D4625 test as a function 

of initial induction time.......................................................................................... 47 

Figure 42. Peroxide number at 4 weeks on the D4625 test for B100 samples, as a function of 

initial peroxide number.......................................................................................... 47 

Figure 43. Change in acid value at 4 weeks on D4625 as a function of initial OSI or Rancimat 

induction time for B100 samples. Data labels indicate initial acid value .............. 48 

Figure 44. B5 OSI induction time as a function of B100 OSI induction time......................... 49 

Figure 45. B5 D2274 total insoluble as a function of B100 OSI or Rancimat induction time 50 

Figure 46. B5 D2274 total insoluble as a function of B100 D2274 total insoluble................. 50 

Figure 47. B20 OSI induction time as a function of B100 OSI induction time....................... 51 

Figure 48. B20 D2274 total insoluble as a function of B100 OSI or Rancimat induction time

.................................................................................................................................................. 51 

Figure 49. B20 D2274 total insoluble as a function of B100 D2274 total insolubles. ............ 52 

Figure 50. Diesel fuel aromatic content affect on D2274 total insolubles for B5 blends........ 54 

Figure 51. Diesel fuel aromatic content affect on D2274 total insolubles for B20 blends...... 55 

Figure 52. Results of 1 week at 80oC aging test followed by D6468 thermal stability test for 

B20 samples prepared from B100 AL-27138 and all diesel samples...................................... 57 

 viii
Introduction 

In support of the U.S. Department of Energy Fuels Technologies Program Multiyear Program 

Plan Goal of identifying fuels that can displace 5% of petroleum diesel by 2010, the National 

Renewable Energy Laboratory (NREL), in collaboration with the National Biodiesel Board 

(NBB) and with subcontractor Southwest Research Institute, performed a study of biodiesel 

oxidation stability. The objective of this work was to develop a database to support specific 

proposals for a stability test and specification for biodiesel and biodiesel blends. B100 

samples from 19 biodiesel producers were obtained during December 2005 and January 2006 

and tested for stability. Eight of these samples were then selected for additional study, 

including long-term storage tests and blending at 5% and 20% with a number of ultra-low 

sulfur diesel (ULSD) fuels. These blends were also tested for stability. The study employed 

accelerated tests as well as tests intended to simulate three real-world aging scenarios: (1) 

storage and handling, (2) vehicle fuel tank, and (3) high-temperature engine fuel system. 

Results were analyzed to determine whether ensuring B100 stability was adequate to ensure 

the stability of B5 and B20 blends. Several tests were also performed with two commercial 

antioxidant additives to determine whether these additives might improve stability. This 

report documents completion of the NREL Fiscal Year 2007 Annual Operating Plan 

Milestone 10.1. 

 1
Background 

Biodiesel produced from vegetable oils and other feedstocks can be more prone to oxidation 

than a typical petroleum diesel unless it is modified or treated with additives. The purpose of 

this project is to provide data that define how stable a biodiesel or biodiesel blend should be to 

prevent the formation of acids or sediment during transportation, storage, and use; and 

subsequent vehicle operational and maintenance problems. 

The general mechanism of fat (or lipid) oxidation is reasonably well understood.1,2

 The fatty 

acid alkyl chains have varying numbers of double bonds. When multiple double bonds are 

present they are in allylic configuration, which means that they are separated by a single 

methylene group called a bis-allylic carbon or position. For biodiesel made from common 

feedstocks, such as oils from soy, rapeseed, and palm, as well as lard and tallow, the fatty acid 

chains contain primarily 16 or 18 carbon atoms and from zero to three double bonds. 

Eighteen-carbon chains contain one double bond for oleic acid, two for linoleic acid, and 

three for linolenic acid. The relative oxidation rates for these C18 esters are linolenic > 

linoleic >> oleic3

 because the di- and tri- unsaturated fatty acids contain the most reactive 

sites for initiating the auto-oxidation chain reaction sequence. Oxidation rate correlates with 

the total number of bis-allylic sites (the methylene CH directly adjacent to the two double 

bonds), not with the total number of double bonds.4 These sites have the highest reactivity for 

the formation of free radicals that can react directly with oxygen to form peroxide radicals. 

This is the initial step in the classic auto-oxidation mechanism with the chain reaction steps of 

initiation, propagation, chain branching, and termination.1,2 The allylic position (a methylene 

adjacent to a single double bond) is much less reactive, explaining the much lower oxidation 

rate of oleic acid. Also, the radicals formed at the bis-allylic sites immediately isomerize to 

form a more stable conjugated structure. The peroxide radicals can cleave to form acids and 

aldehydes, or can react with another fatty acid chain to form a dimer. Peroxide can form via 

this route even at ambient temperature. 

Several studies have examined biodiesel stability. Westbrook5 used the ASTM D4625 test 

wherein the subject fuel or blending component is held for 12 weeks at 43oC in a capped but 

vented glass bottle, and oxidation effects (the amount of sediment formed, acidity, and change 

in viscosity) are periodically measured. Wide variations of insolubles formation, acid number, 

and viscosity increase were observed; the least stable samples exhibited unacceptable levels 

of insolubles and acidity 4 to 8 weeks into the test. To more fully understand the causes of 

these differences, McCormick and coworkers6

 examined the stability characteristics of 

biodiesel samples that were commercially available at blenders and distributors during 2004 

and showed that the stability range results primarily from differences in fatty acid makeup and 

natural antioxidant content. However, samples containing high out-of-specification levels of 

glycerides (unconverted or partly converted feedstock) also tend to form deposits. Storage 

conditions can have a large impact on the degree of oxidation. Thus, for real-world samples 

containing impurities, the correlation of oxidation rate or tendency with the number of bisallylic sites may be skewed or overshadowed by other factors such as natural antioxidant 

content. 

 2
Bondioli and coworkers7

 stored several drum quantity samples of biodiesel at ambient 

conditions for 1 year. One sample was “shaken” once per week to promote intimate contact 

with air. Over this period the quiescent samples exhibited little or no change in properties, 

including only minor reductions in Rancimat induction time. This contrasts strongly with 

results of studies conducted at higher temperatures (for example 43oC as in ASTM D4625), 

which have shown large changes in acid value and other parameters.5,8 Additionally, the 

agitated sample exhibited significant increase in peroxide and acid values and a large 

reduction in Rancimat induction time because of the increased exposure to dissolved oxygen. 

Mittelbach and Gangl also stored biodiesel produced from rapeseed oil and used frying oil 

under different conditions for up to 200 days.9 Degradation caused by oxidation began 

immediately, as shown by the formation of peroxides and reduction in Rancimat induction 

time. However, even at the end of the storage period, limits for viscosity and acidity were not 

exceeded. 

Fang and McCormick10 showed that dimerization of the peroxide species is not the only 

mechanism for molecular weight growth and deposit formation in biodiesel, and identified 

several other mechanisms by which biodiesel can degrade. In particular, aldehydes formed by 

peroxide decomposition could also polymerize via aldol condensation. However, all pathways 

to deposit formation involved peroxide formation as the initial step, highlighting the 

importance of preventing peroxide formation at the point of biodiesel manufacture and 

throughout the biodiesel distribution chain. Fang and McCormick also showed an antagonistic 

or synergistic effect on deposit formation for biodiesel blends. The formation of deposits 

under oxidative stressing was higher than predicted for biodiesel blends based on the weight 

percent biodiesel and the deposits formed from the diesel fuel or biodiesel alone. This effect 

was most significant for blends in the 20% to 30% range. 

Vegetable oils contain naturally occurring antioxidants that can cause oxidation stability to 

vary over a wide range, even for samples with similar fatty acid makeup.6

 The most common 

antioxidants are tocopherols. For example, soy oils contain 500 to 3000 ppm tocopherols, 

along with other antioxidants such as sterols and tocotrienols,11 which may not be affected by 

the ester preparation process.12 However, some production processes include steps to purify 

the methyl esters that can remove antioxidants. Biodiesel produced using distillation to purify 

the product, for example, typically contains little or no natural antioxidant and is less stable 

than biodiesel that does. The stability of biodiesel prepared by distillation, as well as biodiesel 

that contains natural antioxidants, can be improved by adding synthetic antioxidants.2

Westbrook5

 has shown that several antioxidants, including proprietary antioxidants developed 

for petroleum fuels, can improve biodiesel oxidation stability. 

High levels of oxidation can cause operational problems for engine fuel system components. 

Terry and coworkers13 showed that at very high levels of oxidation, biodiesel blends can 

separate into two phases to cause fuel pump and injector operational problems or lacquer 

deposits on fuel system components. Blassnegger performed 500-hour fuel injector bench 

tests with rapeseed methyl ester (RME) (B100) samples that had a range of stability.14 Lower 

stability B100, with a Rancimat induction time of 1.8 to 3.5 hours, produced injector deposits 

and reduced the amount of fuel injected per stroke. Tsuchiya et al demonstrated that the 

formation of high levels of acids, which can be generated from unstable biodiesel during 

 3
extended fuel recirculation, can corrode metal vehicle fuel tanks.15 Thus, there are strong 

arguments for ensuring the stability of biodiesel and biodiesel blends. We conducted this 

empirical study, which is directed at defining a performance-based standard, because of the 

numerous factors can affect oxidation 

 4
Methods 

B100 and Diesel Fuel Properties 

During December of 2005 and January of 2006 a single drum of B100 was obtained from 

each of 14 biodiesel production sites in the United States and two more from Canadian 

production facilities. Additionally, three drums of European rapeseed-derived biodiesel 

(RME) were obtained. The 19 B100 drums were nitrogen purged, and blanketed, and stored in 

a dark room at room temperature. All B100 samples were tested initially for: 

• Total acid number (or acid value), ASTM D664 

• Free and total glycerin, ASTM D6584. 

Detailed characterization was performed on a subset of eight fuels that were selected for more 

detailed testing: 

• Total particulate contamination, ASTM D6217 

• Flash point, ASTM D93 

• Peroxide value, ASTM D3703 

• Karl Fischer moisture, ASTM D6304 

• Iso-octane insoluble, (based on a 4:1 dilution of the sample with iso-octane followed 

by filtration using the modified ASTM D2274 procedures described below) 

• Kinematic viscosity @ 40°C, ASTM D 445 

• Polymer content, ISO 16931 (high performance size-exclusion chromatography) 

• Metals (P, Na, K, Ca, Mg, Cu, Zn), ASTM D5185. 

In addition, six samples (two drums each) of petroleum-derived diesel fuel were obtained 

from petroleum refiners in the United States and Canada. These include one 500-ppm sulfur 

fuel, and five others meeting the 15-ppm sulfur limit (ULSD). The diesel fuels were 

characterized with the following tests: 

• Total particulate contamination, ASTM D6217 

• Flash point, ASTM D93 

• Sulfur, ASTM D5453 

• T90/carbon residue, ASTM D86/D524 

• Total acid number (or acid value), ASTM D664 

• Peroxide value, ASTM D3703 

• Ash content, ASTM D482 

• Supercritical fluid chromatography aromatics, ASTM D5186. 

Peroxide is measured by D3703, a method developed for aviation fuels with peroxide contents 

in the range of 1 to 5 ppm. The D3703 method is therefore not wholly applicable to samples 

with the high peroxide numbers found in many B100 and biodiesel blend samples. An 

interlaboratory study is underway to determine the applicability of this method to biodiesel. 

The absolute accuracy of the test for biodiesel is currently unknown, but we believe it is 

adequate for showing trends over time. 

 5
Accelerated Stability Tests 

All samples, B100 and blends, were analyzed under the same conditions per standard test 

method EN 14112 Fat and oil derivatives—Fatty acid methyl esters (FAME)—Determination 

of Oxidation Stability. The Rancimat apparatus was used and tests were performed at 110oC. 

The Rancimat utilizes a proprietary computer algorithm to analyze the conductivity results 

and determine the induction period. All samples were tested in duplicate and the average 

induction period was reported. If the results for the replicates differed by more than 

approximately 10% of the mean, a third test was conducted and the two results closest to each 

other were averaged. 

Significant problems were often encountered when analyzing blends, especially B5 blends. 

For most blends, the petroleum diesel fraction was sufficiently volatile to evaporate and 

condense in either the air tubes or the measuring vessel. Some of the plastic components of 

the Rancimat were incompatible with the petroleum diesel. This caused swelling of the parts 

and resultant air leaks. We had to replace these parts on a frequent basis. The standard air 

tube would soften and restrict the flow of air to the measuring vessel. We found that standard 

TygonTM laboratory tubing was an acceptable replacement for the original air tubing. As of 

this writing, the manufacturer is evaluating replacement parts that are compatible with 

petroleum for the analysis of blends. 

Also, the test results for the blends were found to be far less repeatable. In many cases, the 

B5 samples would run for several days before an induction period was determined. This was 

due to the lower amount of biodiesel in the sample (compared to B100) and varied with the 

stability of the original B100. For the purposes of this project, we manually stopped 

Rancimat tests once the induction period was found to be greater than 12 hours. 

Oxidation stability as determined by ASTM D2274 was modified for use with biodiesel by 

substituting glass fiber filters for the cellulose ester filters used with petroleum fuels, as 

described by Stavinoha and Howell.16 Additionally, we attempted to keep the filtration time 

as consistent as possible. Iso-octane insolubles of the filtrate were determined by adding 100 

ml of the filtered, post-D2274 B100 to 400 ml of prefiltered iso-octane. This was thorough

mixed and allowed to set for at least 1 hour before filtering to determine insolubles. These 

insolubles or precipitates are a potential measure of oxidation products that remain soluble in 

the very polar B100, but could be insoluble in a diesel fuel blend. Acid value of the filtrate 

was also measured by D664 for some samples. 

ly 

Thermal stability as determined by ASTM D6468 was performed at 150oC for 180 minutes. In 

addition to measurement of filter reflectance, this test was modified to use the same 

gravimetric insoluble measurement procedures used for D2274 (both total and iso-octane). 

Duplicate 50-ml samples were tested; results for reflectance were reported as the average. 

Gravimetric results are reported as the sum of the duplicate samples in mg/100 ml. An 

additional modification to D6468 was examined in preliminary scoping tests to purge the 

ullage or space above the heated liquid with air to ensure that a highly unstable material 

would not consume all the oxygen and thereby produce an invalid result. Results of these 

scoping tests are shown in Table 1, which shows that ullage purge had no significant effect on 

the results, and thus was not used in subsequent tests. 

 6
Table 1. Results of D6468 Ullage Purge Scoping Tests 

Sample Identification AL-27131-F(1) AL-27070-F(2)

Modified ASTM D6468(3) with air flow without air flow with air flow without air flow 

filterable insolubles, 

mg/100 ml 

0.03 0.14 0.77 1.1 

adherent insolubles, 

mg/100 ml 

0.09 0.06 0.14 0.14 

total insolubles, 

mg/100 ml 

0.11 0.2 0.9 1.2 

1

 Soy-based B100 

2

 Low-sulfur No. 2 diesel fuel 

3

 350 ml; 150°C; 180 minutes with and without air flow within ullage

Oxidation stability as determined by ASTM D525 Standard Test Method for Oxidation 

Stability of Gasoline (Induction Period Method), measures an induction time for the start of 

oxygen consumption. This test was shown in a recent study17 to correlate well with Rancimat 

induction time. 

Simulation of Real-World Aging Scenarios 

We envision three scenarios where oxidative degradation of biodiesel or biodiesel blends 

might occur. 

Storage and Handling 

Biodiesel and biodiesel blends must be stored and handled before they are dispensed into 

vehicle fuel tanks. For research purposes there seems to be general agreement that ASTM 

D4625 (43°C/12 weeks) adequately simulates this situation.∗

 The method employs the glass 

vessel shown in Figure 1. Individual glass vessels are stored for 4, 8, and 12 weeks so that an 

independent sample is evaluated at each time interval (as opposed to removing an aliquot 

from one vessel at each time interval). In this study the procedures were modified to employ 

glass fiber filters to determine insolubles. For biodiesel and blends, acid value, peroxide 

value, polymer content, and viscosity, as well as total insolubles, were measured during this 

test. For B100, iso-octane insolubles were also measured. 

Figure 1. Glass vessel used for D4625 stability test 

 

∗

However, the correspondence of 1 week on D4625 to 1 month of underground storage at 21oC that is typically 

assumed for petroleum diesel has not been established for biodiesel. 

