Page 369 - Advances in Eco-Fuels for a Sustainable Environment

324 Advances in Eco-Fuels for a Sustainable Environment

account the positions of the double bonds available for oxidation and these values are
sometimes misleading. The IV does not always correlate well with oxidative stability.
There is an entirely different test for estimating the biodiesel’s stability, and it is
known as the oil stability test (OST).

11.3.3.4 Flash and fire point

The flashpoint for any volatile material is defined as the lowest temperature at which
vapors of the material will ignite when ignited by a source. Similarly, the fire point is
defined as the lowest temperature at which vapors of the material will catch fire and
continue burning even after the ignition source is removed. The fire point is higher
than the flash point because the vapors produced at the flash point are not sufficient
enough to ignite the fuel. Flash and fire points depend upon the volatility of the bio-
diesel. Volatility is the tendency of the substance to vaporize, and it is directly related
to the vapor pressure of the biodiesel at that particular temperature. The biodiesel
exhibiting higher vapor pressure at a given temperature is said to be more volatile than
the one exhibiting lower vapor pressure at the same temperature. Hence the lower the
NBP (normal boiling point), the higher the volatility, which is in turn inversely pro-
portional to its flash and fire point.
The flash and fire point of AMC biodiesel was found to be 164°C and 175°C,
respectively. The flash point of Karanja biodiesel was found to be 97.8°C. The flash
point of Jatropha biodiesel was found to be 192°C. The reason for the close flash point
values of AMC biodiesel and Jatropha biodiesel is their identical average molecular
masses. Also, the length of the fatty acid chains is directly proportional to their boiling
points, and branching is directly proportional to their melting points. Weight percent-
age of long chain fatty acids is greater for Jatropha compared to AMC, even though
they have identical average molecular masses. Therefore, the NBP of Jatropha is more
compared to AMC, owing to its higher flash and fire points. Karanja biodiesel’s aver-
age molecular mass is quite low compared to these two, and hence the NBT is quite
low and very volatile. The source temperature will always be higher than either the
flash or fire point, and both these parameters are independent of ignition temperature.
The flashpoint of fossil diesel is always less than that of biodiesel, and hence it cannot
be safely stored.

11.3.3.5 Cold filter plugging point (CFPP) cloud point and
pour point

It is a challenge to fuel vehicles with biodiesel blends in cold climates because these
biodiesels tend to freeze earlier than conventional petroleum diesel. The type of oil
from which the biodiesel is made decides this freezing point. These cold-weather char-
acteristics are measured by three factors: cloud point (CP), pour point (PP), and cold
filter plugging point (CFPP). The cloud point is the temperature of the fuel at which
small solid crystals can be observed as the fuel cools. The cold filter plugging point is
the temperature at which a fuel filter clogs due to the crystallized fuel components.
The pour point refers to the lowest temperature at which there is absolutely no move-
ment of the fuel components when the container is flipped. The cloud points of AMC