Environmental Engineering Reference
In-Depth Information
• When the FFA content is greater than 0.5% and the moisture content is less than 0.5%, then
a two-stage transesterification process can be selected. If the FFA content and moisture
content are greater than 0.5%, then a three-stage transesterification process is selected.
In the work presented here, biodiesel fuels were produced by a single-stage transesterification
process.
25.3
strateGIes and methodoloGIes
25.3.1 B
iodiESEl
p
ropErtiES
and
q
uality
Biodiesel is a mono-alkyl ester that is derived from vegetable oils or animal fats through
transesterification. The purpose of transesterification is to reduce the viscosity of vegetable oils. The
transesterification process parameters such as alcohol/oil ratio (6:1 molar ratio), catalyst quantity
(NaOH, 0.5 wt %), reaction temperature (65°C), and reaction time (2 h) were optimized for a single
oil and then subsequently adjusted for other oils. An alkali catalyst was used because of its low
cost and because it is easily miscible with methanol. Methanol was used because of its low cost.
The biodiesels produced from different oils were washed and dried. Different biodiesels were then
blended to vary the percentage of unsaturation. The biodiesels produced were checked for quality.
The important fuel properties were measured as per standard methods and compared with the
ASTM limits. The fuel properties were determined following the methods specified in ASTM
standards as given in Table 25.3.
25.3.2 c
omBuStion
p
aramEtErS
25.3.2.1 Ignition delay
Ignition delay is the time or crank angle between the start of fuel injection into the cylinder and the
time of first combustion. The fuel injection is dynamic injection and the first combustion is the heat
release. The ignition delay was calculated from the heat release diagram. The dynamic injection
timing was calculated based on the negative heat release in the heat release diagram. Because the
fuel droplet absorbs heat from the cylinder, there is a negative heat release on the diagram. The point
at which the first negative heat release starts is the dynamic injection time and the start of ignition
delay period. Similarly, at the point where the first positive heat release is seen on the diagram is the
end of the ignition delay period.
25.3.2.2 heat release rate
The heat release rates were determined from the cylinder pressure history. The apparent heat release
rate was calculated based on the first law of thermodynamics as given in equation (25.1).
taBle 25.3
astm methods for determination of Fuel Properties
Property
unit
astm standard
Fatty acid composition
wt %
D6584
Density at 15°C
g/cc
D1298
Cetane number
-
D613
Heating value
MJ/kg
D240
Iodine value
g iodine/100 g oil
D1510