 7
The goals for this test are to: 

• Determine whether there is an accelerated test that predicts D4625 results. 

• Assess the potential of a B100 accelerated stability measurement to predict blend 

stability in this scenario. 

• Reveal how antioxidants can affect storage stability. 

Vehicle Fuel Tank 

Biodiesel blends will ultimately be pumped into a vehicle fuel tank and will be subject to 

periodic heating to higher than ambient temperatures. This can be due to recirculation of hot 

fuel back into the fuel tank, or simply exposure to hot climates. The ASTM Biodiesel Stability 

Working Group discussed the possibility of storing the fuel for about 6 days at 80°C to 

simulate a type of worst-case situation. Although there is no ASTM test with this time and 

temperature duration, the ASTM D4625 procedures and apparatus to can be modified slightly 

to determine total insolubles at the end of this period. The measurement of acid value, 

peroxide value, polymer content, and viscosity may also prove valuable. Because the 

biodiesel is already blended with diesel fuel, the measurement of iso-octane insolubles is not 

likely to be informative. This is not a standard test, so results should be interpreted with 

caution. 

A scoping study was performed to ensure that this test is not being conducted under oxygendeficient conditions. Specifically, the D4625 apparatus (see Figure 1) was modified to allow 

a slow air purge of the bottle ullage during tests of a B100 and a diesel fuel. A comparison of 

these results is shown in Table 2. The results indicate that significantly higher levels of 

insolubles are obtained with the B100 when air purging is used. Because a real vehicle fuel 

tank will be agitated by vehicle motion and is open to the air, ullage purging will be 

employed in this 6-day test. This test is similar to a 24-hour storage stability test proposed by 

Bondioli and coworkers.18

Table 2. Results of D4625 (6-Day, 80oC Modification) Ullage Purge Scoping Tests 

Sample identification AL-27131-F(1) AL-27070-F(2)

Modified ASTM D4625(3) with air flow without air flow with air flow without air flow 

filterable insolubles, mg/100 ml 

replicate 1 1.3 0.14 0.20 0.17 

replicate 2 2.1 0.11 0.20 0.20 

adherent insolubles, mg/100 ml 

replicate 1 1.7 0.80 0.31 0.14 

replicate 2 2.0 0.80 0.20 0.20 

total insolubles, mg/100 ml 

replicate 1 3.0 0.94 0.51 0.31 

replicate 2 4.1 0.91 0.40 0.40 

average total insolubles, mg/100 

ml

3.6 0.93 0.46 0.36 

1

 Soy-based B100 

2

 Low-sulfur No. 2 diesel fuel 

3

 500-ml; 80°C; 1 week storage with and without air flow within ullage 

This test was performed on duplicate 500-ml samples. A 50-ml aliquot was removed from 

each bottle at the end of 1 week of storage. These were combined to make 100 ml and filtered 

to obtain a total insoluble result. The goals for this test are to: 

 8
• Determine whether there is an accelerated test that predicts simulated tank stability 

results. 

• Assess the potential of a B100 accelerated stability measurement to predict blend 

stability in this scenario. 

• Reveal how antioxidants can affect blend stability in the vehicle tank situation 

High-Temperature Fuel System Environment 

Biodiesel blends are subjected to temperatures as high as 150°C for short periods in the 

engine’s fuel system. A substantial fraction of this fuel is recirculated to the vehicle fuel tank. 

Proposing a standard test that simulates this environment is somewhat more challenging. One 

possibility is ASTM D6468 (150°C and 180 minutes) but modified to make a gravimetric 

measurement of deposits. This test can be run on fresh fuel to simulate potential thermal 

stability in or around the injector (mentioned in the discussion of accelerated stability tests), 

or with aged fuel that has been in the fuel system for some time. 

A worst-case scenario would be to test a fuel for 6 days at 80°C with the modified D4625, and 

then perform D6468. In this study one 50-ml aliquot was taken from each duplicate bottle 

after 1 week of storage. These were combined, and then split into two 50-ml samples for the 

D6468 test. Both 50-ml aliquots were filtered through the same filter to determine insolubles 

in mg/100 ml. The goals for this test are to: 

• Determine whether there is an accelerated test that predicts simulated hightemperature zone stability. 

• Assess the potential of a B100 accelerated stability measurement to predict blend 

high-temperature stability in this scenario. 

• Reveal how antioxidants and other additives can effect high temperature stability. 

This test, like the vehicle fuel tank simulation test, is not standard, and results should be 

interpreted with caution. 

 9
Results: Stability of B100 

Accelerated Testing and Characterization 

Table 3 lists the 19 B100 samples obtained, their feedstocks, and preliminary characterization 

results. These samples appear to cover the full range of feedstocks currently used in North 

America. Two samples failed the ASTM D6751 specification for biodiesel: one because of 

high acid value and the other because of high total glycerin. These samples are included in the 

accelerated stability tests, but were not considered for any additional testing in this study 

because of their poor quality. The samples that were selected for additional study were 

characterized much more extensively. 

Table 3. Biodiesel Samples Obtained and Preliminary Characterization (values in bold exceed 

specification limits) 

Sample 

Identification 

Feedstock Total Acid Number, 

mg KOH/g 

Total Glycerin, 

%(mass) 

Free Glycerin, 

%(mass) 

ASTM D664 ASTM D6584 ASTM D6584 

ASTM D6751-03a Limit: 0.80(1) 0.240 0.02 

AL-27128-F Canola 0.23 0.103 0.009 

AL-27129-F Palm Stearin 0.41 0.081 <0.001 

AL-27137-F Soy 0.05 0.144 0.002 

AL-27138-F Soy 0.33 0.016 0.002 

AL-27140-F Soy 0.20 0.022 0.015 

AL-27141-F Soy 0.13 0.121 0.005 

AL-27142-F Soy 0.07 0.216 0.003 

AL-27144-F Soy 0.39 0.221 0.004 

AL-27145-F Soy 0.49 0.192 0.005 

AL-27146-F Rapeseed 0.08 0.161 <0.001 

AL-27148-F Grease 0.69 0.121 <0.001 

AL-27152-F Rapeseed 0.09 0.15 0.001 

AL-27153-F Rapeseed 0.08 0.15 0.001 

AL-27154-F Grease 1.31 0.132 0.003 

AL-27155-F Soy 0.29 0.298 0.007 

AL-27157-F Soy 0.11 0.225 0.015 

AL-27158-F Soy 0.51 0.158 0.001 

AL-27160-F Tallow 0.46 0.188 0.002 

AL-27161-F Grease 0.37 0.151 0.003 

1

 This limit was reduced to 0.50 mg KOH/g in mid-2006. 

 

Oxidation stability data for the 19 B100 samples are tabulated in Appendix A. Figure 2 shows 

a histogram for OSI induction time measured for these samples. The samples show a broad 

distribution with results ranging from less than 1 to more than 9 hours. Figure 3 compares the 

OSI induction time results to ASTM D525 induction time results. Based on an earlier report, 

we anticipated that these tests would correlate to some extent.17 The circled data points 

indicate that no oxidation was observed after 780 minutes, and the results are simply plotted 

as 780 minutes. Figure 3 indicates a poor correlation between these methods (r2

 of 0.4). 

Subsequent testing showed that D525 results were not predictive of B100 or blend 

performance. Consequently, D525 results are not discussed further. 

 10
Rancimat Induction Time, hr

0 1 2 3 4 5 6 7 8 9 10

Count

0

1

2

3

4

5

6

Figure 2. Histogram for B100 OSI or Rancimat induction time 

Rancimat Induction Time, hr

02468 10

ASTM D525 Induction Time, min

0

200

400

600

800

1000

Figure 3. Relationship between B100 OSI or Rancimat induction time and ASTM D525 results. 

Circled data points indicate that no oxidation was observed after 780 minutes and the results 

are simply plotted as 780 minutes 

 11
Figure 4 shows a histogram for the ASTM D2274 deposit test. Ten of the 19 samples tested 

show deposits of less than 2 mg/100 ml; deposits for the other nine fuels cover the range to 

nearly 18 mg/100 ml. As observed previously,19 the amount of adherent insolubles was 2 to 4 

times higher than the amount of filterable insolubles. Figure 5 shows the inverse relationship 

between induction time and D2274 total insolubles. This is very similar to the relationship 

observed previously,19 and in an approximate sense shows the expected inverse correlation. 

The filtrate from this test was also mixed with iso-octane to precipitate materials that are 

insoluble in nonpolar solvents. Fourteen of the samples exhibited less than 20 mg/100 ml; the 

balance ranged to 200 mg/100 ml. Figure 6 shows the relationship between total insolubles 

and iso-octane insolubles. The correlation is not perfect, but the only samples that produced 

very high levels of iso-octane insolubles also produced very high levels of total insolubles. 

This suggests that little new information is acquired by measuring iso-octane insolubles. 

Finally, the acid value of the filtered liquid was also measured and ranged from less than 1 to 

more than 5 mg KOH/g. Change in acid value over D2274 is closely correlated with total 

insolubles and inversely correlated with induction time, as shown in Figures 7 and 8. 

ASTM D2274 Total Insolubles, mg/100 ml

0 2 4 6 8 10 12 14 16 18 20

Count

0

2

4

6

8

10

12

Figure 4. Histogram for B100 ASTM D2274 total insolubles 

 12
Rancimat Induction Time, hr

02468 10

D2274M Total Insoluble, mg/100 ml

0

2

4

6

8

10

12

14

16

18

20

Figure 5. Relationship between B100 OSI or Rancimat induction time and D2274 total 

insolubles 

D2274M Total Insoluble, mg/100 ml

0 2 4 6 8 10 12 14 16 18 20

D2274M i-Octane Insoluble, mg/100 ml

0

20

40

60

80

100

120

140

160

180

Figure 6. Relationship between B100 D2274 total insoluble and iso-octane insoluble 

 13
ASTM D2274 Total Insolubles, mg/100 ml

0 5 10 15 20

D2274 Change in Total Acid Number

0

1

2

3

4

5

6

Figure 7. Change in total acid number on D2274 versus D2274 total insolubles for B100 

samples 

Rancimat Induction Time, hr

02468 10

D2274 Change in Total Acid Number

0

1

2

3

4

5

6

Figure 8. Change in total acid number on D2274 versus OSI or Rancimat induction time for 

B100 samples 

 14
Table 4 lists results for the ASTM D6468 thermal stability test modified for gravimetric 

measurement of deposits. All samples produced low levels of deposits, and there is little 

discrimination among the samples. 

Table 4. Results of ASTM D6468 Performed on B100 Samples at 150°C/180 Minutes and 

Modified for Gravimetric Determination of Deposits 

Sample Identification ASTM D6468 Modified 

 Thermal Stability, deposit, mg 

AL-27128-F 0.3 

AL-27129-F 0.1 

AL-27137-F 0.3 

AL-27138-F 0.3 

AL-27140-F 0.4 

AL-27141-F 0.2 

AL-27142-F 0.3 

AL-27144-F 0.4 

AL-27145-F 0.4 

AL-27146-F 0.5 

AL-27148-F 0.4 

AL-27152-F 0.1 

AL-27153-F 0.5 

AL-27154-F 0.1 

AL-27155-F 0.3 

AL-27157-F 0.3 

AL-27158-F 0.6 

AL-27160-F 0.5 

AL-27161-F 0.2 

Based on these results, eight samples were selected for more detailed characterization, longterm storage tests (D4625 for 12 weeks), and for preparation of B5 and B20 blends. The 

downselection was based on covering the full range (high, medium, low) of values for each of 

the accelerated tests and on trying to include the full range of feedstocks. However, results for 

D6468 showed low levels of deposits (gravimetric) for all samples, so that test is not 

considered here. Additionally, the two B100 samples that failed to meet specifications for 

either acid value or total glycerin were not considered. The samples selected are shown in 

Table 5. Some compromises were made to meet all the study objectives, including covering 

all feedstocks. These eight samples were subjected to more extensive characterization tests. 

Results of these tests are shown in Table 6. All samples met the D6751 requirements for 

which they were tested. 

 15
 16

Table 5. B100 Samples Selected for Long-Term Storage and Blending Studies 

Feedstock OSI/Rancimat D2274 Total D2274 iOctane 

Observed Range 

0.2–9.4 h 

0.3–17.6 

mg/100 ml 

0.6–198 

mg/100 ml 

AL-27128-F Canola 4.2 (med) 6.5 (med) 198 (high) 

AL-27129-F Palm stearin 3.1 (med) 1.9 (low) 2.6 (low) 

AL-27137-F Soy 6.5 (high) 1.0 (low) 2.6 (low) 

AL-27138-F Soy 0.5 (low) 7.6 (med) 4.4 (low) 

AL-27141-F Soy 5.5 (high) 0.3 (low) 0.6 (low) 

AL-27148-F Grease 7.8 (high) 0.9 (low) 19 (med) 

AL-27152-F Rapeseed 7.3 (high) 0.5 (low) 6.4 (low) 

AL-27160-F Tallow 0.2 (low) 17.6 (high) 124 (high) 
 17

Table 6. Characterization Results for B100 Samples Downselected for Further Study and Blen

Test 

Method 

Units AL-27128 AL-27129 AL-27137 AL-27138 AL-27141 AL-27148 

Particulate Contamination 

D6217, 

mod 

mg/l 14.7 0.2 103.9 0.8 3.5 19.5 

Total Water D6304 ppm 656 217 149 562 131 118 Flash Point D93 °C 160 177 179 155 152 131 Elemental Analysis 

D5185 ppm 

P <1 <1 <1 <1 <1 <1 

Na <5 <5 <5 <5 <5 <5 

K <5 <5 <5 <5 <5 <5 

Ca 1 <1 <1 <1 <1 <1 

Mg <1 <1 <1 <1 <1 <1 

Cu <1 <1 <1 <1 <1 <1 

Zn <1 <1 <1 <1 <1 <1 

Mg <1 <1 <1 <1 <1 <1 

Iso-Octane Insoluble 

D4625, 

mod 

mg/100 

ml 

3.9 0.1 1.9 1.1 2.3 0.1 

Peroxide Value 

D3703 217 105 12 50 98 9 

Viscosity @ 40°C 

D445 4.45 5.12 4.10 4.32 4.09 4.67 

Polymer Content 

ISO16931 2.63 0.17 0.82 0.22 1.03 1.46 

Total Acid No. D664 mg 

KOH/g 

0.23 0.41 0.05 0.33 0.13 0.69 

Free Glycerin D6584 wt% 0.009 <0.001 0.002 0.002 0.005 <0.001 Total Glycerin D6584 wt% 0.103 0.081 0.144 0.016 0.121 0.121 * At the time these samples were collected the acid value was limited to 0.80 mg KOH/g maximum. In mid-20reduced to 0.50 mg KOH/g.
Storage Stability of B100 

Storage stability was assessed for the eight B100 samples by using ASTM D4625 (storage for 

12 weeks at 43oC), numerical results are in Appendix B. For petroleum-based diesel fuels, 

each week of testing correlates to approximately 1 month of storage at ambient conditions. 

Figure 9 shows how induction times change over this test. All these biodiesel samples 

exhibited induction times shorter than 3 hours after 4 weeks, and all declined to very low 

levels at 8 weeks. Figure 10 shows peroxide value over the test and indicates that all but one 

of the samples had clearly degraded, even at 4 weeks. Figure 11 shows how acid value 

changes over the D4625 test. All but the most stable samples show a small increase in acidity 

at 4 weeks, but all still meet the 0.80 mg KOH/g limit that was in place when these samples 

were acquired. By 8 weeks (simulated 8 months) acidity had increased to above the 0.80 mg 

KOH/g limit for all samples. Figure 12 shows total insolubles formation over 12 weeks 

(simulated 8 months). These results show acid value and total insolubles in a range similar to 

that observed in previous investigations that used this test.5,8,16 The level of B100 total 

insoluble on this test that is indicative of an unacceptable fuel blending component, and the 

repeatability of this test for B100, are unknown. The acid number increase may be a more 

accurate indicator than sediment formation of deleterious changes in B100 under these 

conditions. The data can mainly be interpreted by looking for a large increase in insolubles or 

by comparing the samples in a relative sense. Generally all the samples are beginning to 

experience significant increases in insolubles formation at the 12-week point. At 4 and 8 

weeks the samples with induction times shorter than 3 hours have the highest levels of 

insolubles. Data for iso-octane insoluble and polymer content have a similar pattern (not 

shown), although polymer content remains low through 8 weeks and increases only at 12 

weeks. Viscosity does not appear to be a sensitive indicator of oxidation for these samples. 

