Viscosity, biodiesel

Krisnangkura, K., Yimsuwan, T., and Pairintra, R. 2006. An Empirical Approach in Predicting Biodiesel Viscosity at Various Temperatures. Fuel 2006, 85,107-113. 

Biodiesel does not present any special safety concerns. Pure biodiesel or biodiesel and petroleum diesel blends have a higher flash point than conventional diesel, making them safer to store and handle. Problems can occur with biodiesels in cold weather due to their high viscosity. Biodiesel has a higher degree of unsaturation in the fuel, which can make it vulnerable to oxidation during storage. 

The first engines invented by Rudolf Diesel ran on groundnut oil, but because of the advent of relatively cheap oil this type of biodiesel never became commercially viable. Since about 1930 the diesel engine has been refined and fine tuned to run on the diesel fraction of crude oil, which consists mainly of saturated hydrocarbons. For this reason the modem diesel engine cannot run satisfactorily on a pure vegetable oil feedstock because of problems of high viscosity, deposit formation in the injection system and poor cold-start properties. Today, however, environmental... 

Vegetable all methyl esters (biodiesel) Kinematic viscosity Cetane no. Lender heeling value (MJJkg) Cloud point l°C Pour point <"C) Flesh point fC) Denelly (kgfl)... 

There are slight but acceptable differences in density and viscosity the higher flash point is a beneficial safety feature and the absence of sulfur in plant oils is the reason for the excellent SO emission profile of biodiesel. 

H. Noureddini, in System and process for producing biodiesel fuel with reduced viscosity and a cloud point below thirty-two (32) degrees fahrenheit , US, 2001. 

Biodiesel has higher viscosity and higher pour points compared to typical diesel fuel, which could affect operation in very cold temperatures. Like diesel fuels, pour point additives are effective at decreasing pour point. 

Clarke, N., J. Casey, E. Brown, E. Oneyma, and K. Donaghy (2006) Preparation and viscosity of biodiesel from new and used vegetable oil. J. Chem. Educ. 83,257-259. 

With respect to viscosity, which controls the fuel injection, the biodiesel shows somewhat higher values compared with petrodiesel, but this can be kept under 5 mm2/s by controlling the feedstock composition or by blending. 

As mentioned above, the viscosity is an important physical parameter. Table 14.7 presents comparatively the values recommended by the standards for diesel fuels in the USA and Europe. It can be observed that they are in a small range, but the upper limit is somewhat higher for biodiesel with respect to petrodiesel. Actually, the fatty esters exhibit larger variation of viscosity due to their chemical nature compared with hydrocarbon molecules. Influencing factors are chain length, position, number, and nature of double bonds, as well as the nature of the... 

Table 14.8 Kinematic viscosity (mm2/s) at 40°C of species implied in biodiesel [26].

Older biodiesel processes are essentially batchwise. The oil is submitted to transesterification in a stirred-tank reactor in the presence of a large amount of methanol, and base catalyst, mostly NaOH or KOH. An excess of methanol is necessary chiefly to ensure full solubility of triglyceride and keep the viscosity of the reaction mixture low, but also for shifting the chemical equilibrium. A minimum molar ratio methanoktriglyceride of 6 1 is generally accepted [16, 17, 29], The reaction... 

The key merit of converting triglycerides into fatty esters is a drastic reduction in viscosity, about one order of magnitude, at a level compatible with the fuel-injection devices. The biodiesel is environmental friendly. Better combustion allows the level of greenhouses gases to be reduced, while sulfur is practically absent. 

Knothe, G., Steidley, K.R., Kinematic viscosity of biodiesel fuel components and related compounds, Fuel, 84, 1059-1065, 2005... 

Although there are numerous publications on the effect of natural and synthetic antioxidants on the stability of oils and fats used as food and feed, until recently relatively little publicly available information was available on the effect of antioxidants on the oxidative stability of biodiesel. One of the earliest studies reporting of the effects of antioxidants on biodiesel was that of Du Plessis et aL (1985), which examined storage stability of sunflower oil methyl esters (SFME) at various temperatures for 90 d. Effects of air temperature, presence of light, addition of TBHQ (see Figure 1.1) and contact with steel were evaluated by analysis of free fatty acid content, PV, kinematic viscosity, anisidine value, and induction period. Addition of TBHQ delayed oxidation of samples stored at moderate temperatures (<30°C). In contrast, under unfavorable (50°C) conditions, TBHQ was ineffective. 

Allen, C. A. W., Watts, K. C., Ackman, R. G., and Pegg, M. J. 1999. Predicting the Viscosity of Biodiesel Fuels from Their Fatty Acid Ester Composition. Fuel, 78, 1319-1326. 

Kerschbaum, S., and Rinke, G. 2004. Measurement of the Temperature Dependent Viscosity of Biodiesel Fuels. Fuel, 83,287-291. 

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