Environmental Engineering Reference
In-Depth Information
taBle 25.12
Brake thermal efficiencies of Biodiesel Fuels at Full load
Percentage of
united states
Brake thermal
efficiency (%)
Biodiesel
Bsec (mJ/kWh)
SFOME
88.00
13.20
27.27
ROME
78.87
13.15
27.38
JOME
75.50
13.12
27.44
KOME
72.32
12.94
27.82
JT 80:20
68.18
12.91
27.89
NOME
60.40
12.88
27.96
JT 50:50
57.92
12.91
27.88
SFCt 50:50
52.05
12.87
27.98
MOME
50.00
12.81
28.11
POME
48.80
12.75
28.23
JCt 50:50
44.44
12.66
28.43
COME
10.00
12.29
29.28
25.4.2.6 Brake thermal efficiency
Thermal efficiency is the ratio between the power output and the energy introduced through fuel
injection, the latter being the product of the injected fuel mass flow rate and the lower heating
value. Thus, the inverse of thermal efficiency is often referred to as BSEC. Because it is usual
to use the brake power for determining thermal efficiency in experimental engine studies, the
efficiency obtained is really the brake thermal efficiency. This parameter is more appropriate than
fuel consumption to compare the performance of different fuels, besides their heating value.
Brake thermal efficiency can be correlated with fuel burn angle and the generic statement is that
the lower the burn angle, the higher the efficiency. But, for the same fuel burn angle, it is difficult
to obtain a correlation with burn angle. Rather it can be well correlated to the shape of the heat
release diagram. Brake thermal efficiency shown in Table 25.12 is higher for COME and is lower
for SFOME. This shows that the order of magnitude of brake thermal efficiency for the biodiesel
fuels matches exactly with the reverse order of BSEC. From the correlation analysis, it was found
that the brake thermal efficiency decreases with an increase in percentage of unsaturation. This is
because the BSEC increases with an increase in percentage of unsaturation. The variation of brake
thermal efficiency with percentage of unsaturation is illustrated in Figure 25.14. From the fitted
line equation
y
= -0.026
x
+ 29.481, a decrease of 0.026 units (%) could be predicted for every
1% increase in unsaturation.
25.5 conclusIons
In this study, minor seed oils such as mahua, karanja, neem, rubber seed, and linseed oil methyl
esters were prepared and studied in a four-stroke, direct injection diesel engine. The availability of
these seeds in India is discussed. Also, the effect of biodiesel fatty ester composition on biodiesel is
studied. In addition, the effect of biodiesel composition and properties on combustion parameters
is studied. The gradient between biodiesel properties, combustion parameters, and percentage of
unsaturation are proposed. It was found that the biodiesel properties that include density and IV are
increased with an increase in biodiesel unsaturation, whereas CN and heating value are decreased
with an increase in unsaturation percentage. The investigation reveals that the dynamic injection
timing advances with increase in unsaturation. The ignition delay increases with an increase in
unsaturation whereas the magnitude of the peak heat release rate and the peak pressure decreased
