Alternative Diesel Fuels from Vegetable Oils and Animal Fats

Abstract

Biodiesel, defined as the mono-alkyl esters of fatty acids derived from vegetable oils or animal fats, is a strong candidate alternative fuel for combustion in compression ignition (diesel) engines. With respect to petroleum middle distillates, biodiesel has superior cetane number and lubricity characteristics, has comparable heats of combustion and kinematic viscosities, and is non-flammable making it safer to store and handle. Biodiesel is renewable and can help reduce dependence upon imported petroleum. Biodiesel is environmentally friendly because it is readily biodegradable and its combustion reduces most harmful exhaust emissions, including carbon monoxide, unburned hydrocarbons, particulate matter, and polyaromatic hydrocarbons. In the United States, the Energy Policy Act (EPACT) of 1992 and Clean Air Act with its subsequent amendments have combined to help establish a favorable atmosphere for development of biodiesel; however, many technological hurdles must be removed before widespread commercialization will be feasible. During cooler weather, biodiesel “gels” at temperatures near freezing (0°C) compared with -15 to -17°C for conventional diesel fuel. Another concern for biodiesel is its long-term storage stability with respect to oxidative degradation. Finally, most reports indicate biodiesel does not significantly reduce nitrogen oxides (NO_x) emissions. This is a particular concern because NO_x may react in the atmosphere to form ozone, a component of smog. This work reviews recent progress in the development of boidiesel with emphasis on removing these technological hurdles.