Biomedical Engineering Reference
In-Depth Information
important to observe the climate and conditions of where the biodiesel would be used. Colder
regions would have to sacrifice higher cetane numbers in order to achieve lower cloud points
and vice versa [4]. Coconut oil derived biodiesel may be fine in regions near the equator, but
would do very poorly in Canada. Soybean oil, commonly used in the United States, is mostly
polyunsaturated.
Olive
Peanut
Palm
Safflower
100
80
60
40
20
0
Yellow
grease
Canola
Sunflower
Soybean
Tallow
Saturated
Monounsaturated
Polyunsaturated
Figure 11. Composition of various biodiesel feedstocks.
Stability of the fuel is also affected by degree of saturation. Stability decreases by a factor
of ten at each increase of un-saturation. This is because reactions with oxygen can occur at
the double bond sites, which forms peroxides. Peroxides further break down into acids,
sediments, and gums which are harmful to the fuel containers [4]. As alluded to in
environmental considerations, longer chain lengths showed decreased NOx emissions, while
increasing unsaturation resulted in higher NOx emissions compared to diesel fuel (see
Figure 12).
Work by Soriano, et al. show the various implications of chain length and un-saturation
on the physical properties discussed earlier. Their explanation is that the double bonds disrupt
the attractive forces in the hydrocarbon chain, causing the physical properties to decrease
[40].
