15-07: The identification and engine testing of potential renewable oxygenated biofuels for the aviation and road transport sectors

Due to the increasing scarcity and expense of fossil fuels, the negative environmental impacts associated with their use, and the lifetime of transport vehicles currently produced, the development of renewable liquid fuels is imperative. Currently two major biofuels – bioethanol and biodiesel – dominate the renewable fuel market. However, there is insufficient arable land to produce both sugar and vegetable oil feedstocks, and both fuels possess non-desirable physical properties such as a lower energy density for bioethanol and poor oxidative stability and low temperature properties for biodiesel.

To address these issues, a range of short-chain ester products were synthesised via the esterification of acids and alcohols potentially obtainable from the fermentation of cellulosic sources. These esters were then examined for their potential as biofuels by assessing their physical properties and comparing these to international standards. Four possible fuels were deemed as potential diesel substitutes; though these fuels would require the use of a cetane improver. One fermentation product was considered viable for use as an aviation fuel substitute.

The most promising fermentation fuel, diethyl succinate, was then tested on a chassis dynamometer, in a 20% blend with diesel. Steady state testing and the New European Drive Cycle were used to assess the fuels performance. While less CO emissions were produced from the fuel blend, most likely due to more complete combustion, the NO_x emissions were shown to increase under certain conditions as were the hydrocarbon emissions. Both of these factors were presumably in part due to the lower cetane number.