1、 SURFACE VEHICLE INFORMATION REPORT J3050 DEC2014 Issued 2014-12 Biodiesel in Automotive Application; Lessons Learned RATIONALE This new J document provides a general summary of the experience with biodiesel in the automotive industry where significant research has been conducted over 20 years. Rece
2、ntly, the railroad industry and the locomotive manufacturers have experienced similar concerns. The purpose of this document is to provide them and other practitioners dealing with biodiesel, with the knowledge and a tool to evaluate if additional research is warranted regarding their specific appli
3、cation. Engine performance, emissions, material compatibility, fuel storage, and long term effects are discussed. Users of any fuel including biodiesel blends should contact their engine manufacturer for advice regarding fuel/equipment compatibility. 1. OBJECTIVE Provide the railroad industry and th
4、e locomotive manufacturers a summary of lessons learned in the automotive industry regarding use of biodiesel. Close the knowledge gap between those who have been participating at ASTM International over the last two decades and those who have not. Merge the activities of the two groups, bring the r
5、ailroads to ASTM, and eliminate duplication of efforts. Lack of participation by any group in standard setting efforts can result in fuel specifications that lack components for a particular application. 1.1 BACKGROUND The Energy Independence Freel; J., Gibbs, L.; Hemighaus, G.; Hoekman, K.; Horn, J
6、.; Ingham, M.; Jossens, L.; Kohler, D.; Lesnini, D.; McGeehan, J.; Nikanjam, M.; Olsen, E.; Scott, B.; Sztenderowicz, M.; Tiedemann, A.; Walker, C.; Lind, J.; Jones, J.; Scott, D.; Mills, J. “Diesel Fuels Technical Review,” Chevron Global Marketing, 2007. 3. ENERGY CONTENT: In addition to carbon and
7、 hydrogen, biodiesel contains a certain amount of oxygen. This, along with a lack of aromatics, is responsible for lower particulate matter (PM) emissions. However, this also contributes to lower energy content. Thermodynamic theory and experimentally measured net heats of combustion indicate that a
8、 given volume of biodiesel will not deliver the same level of energy as that of the same volume of conventional diesel lacking oxygen. The volumetric energy content can be approximately 10% lower for pure biodiesel (B100) compared to conventional diesel. However at blend levels up to 5 volume %, the
9、 difference in fuel economy is generally considered to be too small to measure and not significant statistically. SAE INTERNATIONAL J3050 Issued DEC2014 Page 3 of 6 4. FILTER CLOGGING: Clogging is a result of solids suspended in the fuel passing through the filter. There are several mechanisms for s
10、uch occurrence: x Solvency x Low temperature operability x Stability (thermal and storage) x Impurities x Microbial growth (dead or alive) 5. SOLVENCY: Pure biodiesel is composed of methyl esters and is an excellent solvent for cleaning material. As such it will release varnish and gums from diesel
11、fuel tanks, walls and piping into the bulk fuel with the potential of clogging in-line filters. If the tank to be used for B100 was previously in diesel service it should be cleaned before handling or using B100. It is recommended for transition from conventional diesel to B100 to have extra filters
12、 on hand. Monitoring of filters and strainers also is recommended during the transition. Filter clogging with B100 typically goes away after the first few tanks of biodiesel. From the automotive experience, the use of diesel fuel with up to 5 volume % biodiesel that meets all ASTM D975 and D6751 spe
13、cifications in the appropriate climate should not result in filter issues. 6. LOW TEMPERATURE OPERATION: Similar to conventional diesel, cold temperatures or cold temperature spikes will cause certain biodiesel to form precipitates and even gel. Biodiesel source has a major effect on the temperature
14、 at which precipitates form. B100 will begin to solidify at a higher temperature than most conventional diesel fuel and this should be taken into account in handling B100 and high level biodiesel blends. As the biodiesel begins to gel it can clog filters and strainers or can even become too thick to
15、 pump from storage tanks. This effect is minimized and many times insignificant at blend levels below 5 volume % and with a number of biodiesel sources such as soy. In addition biodiesel has other impurities such as monoglycerides, sterols, and sterol glucosides that may be even more problematic for
16、 low temperature operability, sometimes even at a few degrees above the cloud point. These components can fall out of solution in cold temperature but unlike wax, may not dissolve with a reasonable temperature rise, which can lead to filter clogging. As a result, various specifications are in place
17、to control these types of impurities either by composition such as the test for free and total glycerin (ASTM D6584) or by performance tests such as Cold Soak Filtration (ASTM D7501). SAE INTERNATIONAL J3050 Issued DEC2014 Page 4 of 6 7. STABILITY: Biodiesel has lower oxidative (long-term storage) s