Weeks

0 2 4 6 8 10 12

Oil Stability Index, hr

0

2

4

6

8

10

12

Figure 9. Change in OSI or Rancimat for B100 samples over 4 weeks in D4625 test 

 18
Weeks

0 2 4 6 8 10 12

Peroxide Value

0

500

1000

1500

2000

2500

3000

3500

4.21 

3.11 

6.52 

0.45

5.53 

7.76 

7.26 

0.17 

Initial OSI, hr

Figure 10. Peroxide value measured for B100 samples over the D4625 test 

Weeks

0 2 4 6 8 10 12

Acid Value, mg KOH/g

0

1

2

3

4

4.21 

3.11 

6.52 

0.45 

5.53 

7.76 

7.26 

0.17 

2006 AV Limit of 0.5

2005 AV Limit of 0.8

Initial OSI, hr

Figure 11. Change in acid value for B100 samples on the D4625 test 

 19
Weeks

0 2 4 6 8 10 12

Total Insoluble, mg/100 ml

0

1

2

3

4

5

6

7

4.21 

3.11 

6.52 

0.45 

5.53 

7.76 

7.26 

0.17 

Initial OSI, hr

6.45

1.90

1.02

7.60

0.30

0.90

0.50

17.6

D2274 Total Insoluble,

 mg/100 ml

Figure 12. Total insoluble measured for B100 samples over the D4625 test 

B100 Antioxidant Testing 

Biodiesel samples AL-27129-F and AL-27138-F were treated with two commercial 

antioxidants. Antioxidant treat rates as well as Rancimat induction times and total insolubles 

from ASTM D2274 are given in Table 7. Both additives are effective at increasing induction 

time and reducing insolubles formation for these samples. The biodiesels were selected to 

represent unstable material (AL-27138-F) with an induction time of 0.45 hours and 

moderately stable material (AL-27129-F) with an induction time of 3.11 hours. 

These samples were also tested for long-term storage stability with ASTM D4625; detailed 

results for these tests are reported in Appendix B. Results for total acid number are shown in 

Figure 13. The data indicate that both additives effectively prevented acid formation. Results 

for total insolubles are shown in Figure 14. Both antioxidants effectively suppressed insoluble 

formation in both biodiesel samples at both treat rates. Protection from insoluble and acid 

formation might have been achieved at lower treat rate. 

 20
Table 7. Results of Accelerated Stability Tests for Biodiesel Treated with Antioxidant Additives 

Sample 

Number Description 

Rancimat 

Induction 

Time 

ASTM D2274 

Total 

Insoluble 

i-Octane 

Insoluble 

Acid Value 

h mg/100 ml mg/100 ml mg KOH/g 

AL-27138 with no additive 0.45 7.6 4.4 3.01 

06-0077 AL-27138 plus 1000 ppm additive A 3.18 6.5 1.0 2.35 

06-0078 AL-27138 plus 2000 ppm additive A 5.73 0.3 1.6 0.40 

06-0079 AL-27138 plus 1000 ppm additive B 1.67 3.0 0.6 2.49 

06-0080 AL-27138 plus 2000 ppm additive B 2.64 0.8 0.3 1.28 

AL-27129 with no additive 3.11 1.9 2.6 2.50 

06-0081 AL-27129 plus 1000 ppm additive A 22.8 0.1 0.5 0.45 

06-0082 AL-27129 plus 1000 ppm additive B 6.87 0.2 0.1 0.47 

Weeks

0 2 4 6 8 10 12

Acid Value, mg KOH/g

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

AL-27129 

1000 ppm A 

1000 ppm B 

AL-27138 

1000 ppm A 

2000 ppm A 

1000 ppm B 

2000 ppm B

Initial OSI

3.1

23

6.9

0.45

3.2

5.7

1.7

2.6

Figure 13. Total acid number results for D4625 long-term storage testing of antioxidant-treated 

B100 samples 

 21
Weeks

0 2 4 6 8 10 12

Total Insoluble, mg/100 ml

0

1

2

3

4

5

6

7

AL-27129 no additive

1000 ppm A 

1000 ppm B

Weeks

0 2 4 6 8 10 12

Total Insoluble, mg/100 ml

0

1

2

3

4

5

6

7

AL-27138 no additive

1000 ppm A 

2000 ppm A

1000 ppm B

2000 ppm B

Figure 14. Total insoluble results of ASTM D4625 long-term storage test for antioxidant-treated 

B100 samples 

 22
 23

Results: Stability of Biodiesel Blends 

Diesel Fuel Properties and Stability 

Characterization results for the six diesel fuel samples to be used for blending are shown in 

Table 8. Five are ULSD, and one is an on-road diesel fuel produced before ULSD was 

required. Based on the distillation T90, samples AL-27150F, AL-27166F, and AL-27176F are 

No. 1 diesel fuels; the others are No. 2 diesel fuels. Aromatic content is regarded as an 

important parameter for this study because fuels with higher aromatic content may be able to 

more readily solvate oxidized biodiesel molecules, which would otherwise precipitate as 

deposits in fuels with lower aromatic content. Total aromatics for the ULSD samples range 

from 8.2 to 22.1 mass percent. Because these ULSD were obtained in late 2005 they might 

not be representative of commercial ULSD in use today. All samples exhibited good stability 

on both D2274 and D6468. 

These fuels were also tested for long-term storage stability by using D4625 with measurement 

of insolubles formation. Results are shown in Figure 15 where all diesel samples were stable 

at 8 weeks and one sample, AL-27175, showed the initiation of degradation at 12 weeks. This 

is a No. 2 ULSD with the lowest aromatic content of the samples in this set. Detailed results 

for D4625 are listed in Appendix C. 

The diesel fuels were also tested by using the fuel tank aging simulation of 1 week in the 

D4625 glass vessel at 80oC while the ullage was purged with air. Results are reported at the 

bottom of Table 8. These samples, after the 1 week of aging, were also tested with the D6468 

thermal stability test but with gravimetric measurement of total insolubles. These results are 

also shown in Table 8. Because this test sequence is not standard, there is little information 

with which to compare these numbers. However, they do provide an important baseline for 

comparison with results for biodiesel blend samples. 
 24

Table 8. Characterization Results for Petroleum Diesel Samples To Be Used in Preparation of B5 and 

Sample ASTM D975 

Limit (No. 2 

Diesel) 

AL27150F AL27151F AL27166F AL27171F 

ASTM D93 Flash point, oC 52 56 69 59 73 ASTM D5453 Sulfur, ppm 15 or 500 7.4 6.7 5.8 339.6 ASTM D86 T90, oC 282 min 

338 max 

274 313 269 319 

ASTM D524 Carbon residue (on 10% 

distillation residue), mass% 

0.35 0.07 0.04 0.06 0.13 

ASTM D664 Acid number, mg KOH/g none 0.01 0.03 0.01 0.01 ASTM D3703 Peroxide number none <1 <1 <1 <1 ASTM D2709 Water and sediment, vol% 0.05 0.01 0.01 0.01 0.01 ASTM D482 Ash content, mass% 0.01 <0.001 <0.001 <0.001 <0.001 ASTM D5186 Total Aromatics, mass% none 15.7 22.1 18.1 36.2 

Monoaromatics, mass% none 14.4 19.9 17.1 27.6 Polynuclear aromatics, mass% none 1.3 2.1 1 8.7 

ASTM D6217 Particulate contamination, mg/l none 0.5 0.4 0.8 0.8 ASTM D2274 Total Insolubles, mg/100 ml none 0.25 0.25 0.5 0.2 ASTM D6468 Thermal stability, 150oC/180 min 

% reflectance 

none 100 100 100 98 

ASTM D4625 Modified, 80oC, air purge, 

1 week 

none 

Adherent insoluble, mg/100 ml 0.3 0.4 0.1 0.1 

Filterable insoluble, mg/100 ml 0.7 0.2 0.1 0.1 

Total insoluble 1.1 0.6 0.2 0.2 

ASTM D6468 Modified, 150oC/180 min, 

gravimetric on fuel from D4625, 1 week 80oC, mg/100 ml 

none 2.2 0.2 0.1 0.1 
Weeks

0 2 4 6 8 10 12

Total Insoluble, mg/100 ml

0

1

2

3

4

5

6

7

AL-27150-F 

AL-27151-F 

AL-27166-F 

AL-27171-F 

AL-27175-F 

AL-27176-F 

LSD

Figure 15. Total insolubles for petroleum diesel fuels on the D4625 test 

Stability of B5 Blends 

Accelerated Tests 

Six diesel fuels were acquired, and eight B100 samples were selected from the original 19. 

These were used to prepare 48 B5 blends that have been tested by using the following 

accelerated stability tests: 

• OSI/Rancimat induction time 

• ASTM D2274 (biodiesel modification) 

• ASTM D6468 percent reflectance and gravimetric modification. 

Results for accelerated tests with B5 blends are in Appendix D. Figure 16 shows a histogram 

of the Rancimat induction time results. The samples fall into three categories: short, medium, 

and long induction times. Figure 17 shows the histogram for total insolubles measured on the 

D2274 test. Most of the samples are reasonably stable, with less than 2.5 mg/100 ml. There 

are also samples with intermediate and high levels of insolubles. Figures 18 and 19 show the 

reflectance and gravimetric results from the D6468 thermal stability test. Most samples are 

thermally stable, although several produce significant amounts of insolubles. 

 25
>

Rancimat Induction Time, hr

0 2 4 6 8 10 12

Count

0

10

20

30

40

50

Figure 16. Histogram of OSI or Rancimat induction times for B5 samples 

D2274 Total Insoluble, mg/100 ml

0 10 20 30 40 50

Count

0

10

20

30

40

50

Figure 17. Histogram of D2274 (biodiesel modification) total insolubles results for B5 samples 

 26
D6468, % Reflectance

0 20 40 60 80 100 120

Count

0

10

20

30

40

Figure 18. Histogram of D6468 percent reflectance results for B5 samples 

D6468 Gravimetric Modification, mg/100 ml

0.0 0.5 1.0 1.5 2.0 2.5

Count

0

5

10

15

20

25

30

35

Figure 19. Histogram of D6468 gravimetric insoluble results for B5 samples 

Based on these distributions, and so as not to exclude any one biodiesel or diesel fuel from the 

group, the B5 blend samples listed in Table 9 were selected for more detailed study. This 

included long-term storage testing, as well as tests to simulate aging in the vehicle fuel tank 

 27
and degradation in the high-temperature environment of a diesel engine fuel injection system. 

Biodiesel AL-27138, an unstable material, produced a B5 blend with a short induction time 

and high D2274 insolubles, but is thermally stable. Biodiesel AL-27160, also unstable, 

produced a B5 blend with a short induction time and low D2274 deposits, but appears to be 

thermally unstable. These data confirm previous results and indicate that biodiesel and B5 

blends are generally thermally stable,16 and with the implementation of the 3-hour induction 

period there appears to be no additional information to be gained about blends from the 

thermal stability values of the B100. 

Table 9. B5 Samples Downselected for More Detailed Study 

Sample B100 Diesel Rancimat 

h 

D2274 

mg/100 ml 

D6468 

% Reflectance/Insoluble 

mg/100 ml 

CL06-200 27128 27166 >12 5.5 98/0.1 

CL06-215 27129 27176 >12 1.5 99/0.1 

CL06-227 27137 27175 >12 0.3 94/0.1 

CL06-235 27138 27150 4.8 40.7 88/0.1 

CL06-252 27141 27175 >12 0.3 96/0.1 

CL06-264 27148 27175 >12 0.4 93/0.2 

CL06-273 27152 27151 >12 0.3 99/0.1 

CL06-287 27160 27171 5.5 0.8 19/2.0 

Several B5 samples were also treated with antioxidant additives and evaluated on accelerated 

tests. Results are shown in Table 10. Most of the B5 samples are fairly stable without additive 

on these tests. Antioxidants caused a large reduction in D2274 total insolubles for the one 

sample that exhibits significant instability and increased the induction time for all samples. 

Additive treat rates given are for addition to the B100 before it is blended. 

 28
Table 10. Accelerated Test Results for B5 Samples Treated with Antioxidant 

Sample 

Number Description 

Rancimat 

Induction Time 

h 

ASTM D2274 

Total Insoluble 

 mg/100 ml 

06-236 5% AL-27138 in AL-27151 no additive 5.8 23.5 

06-548 5% AL-27138 plus 1000 ppm additive A in AL-27151 9.0 _ 

06-331 5% AL-27138 plus 2000 ppm additive A in AL-27151 >12 0.3 

06-332 5% AL-27138 plus 1000 ppm additive B in AL-27151 >12 0 

06-333 5% AL-27138 plus 2000 ppm additive B in AL-27151 >12 0 

06-211 5% AL-27129 in AL-27151 no additive >12 1.0 

06-334 5% AL-27129 plus 1000 ppm of additive A in AL-27151 >12 0 

06-550 5% AL-27129 plus 1000 ppm of additive B in AL-27151 >12 _ 

06-214 5% AL-27129 in AL-27175 no additive >12 0.6 

06-552 5% AL-27129 plus 1000 ppm of additive B in AL-27175 >12 _ 

06-239 5% AL-27138 in AL-27175 no additive 6.9 0.2 

06-552 5% AL-27138 plus 1000 ppm of additive A in AL-27175 >12 0.2 

06-516 5% AL-27138 plus 2000 ppm additive A in AL-27175 >12 0.2 

06-518 5% AL-27138 plus 1000 ppm additive B in AL-27175 >12 0 

06-520 5% AL-27138 plus 2000 ppm additive B in AL-27175 >12 0.3 

Storage Stability 

The eight B5 blends listed in Table 9 were tested for long-term storage stability with ASTM 

D4625. Numerical results are given in Appendix E. Figure 20 shows results for peroxide 

value (PV). At 4 weeks, the peroxide value results indicate that some degradation is occurring 

for samples produced from B100 with an induction time shorter than 1 hour, and for one 

sample with a longer induction time. However, at 8 weeks all samples show low peroxides, 

and at 12 weeks the only sample with high peroxides was produced from an unstable B100. 

Acid value increase for B5 blends over the D4625 test is shown in Figure 21. The only B5 

sample in which acid value increased significantly was blended from a B100 with an 

induction time of 0.5 hour. Total insoluble formation is shown in Figure 22. Again, the only 

sample in which insolubles increased significantly was blended from a B100 with an 

induction time of 0.5 hour (AL-27138). Figure 23 shows results for several B5 blends that 

were treated with antioxidants. Treatment of B5 blends containing AL-27138 eliminated the 

increase in insolubles observed at 12 weeks without antioxidant, with all results below 2 

mg/100 ml. Antioxidant treatment also stabilized the induction time for all samples at more 

than 10 hours over the 12-week test. 

 29
Weeks

0 2 4 6 8 10 12

Peroxide Value

0

200

400

600

800

1000

1200

4.2 

3.1 

6.5 

0.5 

5.5 

7.8 

7.3 

0.2 

B100 OSI

Figure 20. Peroxide value over the D4625 test for B5 samples 

Weeks

0 2 4 6 8 10 12

Acid Value, mg KOH/g

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

4.2 hr 

3.1 hr 

6.5 hr

0.5 hr

5.5 hr

7.8 hr

7.3 hr

0.2 hr

B100 OSI

Figure 21. Acid value for B5 blends over the D4625 test 

 30
Weeks

0 2 4 6 8 10 12

Total Insoluble, mg/100 ml

0

10

20

30

40

50

60

4.2 hr 

3.1 hr 

6.5 hr

0.5 hr

5.5 hr

7.8 hr

7.3 hr

0.2 hr

B100 OSI

Figure 22. Total insolubles formation for B5 blends in the D4625 test 

Weeks

0 2 4 6 8 10 12

Total Insoluble, mg/ 100 ml

0

5

10

15

20

25

30

5% AL-27138 plus 2000 ppm of A in AL-27175 

5% AL-27138 plus 1000 ppm of B in AL-27175 

5% AL-27138 plus 2000 ppm of B in AL-27175 

5% AL-27129 plus 1000 ppm of A in AL-27175 

5% AL-27138 plus 2000 ppm of A in AL-27151 

5% AL-27138 plus 1000 ppm of B in AL-27151 

5% AL-27138 plus 2000 ppm of B in AL-27151 

5% AL-27129 plus 1000 ppm of A in AL-27151 

Figure 23. Total insolubles formation for B5 samples treated with antioxidant additives on the 

D4625 test 

 31
Simulated Vehicle Fuel Tank Aging 

As described in the methods section, fuel tank aging was simulated by storing the biodiesel 

blend in the D4625 flask at 80oC for 1 week with ullage purge, followed by measurement of 

peroxide number, acid number, and insolubles. Figures 24, 25, and 26 show results for 

peroxide, acid, and total insolubles, respectively, as a function of the B100 induction time. 

