Page 281 - Biosystems Engineering

Biodiesel and Ethanol in Engines 259

properties. Cold-temperature operation is very critical due to high
viscosity that causes fuel system problems such as starting failure,
unacceptable emission level, and injection pump failure. The engine
shuts down for long duration due to accelerated gum formation
where the fuel contacts the bare metal. This might further impair the
engine or injection system. 19
Calorific value (ASTM D4809) and viscosity can be measured by
a bomb calorimeter and a Redwood viscometer, respectively. The
flash point and the fire point can be determined using the Pensky
Martens apparatus closed-cup method according to ASTM D93. The
pour point is measured according to ASTM D98. The carbon residue
is measured by the Conradson method (ASTM D189), and the CN is
determined according to ASTM D4738. The CN of a diesel fuel (DF) is
related to the ignition delay (ID) time, that is, the time that passes
between injection of the fuel into the cylinder and onset of ignition.
The shorter the ID time, the higher the CN and vice versa.
Standards have been established worldwide for CN determina-
tion, for example, ASTM D613 in the United States and the Interna-
tional Organization for Standardization (ISO) standard ISO 5165
internationally.
Recently, cetane studies on fatty compounds were conducted
using the Ignition Quality Tester (IQT) (Advanced Engine Technology
21
Ltd., Ottawa, Ontario, Canada). The IQT is a further, automated
development of a constant-volume combustion apparatus (CVCA) .
20
The CVCA was originally developed for determining CNs more rap-
idly, with greater experimental ease, better reproducibility, reduced
use of fuel, and therefore cheaper than the ASTM D613 method using
a cetane engine. The IQT method, which is the basis of ASTM D6890,
was shown to be reproducible and the results competitive with those
derived from ASTM D613. The IQT, ID, and CN are related by the
following equation: 20

CN = 83.99 × (ID – 1.512) –0.658 + 3.547 (8.1)
IQT
However, the results for fatty compounds with the IQT are compa-
rable to those obtained by other methods. 20
The difference in properties for different vegetable oils are due to
variations of fatty acid composition and other associated compounds
such as coloring matters and odorant compounds, etc. The fuel prop-
erties of three transesterified vegetable oils (karanja, Jatropha, and
putranjiva) and diesel are shown in Table 8.1. The kinematic viscosi-
ties of 100 percent of fatty acid methyl esters (FAME) at 40°C are
almost same as of diesel. The flash point and the fire point are better
21
than diesel for the engine application. It has been observed that the
calorific values and CNs of the three transesterified oils (karanja,
putranjiva, and Jatropha) are less than that of diesel but are compara-
ble with other available biodiesels as reported by Rakopoulos et al. 22