Page 186 - Biofuels Refining and Performance

Processing of Vegetable Oils as Biodiesel and Engine Performance 169

Engine test results, based on the specific energy, showed that degummed
soybean performed as well as the base fuel, but performance of the
deodorized sunflower was the worst of those tested with an energy con-
sumption 10% higher than the base fuel. Vegetable oils had a much
smaller premixed combustion stage, with the diffused stage of combus-
tion being flatter for sunflower and soybean oil than for the diesel fuel.
Engine inspection showed that heating of the oil reduced the carbon
deposit problem. It was concluded that deposits and overall durability
were related to viscosity differences and the chemical structures of the
other oil as compared to diesel fuel.
Mathur and Das [23] have conducted tests on diesel engines, using
blends of mahua and neem oil with diesel. Results showed that neem
oil could be substituted for up to 35% with marginal reduction in effi-
ciency and power output. Mahua oil with diesel had exhaust charac-
teristics similar to those of diesel. Further, savings in the diesel fuel
through the use of both these nonedible oils outweighed the demerits of
a marginal drop in efficiency and a slight loss in power output.
Goering et al. [24] conducted tests on a diesel engine using a hybrid
fuel formed by micro-emulsion of aqueous ethanol in soybean oil. The
test data were compared with the data from a baseline test on diesel fuel.
The nonionic emulsion produced the same power as diesel fuel, with 19%
lower heating value. Brake specific fuel consumption (BSFC) was 16%
higher, and the brake thermal efficiency was 6% higher, with diesel at
full power. Diesel knock for the hybrid fuel was not worse than for diesel
fuel; thus the low cetane number of the hybrid fuel was not reflected in
engine performance. Hybrid fuels were less volatile than ethanol and
thus safer. The effect of hybrid fuel on the engine durability was
unknown.

6.2 Processing of Vegetable Oils
to Biodiesel
Different techniques adopted for converting vegetable oils to biodiesel are
(a) degumming of vegetable oils, (b) transesterification by acid or alkali,
and (c) enzymatic transesterification.

6.2.1 Degumming of vegetable oils
Degumming is an economical chemical process involving acid treatment
to improve the viscosity and cetane number up to a certain limit so that
the blends of nonedible oils with diesel can be used satisfactorily in a
diesel engine. It is a very simple process by which the gum of the veg-
etable oil is removed to decrease the viscosity of oil by using an appro-
priate acid that can be optimized for reduction in viscosity. The quantity
of acid and the duration of the process are very important to obtain