Properties and Analysis of Liquid Alternative Fuels I: Fatty Acid Esters

Abstract

The importance of alternative fuels is constantly growing due to environmental reasons, saving fossil fuels and reducing the dependence of the world countries on the supply of fossil raw materials from politically unstable regions. This article is further in a series of review articles focused on an overview of technical requirements and testing methods for selected alternative fuels. It is also the first in a series of papers focused on liquid alternative fuels. The aim of this series of articles is to provide an overview of the required properties of individual alternative fuels, the possibilities of their analysis and the importance of the individual analyzes. This article focuses on fuels containing fatty acid esters.Biodiesel can be burned in diesel engines either in a mixture with conventional diesel or as an individual fuel. Unlike conventional diesel, which is composed of hydrocarbons of petroleum origin, biodiesel contains fatty acid methyl esters. In addition to this main component, glycerol (by-product of transesterification), methanol, free fatty acids, glycerides (mono-, di- and tri-), catalyst residues, water, and possibly other components can be present also. These contaminants can, in certain concentrations, cause some undesirable properties both in pure biodiesel and in biodiesel/diesel blends. Compared to conventional diesel, biodiesel has a higher density and viscosity, but a slightly lower higher heating value, and considerably worse oxidation stability. In terms of pollutant emissions, the combustion of biodiesel produces less hydrocarbons, carbon monoxide and solid particles, but slightly more nitrogen oxides than the combustion of mineral diesel. Gas chromatography, infrared spectroscopy, titration methods, and atomic spectroscopy methods have typically been used for the evaluation of these fuels. In addition to the properties monitored by these methods, conventional fuel parameters such as density, viscosity, low-temperature properties, oxidation stability, corrosion properties, flash point, cetane number, and others are monitored for biodiesel and biodiesel/diesel blends. In general, it can be stated that the analysis of fuels containing biodiesel is well managed. Instrumental equipment and (modified) analytical methods used for the analysis of conventional liquid fuels can be used to analyze these fuels.