18、tability than conventional diesel. Factors affecting biodiesels oxidative stability include the degree of saturation of the feedstock, the level of natural antioxidant content, carbon chain length and the presence of glycerides. Biodiesel blend stocks can have significant levels of unsaturation with
19、 fatty acids chains containing one, two, or three unsaturated bonds. Over time these unsaturated sites are oxidized and can form peroxides and then acids and polymer gums. Stability is a broad term but really refers to two issues for fuels: x Long term storage stability x Short term stability at ele
20、vated temperatures Stability is also important for conventional diesel but more critical for biodiesel. In biodiesel, fuel aging and oxidation can lead to high acid numbers, viscosity increase and sediment. It is recommended that B100 be used within six months. B20 and higher blends should also be c
21、onsumed as soon as possible and not stored too long. B5 can remain stable for a longer period but not as long as conventional diesel and it is advisable to consume them also within six months. If the fuel is kept longer, antioxidants should be added as soon as possible after production and periodic
22、tests should be performed to ensure the fuel continues to meet the ASTM D6751 specification. Addition of antioxidants after long storage periods is not as effective. Care should also be taken when biodiesel is heated, which is often done in cold regions or seasons so that it does not fall below its
23、cloud point. If too much heat is applied, the aging process could be greatly accelerated. A cushion of 10 C above the cloud point should be sufficient. It is also recommended that B100 fuel tank testing be done to monitor changes in the product over time. Monitoring the acid number and viscosity ove
24、r time can provide some idea about whether, and how much the fuel is oxidizing. One should keep metals such as copper, brass, bronze, lead, tin and zinc out of contact with the biodiesel as they will accelerate the degradation process. Suitable storage tank materials are steel, aluminum, fluorinated
25、 polyethylene, fluorinated polypropylene and Teflon. Some suppliers use nitrogen blanketed storage vessels to reduce the tendency of stored biodiesel to oxidize and to help keep moisture and condensation out of the tank. 8. MICROBIAL CONTAMINATION: Biodiesel is susceptible to microbial contamination
26、. The higher susceptibility to oxidation can lead to the formation of corrosive acids. These acids will accumulate in the water phase and must be removed on a frequent basis to prevent tank corrosion. The rate of corrosion is currently being investigated. The proactive use of biocides is not recomme
27、nded unless it is to remedy a situation with clear biological growth. It is best to have a preventative approach to obtain dry B100 and keep it dry. In some cases it may be desirable to place desiccants on tank breathers. Keeping water out of tanks will aid in the prevention of corrosion. 9. LUBRICI
28、TY: Due to its polar nature, biodiesel has excellent lubricity. As little as one or two percent biodiesel by volume as a blend component will meet ASTM D975 lubricity requirements and will eliminate the need for additional lubricity additive and provide sufficient lubricity for the injection equipme
29、nt such as pumps and injectors. SAE INTERNATIONAL J3050 Issued DEC2014 Page 5 of 6 10. MATERIAL COMPATIBILITY: 100% biodiesel requires special handling and care. B20 can be used in some newer heavy-duty (HD) applications and in HD vehicles without making material changes. It is recommended that B20
30、not be used in long term storage operations. Diesel with up to 5 volume % biodiesel can typically be handled similar to conventional diesel. Blends between B5 and B20 require caution in wide spread consumer usage. Consult with OEM owners manual. In general, biodiesel can be more chemically aggressiv
31、e than conventional diesel. It can be electrically conductive and therefore more corrosive but also because the molecules are polar, they can adhere to metal surfaces and protect them from water-born ions and galvanic corrosion. The exact effects on corrosion rates are not well understood yet. Pure
32、biodiesel degrades, softens or seeps through some hoses, gaskets, elastomers, seals, glues and plastics with prolonged exposure, which can create fuel system leaks. Nitrile rubber compounds, polypropylene, polyvinyl and Tygon materials are especially susceptible. Using biodiesel blends higher than B
33、20 can damage fuel systems components such as hoses and pump seals, which contain elastomers incompatible with biodiesel. In this situation, users should consider replacement with compatible elastomers. However, this is primarily an issue with older engines manufactured before 1993, according to the
