Page 431 - Advances in Eco-Fuels for a Sustainable Environment

384 Advances in Eco-Fuels for a Sustainable Environment

The CGPP has maximum at advanced FIT and higher NOP due to it providing more
time for air-fuel mixture and improving the spray characteristics of fuel resulted in
more premixed combustion. Among all other blends, biodiesel has the lowest CGPP.
This was because biodiesel has a lower heating value and a higher cetane number,
which improved the evaporation rate and decreased the ignition delay period. As a
result, CGPP was reduced due to a lesser amount of biodiesel fuel burned at the pre-
mixed combustion.
Fig. 13.13 depicts the ignition delay period (ID) of the biodiesel-diesel-alcohol
blend with different NOP and FIT. The period between start of injection and start of
combustion is called the ignition delay period, which consists of physical and chem-
ical delays. The physical delay period depends on the density and viscosity of the
fuel but the chemical delay period is related to the temperature and pressure of
the combustion chamber and it also depends on swirl ratio and fuel properties.
Fig. 13.13 shows that the biodiesel-diesel-alcohol blends have a higher ID period
as compared to diesel and biodiesel fuel. This was due to high latent heat of vapor-
ization and lower cetane number of alcohol blends. B100 has a lower auto ignition
temperature and a higher cetane number, as noticed by Atadashi et al. [50].
Fig. 13.13 shows that an increase in NOP decreased the ID and advances in FIT
increased the ID period. This was because of better atomization that improved
the evaporation rate of fuel, which resulted in the lower ignition delay period.
The B85-D5-H10 blend obtained the minimum delay period of 11°CA at NOP of
600bar and FIT of 19° bTDC. The B85-D5-P10 blend has a maximum delay period
of 18°CA at NOP of 200bar and FIT of 27°CA. Diesel has the maximum ignition
delay period of 19°CA at NOP of 200bar and FIT of 27°CA. The ignition delay
period is decreased when the NOP increases due to better atomization reducing
the droplet size of the fuel and improving the evaporation rate of tested fuels, as
observed by Sayin et al. [33]. The cylinder inside pressure and temperature is
low at advanced FIT. Therefore, fuel could take more time for vaporization,
resulting in higher ignition delay period.
Fig. 13.14 shows the heat release rate (HRR) of biodiesel-diesel-alcohol blend at
100% load condition. In Fig. 13.14, the negative slope was identified for all tested
fuels due to fuel vaporization caused by the cooling effect, followed by two positive
curves that appeared such as premixed combustion zone and controlled combustion
zone. Fig. 13.14 shows that the HRR is increased with an increase in biodiesel-diesel-
alcohol blends at advanced FIT and higher NOP. The maximum HRR of 46.89J/°CA
was obtained in diesel fuel at FIT of 27°CA and NOP of 500bar. B100 fuel has min-
imum HRR when compared to other tested fuels irrespective of FIT and NOP. This
was due to higher viscosity, higher molecular weight, and lower burning velocity of
biodiesel, resulting in the lowest HRR of biodiesel. The HRR of 44.85, 39.27, and
42.50J/°CA was obtained for B90-D5-H5, B85-D5-P10, and B90-D5-P5 blends at
NOP of 500bar and FIT of 27°CA bTDC. The biodiesel-diesel-alcohol blends
achieved maximum HRR as compared to biodiesel at advanced FIT and higher
NOP. This was due to more ignition delay period, which improved the evaporation
rate of fuel and air-fuel mixing process and resulted in complete combustion and
higher heat release rate [51].