Detailed results are given in Appendix E. For all three measures, significant degradation 

occurs only for B100 induction times shorter than 1 hour. Similar plots could be made as a 

function of the B5 induction times (not shown) and indicate that degradation is not observed 

for B5 induction times longer than 6 hours. Although also not shown, antioxidant additives 

reduced insolubles formation on this test for the one biodiesel sample that generated high 

levels of insolubles. 

B100 OSI, hr

02468 10

1 Week 80oC Ageing

Peroxide Value

0

500

1000

1500

2000

2500

3000

3500

Figure 24. Peroxide value for B5 blends after 1 week aging at 80oC, as a function of B100 OSI or 

Rancimat induction time 

 32
B100 OSI, hr

02468 10

1 Week 80oC Ageing

Acid Value, mg KOH/g

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Figure 25. Acid value for B5 blends after 1 week aging at 80oC, as a function of B100 OSI or 

Rancimat induction time 

B100 OSI, hr

02468 10

1 Week 80oC Ageing

Total Insoluble, mg/100 ml

0

50

100

150

200

250

300

Figure 26. Total insoluble for B5 blends after 1 week aging at 80oC, as a function of B100 OSI or 

Rancimat induction time 

 33
Simulated Vehicle Tank Aging Followed by High Temperature Testing 

To simulate the stability in the high-temperature environment of a diesel engine fuel injection 

system, we subjected the samples that had been aged for 1 week at 80oC (see previous 

section), then conducted the D6468 thermal stability test (150oC for 180 minutes). In addition 

to measuring filter reflectance, the amount of deposits on the filter was also quantified 

gravimetrically by using procedures that are identical to those in D2274. Results are shown in 

Figure 27 as a function of the blending B100 induction time. Detailed results are listed in 

Appendix E. Low values of reflectance or high values of gravimetric insoluble occur only for 

B100 with induction times shorter than 1 hour. Treatment of this B100 with antioxidants 

eliminated the formation of insolubles for this sample (not shown). Notably, the B5 blend 

produced from AL-27160, which demonstrated poor thermal stability on the D6468 test 

before aging, does not generate high deposits on this test after 1 week of aging. 

 34
B100 OSI, hr

02468 10

1 Week 800C Ageing

D6468 Reflectance %

50

60

70

80

90

100

110

B100 OSI, hr

02468 10

1 Week 80oC Ageing

Gravimetric Insoluble, mg/100 ml

0

20

40

60

80

Figure 27. Filter reflectance and gravimetric insolubles formation for B5 samples aged for 1 

week at 80oC and tested with the D6468 thermal stability test as a function of B100 OSI or 

Rancimat induction time 

 35
Stability of B20 Blends 

Accelerated Tests 

Six diesel fuels were acquired, and eight B100 samples were selected from the original 19. 

These were used to prepare 48 B20 blends that were tested with the following accelerated 

stability tests: 

• OSI/Rancimat induction time 

• ASTM D2274 (biodiesel modification) 

• ASTM D6468 percent reflectance and gravimetric modification. 

Detailed results are listed in Appendix F. Figure 28 shows a histogram of the Rancimat 

induction time results. Figure 29 shows the histogram for total insolubles measured on the 

D2274 test. Most of the samples are stable, with less than 2.5 mg/100 ml. There are also 

samples with intermediate and high levels of insolubles. Figures 30 and 31 show the 

reflectance and gravimetric results from the D6468 thermal stability test. Only one sample 

exhibited poor D6468 reflectance values (below 70, the generally accepted level for 

petrodiesel). Although no generally accepted gravimetric value has been established for 

D6468, most values were below 1 mg/100 ml, and four samples gave higher results. There 

were fewer poor samples for D6468, but the sample set did contain samples that could be 

considered both stable and unstable on all the stability tests. 

>

B20 Rancimat Induction Time, hr

0 2 4 6 8 10 12

Count

0

5

10

15

20

25

30

Figure 28. Histogram of OSI or Rancimat induction times for B20 samples 

 36
B20 D2274M total Insoluble, mg/100 ml

0 50 100 150 200 250

Count

0

10

20

30

40

Figure 29. Histogram of D2274 (biodiesel modification) total insolubles results for B20 samples 

D6468 Percent Reflectance

40 50 60 70 80 90 100 110

Count

0

5

10

15

20

25

30

35

Figure 30. Histogram of D6468 percent reflectance results for B20 samples 

 37
D6468 Gravimetric, mg/100 ml

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Count

0

5

10

15

20

25

30

35

Figure 31. Histogram of D6468 gravimetric insoluble results for B20 samples 

Based on these distributions, and so as not to exclude any one biodiesel or diesel fuel from the 

group, we selected the samples listed in Table 11 for further testing of long-term storage 

stability, stability conditions simulating a vehicle fuel tank, and conditions simulating the 

high-temperature conditions of a diesel engine fuel injection system. 

Table 11. B20 Samples Downselected for More Detailed Study 

Sample B100 Diesel Rancimat 

h 

D2274 

mg/100 ml 

D6468 

% Reflectance/Insolubles 

mg/100 ml 

CL06-196 27128 27175 7.8 0.3 95/0.1 

CL06-204 27129 27150 >12 0.4 98/0.1 

CL06-237 27137 27171 >12 0.6 82/0.9 

CL06-242 27138 27151 1.8 124.8 99/0.1 

CL06-256 27141 27166 10.6 0.4 99/0.1 

CL06-268 27148 27166 >12 0.3 97/0.2 

CL06-282 27152 27175 >12 1.2 97/0.1 

CL06-295 27160 27176 4.1 33.7 72/0.1 

Several additional B20 samples prepared with antioxidant treated B100 were also tested for 

stability. Results are shown in Table 12. The antioxidants generally reduced insoluble levels 

effectively and increased induction time for the samples prepared from the highly unstable 

B100 AL-27138. Additive treat rates given are for adding antioxidant to the B100. 

 38
Table 12. Accelerated Test Results for B20 Samples Treated with Antioxidant 

Sample 

Number 

Description 

Rancimat 

Induction 

Time 

h 

ASTM D2274 

Total 

Insolubles 

mg/100 ml 

06-242 20% AL-27138 in AL-27151 no additive 1.8 124.8 

06-549 20% AL-27138 plus 1000 ppm additive A in AL-27151 4.4 – 

06-335 20% AL-27138 plus 2000 ppm additive A in AL-27151 9.4 0.5 

06-336 20% AL-27138 plus 1000 ppm additive B in AL-27151 4.6 0.3 

06-337 20% AL-27138 plus 2000 ppm additive B in AL-27151 7.0 0.1 

06-205 20% AL-27129 in AL-27151 no additive >12 0.3 

06-338 20% AL-27129 plus 1000 ppm of additive A in AL-27151 >12 0.2 

06-551 20% AL-27129 plus 1000 ppm of additive B in AL-27151 >12 – 

06-208 20% AL-27129 in AL-27175 no additive >12 0.3 

06-553 20% AL-27129 plus 1000 ppm of additive B in AL-27175 >12 – 

06-245 20% AL-27138 in AL-27175 no additive 1.7 222.8 

06-523 20% AL-27138 plus 1000 ppm additive A in AL-27175 6.0 1.7 

06-517 20% AL-27138 plus 2000 ppm of additive A in AL-27175 >12 0.2 

06-519 20% AL-27138 plus 1000 ppm additive B in AL-27175 4.5 0.5 

06-521 20% AL-27138 plus 2000 ppm additive B in AL-27175 6.6 0.2 

Storage Stability 

The eight B20 blends listed in Table 11 were tested with ASTM D4625 for long-term storage 

stability. Numerical results are given in Appendix G. Figure 32 shows results for peroxide 

value. The two unstable B100 samples, with induction times shorter than 1 hour, produced 

B20 blends that clearly degraded on this test. Acid value increase for B20 blends over the 

D4625 test is shown in Figure 33. B20 prepared from unstable B100 shows a significant 

increase in acidity. One other B100 (with an induction time of 6.5 hours) shows a small 

acidity increase, but this sample shows no increase in peroxide, so it may not actually be 

degrading. The acid number increase for this sample is also close to the reproducibility of the 

test method. Total insolubles formation is shown in Figure 34. The only sample that increased 

significantly in insolubles was blended from a B100 sample with an induction time of 0.5 

hours (AL-27138). One B100 sample with a short induction time (0.2 hours) did not exhibit 

insolubles formation in B20 over the 12-week D4625 test. This indicates that the B100 

induction period may be a conservative measurement of blend performance as the data 

indicate not all B100 failing the 3-hour induction period would form deleterious amounts of 

sediment when aged under these conditions. 

Figure 35 shows results for several B20 blends treated with antioxidants, primarily B20 

produced from the unstable B100, AL-27138. None of the antioxidant-treated samples 

showed a significant increase in insolubles formation. Antioxidant treatment also stabilized 

the induction time for these samples such that there was little change over the 12-week test. 

This result could indicate another potential solution to addressing stability with biodiesel and 

biodiesel blends, that being the mandatory addition of antioxidants. This would require further 

study, but confirmed use of antioxidants might be a better control strategy than any of the 

tests proposed here. 

 39
Weeks

0 2 4 6 8 10 12

Peroxide Value

0

500

1000

1500

2000

2500

3000

B100 OSI

4.2 

3.1 

6.5 

0.5 

5.5 

7.8 

7.3 

0.2 

Figure 32. Peroxide value for B20 samples tested on D4625 test 

Weeks

0 2 4 6 8 10 12

Acid Value, mg KOH/g

0.0

0.5

1.0

1.5

2.0

2.5

4.2 

3.1 

6.5 

0.5 

5.5 

7.8 

7.3 

0.2 

B100 OSI

Figure 33. Acid value for B20 samples tested on the D4625 test 

 40
Weeks

0 2 4 6 8 10 12

Total Insoluble, mg/100 ml

0

50

100

150

200

4.2 hr

3.1 hr

6.5 hr

0.5 hr

5.5 hr

7.8 hr

7.3 hr

0.2 hr

B100 OSI

Figure 34. Total insolubles formed from B20 samples tested on the D4625 test 

Weeks

0 2 4 6 8 10 12

Total Insoluble, mg/100 ml

0

5

10

15

20

25

30

20% AL-27138+1000 ppm A in AL-27175

20% AL-27138+2000 ppm A in AL-27175

20% AL-27138+1000 ppm B in AL-27175

20% AL-27138+2000 ppm B in AL-27175

20% AL-27138+2000 ppm A in AL-27151

20% AL-27138+1000 ppm B in AL-27151

20% AL-27138+2000 ppm B in AL-27151

20% AL-27129+1000 ppm A in AL-27151 

Figure 35. Total insolubles formation for B20 samples treated with antioxidant additives on the 

D4625 test 

 41
Simulated Vehicle Fuel Tank Aging 

As described in the methods section, worst-case fuel tank aging was simulated by storing the 

biodiesel blend in the D4625 flask at 80oC for 1 week with ullage purge, followed by 

measurement of peroxide number, acid number, and insolubles. This is not a standard test, 

and results should be interpreted with caution. Detailed results are given in Appendix G. An 

increase in peroxides is observed for all these B20 samples under these severe test conditions, 

as shown in Figure 36; however, the largest increase in acid value was observed for blends 

prepared from B100 with induction times shorter than 1 hour (Figure 37). B20 induction time 

is a somewhat better predictor of the final acidity on this test, as shown in Figure 38. The 

B100 induction time was not predictive of insolubles formation on this test for B20 samples 

as shown in Figure 39, nor was B20 induction time or B100 D2274 total insolubles (not 

shown). Antioxidant additives effectively reduced total insolubles formation on this test (not 

shown), although in some cases the additive treat rate may have been too low to completely 

eliminate insolubles (see Appendix G). 

Because we cannot correlate results on this test to what actually happens in a vehicle fuel 

tank, the levels of insolubles shown in Figure 39, and the levels of acidity developed for the 

more stable B100 in Figure 37, may not indicate that these fuels would cause vehicle 

operational or durability problems. Interpretation would be more straightforward if we 

observed large differences for less stable versus more stable B100, as was the case for B5 

blends. Neither anecdotal nor detailed field data on B20 show a propensity for significant 

vehicle fuel filter clogging, which should be the case if sediment actually forms at levels 

similar to this 1-week aging test in the field.20

Initial B100 OSI, hr

02468 10

0

1000

2000

3000

4000

5000

1 Week 80oC Ageing

Peroxide Value

Figure 36. Peroxide value for B20 blends after 1 week aging at 80oC, as a function of B100 OSI 

or Rancimat induction time 

 42
Initial B100 OSI, hr

02468 10

Acid Value after 1 week 80o

C

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Figure 37. Acid value for B20 blends after 1 week aging at 80oC, as a function of B100 OSI or 

Rancimat induction time. 

Initial B20 OSI, hr

0 2 4 6 8 10 12

Acid Value after 1 week 80o

C

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

>

Figure 38. Acid value for B20 blends after 1 week aging at 80oC, as a function of B20 OSI 

induction time 

 43
Initial B100 OSI

02468 10

0

50

100

150

200

250

1 Week 80oC Ageing

Total Insoluble, mg/100 ml

Figure 39. Total insolubles for B20 blends after 1 week aging at 80oC, as a function of B100 OSI 

induction time 

Simulated Vehicle Tank Aging Followed by High-Temperature Testing 

Worst-case stability in the high-temperature environment of a diesel engine fuel injection 

system is simulated by subjecting the samples that had been aged for 1 week at 80oC (see 

previous section) to the D6468 thermal stability test (150oC for 180 minutes). We measured 

filter reflectance, and used procedures identical to those in D2274 to gravimetrically quantify 

the amount of deposits on the filter. Results are shown in Figure 40 as a function of the 

blending B100 induction time. Detailed results are listed in Appendix G. Low reflectance 

values are not observed for any of the B20 samples. High values of gravimetric insolubles 

occur only for B100 with induction times shorter than about 4 hours. Treating these B100 

blends with antioxidants eliminated the formation of insolubles on this test (not shown). 

Notably, the B20 blend produced from AL-27160, which demonstrated marginal thermal 

stability on the D6468 test before aging, does not generate high deposits on this test after 1 

week of aging. Similar results were observed for the B5 blend prepared from this B100. 

As noted for the fuel tank simulation test, because we have no correlation of this test sequence 

(1 week at 80oC followed by D6468 thermal stability testing) with performance in actual 

engine fuel systems, whether any of the fuels tested would actually cause engine operational 

or durability problems is unclear. The B100 induction time specification of 3 hours does, 

however, eliminate the highest sediment-forming blend under these test conditions. But 

overall this testing approach does not provide an obvious delineation between fuels that are 

stable and those that are not under these conditions. 

 44
Initial B100 OSI, hr

02468 10

50

60

70

80

90

100

110

1 Week 800C Ageing

D6468 Reflectance %

Initial B100 OSI, hr

02468 10

0

5

10

15

20

1 Week 80oC Ageing

Gravimetric Insoluble, mg/100 ml

Figure 40. Filter reflectance and gravimetric insoluble formation for B20 samples aged for 1 

week at 80oC and tested in the D6468 thermal stability test 

 45
Discussion 

Do Accelerated Tests Predict B100 Storage Stability? 

