Diesel biofuel viscosity and heat of combustion

Abstract

Measurements have been made on the kinematic viscosity at 20-80°C and on the upper heat of combustion of methyl esters of fatty acids from rapeseed, mustard, and colza oils and the oil of oily radish, as well as the ethyl esters of rapeseed oil. A method is proposed for calculating the viscosity of a mixture of esters from the fatty-acid composition. Matched data have been obtained on the specific heat of combustion of plant oils and their esters.EN 14214:2003 lays down the specifications for biofuel or the methyl esters (ME) of fatty acids, which is used as diesel fuel either in pure form (Germany and Austria) and in the form of 5% additive to oil-based diesel fuel (EN 590:2004). In many countries, the second is common in accordance with the modified analogs adopted there to the European standard EN 590; for example, in Russia we have GOST R 52368-2005, in Belarus STB 1658-2006, and in the Ukraine DSTU 4840-2007. It is possible to use ME also as boiler fuel (EN 14213). No corresponding standard has yet been developed for the ethyl esters (EE) of fatty acids.The feedstocks for making ME and EE are provided by plant oils, animal and fish oils, tallow, and others (including wastes, in which the main component is an oil. The composition of these fats corresponds to the fatty-acid composition of the synthesized esters, which directly govern the physicochemical characteristics such as the viscosity, heat of combustion, iodine number, density, and so on.There are several papers [1-4] dealing with the dependence of the ester characteristics on the composition. In particular, various correlations have been established for the viscosity [5][6][7][8][9][10][11][12], the solid point [8,13], the density [9, 10], the surface tension [10,14], the heat of combustion [15], the boiling point [16] and the cetane number [17], and so on. The large number of papers on the viscosity is due to the considerable practical significance of this and the variation that is wide for different specimens. For example, the viscosities of plant oils are about ten times larger than those of the corresponding ME at 20°C [18], while those of ME mixtures may differ by as much as a factor 2 [2, 7] because of differences in viscosity of the individual esters, for example, the viscosity of methyl linolenate (S18:3) is 3.14 mm 2 /sec, while that of methyl erucate (S22:1) is 7.33 mm 2 /sec [5].Ester mixtures should be examined as fuels in order to forecast their characteristics from the fatty acid composition of the feedstock. This is particularly important in connection with the rapid development of methods