112
Alternative Fuels for Transportation
M15, respectively. Advancing the injection timing caused an earlier start of
combustion relative to the TDC. Because of this, the cylinder charge, being
compressed as the piston moved to the TDC, had relatively higher temperatures and thus lowered the UHC emissions (Ajav, Singh, and Bhattacharya
1998; Pukrakek 1997).
4.7.2.3 Nitrogen Oxides (NO x ) Emissions
The most troublesome emissions from CI engines are NO x emissions. The
oxides of nitrogen in the exhaust emissions contain nitric oxide (NO) and
nitrogen dioxides (NO 2 ). The formation of NO x is highly dependent on incylinder temperatures, the oxygen concentration and residence time for
the reaction to take place. In a diesel engine, the fuel distribution is nonuniform. The pollutant formation process is strongly dependent upon the
changes in the fuel with time because of mixing. The oxides of nitrogen form
in the high-temperature burned region, which is nonuniform, and the formation rates are highest in the regions closest to the stoichiometric region
(Agarwal 2007).
Canakci, Sayin, and Gumus (2008) found that increasing the methanol ratio
in the blend raised NO x emissions. For example, as presented in Figure 4.14b,
the change in NO x emissions was compared to M0 and showed that NO x
augmented by 14%, 35%, and 49% for M5, M10, and M15, correspondingly,
at 15 Nm load and ORG injection timing. Methanol contains 34% oxygen,
and its cetane number is lower than diesel fuel, which boost peak temperature in the cylinder. On the other hand, the LHV of methanol is nearly two
times lower than diesel fuel and latent heat of vaporization of methanol is
about four times greater than diesel fuel, which decreases peak temperature
in the cylinder. However, as shown in Figure 4.11, the exhaust temperature
increased with an increasing methanol ratio in the fuel mixture. It is clear
from the figure that the cetane number and oxygen content are more effective than LHV and latent heat of vaporization with regard to increasing peak
temperature in the cylinder. Therefore, the concentration of NO x increased
as the methanol content was increased in the fuel blend (Nwafor, Rice, and
Ogbonna 2000).
Unlike CO and UHC emissions, NO x emissions increased with an increasing engine load. For example, in comparison to Figures 4.13c and 4.14c, it
was detected that NO x emissions increased by around 6% for M5 as the
engine load augments from 10 to 15 Nm constant loads at the retarded injection timing. Figure 4.14a through c demonstrates the percentage change in
NO x emissions with different methanol blends at different injection timings
for 15 Nm load. As shown in the figures for M15, retarded injection timing
reduced in NO x emission by 10% and advanced injection timing increased
in NO x emission by 6% compared to ORG injection timing, correspondingly.
When the injection timing was retarded, it was observed that NO x emissions
decreased for all fuel mixtures. Retarding the injection timing decreased the
Alternative Fuels for Transportation
M15, respectively. Advancing the injection timing caused an earlier start of
combustion relative to the TDC. Because of this, the cylinder charge, being
compressed as the piston moved to the TDC, had relatively higher temperatures and thus lowered the UHC emissions (Ajav, Singh, and Bhattacharya
1998; Pukrakek 1997).
4.7.2.3 Nitrogen Oxides (NO x ) Emissions
The most troublesome emissions from CI engines are NO x emissions. The
oxides of nitrogen in the exhaust emissions contain nitric oxide (NO) and
nitrogen dioxides (NO 2 ). The formation of NO x is highly dependent on incylinder temperatures, the oxygen concentration and residence time for
the reaction to take place. In a diesel engine, the fuel distribution is nonuniform. The pollutant formation process is strongly dependent upon the
changes in the fuel with time because of mixing. The oxides of nitrogen form
in the high-temperature burned region, which is nonuniform, and the formation rates are highest in the regions closest to the stoichiometric region
(Agarwal 2007).
Canakci, Sayin, and Gumus (2008) found that increasing the methanol ratio
in the blend raised NO x emissions. For example, as presented in Figure 4.14b,
the change in NO x emissions was compared to M0 and showed that NO x
augmented by 14%, 35%, and 49% for M5, M10, and M15, correspondingly,
at 15 Nm load and ORG injection timing. Methanol contains 34% oxygen,
and its cetane number is lower than diesel fuel, which boost peak temperature in the cylinder. On the other hand, the LHV of methanol is nearly two
times lower than diesel fuel and latent heat of vaporization of methanol is
about four times greater than diesel fuel, which decreases peak temperature
in the cylinder. However, as shown in Figure 4.11, the exhaust temperature
increased with an increasing methanol ratio in the fuel mixture. It is clear
from the figure that the cetane number and oxygen content are more effective than LHV and latent heat of vaporization with regard to increasing peak
temperature in the cylinder. Therefore, the concentration of NO x increased
as the methanol content was increased in the fuel blend (Nwafor, Rice, and
Ogbonna 2000).
Unlike CO and UHC emissions, NO x emissions increased with an increasing engine load. For example, in comparison to Figures 4.13c and 4.14c, it
was detected that NO x emissions increased by around 6% for M5 as the
engine load augments from 10 to 15 Nm constant loads at the retarded injection timing. Figure 4.14a through c demonstrates the percentage change in
NO x emissions with different methanol blends at different injection timings
for 15 Nm load. As shown in the figures for M15, retarded injection timing
reduced in NO x emission by 10% and advanced injection timing increased
in NO x emission by 6% compared to ORG injection timing, correspondingly.
When the injection timing was retarded, it was observed that NO x emissions
decreased for all fuel mixtures. Retarding the injection timing decreased the