Jatropha - Bioenergy Crop Plants - page 341

when operated with JB, JBB, and JO is summarized in Table 14.11 and it increases with an increase
in engine load. The minimal and maximal EGT for a 10.3-kW diesel engine when fueled with B20
were found to be 182 and 375°C, respectively, as compared with 166 and 380°C for diesel for no
load to full load. For both of the fuels tested, EGT was increased with an increase in engine load;
however, at higher loads, it was comparable for both of the fuels (Tiwari 2007). For higher blends,
it was higher than that of diesel.
Agarwal and Agarwal (2007) studied the performance of a 7.4-kW diesel engine when fueled
with unheated and heated JO and found that EGT for unheated JO was found to be higher as com-
pared with diesel and heated JO. A higher EGT was also reported for the blends of JO and diesel
having a high percentage of JO.
14.5.3 E miSSion c haractEriSticS
Exhaust emissions due to combustion of fuels are becoming increasingly important in view of the
present-day awareness of environmental pollution. If the combustion were complete, the exhaust
would consist only of CO 2 and water vapors plus air that did not enter into the combustion process.
However, for several reasons, oxidation of fuel during combustion remains incomplete and produces
carbon monoxide (CO), a deadly poisonous gas, unburned hydrocarbons, and oxides of nitrogen
(NO x ) other than particulate matter in the form of smoke. These emissions formed during burning
of the air/fuel mixture depend on the conditions during combustion, expansion stroke, and espe-
cially before the exhaust valve opening. Emission characteristics of diesel engines operated with
diesel, JO, JB, and their blends are summarized in Table 14.12.
14.5.3.1 co and co 2
CO is a product of the incomplete combustion due to either inadequate oxygen or insufficient time
for completion of the reaction. Generally, the CO values are found to vary between 0 and 2% in the
case of diesel engines. It is also said that complete elimination of CO is not possible and 0.5% CO
should be considered as a reasonable goal. Although diesel engines always operate with consider-
able excess air, CO emissions are still considered a significant problem regarding environmental
pollution. CO emission levels were found to be higher with JB and JO as compared with diesel at all
engine loads of a 3.7-kW diesel engine (Kumar et al. 2003a). However, a reverse trend was reported
by Tiwari (2007) while studying exhaust emissions from a single-cylinder 10.3-kW diesel engine
when operated with B20, i.e., the minimal and maximal CO produced was 0.38% at no load and
0.55% at full load as compared with 0.57% at no load and 0.74% at full load for diesel. Banapurmath
et al. (2008) reported slightly more CO for JB (0.155%) than the diesel (0.1125%) for a four-stroke
5.2-kW CI engine. Tiwari (2007) reported that the amount of CO 2 produced for B20 was comparable
with diesel at higher loads, i.e., the maximal CO 2 produced was 7.79 and 7.8% at 100% load for B20
and diesel, respectively.
Kumar et al. (2003b) reported that induction of 7% hydrogen in a jatropha-fueled diesel engine
was found to be the optimum for reducing CO from 0.26 to 0.17%. The corresponding reduction
in CO with diesel as a pilot fuel was found to be from 0.2 to 0.1%. Agarwal and Agarwal (2007)
studied the emissions of a 7.4-kW diesel engine fueled with unheated and heated JO and found that
CO and CO 2 were higher for JO compared with those produced with diesel. These emissions were
found to be closer to diesel for preheated JO and were increased with an increasing proportion of JO
in the blends as compared with diesel.
14.5.3.2 no x
Higher combustion temperature and availability of oxygen favors the formation of NO x emissions.
Unlike diesel, biodiesel and its blend with diesel contain more oxygen. This, factored together with
higher combustion temperature, favors the production of higher NO x . The other reason could be
the presence of higher quantities of nitrogen in the fuel. The NO x emission for B20 is 8% higher,