Environmental Engineering Reference
In-Depth Information
14.4.3.8 Water content
Water present in fuel interferes with its smooth flow through lines and combustion inside of
the cylinder. The water content of JO has been reported as 1.4% (Tiwari et al. 2007), which is
much higher than the ASTM prescribed limits of less than 0.03%. However, the water content
of JB is approximately 0.16%, which is well within the limits prescribed by the ASTM and DIN
standards.
14.4.3.9 ash content
Ash is the incombustible material that remains after burning and correlates with the amount of
deposits formed in the combustion chamber. Therefore, fuels having less ash content are preferred
for better engine operation and maintenance. JO has a very high level of ash content, which is
one of the main reasons for its unsuitability as a fuel in the long run (Tiwari 2007). However,
upon conversion of the JO to JB, the ash content is reduced to 0.013%, which is very similar to
that of diesel.
14.4.3.10 carbon residue
The property that correlates with the amount of carbonaceous deposits, the fuel that will form in the
combustion chamber of the engine is known as carbon residue—the non-volatile residue left when
fuel is heated to a high temperature in the absence of air. The higher this value is, the greater the
expected carbon deposits in the combustion chamber. JO has a high carbon residue level of 0.38%.
However, the carbon residue of JB is very similar to that of diesel and is within the specified limit
of 0.3%.
All of these fuel properties except flash point and cetane number are improved by increasing the
percentage of diesel in the blend. However, a reverse trend has been reported for the flash point and
cetane number with increasing diesel in the blend.
The influence of the quality of biodiesel on major fuel properties and on engine performance is
summarized in Table 14.9.
14.5 enGIne PerFormance usInG JatroPha BIodIesel and oIl
To get more market acceptance of JO/JB, engine performance evaluation is required along with
quality checking of biodiesel. The specific need will decide whether to go for JB (B100, i.e., pure
biodiesel) or a particular blend to substitute diesel fuel with little sacrifice on engine output and
economy. In this section, efforts have been made to review different aspects such as combustion,
performance, and emission characteristics of diesel engine while running with JO, JB, and jatropha
biodiesel blend (JBB).
14.5.1 c omBuStion of B iodiESEl
Combustion in CI engines is a three-dimensional, unsteady, and heterogeneous process and is
affected by type of fuel, fuel characteristics, design of combustion chamber, fuel injection system,
and the engine's operating conditions (Heywood 1988). The main aspects of combustion are a rise
in cylinder pressure, heat release rate, and ignition delay. Ignition delay of the fuel is extremely
important in CI engines primarily because of its effect on combustion rate and detonation. It may
influence the starting ability of the engine. The combustion characteristics for JB, JBB, and JO in
CI engines are briefly summarized in Table 14.10.
14.5.1.1 cylinder Pressure
The peak cylinder pressure in a CI engine depends upon the rate of combustion at the initial stage,
which is influenced by the fuel taking part in the uncontrolled heat release phase. The high vis-
cosity and low volatility of JO leads to poor atomization and mixture preparation with air during
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