ANALYTICAL INSTRUMENTATION


results in improving lubricity when blended with a low lubricity diesel fuel, such as renewable diesel. A low lubricity diesel fuel combined with 1% JCL yields a wear scar of 198 µm which is an approximate 550 µm reduction in the lubricity measurement. Increasing the concentration of the JCL oil in the base fuel from 0.5 % to 1.0% resulted in enhanced lubricity as shown by the reduced wear scar [12]. The addition of RME to a base fuel, as depicted in Figure 6, also shows a reduction in wear scar and therefore improved lubricity. The concentration of RME needed for such change to occur is quite high. According to D975, 1% or less added component can be considered an additive. Addition of greater than 1%, particularly 5-15%, is not an additive, but rather a fuel component [5]. In this study RME can be considered as a fuel component based on the amounts present. The inclusion of 15%, by weight, RME in the base fuel showed the most improved results of an approximate 160 µm wear scar diameter, although any improvement below 300 µm is similarly performant. All values tested with additives included were within the requirements of the Standard Specification for Diesel Fuel Oils in ASTM D975.


In testing for the coefficient of friction, JCL performs well with an impressive average of 0.11. RME shows a sufficient average of about 0.14 [14]. A lower coefficient of friction value often indicates better lubrication. Both additives show excellent lubricity improving properties. The addition of Jatropha curcas L. oil and rapeseed methyl ester could aid in solving the challenging lubrication problem in renewable diesel fuels.


Figure 4. Fuel Properties Comparison [10]


and regular fossil diesel [10]. As shown in Figure 4, the lubricity of regular petroleum diesel and HVO using HFRR are 653 µm and 580 µm, respectively [10]. It is important to note that these values are taken without the addition of any lubricity additives. Renewable diesel on its own fails to meet ASTM diesel fuel regulations for lubricity wear-scar and therefore requires additives to improve this crucial measurement.


Blending hydrotreated vegetable oil (HVO) derived renewable diesel with petroleum diesel improves the lubricity, but to maximize environmental benefits, we need to investigate effective additives to improve the lubricity of pure renewable diesel, which does not meet ASTM specifications. Testing the effectiveness of these additives is done by comparing their wear scar values to those of untreated HVO renewable diesel. The sliding wear is determined in the test method ASTM D6079 [4]. The larger the wear scar value is, the worse the lubricating properties of the fuel are [11]. Two additives, rapeseed methyl ester (RME) and Jatropha curcas L. oil (JCL), are tested to determine their effects on lubricity. Both biodegradable oil-derived substances were subjected to an HFRR test to determine the amount of friction present and wear scar on the surface. As shown in Figure 5, JCL presents outstanding


Some other critical facts to mention about lubricity improvers are that lubricity typically improves with a longer chain length additive and the lubricity also improves with the increased presence of double bonds in the additive [15]. Additionally, it has been studied that different oxygenated compounds have a greater effect on the lubricity of diesel fuels. They are ordered in regards to their lubricity improving potential (COOH > CHO > OH > COOCH3 > C=O > C-O-C) [15].


One similarity between all the functional groups is the inclusion of oxygen in its structure. The addition of oxygen-containing compounds remaining after the refining process can greatly affect a fuel’s lubricity.


Another solution to this challenging lubrication problem is the combination of renewable diesel with other diesel blends. As mentioned previously, renewable diesel blended with traditional petroleum diesel does improve lubricity, but this combination is not the most environmentally friendly. Most recently, the combination of renewable and biodiesel has been explored. Biodiesel production involves the transformation of long chain triglyceride fatty acids into long chain fatty acid methyl esters, or FAME, by the process of transesterification. Biodiesel has exhibited excellent lubricity in practice. Oxygen and other heteroatoms are not removed during this process, which is the principal reason for the increased lubricity. As previously mentioned, renewable diesel requires additives to reach lubricity regulations. REG ultraclean diesel is a new blend of renewable diesel and biodiesel that has improved properties such as a higher cetane number, a longer engine life, reliable operation in colder temperatures, and most importantly lubricity [16]. This name is certainly misleading as biodiesel is not fully environmentally friendly. Some biodiesels have been shown to give off a significant amount of nitrogen oxide


11


(NOx) in the exhaust during combustion [17]. This alone provides a reason to expand the research on renewable diesel as it is much better at preventing harmful emissions. REG ultra clean is a clear improvement over traditional crude oil-derived diesel, but there are still plenty of things that can be improved.


Renewable diesel has the ability to match and exceed the performance of traditional petroleum diesel in specific categories. Correcting the lubricity of both renewable diesel and traditional petroleum is a challenge. Fortunately, there is a multitude of different lubricity additive options that can vastly improve the lubricity characteristics of these diesels. When blended with highly effective biodegradable fuel components, such as RME, the poor lubricity of untreated renewable diesel can be corrected to meet ASTM regulations. In addition, by offering a significant reduction of greenhouse gas emissions and other major environmental benefits, renewable diesel has the potential to become the next dominant source of energy for transportation in the future.