The D4625 storage data for B100 at 8 and 12 weeks indicate that none of the accelerated tests 

are good—or even average—predictors of the degree of biodiesel degradation on this test at 

these storage times. Almost all samples at both 4 and 8 weeks had sediment formation below 

2 mg/100 ml, which indicates fairly low sediment formation on this test, but all samples 

exhibited an increase in acid number at 8 weeks to out-of-specification levels. Attempts to 

correlate biodiesel degradation at 4 weeks with results of initial stability tests were slightly 

more successful. Figure 41 shows that initial induction time is a rough predictor (r2 = 0.55) of 

induction time at 4 weeks. Figure 42 suggests that if the initial degree of oxidative 

degradation (as measured by the peroxide number or value) is low, the peroxide number will 

be low at 4 weeks. However, the curve is very steep at low peroxide levels. Nevertheless, this 

confirms that exposure of the biodiesel to oxidative conditions that cause peroxide formation 

should be avoided. Figure 43 shows the change in acid value over 4 weeks as a function of the 

initial induction time. Samples with longer induction times in general experience a smaller 

change in acid value, although clearly other factors affect the results. Operating on the idea 

that the initial degree of degradation (peroxide number) combined with some measure of 

stability (induction time or D2274 insoluble) might be a better predictor, we performed simple 

multiple regression analysis, but r2

 values for these regressions were quite low. 

Real-world experience and common sense suggest that samples with longer induction times or 

lower levels of D2274 deposits are more stable, but the results of these accelerated tests are 

not strong predictors of storage stability on the D4625 test at 4, 8, or 12 weeks. One 

possibility not examined here is that even at 4 weeks these samples have degraded so far that 

their initial state is no longer predictive of their condition. Storage results for a shorter period 

(2 weeks, for example) might yield stronger correlations. However, the data in Figure 9 show 

that if induction time is near or below the 3-hour limit, B100 will most likely fail to meet its 

specification for stability before 4 months. Even samples with induction times longer than 6 

hours are out of specification for oxidation stability at 4 weeks on this test, suggesting that 

any B100 not treated with antioxidant should not be stored for more than 2 or 3 months. The 

B100 could be stored significantly longer before it goes out of specification for acid value or 

before significant levels of deposits form. 

The D4625 test condition of 43oC may not be appropriate for B100. This test was developed 

to provide slightly accelerated conditions for assessing the stability of petroleum-derived 

fuels. For these fuels reactions that occur at typical storage temperatures are apparently the 

same as those that occur at 43oC. This may not be the case for B100. For example, Bondioli 

and coworkers18 compared the results from D4625 tests8

 and storage for 1 year in drums at 

ambient conditions.7

 They observed only modest degradation in the 1-year storage study, but 

for D4625 storage they saw significant increases in peroxide value and insolubles at only 4 

weeks, along with significant increases in acidity at 8 to 12 weeks. These results suggest that 

degradation reactions that occur in B100 are accelerated much more by increasing the 

temperature to 43oC than are those that occur in conventional diesel fuels at this temperature. 

 46
Initial OSI, hr

02468 10

OSI at 4 Weeks in D4625, hr

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Figure 41. B100 OSI or Rancimat induction period at 4 weeks on the D4625 test as a function of 

initial induction time 

Initial Peroxide Number

0 50 100 150 200 250

4 week D4625 Peroxide Number

0

200

400

600

800

1000

Figure 42. Peroxide number at 4 weeks on the D4625 test for B100 samples, as a function of 

initial peroxide number 

 47
Initial OSI, hr

02468

Change in Acid Value, 4 Weeks D4625

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.46

0.24

0.41

0.23

0.13

0.05

0.09

0.69

Figure 43. Change in acid value at 4 weeks on D4625 as a function of initial OSI or Rancimat 

induction time for B100 samples. Data labels indicate initial acid value 

Is B100 Stability a Predictor of Blend Stability? 

Accelerated Tests 

The accelerated test data indicate that B100 stability is, in some sense, a good predictor of 

blend stability for both B5 and B20 blends. For B5 blends the B5 induction time as a function 

of the B100 induction time is shown in Figure 44. The experiment was ended at 12 hours for 

B5 blends. If the B100 has an induction time of about 3 hours or longer, the B5 blend is 

guaranteed to have a 12-hour or longer induction time. A similar plot for B5 D2274 total 

insolubles is shown in Figure 45. Again, if the B100 has an induction time longer than about 3 

hours, the B5 blend will always have D2274 deposits of less than 2.5 mg/100 ml. For less 

stable B100, high levels of insolubles—in fact, much higher than those observed for the B100 

used to make the blend—can form. Another way to look at the data is to compare B5 D2274 

total insolubles with B100 D2274 total insolubles as shown in Figure 46. If the B100 total 

insolubles are less than about 6 mg/100 ml, the B5 blend produces total insolubles below 2.5 

mg/100 ml. The 2.5 mg/100-ml level was chosen because it is used as a stability requirement 

for diesel fuels in several pipeline systems. 

Figure 47 compares B20 induction time to B100 induction time. For all but one of 48 

samples, if the B100 induction time is longer than about 3 hours, the B20 induction time will 

exceed 6 hours. Figure 48 shows that if B100 induction time is longer than about 3 hours, the 

B20 D2274 total insolubles will be below 2.5 mg/100 ml. If B100 induction time is shorter 

than 3 hours, high levels of insolubles can form, much higher than those observed for the 

B100 that was used to make the blend. Figure 49 shows that if B100 D2274 total insolubles 

are below about 6 mg/100 ml, B20 total insolubles will be below 2.5 mg/100 ml. 

 48
Thus, accelerated tests do not show a direct proportionality or correlation between B100 

stability and blend stability, but if the B100 stability is above a certain level (roughly a 3-hour 

induction time), blends prepared from that B100 appear to be stable. Based in part on these 

results, ASTM has recently included a 3-hour minimum induction time requirement in the 

D6751 specification for B100 (this was originally included in D6751-06b). 

Fang and McCormick recently reported on a negative synergism or antagonism for deposit 

formation from biodiesel blends on the D2274 test.10 As noted in the Background chapter, 

blends in the B20 to B30 range produced much higher levels of deposits than would be 

predicted from a weighted average of the results obtained for the diesel and biodiesel blending 

components. Figures 45 and 48 also show this effect, here even for B5 blends, although 

deposit levels are much higher for B20 blends. 

B100 OSI, hr

0 2 4 6 810

B5 OSI, hr

0

2

4

6

8

10

>12

Figure 44. B5 OSI induction time as a function of B100 OSI induction time 

 49
B100 OSI, hr

02468 10

B5 D2274 Total Insoluble, mg/100 ml

0

10

20

30

40

50

Figure 45. B5 D2274 total insoluble as a function of B100 OSI or Rancimat induction time 

B100 D2274M Total Insoluble, mg/100 ml

0 2 4 6 8 10 12 14 16 18 20

B5 D2274M Total Insoluble, mg/100 ml

0

10

20

30

40

50

Figure 46. B5 D2274 total insoluble as a function of B100 D2274 total insoluble 

 50
B100 OSI, hr

02468 10

B20 OSI, hr

0

2

4

6

8

10

>12

Figure 47. B20 OSI induction time as a function of B100 OSI induction time 

B100 OSI, hr

02468 10

B20 D2274M Total Insoluble, mg/100 ml

0

50

100

150

200

250

012345678

0

5

10

15

20

25

Figure 48. B20 D2274 total insoluble as a function of B100 OSI or Rancimat induction time 

 51
B100 D2274M Total Insoluble, mg/100 ml

0 2 4 6 8 10 12 14 16 18 20

B20 D2274M Total Insoluble, mg/100 ml

0

50

100

150

200

250

Figure 49. B20 D2274 total insoluble as a function of B100 D2274 total insolubles 

Aging and In-Use Scenario Tests (Storage, Vehicle Tanks, High-Temperature 

Environment) 

These tests include the D4625 12-week storage test, the 1 week at 80oC test, and the 

subsequent high-temperature thermal stability test. B100 stability on accelerated tests seems 

to be a reasonable predictor of stability of B5 and B20 blends on the D4625 test. As shown in 

Figures 20, 21, and 22; the only B5 blend that exhibited oxidative deterioration on this test 

was prepared from a B100 with an induction time of 0.5 hours. Similarly for B20, Figures 32, 

33, and 34 show that only B20 prepared from B100 with short induction times (in this case 

0.5 and 0.2 hours) exhibited oxidative degradation. So, although questions remain about the 

suitability of the 43oC storage test for B100 and about whether 1 week of storage on this test 

for biodiesel and biodiesel blends equates to 1 month of real-world storage (as is generally 

assumed for petroleum-derived fuels), biodiesel blends prepared from B100 with 3-hour or 

longer induction times do not appear to degrade under these conditions. 

For the worst-case simulated fuel tank aging test (1 week at 80oC) Figures 24, 25, and 26 

show significant oxidative degradation only for B5 blends prepared from a B100 with 0.5 

hour induction time. The picture is less clear cut for B20, where Figures 36 through 39 

indicate little relationship between B100 induction time and oxidative degradation under these 

conditions. However, B20 induction time was reasonably predictive of the acid value (and 

acid value increase) on this test. Thus we conclude that for these test conditions stable B100 

will lead to stable B5 blends. We may also reasonably conclude that stable B100 will 

eliminate the most unstable B20 as measured by acid value, but the test cannot differentiate 

 52
between intermediate and highly stable samples for acid number or sediment formation under 

these worst-case test conditions. This may be because these test conditions are too severe for 

B20 blends, such that stable and unstable blends are degraded. Additionally, because we 

cannot correlate results on this test to what actually happens in a vehicle fuel tank, it is not 

clear that the levels of insolubles shown in Figure 39, or the levels of acidity developed for 

the more stable B100 in Figure 37, actually indicate that these B20 blends would cause 

problems. 

Blends were aged for 1 week at 80oC, then tested for thermal stability with D6468 (150oC for 

180 minutes) to simulate reaction of the fuel in the high-temperature environment of the fuel 

injection system. Filter reflectance was measured and insolubles were quantified 

gravimetrically. For B5 blends the only sample exhibiting significant deposits was produced 

from a B100 with an induction time of 0.5 hours (see Figure 27). As shown in Figure 40, none 

of the B20 samples exhibited thermal instability based on reflectance. Most samples with 

B100 induction times of roughly 4 hours or less exhibited higher gravimetric deposits than 

other samples. We conclude that for B5 blends a stable B100 will lead to a thermally stable 

B5 blend, based on these test conditions, even after aging. For B20 blends additional data may 

be required, or the test conditions may be so severe that we cannot distinguish between stable 

and unstable samples. And as before, because we have no correlation of this test sequence (1 

week at 80oC followed by D6468 thermal stability testing) with performance in actual engine 

fuel systems, we cannot be certain that any of the fuels tested would actually cause engine 

operational problems. This testing approach does not provide a clear performance delineation 

between fuels that are stable and those that are not under these conditions. 

An important caveat is that these tests have all been conducted in glassware. We recommend 

that additional tests be performed in real equipment to validate these conclusions. For storage 

this might be accomplished by storing the fuels in drums at ambient conditions; for the fuel 

tank simulation perhaps blends from biodiesel of varying stability levels could be examined in 

stand-alone vehicle fuel systems, similar to the approach taken by Tsuchiya and coworkers.15

Unfortunately, there is no standard engine test for assessing the impact of fuel stability on fuel 

system and injector deposits and durability. Nevertheless, some testing with blends of varying 

stability in real fuels systems is required to validate these results. 

How Do Diesel Fuel Properties Effect Stability? 

Diesel fuel properties that might affect biodiesel blend stability include: 

• Aromatic content. Higher aromatic fuels may be better able to hold polar biodiesel and 

diesel fuel oxidation products in solution. 

• Sulfur content. Sulfur compounds can function as antioxidants. 

• Diesel fuel oxidative and thermal stability. 

Table 8 and Figure 15 show property and stability data for the diesel fuels used in this study. 

Total aromatic content ranges from about 8 to about 36 mass percent. One fuel (AL-27171) 

contains 340 ppm of sulfur; the remaining five contain less than 10 ppm. D2274 and D6468 

indicate all six fuels are stable with little to distinguish one from another. Aging for 12 weeks 

in D4625 showed one fuel (AL-27175) beginning to show instability at 12 weeks. Notably 

 53
this is the diesel fuel with the lowest aromatic content of 8%. Aging for 1 week at 80oC 

indicated little difference between the diesel fuels. 

Examining accelerated test data, Figures 50 and 51 show how diesel fuel aromatic content 

affects D2274 total insolubles for B5 and B20 blends, respectively. In both cases the only 

samples exhibiting high levels of insolubles were prepared from B100 with induction times 

shorter than 1 hour, independent of fuel aromatic content. D4625 storage data for B5 blends 

show one sample with instability at 12 weeks (Figures 20–22, Appendix E). This fuel was 

prepared from an unstable B100 and the low-sulfur diesel fuel (AL-27171) with 36% aromatic 

content. This B5 blend was also unstable in simulated fuel tank aging and in high-temperature 

stability tests. A B20 blend prepared from these same blending components, as well as a 

second B20 prepared from an unstable biodiesel and a ULSD with 16% aromatic content also 

demonstrated instability on D4625. 

Diesel Fuel Total Aromatic, wt%

0 10 20 30 40

B5 ASTM D2274 Total Insoluble, mg/100 ml

0

10

20

30

40

50

B100 OSI~0.5 hr

Figure 50. Diesel fuel aromatic content affect on D2274 total insolubles for B5 blends 

 54
Diesel Fuel Total Aromatic Content, wt%

0 10 20 30 40

B20 ASTM D2274 Total Insoluble, mg/100 ml

0

50

100

150

200

250

B100 OSI~0.5 hr

Figure 51. Diesel fuel aromatic content affect on D2274 total insolubles for B20 blends 

To examine the issue of diesel fuel aromatic content in more detail, an unstable B100 (AL27138) was blended with each diesel fuel at 20% and tested on the fuel tank aging and hightemperature stability simulation tests. Results are shown in Figure 52. Four of the six samples 

produced total insolubles after 1 week of aging above 100 mg/100 ml, somewhat higher than 

observed when a range of B20 samples from various biodiesels were subjected to this test 

(Figure 39). A blend of AL-27138 (B100) and AL-27151 (ULSD) was tested twice, once in 

November 2006 for the dataset shown in Figure 39 and again in April 2007 for the dataset 

shown in Figure 52. In November this sample produced 35.7 mg/100 ml; in April it generated 

200 mg/100 ml, suggesting that the already unstable B100 had aged further in the intervening 

months. Nevertheless, these tests show no correlation between stability and diesel fuel 

aromatic content. 

Our results suggest that diesel fuel aromatic content does not play a role in the stability of 

biodiesel blends and that B100 stability is the most important factor, consistent with the 

discussion in the previous section. However, we have noted the antagonistic effect where 

D2274 deposits for biodiesel blends are much higher than would be predicted based on the 

individual stability of the petroleum and biodiesel blend components. The cause of this 

antagonism is unknown, but based on these results does not appear to be related to aromatic 

content. The antagonism requires an unstable biodiesel, however, and perhaps unstable 

biodiesel degrades to produce polar components that are soluble in oxidized B100 but 

insoluble in any diesel fuel, independent of aromatic content. 

The impact of diesel fuel sulfur content is less easily assessed because the dataset consists of 

essentially five samples with very low sulfur content (below 10 ppm) and one with 340 ppm. 

 55
The accelerated and real-world simulation results show that when an unstable B100 is blended 

with the 340 ppm sulfur diesel fuel an unstable blend is formed. Because there was little 

difference between the diesel fuels for stability, the impact of diesel stability on biodiesel 

blend stability cannot be assessed from these data. These results also support the idea that 

B100 stability is the main factor that affects the stability of B5 and B20 blends. However, an 

important caveat is that the diesel fuels included here were obtained before ULSD was 

mandated in the United States. Confirmatory testing should be conducted with fuels that are 

more representative of in-use fuels today. 

