Page 183 - Biofuels Refining and Performance

166 Chapter Six

Several studies have reported the effects of fuel and engine parame-
ters on diesel exhaust emissions. Chowdhury [4] claims to have suc-
cessfully used raw vegetable oils in diesel engines. He observed that no
major changes were necessary in the engine, but the engine could not
be run for more than 4 h. The performance and economic aspects of
vegetable oil were also discussed.
Barve and Amurthe [5] cite an example of using groundnut oil as
fuel in a diesel engine generator set (103 kW) of a local water pump
house. They claimed that the power output and fuel consumption were
very much comparable with certified diesel fuel. Weibe and Nowakowska
[6] have reported the use of palm oil as a motor fuel. The performance
was found satisfactory with higher fuel consumption. Fang [7] has
reported that soybean and castor oil blended with diesel fuel burns
adequately in a small diesel engine. Engelman et al. [8] has presented
data on the performance of soybean diesel oil blends compared with
diesel fuel. Results from a short-duration test showed that the use of
blends was feasible in the diesel engine; but in fact, in the long-term,
test problems associated with lubrication, sticking piston rings, and
injector atomization patterns contributed to mechanical difficulties in
the engine. Cruze et al. [9] have found that atomization of the fuel by
the injector, in some cases, has caused delayed ignition characteristics
and reduced efficiency of mechanical power production, compared to
diesel fuel. Pryde [10] has stated that raw vegetable oil has had no great
promise for engine tests and that modified oil esters were required for
further engine tests. Bruwer [11] has reported that even without mod-
ification, nine diesel engines started and operated almost normally on
sunflower oil and delivered power equal to that of diesel fuel. Brake
thermal efficiency and maximum engine power were 3% lower, while
the specific fuel consumption was 10% higher than that of diesel fuel.
The bench test, however, showed that atomization of 100% sunflower
oil was much poorer than diesel but could be improved by reducing
the viscosity of oil. Energy wise, sunflower oil was favorable for run-
ning diesel engines for a shorter duration.
Baranescu et al. [12] have conducted tests on a turbocharged engine,
using mixtures of sunflower oil in 25%, 50%, and 75% with diesel fuel.
They have concluded that the use of sunflower oil blended with diesel
brought modification in the fuel injection process that mainly included
an increase in injection pressure and a longer ignition duration. These
effects led to longer combustion duration. Cold-temperature operation
was very critical due to high viscosity that caused fuel system problems
such as starting failure, unacceptable emission levels, and injection
pump failure. Engine shutdown for a long duration accelerated gum
formation, where the fuel contacted the bare metal. This might further
impair the engine or injection system.