Environmental Engineering Reference
In-Depth Information
14.4.3.2 kinematic viscosity
The main problem of using JO as a fuel is its high viscosity, which is approximately 46.82 cSt,
which is 18 times more than that of diesel at 30°C (Table 14.4). The high viscosity of JO in contrast
with diesel may be due to the greater intermolecular attraction of the long chains of its glyceride
molecules. This higher viscosity of JO hinders its smooth flow through pipelines, injector nozzles,
and orifices. A viscosity that is too high can cause excessive heat generation in the injection equip-
ment because of viscous shear in the clearance between the pump plunger and cylinder of a fuel
injector. Higher viscosity reduces the injector spray cone angle, fuel distribution, and penetration
while increasing the droplet size, thus affecting injection timing. On conversion to JB, the kine-
matic viscosity is reduced (i.e., it becomes 1.97 times higher than that of diesel). The viscosity of
biodiesel and oil blends with diesel increases with the increase in concentration of biodiesel/oil in
the blends.
14.4.3.3 calorific value
The amount of heat generated by combustion of a unit weight of fuel is expressed in terms of
calorific value. The gross calorific values of JO and JB are approximately 38.63 and 39.65 MJ/kg,
respectively, as compared with 42 MJ/kg for diesel (Pramanik 2003; Tiwari et al. 2007; Sahoo and
Das 2009a). This could be due to the difference in their chemical composition from that of diesel
or the difference in the percentage of carbon and hydrogen content, or the presence of oxygen
molecules in the molecular structure of JO and JB. The oxygen molecule present unites with the
hydrogen of the oil to form water vapor even before secondary air or oxygen supplied for combus-
tion reaches the hydrogen. This results in a decrease in the available hydrogen, thus decreasing the
calorific value. The calorific value of the JO and JB blends with diesel proportionately decreases
with the increase in biodiesel or oil percentage in the blends.
14.4.3.4 cetane number
The cetane number is a measure of the ignition quality of fuels. The higher the cetane number, the
more efficient the fuel will be , and it will ignite easily when injected into the engine (Demirbas
2008). The cetane number of JO and JB is 4.08 and 9.69% higher than that of diesel, respectively
(Achten et al. 2008; Vyas et al. 2009). This higher cetane number is due to the higher oxygen content
in the fuel.
14.4.3.5 Flash Point
The flash point of JO and JB is 235 and 186°C, respectively, as compared with 68°C for diesel
(Tables 14.4 and 14.8). This might be due to the presence of components of longer chains in their
molecules and a higher degree of unsaturation (79.9%). Generally, a material with a flash point of
approximately 90°C or higher is considered as nonhazardous from a storage and fire-hazard point
of view.
14.4.3.6 acid value
The presence of FFAs in the fuel leads to corrosion as well as gum and sludge formation. The acid
value of JO has been reported to be vary between 0.92 and 29.8 mg KOH/g (Tiwari et al. 2007;
Achten et al. 2008; Berchmans and Hirata 2008; Vyas et al. 2009). On conversion to JB, its acid
value is reduced to 0.27 mg KOH/g.
14.4.3.7 Pour Point
The pour point is used to characterize the cold flow operability of a fuel because this property of
fuel affects the utility of the fuel, especially in the cold climate condition. The pour point of JO,
JB, and their blends with diesel are higher than that of diesel. This might be due to the presence of
wax and the higher amount of saturated fatty acids (Alptekin and Canakci 2009), which begins to
crystallize with a decrease in temperature.