 56
Diesel Fuel Total Aromatic Content, wt%

0 10 20 30 40

One Week 80oC Ageing

Total Insoluble, mg/100 ml

0

50

100

150

200

250

Diesel Fuel Total Aromatic Content, wt%

0 10 20 30 40

One Week 80oC Ageing

D6468 Gravimetric Insoluble, mg/100 ml

0

5

10

15

20

25

Figure 52. Results of 1 week at 80oC aging test followed by D6468 thermal stability test for B20 

samples prepared from B100 AL-27138 and all diesel samples 

 57
How Do Antioxidant Additives Affect Stability? 

The hindered phenolic antioxidants tested here prevented oxidative degradation of B100 in 

the storage simulation, and prevented degradation of biodiesel blends in the storage, fuel tank, 

and high-temperature simulations. The dramatic suppression in insoluble formation for the 

highly unstable B100 AL-27138 (Figure 14), and for B5 (Figure 23) and B20 (Figure 35) 

blends produced from it, during the 12-week storage test is striking, even for cases where the 

antioxidant did not increase B100 induction times to longer than 3 hours. For B5 blends, 

antioxidants also prevented insolubles from forming in the fuel tank and high-temperature 

simulations. In some B20 cases the additive treat rates were too low to prevent insolubles 

from forming for the fuel tank and high-temperature stability simulations, but did reduce 

insolubles formation. In these cases, a higher treat rate eliminated insolubles. No effort was 

made to optimize additive treat rate. Additionally, the amount of active ingredient in the 

additives is unknown. So the results mainly confirm that additives can be effective, but 

individual producers and blenders will have to select appropriate additives and determine 

optimal treat rates for their specific situations. 

Is a 3-Hour B100 Induction Time Adequate? 

Beginning with the publication of ASTM D6751-06b in January 2007, B100 is required to 

have a minimum 3-hour induction time. This requirement is largely based on the accelerated 

stability data and analysis presented in the section titled, Is B100 Stability a Predictor of 

Blend Stability? Additional data are now available from the aging simulation tests (storage, 

vehicle fuel tank, and high temperature) and the extent to which these new data support the 3-

hour minimum induction time requirement is of interest. 

Storage Stability 

As discussed, none of the accelerated stability tests were particularly strong predictors of the 

stability of B100 on the D4625 test at 43oC. However, as indicated in Figure 43, having a 

minimum induction time of 3 hours limits acid value increase over 4 weeks of storage on this 

test to less than 0.2 mg KOH/g. Figure 11 shows that at 4 weeks the only samples that had 

gone out of specification for acid value had initial induction times of 3.1 hours or lower. Our 

experience agrees with that of other researchers,5,7,8,9,14,15,17 that B100 samples with longer 

induction times are more stable in real-world settings. Thus, we take these results to mean that 

most biodiesel samples, regardless of initial induction time, will begin to oxidize immediately 

during storage. If induction time is near or below the 3-hour limit, the B100 will most likely 

go out of specification for either stability or acid value within 4 months. For longer induction 

times the biodiesel might be stored for several months. However, the results in Figure 9-12 

indicate that even B100 with induction times longer than 7 hours will be out of specification 

for oxidation stability at only 4 months, although these samples may not have shown a 

significant increase in acidity or in deposit formation. The 3-hour limit appears to be adequate 

to prevent oxidative degradation for B5 and B20 blends in storage for up to 12 months 

(assuming that we accept the relationship that 1 week on D4625 is equivalent to 1 month of 

real-world storage at 21oC for blends). 

Given these observations, we recommend that the 3-hour limit be considered as adequate to 

protect B100 and blends in storage, and that additional data on B100 storage be acquired at 

more realistic storage temperatures and for longer periods. Blenders of biodiesel and others 

 58
who need to store B100 should be made aware of limitations on the number of months this 

material can be stored. In developing a follow-up testing plan, the actual B100 storage 

conditions should be considered. In many cases, B100 may be stored in aboveground tanks 

that are heated to roughly 15oC during the winter months, but might experience higher 

temperatures during the summer months. 

Stability in Simulated Vehicle Fuel Tank and High-Temperature Environments 

The results of B5 testing shown in Figures 24 to 27 clearly indicate that B100 with a 3-hour or 

longer induction time produced B5 blends that were stable on the testing protocols employed 

here. Even if these test conditions are later found to have been too severe, the B5 blends did 

not exhibit instability if the B100 had at least a 3-hour induction time. 

For B20 blends the situation is less clear cut. For the most part there was little to distinguish 

blends produced from minimum 3-hour induction time B100 from blends produced from less 

stable biodiesel. As shown in Figure 38, the B20 induction time was a better predictor of acid 

formation on the fuel tank aging simulation, as B20 induction time of roughly 4 hours was 

adequate to prevent a large increase in acidity. 

Compared to the fuel tank aging simulation test, the D2274 test is conducted at conditions of 

95oC with bubbling of oxygen through the fuel for 16 hours, in some ways more severe than 

the 80oC for 1 week test conditions. Increased contact of B100 and air via mixing or bubbling 

has been shown to produce a dramatic increase in oxidation rates.7

 Figure 48 shows that B100 

with a minimum 3-hour induction time produces stable B20 on this test. The accelerated test 

results shown in Figure 48 strongly support the conclusion that the B100 minimum 3-hour 

induction time produces B20 that is stable in the vehicle fuel tank and high-temperature 

environments. In other ways the 1-week storage test conditions may be more severe. 

Temperature and air contacting are less severe than D2274, but the test lasts more than 10 

times longer (168 hours versus 16 hours). Perhaps we could better discriminate between 

stable and unstable B20 by reducing the test time from 1 week to 2 or 3 days, especially given 

that the test temperature of 80oC is likely higher than would be encountered in a real vehicle 

fuel tank over extended periods without being fueled with fresh fuel. Also, because Figure 47 

indicates that if B100 induction time is longer than 3 hours, B20 induction time is almost 

always longer than 6 hours; therefore, the idea of a separate stability requirement for B20 may 

not provide additional protection. So although additional data are needed to confirm, the 

picture emerging from the available data is that B20 blends prepared from B100 with a 

minimum 3-hour induction time are stable in vehicle fuel tank and high-temperature engine 

fuel system environments. 

 59
Conclusions and Recommendations 

The B100 samples examined here show a broad distribution of stability on accelerated tests, 

with induction time (OSI) results ranging from less than 1 hour to more than 9 hours and 

ASTM D2274 total insolubles ranging from less than 2 mg/100 ml to nearly 18 mg/100 ml. 

Samples that produce very high levels of iso-octane insolubles on the D2274 test also 

produced very high levels of total insolubles. This suggests that little new information is 

acquired by measuring iso-octane insolubles. The change in acid value of the filtered liquid 

over the D2274 test was closely correlated with total insolubles and the initial induction time. 

The accelerated test data indicate that if the B100 stability is above a roughly 3-hour induction 

time, blends prepared from that B100 appear to be stable on the OSI and D2274 tests. 

The D4625 long-term storage results for B100 indicate that most biodiesel samples, regardless 

of initial induction time, will begin to oxidize immediately during storage. If induction time is 

near or below the 3-hour limit, the B100 will most likely go out of specification for either 

stability or acid value within 4 months. Even B100 with induction times longer than 7 hours 

will be out of specification for oxidation stability at only 4 months, although these samples 

may not have shown a significant increase in acidity or in deposit formation. B100 should 

probably not be stored longer than several months in any case unless it is treated with a 

synthetic antioxidant. Blenders of biodiesel and others who need to store B100 should be 

made aware of limitations on the number of months this material can be stored. 

The 3-hour B100 induction time limit appears to be adequate to prevent oxidative degradation 

for both B5 and B20 blends in storage for up to 12 months. Questions remain as to whether 1 

week of storage on the D4625 test for biodiesel and biodiesel blends equates to 1 month of 

real world storage, as is generally assumed for petroleum-derived fuels. 

For tests that simulated fuel tank aging and high-temperature stability, we conclude that stable 

B100 (longer than 3 hour OSI) leads to stable B5 blends. For B20, considering the entire 

dataset available today, we provisionally conclude that stable B100 (longer than 3 hour OSI) 

leads to stable B20 blends, but the test cannot differentiate between intermediate and highly 

stable samples for acid number or sediment formation under these worst-case test conditions. 

Anecdotal and detailed field data collections on B20 do not show a propensity for significant 

vehicle fuel filter clogging. Additional work is required to confirm this or to determine 

whether an additional stability test is required for the B20 blend. 

These results support the idea that B100 stability is the main factor that affects the stability of 

B5 and B20 blends, independent of diesel fuel aromatic content, sulfur level, or stability. 

However, the diesel fuels included here were obtained before ULSD was mandated in the 

United States. Confirmatory testing should be conducted with fuels that are more 

representative of actual in-use fuels. Additionally, the factors leading to the negative 

antagonism for deposit formation that occurs with blending of unstable B100 in to diesel fuel 

remain unknown, and future studies should endeavor to understand this phenomenon. 

 60
The hindered phenolic antioxidants tested here prevented oxidative degradation of B100 in 

the storage simulation, and prevented degradation of biodiesel blends in the storage, fuel tank, 

and high-temperature simulations. Individual producers, blenders, and additive suppliers will 

have to select appropriate additives and determine optimal treat rates for their specific 

situations. 

We recommend that additional data be acquired in real equipment to verify these conclusions. 

For storage this might be accomplished with storage in drums at ambient conditions; for the 

fuel tank simulation perhaps blends from biodiesel of varying stability levels could be 

examined in stand-alone vehicle fuel systems or more intense monitoring and measurement of 

fuel in actual use. Unfortunately there is no standard engine test to assess the impact of fuel 

stability on fuel system and injector deposits and durability. Nevertheless, some testing with 

blends of varying stability in real fuel systems is required to confirm these results. 

 61
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 63
Appendix A: B100 Characterization and Stability Test Data 

Sample Identification Method AL-27128-F AL-27129-F AL-27137-F AL-27138-F Oxidation Stability, hours EN 14112 Replicate 1 4.22 3.09 6.41 0.13  Replicate 2 4.18 3.10 6.55 0.62  Replicate 3 4.24 3.14 6.61 0.59  Mean 4.21 3.11 6.52 0.45 Oxidation Stability, mg/ 100 ml Modified ASTM D2274 Replicate 1  Filterable insolubles 4.7 1.3 0.7 6.1  Adherent Insolubles 1.6 1.0 1.1 0.9  Total Insolubles 6.3 2.3 1.8 7.0  Iso-Octane Insolubles 197.4 4.7 2.4 4.0  Replicate 2  Filterable insolubles 5.0 1.0 0.2 6.9  Adherent Insolubles 1.6 0.5 0.0 1.3  Total Insolubles 6.6 1.5 0.2 8.2  Iso-Octane Insolubles 198.0 0.4 2.8 4.8 Mean Total Insolubles 6.5 1.9 1.0 7.6 Mean Iso-Octane Insolubles 197.7 2.6 2.6 4.4 Oxidation Stability, Pressure Vessel 

ASTM D525

Induction Period Method, minutes 341 169 34 80 Thermal Stability, deposit, mg ASTM D6468 Modified 0.3 0.1 0.3 0.3 Total Acid Number, mg KOH/g ASTM D664 0.23 0.41 0.05 0.33 Total Acid Number after D2274, mg KOH/g  Replicate 1 1.84 2.92 0.24 2.75  Replicate 2 2.03 2.07 0.15 3.26  Mean 1.94 2.50 0.20 3.01 Total Glycerin, %(mass) ASTM D6584 0.103 0.081 0.144 0.016 Free Glycerin, %(mass) ASTM D6584 0.009 <0.001 0.002 0.002 

 64
Sample Identification Method AL-27142-F AL-27144-F AL-27145-F AL-27146-F 

Oxidation Stability, hours EN 14112 Replicate 1 4.56 3.69 3.70 9.28  Replicate 2 4.46 4.02 4.01 9.33  Replicate 3 4.40 4.10 4.16 9.16  Mean 4.47 3.94 3.96 9.26 Oxidation Stability, mg/ 100 ml Modified ASTM D2274 Replicate 1  Filterable insolubles 0.9 2.0 2.0 0.3  Adherent Insolubles 0.2 0.3 0.4 0.1  Total Insolubles 1.1 2.3 2.4 0.4  Iso-Octane Insolubles 0.3 1.4 2.7 0.4  Replicate 2  Filterable insolubles 0.9 2.2 2.0 0.2  Adherent Insolubles 0.2 0.1 0.2 0.0  Total Insolubles 1.1 2.3 2.2 0.2  Iso-Octane Insolubles 0.7 1.3 0.7 0.4 Mean Total Insolubles 1.1 2.3 2.3 0.3 Mean Iso-Octane Insolubles 0.5 1.4 1.7 0.4 Oxidation Stability, Pressure Vessel 

ASTM D525

Induction Period Method, minutes 

507 62 721 649 

Thermal Stability, deposit, mg ASTM D6468 Modified 0.3 0.4 0.4 0.5 Total Acid Number, mg KOH/g ASTM D664 0.07 0.39 0.49 0.08 Total Acid Number after D2274, mg KOH/g  Replicate 1 1.11 1.91 2.18 0.19  Replicate 2 0.90 1.83 2.13 0.20  Mean 1.01 1.87 2.16 0.20 Total Glycerin, %(mass) ASTM D6584 0.216 0.221 0.192 0.161 Free Glycerin, %(mass) ASTM D6584 0.003 0.004 0.005 <0.001 

Sample Identification Method AL-27153-F AL-27154-F AL-27155-F AL-27157-F 

Oxidation Stability, hours EN 14112 Replicate 1 9.36 0.14 2.60 4.67 

 65
 Replicate 2 9.36 0.18 2.59 4.56 

 Replicate 3 9.35 0.18 2.27 4.47  Mean 9.36 0.17 2.49 4.57 Oxidation Stability, mg/ 100 ml Modified ASTM D2274 Replicate 1  Filterable insolubles 0.2 12.3 9.4 1.5  Adherent Insolubles 0.1 1.3 1.5 0.5  Total Insolubles 0.3 13.6 10.9 2.0  Iso-Octane Insolubles 0.2 87.6 94.6 2.8  Replicate 2  Filterable insolubles 0.2 11.1 8.5 1.5  Adherent Insolubles 0.0 1.5 1.3 0.8  Total Insolubles 0.2 12.6 9.8 2.3  Iso-Octane Insolubles 0.2 ND 95.8 2.8 Mean Total Insolubles 0.3 13.1 10.4 2.2 Mean Iso-Octane Insolubles 0.2 87.6 95.2 2.8 Oxidation Stability, Pressure Vessel 

ASTM D525

Induction Period Method, minutes No break 150 270 487 Thermal Stability, deposit, mg ASTM D6468 Modified 0.5 0.1 0.3 0.3 Total Acid Number, mg KOH/g ASTM D664 0.08 1.31 0.29 0.11 Total Acid Number after D2274, mg KOH/g  Replicate 1 0.21 5.54 3.21 1.05  Replicate 2 0.27 ND 2.93 1.19  Mean 0.24 5.54 3.07 1.12 Total Glycerin, %(mass) ASTM D6584 0.15 0.132 0.298 0.225 Free Glycerin, %(mass) ASTM D6584 0.001 0.003 0.007 0.015 

 66
Sample Identification Method AL-27161-F

Oxidation Stability, hours EN 14112 Replicate 1 5.13 Replicate 2 5.11 Replicate 3 5.09 Mean 5.11Oxidation Stability, mg/ 100 ml Modified ASTM D2274 Replicate 1  Filterable insolubles 1.0 Adherent Insolubles 0.1 Total Insolubles 1.1 Iso-Octane Insolubles 0.60 Replicate 2  Filterable insolubles 0.8 Adherent Insolubles 0.2 Total Insolubles 1.0 Iso-Octane Insolubles 0.80Mean Total Insolubles 1.1Mean Iso-Octane Insolubles 0.7Oxidation Stability, Pressure Vessel 

ASTM D525

Induction Period Method, minutes No breakThermal Stability, deposit, mg ASTM D6468 Modified 0.2Total Acid Number, mg KOH/g ASTM D664 0.37Total Acid Number after D2274, mg KOH/g  Replicate 1 1.63 Replicate 2 1.50 Mean 1.57Total Glycerin, %(mass) ASTM D6584 0.151Free Glycerin, %(mass) ASTM D6584 0.003 67
Appendix B: D4625 Results for B100 Samples 

