Environmental Engineering Reference
In-Depth Information
890
y
= 0.268
x
+ 860.47
r
2
= 0.913
886
882
878
874
870
40
50
60
70
80
90
100
% of unsaturation
FIGure 25.5
Variation of density with percentage of unsaturation.
41.0
y
= -0.027
x
+ 41.63
r
2
= 0.755
40.5
40.0
39.5
39.0
40
50
60
70
80
90
100
% of unsaturation
FIGure 25.6
Variation of heating value with percentage of unsaturation.
25.4.1.2 heating value
Heating value, or the energy content or heat of combustion, is a measure of the energy available in a
fuel. It is a critical property of fuel intended for use in weight-limited vehicles. The energy content
of various biodiesel fuels can be observed from Table 25.5.
From the literature (Demirbas et al. 1998; Knothe 2005), it was observed that the heating value,
cetane number, and viscosity increase with an increase in carbon number and decrease with the
degree of unsaturation.
• The molecular weight of fatty acids increases with chain length.
• The heating value increases with chain length (molecular weight) and decreases with
increase in the number of double bonds.
The increase in heat content may be due to the increase in the number of carbons and hydrogens.
The possible cause for decrease in heat content may be the deficiency of hydrogen atoms (greater
unsaturation). From Table 25.5, it can be noticed that LOME has the lower energy content and
MOME has the higher energy content. Because MOME is dominated by a higher carbon chain
(16 to 18), it exhibits a higher energy content, whereas LOME, which is dominated by a lower car-
bon chain, exhibits lower energy content as compared with other biodiesel fuels. The scatterplot
between the heating value and percentage of unsaturation with a fitted trend line equation is illus-
trated in Figure 25.6.
