Although vegetable oils are apparently an advantageous alternative fuel for direct use in
traditional diesel engines with no modification necessary, in practice many problems are
regularly discussed in the literature including filter clogging, breakage of certain types of
injection pumps, and deposits of carbon on the cold parts of engines.
Several technological solutions have been proposed to overcome these problems but
the majority of papers discuss them individually and have not actually compared them
in similar conditions. The purpose of the present study was to use the same experimental device to compare the three most widely recognised technological options for the use
of Jatropha curcas vegetable oil as a fuel in a direct injection diesel engine: preheating,
blending with diesel, and recirculating exhaust gases. Power output, specific consumption,
thermal efficiency and exhaust gas emissions were compared to those of diesel used as the
reference. The results obtained were similar for preheated and non-preheated Jatropha oil,
but differed from the results obtained with diesel. Similar combustion performance and
similar emissions were obtained with a blend of 20% Jatropha oil and diesel to those obtained with diesel alone. Exhaust gas recirculation (EGR) with Jatropha oil could lead to
fouling in the combustion chamber. In contrast to widely accepted theory, this study also
clearly demonstrates that the viscosity of vegetable oil is not the main cause of poorer
combustion quality and, consequently, of deposits in the combustion chamber.

Jatropha curcas Vegetable oil Biofuel Direct injection diesel engine