AL-27128 AL-27129 AL-27137 AL-27138 AL-27141 AL-27

0 Weeks IsoOctane 

Insoluble 

D 4625, mod 

mg/100 

ml 

3.9 0.1 1.9 2.3 0.1 

Peroxide Value D 3703 217 105 12 98 8 Viscosity @ 40°C 

D 445 4.45 5.12 4.10 4.09 4.67 

Polymer Content 

ISO 16931 

2.63 0.17 0.82 1.03 1.46 

Total Acid No. D 664 mg 

KOH/g 

0.23 0.41 0.05 0.33 0.13 0.69 

Total insoluble D2274 mg/100ml 6.45 1.9 1.015 7.6 0.3 0.9 IsoOctane Insols 

D2274 mg/100ml 197.7 2.6 2.6 4.4 0.6 18.9 

Rancimat IP h 4.21 3.11 6.52 0.45 5.53 7.76 

4 Weeks Filterable Insols D 4625, 

mod 

mg/100 

ml 

0.7 0.1 1.03 1.8 0.4 0.9 

Adherent Insols D 4625, 

mod 

mg/100 

ml 

0 0 0 0.1 1 0 

Total Insols D 4625, 

mod 

mg/100 

ml 

0.7 0 1.3 1.9 1.4 0.9 

IsoOctane Insols 

D 4625, mod 

14.8 0.7 3.3 0.2 4 1.2 

Peroxide Value D 3703 601 633 403 841 65 Viscosity @ 40°C 

D 445 5.5 4.78 4.13 4.22 4.69 

Polymer Content 

ISO 16931 

2.8 0.49 0.89 1.26 1.5 

Total Acid No. D 664 mg 

KOH/g 

0.41 0.53 0.07 0.57 0.19 0.74 

Rancimat IP h 0.88 0.17 1.91 1.67 1.23 

8 Weeks Filterable Insols D 4625, 

mod 

mg/100 

ml 

1 0.1 0.3 1.1 0.3 0.2 

 68
Adherent Insols D 4625, 

mod 

mg/100 

ml 

0.1 0.1 0.1 0.1 0.1 0.1 

Total Insols D 4625, 

mod 

mg/100 

ml 

1.1 0.2 0.4 1.2 0.4 0.3 

IsoOctane Insols 

D 4625, mod 

59.7 0.5 3.6 1.9 3.6 1.9 

Peroxide Value D 3703 1237 1759 2039 1654 225 Viscosity @ 40°C 

D 445 5.75 5.03 4.54 4.49 4.73 

Polymer Content 

ISO 16931 

3.59 1.33 1.92 2.01 1.54 

Total Acid No. D 664 mg 

KOH/g 

1.22 1.41 0.98 1.2 0.98 1.64 

Rancimat IP h >12 >12 >12 0.4 1.29 

12 Weeks 

Filterable Insols D 4625, 

mod 

mg/100 

ml 

3.1 1.4 1 5.9 4.1 3.2 

Adherent Insols D 4625, 

mod 

mg/100 

ml 

0.7 0.5 0.7 0.3 0.4 0.2 

Total Insols D 4625, 

mod 

mg/100 

ml 

3.8 1.9 1.7 6.2 4.5 3.4 

IsoOctane Insols 

D 4625, mod 

17.6 1.1 7.3 6.4 13.

Peroxide Value D 3703 2037 2026 3099 2951 881 Viscosity @ 40°C 

D 445 4.83 4.93 4.72 4.67 4.84 

Polymer Content 

ISO 16931 

4.45 1.99 3.07 3.26 2.02 

Total Acid No. D 664 mg 

KOH/g 

1.10 1.10 0.69 3.18 0.68 1.04 

Rancimat IP h >12 >12 >12 0.58 0.98 

 69
B100 Storage with Antioxidants AL-27138 

Neat 

AL-27138 + 

1000 ppm 

A 

AL-27138 + 

2000 ppm 

A 

AL-27138 

+ 1000 

ppm B 

AL-27138 

+ 2000 

ppm B 

After 4 Weeks Storage at 43°C 

Filterable Insolubles D 4625, 

mod 

mg/100 ml 1.8 0.2 0.2 0.2 0.2 

Adherent Insolubles D 4625, 

mod 

mg/100 ml 0.1 0.1 0.1 0.1 0.1 

Total Insolubles D 4625, 

mod 

mg/100 ml 1.9 0.3 0.3 0.3 0.3 

Isooctane Insolubles D 4625, 

mod 

mg/100 ml 0.2 0.4 0.7 0.2 0.2 

Total Acid Number D 664 mg KOH/g 0.57 0.35 0.35 0.32 0.35 

After 8 Weeks Storage at 43°C 

Filterable Insolubles D 4625, 

mod 

mg/100 ml 1.1 0.3 0.3 0.3 0.3 

Adherent Insolubles D 4625, 

mod 

mg/100 ml 0.1 0.7 0.2 0.1 0.2 

Total Insolubles D 4625, 

mod 

mg/100 ml 1.2 1.0 0.5 0.4 0.5 

Isooctane Insolubles D 4625, 

mod 

mg/100 ml 1.9 1.6 1.8 1.6 5.8 

Total Acid Number D 664 mg KOH/g 1.20 * 1.28 1.29 1.23 

After 12 Weeks Storage at 43°C 

Filterable Insolubles D 4625, 

mod 

mg/100 ml 5.9 0.3 0.4 0.3 0.4 

Adherent Insolubles D 4625, 

mod 

mg/100 ml 0.3 0.1 0.2 0.2 0.4 

Total Insolubles D 4625, 

mod 

mg/100 ml 6.2 0.4 0.6 0.5 0.8 

Isooctane Insolubles D 4625, 

mod 

mg/100 ml 1.4 3.2 1.5 2.1 

Total Acid Number D 664 mg KOH/g 3.18 0.41 0.37 0.66 0.41  70
Appendix C: D4625 Results for Petroleum-Derived Diesel Fuels 

AL-27150 AL-27151 AL-27166 AL-2717 AL-27175 

4 Weeks Filterable 

Insols 

D 4625, mod 

mg/100 

ml 

0.0 0.1 < 0.1 0.3 0.1 

Adherent Insols 

D 4625, mod 

mg/100 

ml 

0.1 0.3 < 0.1 0.1 < 0.1 

Total Insols D 4625, 

mod 

mg/100 

ml 

0.1 0.4 0.1 0.4 0.1 

8 Weeks Filterable 

Insols 

D 4625, mod 

mg/100 

ml 

0.0 0.1 0.1 0.3 0.1 

Adherent Insols 

D 4625, mod 

mg/100 

ml 

0.0 0.2 0.0 0.4 0.0 

Total Insols D 4625, 

mod 

mg/100 

ml 

0.0 0.3 0.1 0.7 0.2 

12 Weeks Filterable 

Insols 

D 4625, mod 

mg/100 

ml 

0.0 0.1 0.1 0.2 2.6 

Adherent Insols 

D 4625, mod 

mg/100 

ml 

0.3 0.6 0.2 0.6 0.3 

Total Insols D 4625, 

mod 

mg/100 

ml 

0.3 0.6 0.2 0.8 2.9 

 71
Appendix D: Accelerated Test Results for B5 Blends 

CL# Biodiesel % Diesel Diesel Rancimat D2274, mod, mg/100 ml D525* 

I C BP, ° IP, h Filt 

Insols 

Adh 

Insols 

Tot 

Insols 

IP, h Refle

CL06-

198 

27128 95 27150 154 >20 0.8 0.6 1.4 No 

break 

CL06-

199 

27128 95 27151 167 >20 0.2 0.3 0.5 No 

break 

CL06-

200 

27128 95 27166 165 >20 0.3 0.3 0.6 No 

break 

CL06-

201 

27128 95 27171 190 >20 0.5 0.2 0.7 No 

break 

CL06-

202 

27128 95 27175 164 >20 0.2 0.2 0.4 No 

break 

CL06-

203 

27128 95 27176 183 >20 0.2 0.1 0.3 No 

break 

CL06-

210 

27129 95 27150 154 >20 0.2 0.4 0.6 No 

break 

CL06-

211 

27129 95 27151 167 >20 0.8 0.2 1.0 No 

break 

CL06-

212 

27129 95 27166 165 >20 0.1 0.1 0.2 No 

break 

CL06-

213 

27129 95 27171 190 >20 0.1 0.1 0.2 No 

break 

CL06-

214 

27129 95 27175 164 >20 0.5 0.1 0.6 No 

break 

CL06-

215 

27129 95 27176 183 >20 0.1 1.4 1.5 1.8 

CL06-

223 

27137 95 27150 154 >20 0.2 1.4 1.6 No 

break 

CL06-

224 

27137 95 27151 167 >20 0.1 0.9 1.0 No 

break 

CL06-

225 

27137 95 27166 165 >20 0.1 0.9 1.0 No 

break 

 72
CL06-

226 

27137 95 27171 190 >20 0.3 0.1 0.4 No 

break 

CL06-

227 

27137 95 27175 164 >20 0.2 0.1 0.3 No 

break 

CL06-

228 

27137 95 27176 183 18.5 0.3 0.1 0.4 No 

break 

CL06-

235 

27138 95 27150 154 4.8 39 1.7 40.7 8.3 

CL06-

236 

27138 95 27151 167 5.8 23 0.5 23.5 No 

break 

CL06-

237 

27138 95 27166 165 5.0 32 3.9 35.9 No 

break 

CL06-

238 

27138 95 27171 190 >12 0.2 0.1 0.3 No 

break 

CL06-

239 

27138 95 27175 164 6.9 0.1 0.1 0.2 No 

break 

CL06-

240 

27138 95 27176 183 0.7 0.2 0.1 0.3 No 

break 

CL06-

248 

27141 95 27150 154 >12 0.1 0.5 0.6 No 

break 

CL06-

249 

27141 95 27151 167 >12 0.1 0.1 0.2 No 

break 

CL06-

250 

27141 95 27166 165 >12 0.2 0.1 0.3 No 

break 

CL06-

251 

27141 95 27171 190 >12 0.1 0.1 0.2 No 

break 

CL06-

252 

27141 95 27175 164 >12 0.2 0.1 0.3 No 

break 

CL06-

253 

27141 95 27176 183 >12 0.2 0.1 0.3 No 

break 

CL06-

260 

27148 95 27150 154 >12 0.2 0.1 0.3 No 

break 

CL06-

261 

27148 95 27151 167 >12 0.1 0.1 0.2 No 

break 

CL06-

262 

27148 95 27166 165 >12 0.2 0.1 0.3 No 

break 

 73
CL06-

263 

27148 95 27171 190 >12 0.1 0.3 0.4 No 

break 

CL06-

264 

27148 95 27175 164 >12 0.2 0.2 0.4 No 

break 

CL06-

265 

27148 95 27176 183 >12 0.1 0.1 0.2 No 

break 

CL06-

272 

27152 95 27150 154 >12 0.1 0.1 0.2 No 

break 

CL06-

273 

27152 95 27151 167 >12 0.1 0.2 0.3 No 

break 

CL06-

274 

27152 95 27166 165 >12 0.1 0.1 0.2 No 

break 

CL06-

275 

27152 95 27171 190 >12 0.1 0.3 0.4 No 

break 

CL06-

276 

27152 95 27175 164 >12 0.1 0.2 0.3 No 

break 

CL06-

277 

27152 95 27176 183 >12 0.1 0.1 0.2 No 

break 

CL06-

284 

27160 95 27150 154 >12 2.4 0.2 2.6 No 

break 

CL06-

285 

27160 95 27151 167 >12 2.0 0.2 2.2 No 

break 

CL06-

286 

27160 95 27166 165 >12 4.6 0.6 5.2 No 

break 

CL06-

287 

27160 95 27171 190 5.5 0.6 0.2 0.8 No 

break 

CL06-

288 

27160 95 27175 164 >12 0.1 0.1 0.2 No 

break 

CL06-

289 

27160 95 27176 183 >12 0.2 0.1 0.3 No 

break 

 74
Appendix E: B5 Blend Storage, Fuel Tank, and High Temperature Stability R

C 2 C 3 C 4 C 5 C 6 C 

L06-46 L06-46 L06-46 L06-46 L06-46 L

5% AL27128 in95% AL27166 

5% AL27129 in95% AL27176 

5% AL27137 in95% AL27175 

5% AL27138 in95% AL27150 

5% AL27141 in95% AL27175 

5% 279527

0 

eeks 

Peroxide D 3703 

W Value 

41.24 8.14 18.79 21.16 32.27 1

Viscosity@40 D 445 1.72 1.61 2.37 1.67 2.31 C 

Total Acid D 664 mg KOH/g 0.03 0.06 0.03 0.05 0.04 No. 

4 Weeks 

Filterable Insols 

D 4625, mod 

mg/100 ml 0.2 0.3 0.1 -0.2 0.2 

Adherent Insols 

D 4625, mod 

mg/100 ml 1 0.6 0.2 0.5 0.2 

Total Insols D 4625, 

mod 

mg/100 ml 1.2 0.9 0.3 0.3 0.4 

Peroxide Value 

D 3703 64.71 77.97 61.58 217.33 68.75 1

Viscosity@40C 

D 445 1.76 1.6 2.33 1.66 2.31 

Total Acid No. 

D 664 mg KOH/g 0.01 0.01 0.04 0 0.04 

8 Weeks 

Filterable Insols 

D 4625, mod 

mg/100 ml 0.3 0.5 0.2 0.5 0.3 

Adherent Insols 

D 4625, mod 

mg/100 ml 0.6 0.1 0 0.6 0.8 

Total Insols D 4625, 

mod 

mg/100 ml 0.9 0.6 0.2 1.1 1.1 

Peroxide Value 

D 3703 17.58 10.38 12.39 44.71 23.92 

Viscosity@40C 

D 445 1.73 1.61 2.37 1.67 2.33 

 75
Total Acid 

No. 

D 664 mg KOH/g 0.01 0.03 0.01 0.02 0.01 

12 Weeks 

Filterable Insols 

D 4625, mod 

mg/100 ml 0.3 1.4 0.2 34.3 0.3 

Adherent Insols 

D 4625, mod 

mg/100 ml 1.3 0.7 1.3 22.7 1 

Total Insols D 4625, 

mod 

mg/100 ml 1.6 2.1 1.5 57 1.3 

Peroxide Value 

D 3703 21.98 10.79 12.79 1001.99 25.18 

Viscosity@40C 

D 445 1.73 1.58 2.31 1.69 2.31 

Total Acid D 664 mg KOH/g 0.03 0.01 0.02 0.32 0.04 

1 Week Filterable 

Insols 

D 4625, 

mod @ 

80C 

mg/100 ml 0.4 0.4 1.3 98.9 1.3 

Adherent Insols 

D 4625, 

mod @ 

80C 

mg/100 ml 0.9 0.4 0.6 149.5 0.9 

Total Insols D 4625, 

mod @ 

80C 

mg/100 ml 1.3 0.8 1.9 248.4 2.2 

Peroxide Value 

D 3703 45.99 42.38 41.56 3046.12 118.73 1

Viscosity@40

C 

D 445 2.31 1.85 3.73 2.71 3.69 

Gravimetric D 6468 % 

Reflectance 

98.8 99.1 91.8 77.3 91.1 

Heptane 

Rinse 

mg/150ml 

0.15 0.3 0.15 75 0.15 

Total Acid No. 

D 664 mg KOH/g 0.05 0.07 0.03 1.84 0.05 

 76
Antioxidant Treated B5 Blends CL06-

331 

CL06-332 

CL06-333 

CL06-334 

CL06-516 

CL06-518 

5% 

27138 + 2000 ppm A 95% 27151 

5% 27138 + 1000 ppm B 95% 271 51

5% 27138 + 2000 ppm B 95% 271 51

5% 27129 + 1000 ppm A 95% 271 51

5% 27138 +2000ppm A, 95% 27175 

5% 27138 +1000ppm B, 95% 27175 

0 Weeks 

Filterable Insols 

D 2274, mod 

mg/100 ml 0.1 0 0 0 0.0 0.0 

Adherent Insols 

D 2274, mod 

mg/100 ml 0.2 0 0 0 0.2 0.0 

Total Insols 

D 2274, mod 

mg/100 ml 0.3 0 0 0 0.2 0.0 

Rancimat IP 

h >12 >12 >12 >12 >12 >12 

4 Weeks 

Filterable Insols 

D 4625, mod 

mg/100 ml 0.2 0.2 0.2 0.2 0.1 0.1 

Adherent Insols 

D 4625, mod 

mg/100 ml 0.5 0.5 0.6 0.3 0.2 0.5 

Total Insols 

D 4625, mod 

mg/100 ml 0.7 0.7 0.8 0.5 0.3 0.6 

Rancimat IP 

h 7.75 9.57 10.46 0 >12 >12 

Total Acid No. 

