Page 371 - Advances in Eco-Fuels for a Sustainable Environment

326 Advances in Eco-Fuels for a Sustainable Environment

acids (FFA) present in the biodiesel divided by the entire weight of biodiesel gives the
FFA percentage.

AV ¼ 1:99FFA% (11.9)

The acid values of AMC biodiesel, Karanja biodiesel, and Jatropha biodiesel are found
to be 0.2, 0.42, and 0.074, respectively. Saponification value reflects the amount of fat
present in the biodiesel or the number of fatty acids present in triglycerides, whereas
the acid value denotes the percentage of free fatty acids (FFA) that are not linked with
any other molecules (triglycerides or methyl esters) and remain free as acids in bio-
diesel. In general, acid values are inversely proportional to saponification values
because when a number of fatty acids are present in the biodiesel as triglycerides,
the greater the saponification value; therefore, the number of free fatty acids present
is low, thus giving a lower acid value. Hence, it can be observe that Karanja biodiesel
has the highest acid value (almost close to the max limit of ASTM standards),
followed by AMC biodiesel and Jatropha biodiesel.

11.3.3.7 Viscosity

Fuel viscosity plays a vital role in determining the combustion characteristics of any
fuel. For achieving high thermal efficiency, the direct injection of the fuel into the
combustion chamber through the nozzle and fuel spray pattern should be perfect
and effective, and viscosity has a crucial role to play in this. When the viscosity of
fuel is too low, it leads to internal pump leakage, which can bring down the system
pressure to an unacceptable level that will ultimately affect the fuel’s spray atomiza-
tion and ignition characteristics. At low load conditions where the speed of operation
becomes low, viscosity becomes more critical.
The viscosities of AMC biodiesel, Karanja biodiesel, and Jatropha biodiesel are
found to be 3.6, 5.60, and 4.84 centistokes, respectively. The viscosity of biodiesel
is always higher than petroleum diesel, often by a factor of two; the viscosity increases
as the percentage of biodiesel increases. At low ambient temperatures and cold start
engine conditions, viscosity effects become more critical and significant. As the chain
length of the fatty acid in the parent oil increases or the alcohol group involved in the
transesterification process is heavier, viscosity increases. The weight percentage of
long chain fatty acids (C 20 ,C 22 , and C 24 ) is highest for Karanja. Hence it has the
highest viscosity value whereas the long chain fatty acids (C 20 ,C 22 , and C 24 ) are least
for AMC biodiesel. Hence it has the least viscosity value. Jatropha lies somewhere in
between these two regarding the weight percentage of long chain fatty acids.

11.3.3.8 Lubricity
Lubricity is the measure of the reduction in friction and/or wear by a lubricant. Lubric-
ity is determined by the amount of wear caused to a surface by a wear-producing
object for a given set of conditions and time. For two fluids with identical viscosities,