Environmental Engineering Reference
In-Depth Information
of JBB (B20) and diesel is almost negligible at higher engine loads. The BSFC for B20 was found to
be even less than diesel (Sivprakasam and Saravanan 2007). While testing a 7.47-kW, two-cylinder,
four-stroke diesel engine, Sivprakasam and Saravanan (2007) reported the fuel consumption to be
7% lower for a B20 blend and 4% higher for JB (B100) as compared with the diesel fuel. The fuel
consumption of other blends of biodiesel had a small variation between these two fuels.
Pramanik (2003) evaluated the performance of a single-cylinder 3.7-kW diesel engine using JO
and its blends with diesel under the break load ranging from 0 to 3.078 kW. The specific fuel con-
sumption was found to be close to diesel at 0.338 and 0.365 kg/kWh at a load of 3.078 kW for blends
containing 30:70 JO/diesel and 40:60 JO/diesel, respectively. The corresponding value for diesel
was found to be 0.316 kg/kWh. For blends of JO and diesel, BSFC was found to be higher compared
with diesel for a 7.4-kW diesel engine (Agarwal and Agarwal 2007).
14.5.2.2 Bte
BTE is the ratio of brake power to the fuel energy. It is considered important because it is ultimately
the brake power that is of the most concern. The efficiency of any internal combustion engine
depends on the physical process involved, such as atomization, evaporation, combustion tempera-
ture, etc., which in turn are governed by the type of fuel and operating conditions of the engine. The
BTE of a CI engine increases with an increase in engine load for JB, JBB, and JO, and maximal
BTE is obtained at maximal brake power. Tiwari (2007) studied the performance of a 10.3-kW,
single-cylinder, four-stroke diesel engine when fueled with B20 and diesel. The maximal BTE was
found to be 28.98 and 29.80% for B20 and diesel, respectively. The difference in BTE between
B20 and diesel is almost negligible. However, with a further increase in biodiesel percentage in the
JBB, the BTE decreased. This drop in thermal efficiency is due to poor combustion characteristics
because of the higher viscosity and lower volatility of blend fuels.
Kumar et al. (2003a) evaluated the performance of a 3.7-kW diesel engine using single-fuel oper-
ation (JO and JO/methanol blends) and dual-fuel operation (induction of methanol while running
the engine with JO). The thermal efficiency for JO and JO/methanol blends was found to be slightly
reduced as compared with diesel. Maximal BTE was found to be 27.4 and 30.2% with JO and diesel,
resp e ct ively.
Use of a JO methanol blend as compared with neat JO resulted in an increase in BTE
from 27.4 to 28.1%. In the dual-fuel operation with methanol induction and JO as the pilot fuel, an
increase of peak BTE from 27.4 to 28.7% was observed. While testing a 3.7-kW, single-cylinder,
four-stroke diesel engine, Pradeep and Sharma (2007) reported that the BTE with JB was compa-
rable with diesel at all loads with and without EGR.
The BTE of a single-cylinder 3.7-kW diesel engine when operated with JO and its blends with
diesel was found to be lower than that of diesel for the entire range of loads (Pramanik 2003).
Among the blends tested, thermal efficiency and maximal power output of 30:70 JO/diesel and
40:60 JO/diesel blends were found to be closer to those of diesel.
The thermal efficiency of a 7.4-kW diesel engine was found to be lower for unheated JO com-
pared with heated JO and diesel (Agarwal and Agarwal 2007). However, the BTE was found to be
closer to that of diesel for JO and diesel blends (J20).
14.5.2.3 eGt
The EGT gives an indication of the thermal efficiency of the engine. Heat loss is important for
engines because it leads to lower working temperature and ultimately to reduced efficiency. The
combustion is supposed to be complete at the end of the constant pressure burning in the case of CI
engines. However, in actual practice, it continues up to approximately half of the expansion stroke.
This “after-burning” may continue up to an exhaust stroke in the case of improper ignition charac-
teristics because of faulty engine settings. In general, approximately 30-33% of the energy supplied
to a diesel engine is lost as exhaust heat and another 28-30% is lost in cooling (Thipse 2008). The
EGT for a given engine depends upon the fuel-air ratio and the combustion characteristics of the
fuel, which in turn depend upon the type of fuel and loading conditions. The EGT of CI engines