D 664 mg KOH/g 0.93 0.92 0.91 0.93 

8 Weeks 

Filterable Insols 

D 4625, mod 

mg/100 ml 0.2 0.2 0.2 0.1 0.2 0.4 

 77
Adherent 5, mg/100 ml 1.7 1.5 1.1 0.7 0.2 0.7 

Insols 

D 462mod 

Total Insols 

D 4625, mod 

mg/100 ml 1.9 1.7 1.3 0.8 0.4 1.1 

Rancimat IP 

 h >12 9.87 >12 >12 >12 >12 

Total Acid No. 

D 664 mg KOH/g >12 9.91 >12 >12 

12 Weeks 

Filterable Insols 

D 4625, mod 

mg/100 ml 0.2 0.2 0.1 0.2 0.3 0.3 

Adherent 

Insols 

D 4625, mod 

mg/100 ml 0.5 0 .2 .2 1.2 0.7 

-0 -0

Total 

Insols 

D 4625, mod 

mg/100 ml 0.7 0.2 .1 0 1.5 1.0 

-0

 Rancimat 

IP 

h 11.27 10.74 >12 >12 

Total 

Acid No. 

D 664 mg KOH/g 0.08 0.08 0.06 0.09 

1 Weeks 

Filterable Insols 

D 4625, mod 

mg/100 ml 0.4 0.6 0.8 0.8 2.1 1.6 

80C Adherent 

Insols 

D 4625, mod 

mg/100 ml 0.3 0.4 0.1 0.3 0.5 .2 

-0

Total Insols 

D 4625, mod 

mg/100 ml 0.7 1.0 0.9 1.1 2.6 1.4 

Thermal Stability 

D 6468 % 

Reflectanc

e 

99.0 99.2 99.0 98.1 91.0 92.6 

mg/100ml Heptane 0.15 0.15 0.15 0.15 0.15 0.15 Rinse 

Additiona Antioxidant T ated B5 Blends l re CL06-546 CL06-548 CL06-550 

95% 2 5 95% 2 1 95% 2 1 

5% 27138 + 1000 ppm A 

717

5% 27138 + 1000 ppm A 

715

5% 27129 + 1000 ppm B 

715

 78
1 Weeks Filterable 

Insols 

D 4625, mod mg/100 ml 21.5 89 2.5 

80C Adherent 

Insols 

D 4625, mod mg/100 ml 0.7 11 0.2 

Total Insols D 4625, mod mg/100 ml 22.2 100 2.7 

Thermal

Stability 

D 6468 % Reflectance 77.5 92 98 

ne e 

mg/100ml 

Hepta Rins 2.1 10.5 0.15 

 79
Appendix F: Accelerated Test Results for B20 Blends 

CL# Biodiesel % Diesel Rancim

at 

D2274, mod, mg/100 ml D525 D6468 

IP, h Filt 

Insols 

Adh 

Insols 

Tot 

Insols 

IP, h Reflectance, % 

CL06-192 27128 80 27150 8.9 0.1 0.2 0.3 No 

break 

97.9 

CL06-193 27128 80 27151 10.2 0.1 0.1 0.2 No 

break 

99.1 

CL06-194 27128 80 27166 8.2 0.2 0.5 0.7 No 

break 

98.4 

CL06-195 27128 80 27171 5.5 0.8 0.2 1 No 

break 

91.0 

CL06-196 27128 80 27175 7.8 0.2 0.1 0.3 No 

break 

94.7 

CL06-197 27128 80 27176 9.5 0.1 0.1 0.2 No 

break 

98.9 

CL06-204 27129 80 27150 >12 0.3 0.1 0.4 11.5 97.6 CL06-205 27129 80 27151 >12 0.2 0.1 0.3 No 

break 

98.4 

CL06-206 27129 80 27166 >12; 7.3 0.2 0.1 0.3 11.9 95.9 CL06-207 27129 80 27171 >12 0.2 0.3 0.5 No 

break 

89.4 

CL06-208 27129 80 27175 >12 0.1 0.2 0.3 No 

break 

97.9 

CL06-209 27129 80 27176 >12; 12 0.2 0.4 0.6 No 

break 

99.0 

CL06-229 27137 80 27150 >12 0.2 0.4 0.6 No 

break 

98.2 

CL06-230 27137 80 27151 >12 0.4 0.6 1 No 

break 

98.8 

CL06-231 27137 80 27166 11.6 0.1 0.2 0.3 No 

break 

99.0 

CL06-232 27137 80 27171 >12 0.2 0.4 0.6 No 82.1 

 80
break 

CL06-233 27137 80 27175 >12 0.1 0.1 0.2 No 

break 

98.0 

CL06-234 27137 80 27176 >12; 12 0.1 0.1 0.2 No 

break 

98.9 

CL06-241 27138 80 27150 1.8 47.6 132.4 180 1.5 91.1 CL06-242 27138 80 27151 1.8 42.4 82.4 124.8 1.4 99.2 CL06-243 27138 80 27166 1.9 36.8 109.4 146.2 2.2 91.3 CL06-244 27138 80 27171 3.5 6.1 4.8 10.9 No 

break 

54.1 

CL06-245 27138 80 27175 1.7 51.7 171.1 222.8 2.4 97.8 CL06-246 27138 80 27176 3.2 42.2 85 127.2 4.3 99.3 CL06-254 27141 80 27150 12.2 0.2 0.1 0.3 No 

break 

98.2 

CL06-255 27141 80 27151 12.5 0.3 0.1 0.4 No 

break 

99.3 

CL06-256 27141 80 27166 10.6 0.3 0.1 0.4 No 

break 

98.7 

CL06-257 27141 80 27171 >12 0.8 0.1 0.9 No 

break 

94.2 

CL06-258 27141 80 27175 11.1 0.2 0.1 0.3 No 

break 

98.8 

CL06-259 27141 80 27176 10.2 0.3 0.1 0.4 No 

break 

99.3 

CL06-266 27148 80 27150 >12 0.3 0.1 0.4 No 

break 

97.3 

CL06-267 27148 80 27151 >12 0.2 0.1 0.3 No 

break 

97.1 

CL06-268 27148 80 27166 >12 0.2 0.1 0.3 No 

break 

97.1 

CL06-269 27148 80 27171 >12 0.4 0.1 0.5 No 

break 

92.6 

CL06-270 27148 80 27175 >12 0.4 0.1 0.5 No 

break 

87.6 

CL06-271 27148 80 27176 >12 0.5 0.1 0.6 No 

break 

97.0 

 81
CL06-278 27152 80 27150 >12 0.5 0.1 0.6 No 

break 

98.5 

CL06-279 27152 80 27151 >12 0.2 0.1 0.3 No 

break 

99.5 

CL06-280 27152 80 27166 >12 0.3 0.1 0.4 No 

break 

99.0 

CL06-281 27152 80 27171 >12 0.3 0.1 0.4 No 

break 

96.0 

CL06-282 27152 80 27175 >12 1.1 0.1 1.2 No 

break 

97.2 

CL06-283 27152 80 27176 >12 0.1 0.1 0.2 No 

break 

99.4 

CL06-290 27160 80 27150 2.3 34 60.9 94.9 3.9 93.7 CL06-291 27160 80 27151 2.7 38.8 41.6 80.4 3.3 90.3 CL06-292 27160 80 27166 2.3 40.4 44.5 84.9 3.2 84.0 CL06-293 27160 80 27171 4.5 5.7 0.3 6 No 

break 

90.5 

CL06-294 27160 80 27175 2.9 48.1 52.2 100.3 No 

break 

78.9 

CL06-295 27160 80 27176 4.1 31.7 2 33.7 7.5 71.5 

 82
Appendix G: B20 Blend Storage, Fuel Tank, and High-Temperature Stability 

CL06-480 CL06-481 CL06-482 CL06-483 CL06-484 CL06

20%AL27128 in AL27175-F 

20%AL27129 in AL27150-F 

20%AL27137 in AL27171-F 

20%AL27138 in AL27151-F 

20%AL27141 in AL27166-F 

20%A2714AL2716

0 Weeks Peroxide Value D 3703 108.51 28.52 66.07 274.84 75.37 61

Viscosity@40C D 445 2.56 1.89 3.10 2.51 1.92 1.Total Acid No. D 664 mg KOH/g 0.06 0.09 0.01 0.09 0.02 0.

4 Weeks Filterable 

Insols 

D 4625, mod 

mg/100 ml 0.2 0.1 0.3 0.5 1.3 0

Adherent Insols 

D 4625, mod 

mg/100 ml <0.1 0 0.1 0.7 0.5 <0

Total Insols D 4625, 

mod 

mg/100 ml 0.1 0.1 0.4 1.2 1.8 <0

Peroxide Value D 3703 55.56 26.36 17.19 1183.43 103.15 17Viscosity @40°C 

D 445 2.53 1.93 3.14 2.62 1.94 1.

Total Acid No. D 664 mg KOH/g 0.07 0.11 0.07 0.2 0.05 0.

8 Weeks Filterable 

Insols 

D 4625, mod 

mg/100 ml 0.2 0.1 0.2 64.8 0.3 0

Adherent Insols 

D 4625, mod 

mg/100 ml 0.8 0.7 0.4 110.3 4.3 0

Total Insols D 4625, 

mod 

mg/100 ml 1 0.8 0.6 175.1 4.6 0

Peroxide Value D 3703 99.11 43.96 82.73 2733.56 147.48 33Viscosity@40C D 445 2.57 1.92 3.11 2.91 1.96 1.Total Acid No. D 664 mg KOH/g 0.09 0.11 0.33 1.7 0.08 0.

12 Weeks 

Filterable Insols 

D 4625, mod 

mg/100 ml 0.8 0.4 0.3 55.1 0.8 0

 83
Adherent 

Insols 

D 4625, mod 

mg/100 ml 0.3 2.6 0.4 141.5 1.2 0

Total Insols D 4625, 

mod 

mg/100 ml 1.1 3.0 0.7 196.6 2.0 0

Peroxide Value D 3703 115.45 47.18 77.41 1379.57 162.24 30Viscosity @40°C 

D 445 2.52 1.93 3.14 3.02 1.95 1.

Total Acid No. D 664 mg KOH/g 0.02 0.13 0.39 2.19 0.09 0.

1 Weeks Filterable 

Insols 

D 4625, mod @80C 

mg/100 ml 56 17.7 10 26.1 25.4 48

Adherent Insols 

D 4625, mod @80C 

mg/100 ml 2.4 0.8 2 9.6 0.9 0

Total Insols D 4625, 

mod @80C 

mg/100 ml 58.4 18.5 12 35.7 26.3 48

Peroxide Value D 3703 353.15 4474.52 494.89 2230.16 1336.25 132Viscosity @40°C 

D 445 5.38 5.16 4.09 5.00 3.66 3.

Gravimetric D 6468 % 

Reflectance 

91.5 89.6 91.1 88.5 99.5 77

Heptane 

Rinse 

mg/150ml 

4.95 12.3 0.3 18.6 0.45 3

Total Acid No. D 664 mg KOH/g 0.66 2.88 0.11 1.79 0.25 0.

Antioxidant Treated B20 Blends CL06-335 CL06-336 CL06-337 CL06-338 CL06-517 CL06

20% 

27138 + 

2000 

ppm A 

80% 

2 7151

20% 

27138 + 

1000 

ppm B 

80% 

2 1 715

20% 

27138 + 

2000 

ppm B 

80% 

2 1 715

20% 

27129 + 

1000 

ppm 

A80% 

27151 

20% 

27138 

+2000pp

m A 80% 

27175 

20

271

+100

m B, 

271

0 Weeks Filterable 

Insols 

D 2274, mod 

mg/100 ml 35.7 0.3 0.1 0 0.1 0

 84
Adherent 

Insols 

D 2274, mod 

mg/100 ml 65.1 0 0 0.2 0.1 0

Total Insols D 2274, mg/100 ml 

mod 

100.8 0.3 0.1 0.2 0.2 0

Rancimat IP h 9.35 4.63 6.98 >12 >12 4.4

4 Weeks Filterable 

Insols 

D 4625, mod 

mg/100 ml 0.8 0.5 0.3 0.3 0.1 0

Adherent Insols 

D 4625, mod 

mg/100 ml 0.4 0.3 0.4 0.3 4.1 0

Total Insols D 4625, mg/100 ml 

mod 

1.2 0.8 0.7 0.6 4.2 0

Rancimat IP h 4.75 3.25 5.46 >12 8.27 4.Total Acid No. D 664 mg KOH/g 0.94 1.01 1.02 1.02 

8 Weeks Filterable 

Insols 

D 4625, mod 

mg/100 ml 0.5 1 0.4 0.2 0.2 0

Adherent Insols 

D 4625, mod 

mg/100 ml 0.8 1.4 0.3 0.3 1.1 0

Total Insols D 4625, mg/100 ml 1

mod 

1.3 2.4 0.7 -0.1 1.3 

Rancimat IP h 7.78 3.43 5.86 >12 8.65 4 Total Acid No. D 664 mg KOH/g 0.94 1.01 1.02 1.02 

12

Weeks

Filterable Insols 

D 4625, mod 

mg/100 ml 0.2 0.2 0.2 0.1 0.5 0

Adherent Insols 

D 4625, mod 

mg/100 ml 1.1 0.7 1.2 0.6 0.6 0

Total Insols D 4625, mg/100 ml 1 1

mod 

1.3 0.9 1.4 0.7 .1

Rancimat IP h 6.66 3.47 5.81 >12 Total Acid No. D 664 mg KOH/g 0.06 0.08 0.11 0.11 

eeks Filterable 

Insols 

D 4625, mod 

1 W mg/100 ml 0.6 1.1 0.8 0.5 2.2 6

80C Adherent 

Insols 

D 4625, mod 

mg/100 ml 0.1 0.4 0.1 0.3 -0.3 -0

Total Insols D 4625, mg/100 ml 

mod 

0.7 1.5 0.9 0.8 1.9 5

 85
Thermal 

Stability 

D 6468 % 91

Reflectance 

99.3 99.5 97.1 99 97.6 

mg/150ml 

Heptane 1.05 0.45 0.45 0.6 0.15 4

Rinse 

Addition i idant Treated 20 Blends al Ant ox B CL06-547 CL06-549 CL06-551 CL06-

80% 5 80 1 80% 1 80 

20% 27138 + 

1000 m A pp

 2717

20% 27138 + 

100 m A 0 pp

% 2715

20% 27138 + 

1000 m B pp

 2715

20% 271

200 

0 pp

% 27

eeks Filterable 

Insols 

1 W D 4625, mod mg/100 ml 4.3 15.5 0.7 11.9 

80C Adherent 

Insols 

D 4625, mod mg/100 ml 0.7 0.6 0.1 0.2 

Total Insols 5, mod D 462 mg/100 ml 5.0 16.1 0.8 12.1 Thermal Stability 

 6468 

ce 

D % 

Reflectan

89 97 99 96 

mg/150ml 

Heptane 7.8 19.8 0.15 0.15 

Rinse 

 86
F1147-E(12/2004) 

REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188

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May 2007 

2. REPORT TYPE

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3. DATES COVERED (From - To)

 

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

Empirical Study of the Stability of Biodiesel and Biodiesel Blends: 

Milestone Report 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/TP-540-41619 

5e. TASK NUMBER

FC079400 

6. AUTHOR(S)

R.L. McCormick and S.R. Westbrook 

5f. WORK UNIT NUMBER

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National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 

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NREL/TP-540-41619 

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13. SUPPLEMENTARY NOTES

14. ABSTRACT (Maximum 200 Words)

The objective of this work was to develop a database that supports specific proposals for a stability test and 

specification for biodiesel and biodiesel blends. B100 samples from 19 biodiesel producers were obtained in 

December of 2005 and January of 2006 and tested for stability. Eight of these samples were then selected for 

additional study, including long-term storage tests and blending at 5% and 20% with a number of ultra-low sulfur 

diesel fuels. 

15. SUBJECT TERMS

biodiesel; database; B100; biodiesel blend; storage test 

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