References:


[1] COORDINATING RESEARCH COUNCIL “Renewable Hydrocarbon Diesel Fuel Properties and Performance Review” Sept 2018.


[2] Kokayeff P., Zink S., Roxas P. (2014) Hydrotreating in Petroleum Processing. In: Treese S., Jones D., Pujado P. (eds) Handbook of Petroleum Processing. Springer, Cham. https://doi. org/10.1007/978-3-319-05545-9_4-1


[3] Wei Danping, H.A. Spikes, The lubricity of diesel fuels, Wear, Volume 111, Issue 2, 1986, Pages 217-235, ISSN 0043-1648, https://doi.org/10.1016/0043-1648(86)90221-8.


[4] ASTM D6079-18, Standard Test Method for Evaluating Lubricity of Diesel Fuels by the High-Frequency Reciprocating Rig (HFRR), ASTM International, West Conshohocken, PA, 2018, www.astm.org


[5] ASTM D975-20c, Standard Specification for Diesel Fuel, ASTM International, West Conshohocken, PA, 2020, www.astm.org


[6] Hoekman, S. & Broch, Amber & Robbins, Curtis & Ceniceros, Eric & Natarajan, Mani. (2012). Review of biodiesel composition, properties, and specifications. Renewable & Sustainable Energy Reviews - RENEW SUSTAIN ENERGY REV. 16. 10.1016/j. rser.2011.07.143.


[7] Sava, Jerome P. “TAKING THE MYSTERY OUT OF LUBRICITY: Fuel Oil News.” Fuel Oil News , March 3, 2010. http://web.archive. org/web/20201223181540/https://fueloilnews.com/2010/03/04/ taking-the-mystery-out-of-lubricity/


[8] Yoon, Jesse Jin. What’s the Difference between Biodiesel and Renewable (Green) Diesel . Advanced Biofuels USA, www. advancedbiofuelsusa.info/wp-content/uploads/2011/03/11-0307- Biodiesel-vs-Renewable_Final-_3_-JJY-formatting-FINAL.pdf.


[9] “Hydrotreatment to HVO.” ETIP Bioenergy-SABS, www. etipbioenergy.eu/value-chains/conversion-technologies/ conventional-technologies/hydrotreatment-to-hvo.


[10] Lehto, K., Vepsäläinen, A., Kiiski, U., and Kuronen, M., “Diesel Fuel Lubricity Comparisons with HFRR and Scuffing Load Ball- on-Cylinder Lubricity Evaluator Methods,” SAE Int. J. Fuels Lubr. 7(3):842-848, 2014, https://doi.org/10.4271/2014-01-2761.


[11] Hartikka, T., Kuronen, M., and Kiiski, U., “Technical Performance of HVO (Hydrotreated Vegetable Oil) in Diesel Engines,” SAE Technical Paper 2012-01-1585, 2012, https://doi. org/10.4271/2012-01-1585.


[12] Prasad, Lalit & Das, Lalit & Naik, Satya. (2012). Effects of Jatropha Curcas Oil and Alkyl Ester as Lubricity Enhancer for Diesel Fuel. Proceedings of the Spring Technical Conference of the ASME Internal Combustion Engine Division. 10.1115/ICES2012-81209.


[13] M.W. Sulek, A. Kulczycki, A. Malysa, Assessment of lubricity of compositions of fuel oil with biocomponents derived from rape- seed, Wear, Volume 268, Issues 1–2, 2010, Pages 104-108, ISSN 0043-1648, https://doi.org/10.1016/j.wear.2009.07.004


[14] Alessandro Ruggiero, Roberto D’Amato, Massimiliano Merola, Petr Valašek, Miroslav Müller, Tribological characterization of vegetal lubricants: Comparative experimental investigation on Jatropha curcas L. oil, Rapeseed Methyl Ester oil, Hydrotreated Rapeseed oil, Tribology International, Volume 109, 2017, Pages 529-540, ISSN 0301-679X, https://doi.org/10.1016/j. triboint.2017.01.030.


[15] Knothe G. Steidley KR. Lubricity of components of biodiesel and petrodiesel. The origin of biodiesellubricity. Energy Fuels 2005;19(3):1192-200.


[16] REG ULTRA CLEAN® — THE LATEST INNOVATION IN RENEWABLE FUEL, Renewable Energy Group , 2020.


[17] “Biodiesel vs. Renewable Diesel: Are They the Same?” Veolia, 29 Apr. 2019, blog.veolianorthamerica.com/biodiesel-vs.- renewable-diesel-are-they-the-same.


Figure 5. Additive JCL effect on wear scar [12] Figure 6. Additive RME effect on wear scar [13]


OCTOBER / NOVEMBER


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