Page 185 - Biofuels Refining and Performance

168 Chapter Six

There was no significant problem with engine operation when the blend
of safflower oil was used. That investigation revealed that chemical dif-
ferences between vegetable oil and diesel had a very important influence
on long-term engine performance. Bhattacharya et al. [17] have reported
that a blend of 50% rice bran oil with diesel could be a supplementary
fuel for their 10-bhp CI engine. No significant difference in the brake
thermal efficiency was reported.
Samson et al. [18] have reported the use of tallow and stillingia oil in
25–75% and 50–50% blends by mass with diesel. The fuel properties of the
blends were found to be within the limits proposed for diesel. The heat of
combustion appeared to decrease. Specific gravity and kinematic viscos-
ity increased with the increase in concentration of oil. Dunn et al. [19] con-
ducted the test on rubber seed oil blended with diesel in 25%, 50%, 75%,
and 100% in an air-cooled engine with 4.9 kW at 3600 rpm. Higher spe-
cific fuel consumption and slightly higher thermal efficiency were observed.
But, carbon deposits were heavier than those for pure diesel fuel.
Samga [20] conducted a test on a water-cooled single-cylinder diesel
engine, using hone oil (ken seed oil). He concluded that hone oil gave
acceptable performance, smooth running, and ease in starting without
preheating. The exhaust temperature and specific fuel consumption
were higher than those for diesel. The partial-load efficiency was lower,
but full-load efficiency was better than with diesel fuel.
Auld et al. [21] evaluated the potential yield and fuel qualities of
winter rape, safflower, and sunflower as sources of fuel for diesel engines.
Vegetable oils contained 94–95% heat value of diesel fuel, but were
11.1–17.6 times more viscous and also 7–9% heavier than diesel fuel.
Viscosities of vegetable oils were closely related to fatty acid chain length
and number of unsaturated bonds. During short-term engine tests, all
vegetable oils produced power comparable to that of diesel, and the
thermal efficiency was 1.8–2.8% higher than that of diesel. Based on the
results, they concluded that vegetable oil as fuel should be selected on
identification of the crop species that produced the most optimum yield
of fuel quality vegetable oils.
Ryan et al. [22] have tested four different types of vegetable oils (soybean,
sunflower, cottonseed, and peanut) in at least three different stages of
processing. All the oils were characterized according to their physical and
chemical properties. The spray characteristics of oils were determined
at different fuel temperatures, using a high-pressure, high-temperature
injection bomb, and high-speed motion picture camera. The injection
study pointed out that vegetable oil behaved differently from diesel fuel.
Normally, as the viscosity decreased, the penetration rate decreased
and the spray cone angle increased. Using vegetable oils, however,
increased the penetration rate, and increasing the temperature of the
oil from 45 C to 145 C reduced the cone angle and decreased the viscosity.