34、 DOE. The recent switch to S15 (commonly known as ultra-low sulfur diesel, ULSD) has meant most OEMs have converted to components that are also suitable for use with biodiesel. B5 and lower blends have not exhibited elastomer deterioration and may not require modifications. B20 and higher biodiesel
35、blends will degrade and create sediments after prolonged contact with bronze, brass, tin, copper, zinc and lead. Copper pipes and fittings, brass regulators, zinc linings and lead solders should also be avoided. Biodiesel is hygroscopic, meaning it attracts moisture. Once it comes in contact with mo
36、isture, it can hydrolyze and form a variety of organic acids which are partly responsible for its compatibility problems with various seal, elastomers, and metals. Biodiesel is capable of permeating some non-metallic materials. It contains chemical functional groups that increase chemical activity,
37、reactivity, and bioavailability. It increases biodegradability significantly at B100 but not at B5 level. 11. OIL DILUTION: Compared to conventional diesel, biodiesel has lower volatility, a narrower distillation curve, a higher density, higher surface tension, and higher viscosity. As such it lacks
38、 the light ends that can evaporate easily. Small fuel volumes that pass the piston rings and find their way to the crankcase can reside in the oil and result in oil dilution and viscosity change. This is less of a concern at the 5 volume % level and in normal automotive operations in which oil is ch
39、anged frequently. While the use of B5 is generally trouble-free in the case of older diesel passenger cars and heavy-duty trucks without diesel particulate filters (DPFs), increasing problems have been detected in newer engines with DPFs. In some applications, OEMs are using a late “post” injection
40、to help regenerate DPFs. This late injection may create higher levels of fuel dilution. Biodiesel is more persistent once it enters the crankcase and thermally decomposes forming insolubles and deposits. OEMs have noted situations where fuel dilution rates ran up to 15 percent in vehicles operated w
41、ith DPF and post injection. In order to address some of these issues, most European OEMs prescribe a 50-70 percent reduction in oil drain intervals with the use of biodiesel blends above B5. 12. INCREASED NOX EMISSIONS: Biodiesel causes a slight increase in emissions of ozone-forming nitrogen oxides
42、 (NOx). The precise composition of biodiesel influences NOx emissions. Although biodiesel itself contains very little bound nitrogen, NOx is created in the engine as nitrogen and oxygen in the intake air react at the high in-cylinder combustion temperatures. Some effort is being made to solve this p
43、roblem with the use of exhaust after-treatment systems in newer engines, but the possible increase in the NOx levels when biodiesel is used in older engines is a concern. There are research efforts underway by the California Air Resources Board (CARB) and by the EPA to define the problem of NOx incr
44、ease more precisely. Some past work has indicated the increased NOx is related to differences in injection rates into the combustion chamber caused by biodiesels higher viscosity and bulk modulus, which makes it less compressible than conventional diesel. The higher bulk modulus and higher speed of
45、sound of biodiesel means the pressure rises in the fuel lines and develops an advance of nearly two degrees in injection timing. This in turn generates a faster pressure and temperature rise in the combustion. SAE INTERNATIONAL J3050 Issued DEC2014 Page 6 of 6 13. BIODIESEL BLENDING: Biodiesel is de
46、nser than typical conventional diesel by a few percent. The density of conventional diesel fuels can vary, but a typical number is around 0.85 kg/L while the densities of most B100 biodiesels are around 0.88 kg/L. If these components are not properly blended then stratification is a risk with biodie
47、sel settling on the bottom. Proper mixing is critical to ensuring a homogeneous Bxx blend and may be accomplished by inline injection, ratio blending, and the use of mixers. In addition, if the B100 biodiesel is heated during storage, then one should be aware of mixing warm biodiesel into cold conve
48、ntional diesel, which may result in flash cooling and poor mixing. The blend level of Bxx biodiesel blends can be verified with reasonable accuracy using portable infrared analyzers. Also, because density blends linearly, the Bxx blend level can be verified by a density measurement, but only if the
49、B0 and B100 densities are also known. 14. NOTES 14.1 Marginal Indicia A change bar (l) located in the left margin is for the convenience of the user in locating areas where technical revisions, not editorial changes, have been made to the previous issue of this document. An (R) symbol to the left of the document title indicates a complete revision of the document, including technical revisions. Change bars and (R) are not used in original publications, nor in documents that contain editorial changes only. PREPARED BY THE SAE FUELS AND LUBRICANTS TC 7 FUELS COMMITTEE
