Page 171 - Biofuels Refining and Performance

154 Chapter Five

are included in Table 5.1. For the IQT, ID and CN are related by the fol-
lowing equation [9]:
CN IQT 83.99 (ID 1.512) 0.658 3.547 (5.1)

In the recently approved method ASTM D6890, which is based on this
technology, only ID times of 3.6–5.5 ms [corresponding to 55.3–40.5
DCN (derived CN)] are covered as the precision may be affected outside
that range. However, for fatty compounds, the results obtained by using
the IQT are comparable to those obtained by other methods [9].
Generally, the results of cetane testing for compounds with lower CNs,
such as more unsaturated fatty compounds, show better agreement over
various related literature references than the results for compounds
with higher CNs, because of the nonlinear relationship [see Eq. (5.1)]
between the ID time and the CN, which was observed previously [30].
Thus, small changes at shorter ID times result in greater changes in CN
than at longer ID times. This would indicate a leveling-off effect on
emissions such as NO , as discussed above, once a certain ID time with
x
corresponding CN has been reached as the formation of certain species
depend on the ID time. However, for newer engines, this aspect must
be modified as discussed above.

5.3 Cold-Flow Properties
One of the major problems associated with the use of biodiesel is poor
low-temperature flow properties, documented by relatively high cloud
points (CPs) and pour points (PPs) [1, 2]. The CP, which usually occurs
at a higher temperature than the PP, is the temperature at which a fatty
material becomes cloudy due to the formation of crystals and solidifi-
cation of saturates. Solids and crystals rapidly grow and agglomerate,
clogging fuel lines and filters and causing major operability problems.
With decreasing temperature, more solids form and the material
approaches the PP, the lowest temperature at which the material will
still flow. Saturated fatty compounds have significantly higher melting
points than unsaturated fatty compounds (Table 5.1), and in a mixture,
they crystallize at higher temperatures than the unsaturates. Thus,
biodiesel fuels derived from fats or oils with significant amounts of sat-
urated fatty compounds will display higher CPs and PPs.
Besides the CP (ASTM D2500) and PP (ASTM D97) tests, two test
methods for the low-temperature flow properties of petrodiesel exist,
namely, the low-temperature flow test (LTFT) (used in North America;
e.g., ASTM D4539) and cold filter plugging point (CFPP) (used outside
North America; e.g., the European standard EN 116). These methods
have also been used to evaluate biodiesel and its blends with No. 1 and