The renewed interest in environmentally compatible fuels has led to the choice of rapeseed oil as the main
alternative to diesel fuel in Europe. Transesterified rapeseed oil (viz. rape methyl ester) has been the predominant
vegetable oil fuel used because its characteristics are quite similar to diesel. However, it is an expensive product due to
high feedstock costs. The objective of this research was to produce and test an economic and high quality nonesterified
rapeseed oil suitable for use as a diesel fuel extender. This was achieved by acidified hot water degumming combined with
filtration to five microns. This rapeseed oil, designated as a Semi Refined Oil (SRO), has a high viscosity in comparison
with diesel (589 mPa·s vs 22 mPa·s at –12°C). Hence, SRO fuel can be used only as a diesel fuel extender at inclusion
rates up to 25%, the resultant blend having a viscosity of 55 mPa·s at –12°C. When used with direct injection (DI)
engines, power output (at 540 rpm at the power take-off shaft) was reduced by c. 0.06% for every 1% increase in SRO
inclusion rate, and brake specific fuel consumption (BSFC) increased by c. 0.14%/1% increase in SRO inclusion rate (viz.
a 25% SRO/diesel blend had a 1.5% decrease in power and a 3.5% increase in BSFC compared with diesel). These
values are in accordance with the lower energy density of rapeseed oil fuels compared with diesel. Chemical and viscosity
analyses of engine lubrication oil using both diesel and a 15% SRO inclusion rate (after c. 170 h/fuel tested), including
metal contamination as an indicator of engine wear, showed that there was no measurable effect on engine lubricating oil
due to SRO inclusion in diesel oil. However, the injector fouling results showed that shorter injector service intervals are
required. In contrast to the DI results, above, when SRO was used to fuel indirect injection (IDI) engines, power was
considerably reduced mainly due to inadequate air/fuel mixing. As most agricultural tractors are DI, SRO has a potential
as a diesel fuel extender for agricultural equipment.