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Physicochemical fuel properties and tribological behavior of aegle marmelos correa biodiesel 331

antioxidants and natural antioxidants. Fatty oils derived from plants contain natural antiox-
idants such as tocopherols.
The content of tocopherol (all isomers) is different for different oil sources. Naturally
occurring levels of tocopherols are directly optimized for their antioxidant capability.
More artificial addition of tocopherol has either no beneficial effect or may even
become harmful to the oil or biodiesel. Tocopherols may be completely lost, partially
lost, or completely retained, depending on the biodiesel processing conditions. Some-
times after the transesterification process of biodiesel, all the tocopherols that were
initially present in the parent oil might be removed.

11.3.3.11 Calorific value
Calorific value is the amount of energy released or produced when 1kg of fuel burns or
any other substance is burnt in the presence of oxygen and the products of combustion
are cooled to STP. Its SI unit is kJ/kg. Basically 1 mole of hydrogen, which is 1g, will
yield some 30 calories of heat, whereas 1mol of carbon, which is 12g, yields some
96 calories. So hydrogen will yield 30 calories per gram while carbon produces only
about 8 calories per gram. The calorific values of AMC, Karanja, and Jatropha are
found to be 37.5 (MJ/kg), 36.57 (MJ/kg), and 38.5 (MJ/kg), respectively.
All the biodiesels contain mixtures of various hydrocarbons (acids, esters), long
chained or short chained, but Jatropha biodiesel contains much hydrogen owing to
the percentages of various fatty acid constituents. It is followed by AMC and Karanja.
Hence, hydrogen is the overriding factor in determining the combustion characteris-
tics of the fuel. Hence Jatropha biodiesel has far more energy-rich hydrogen compared
to AMC and Karanja biodiesel.

11.3.4 Tribological analysis

Fig. 11.6 shows that in the first few seconds of the experiment, the coefficient of fric-
tion (COF) was unsteady for the fuel due to the initial friction between the bottom
three stationary balls and the top rotating ball. After a few seconds, the contact surface
between the rotating and stationary balls gets smoothed, which leads to reaching the
COF becoming a steady state. The experiment was conducted for 3600s at 1200rpm in
which the first 5s were found to be run in period (Fig. 11.7).
Diesel (B0) has the highest run in the period compared to biodiesel (B100). More-
over, COF of diesel was suddenly rose in the first 5 s and as well as it has longer period
of the unsteady state compared to B100. B100 takes a short period to reach the steady
state due to its high smoothing capability. The steady-state COF for the last 1000s of
diesel was 13% higher than the biodiesel.
The good lubricity of biodiesel is because of its hydrophilic and hydrophobic
nature. The ester functional group present in the biodiesel easily gets absorbed on
the surface of the metal, which forms a lubricating film on the metal surface. There
is another type of interaction between metal and fuel that mainly depends on the chain
length and unsaturation percentage. The lubricity of biodiesel is increasing with an
increase in chain length.