Properties and Analysis of Liquid Alternative Fuels III: Vegetable Oils and Hydrotreated Vegetable Oils

Abstract

The importance of alternative fuels and biofuels is constantly growing due to energy security, sustainability, and social responsibility. This article is another in a series of review articles designed to recapitulate information on the required properties of individual alternative fuels, their testing methods, and the significance of individual analyses. This article is focused on fuels based on vegetable oils and hydrotreated vegetable oils. Rapeseed oil is a triglyceride-based fuel that can be burned in modified diesel engines. Modification of the engine consists in the inclusion of preheating of the fuel or modification of the injection system, due to the high viscosity of this fuel. Rapeseed oil and vegetable oils in general have a higher oxygen content than conventional diesel fuels, which is associated with a lower energy content than that of diesel fuels. Compared to diesel, vegetable oils have a higher density, a lower cetane number, and a significantly higher flash point and viscosity. Vegetable oils also have low oxidative stability. Physical properties monitored in rapeseed oils include density, viscosity, flash point, and calorific value. From the chemical properties, the iodine number, acidity number, water content, calcium, magnesium, sulfur, and phosphorus are monitored. From the other properties, oxidative stability, ignitability, ash content, carbonation residue, content of impurities, and appearance are monitored for rapeseed oils. HVO is a high-quality fuel for standard diesel engines. Due to the hydrocarbon character of HVO, no engine modification is required. HVO has a very high cetane number, very good low-temperature properties, optimal viscosity, high flash point, excellent oxidative stability, and a very low content of undesirable contaminants such as aromatic hydrocarbons, sulfur, nitrogen, and oxygen-containing compounds. Compared to diesel fuels, HVO has a lower density. The observed qualitative parameters and testing methods are very similar to those of conventional diesel fuel B7. The main difference lies in the modified determination of aromatic hydrocarbons.