Abstract
A range of short-chain ester products were synthesised via the esterification of acids and alcohols obtainable from fermentation. The fuel properties, including the kinematic viscosity, lower calorific value, oxidative stability, toxicity, lubricity, cetane number and octane number were determined and compared to international fuel standards. Out of 21 compounds screened only four (diethyl succinate, dibutyl succinate, dibutyl fumarate and dibutyl malonate) were deemed suitable as potential diesel substitutes. While the physical properties of these compounds fall with EN 590, the cetane number of these fuels was determined to be below the minimum stated by EN 590 and ASTM D975. Blending, or the use of a cetane improver additive, is therefore necessary. An additional fermentation product, butyl butyrate, was considered viable as an additive for aviation kerosene. The most industrially viable fuel – diethyl succinate – was subsequently tested, in a 20% blend with diesel (DES20), for its performance on engine. Steady state testing was used to assess the engine performance and emissions. In comparison to mineral diesel less CO emissions were produced using DES20, most likely due to more complete combustion due to the increased oxygen content. The THC and NOx emissions however, were shown to increase on using the DES blend. Both of these factors were presumably due to the lower cetane number.
KEYWORDS Biofuel, aviation, microbe, fermentation, engine