Page 424 - Advances in Eco-Fuels for a Sustainable Environment

Engine modification for alternative fuels usage in diesel engine 377

the maximum BTE of 36.79% at 500bar and 25°CA bTDC. The maximum BTE was
obtained at higher NOP and advanced FIT. This was due to better atomization, and
more ignition delay period improved the air-fuel mixture rate that led to complete
combustion resulting in higher brake thermal efficiency. From Fig. 13.7, it can be seen
that the BTE was slightly decreased with an increase in alcohol content in biodiesel
blends due to a lower cetane number and calorific value [44, 45]. B100 has the min-
imum BTE when compared to all tested fuels, irrespective of FIT and NOP, such as
24.1% at 200bar and 19°CA bTDC and 32.54% at 600bar and 19°CA bTDC, respec-
tively. B100 has the minimum BTE and maximum BSFC as compared to other tested
fuels irrespective of NOP and FIT. This was because lower calorific value fuels
required more fuel to provide the same power output. The minimum BTE of
24.78% was obtained for B85-D5-P10 fuel at NOP of 200bar and FIT of 19° bTDC.
The comparison of carbon monoxide (CO) emissions of various biodiesel-diesel-
alcohol blends at 100% load condition is depicted in Fig. 13.8. From Fig. 13.8, it was
noticed that the higher NOP and advanced FIT decreased the CO emission for all
tested biodiesel-diesel-alcohol blends. The CO emission is significantly decreased
for biodiesel-diesel-alcohol blends when related to diesel due to the oxygen presence
in biodiesel-diesel-alcohol blends, which enhanced the combustion efficiency and
resulted in lower CO emissions. By increasing the higher alcohol proposition in
biodiesel-diesel blends, the CO emission is increased due to poor in-cylinder charge
mixing, higher viscosity, and low combustion temperature, leading to incomplete
combustion. The minimum CO emission of 0.07, 0.06, 0.04, and 0.04% vol. was
obtained in diesel, B100, B90-D5-P10, B90-D5-H10 blend at NOP of 500bar and
FIT of 27°CA bTDC, respectively. The maximum CO emission of 0.17 and 0.12%
vol. was obtained in diesel, biodiesel at 200bar and 19°CA bTDC, respectively.
The CO emission is increased at retarded injection timing rather than advanced fuel
injection timing irrespective of NOP due to less time availability for the fuel-air mix-
ture, which led to incomplete combustion and caused more CO emission. The
biodiesel-diesel-hexanol blend obtained the maximum CO emission when compared
to biodiesel-diesel-pentanol blends due to its higher viscosity, bulk modules, and
higher latent heat of evaporation [46, 47].
Fig. 13.9 represents the unburned hydrocarbon (UBHC) emission for biodiesel-
diesel-alcohol blends at various NOP and FIT at full load condition. From
Fig. 13.9, it is observed that an increase in NOP and advanced FIT reduced the UBHC
emission for tested fuels. This was because higher NOP improved the fuel spray char-
acteristics, which led to complete combustion and lower UBHC emission. In Fig. 13.9,
the UBHC emission is increased at retarded FIT. This was due to a lesser ignition
delay period, lower wall temperature, and poor air-fuel mixture. The minimum UBHC
emission of 14ppm was obtained in the B85-D5-P10 blend at NOP and FIT of 500bar
and 27°CA bTDC. The maximum UBHC emission of 31ppm was obtained in diesel at
NOP and FIT of 200bar and 19°CA bTDC. Among all the blends, B85-D5-P10 had
the lowest UBHC emission as compared to neat diesel, irrespective of FIT and NOP.
Fig. 13.10 depicts the nitric oxide (NO) emission with respect to different FIT and
NOP for biodiesel-diesel-alcohol blends. The NO emission is mainly because of oxy-
gen availability, residence time, and cylinder temperature. From Fig. 13.10, it noticed