108
Alternative Fuels for Transportation
When the engine load increases, the combustion temperature increases and
CO emissions start to decrease (Abdel-Rahman 1998).
For example, in comparison to Figures 4.13b and 4.14b, it was seen that
the percentage change in CO emissions diminished by around 21% for M5
as the engine load increased from 10 to 15 Nm constant loads at ORG injection timing. Figure 4.13a through c illustrates the percentage change in CO
emissions with different methanol blends at different injection timings for
10 Nm load. From these figures, it was concluded that advanced injection
timing decreased the CO emission by 8% and retarded injection timing
increased the CO emission by 7% compared to ORG injection timing for M10,
respectively. The advanced injection timing produced the higher cylinder
temperature and increasing oxidation process between carbon and oxygen
molecules. These lead to a decrease in the percentage change in CO emissions (Gumus 2008).
4.7.2.2 Unburned Hydrocarbon (UHC) Emissions
The UHC emissions consist of fuel that is incompletely burned. Most of the
UHC is caused by an unburned fuel–air mixture, whereas the other source
is the engine lubricant and incomplete combustion. The term UHC means
organic compounds in the gaseous state; solid HCs are the part of the PM.
Typically, HCs are a serious problem at low loads in CI engines. At low loads,
the fuel is less apt to impinge on surfaces; but, because of poor fuel distribution, large amounts of excess air and low exhaust temperature, lean fuel–air
mixture regions may survive to escape into the exhaust (Canakci 1996; Sayin
et al. 2007).
With regard to the effect of different methanol contents on UHC emission, it was found that increasing the methanol ratio in the fuel-blend
reduced UHC emissions. For instance, the UHC emissions compared to M0
at ORG injection timing decreased by 14%, 24%, and 40% for M5, M10, and
M15, respectively, at 10 Nm load and retarded injection timing, as seen in
Figure 4.13c. When methanol was added to the diesel fuel, it provided more
oxygen for the combustion process and led to the improving combustion.
In addition, methanol molecules are polar and cannot be absorbed easily
by the nonpolar lubrication oil, and therefore, methanol can lower the possibility of the production of UHC emissions (Alla et al. 2002). UHC emissions lessened reasonably with increasing load, which was the same trend
as with CO. For example, in comparison of Figures 4.13a through 4.15a, it
was observed that the change in UHC emissions diminished by 7% for M10
as the engine load increased from 10 to 20 Nm constant loads at advanced
injection timing. Figures 4.15a through c shows the change in UHC emissions with different methanol blends at different injection timings for 20 Nm
load compared to M0. From these figures, it was found that advanced injection timing caused a reduction in UHC emission by 9% and retarded injection timing boosted the UHC emission by 3% compared to ORG timing for
Alternative Fuels for Transportation
When the engine load increases, the combustion temperature increases and
CO emissions start to decrease (Abdel-Rahman 1998).
For example, in comparison to Figures 4.13b and 4.14b, it was seen that
the percentage change in CO emissions diminished by around 21% for M5
as the engine load increased from 10 to 15 Nm constant loads at ORG injection timing. Figure 4.13a through c illustrates the percentage change in CO
emissions with different methanol blends at different injection timings for
10 Nm load. From these figures, it was concluded that advanced injection
timing decreased the CO emission by 8% and retarded injection timing
increased the CO emission by 7% compared to ORG injection timing for M10,
respectively. The advanced injection timing produced the higher cylinder
temperature and increasing oxidation process between carbon and oxygen
molecules. These lead to a decrease in the percentage change in CO emissions (Gumus 2008).
4.7.2.2 Unburned Hydrocarbon (UHC) Emissions
The UHC emissions consist of fuel that is incompletely burned. Most of the
UHC is caused by an unburned fuel–air mixture, whereas the other source
is the engine lubricant and incomplete combustion. The term UHC means
organic compounds in the gaseous state; solid HCs are the part of the PM.
Typically, HCs are a serious problem at low loads in CI engines. At low loads,
the fuel is less apt to impinge on surfaces; but, because of poor fuel distribution, large amounts of excess air and low exhaust temperature, lean fuel–air
mixture regions may survive to escape into the exhaust (Canakci 1996; Sayin
et al. 2007).
With regard to the effect of different methanol contents on UHC emission, it was found that increasing the methanol ratio in the fuel-blend
reduced UHC emissions. For instance, the UHC emissions compared to M0
at ORG injection timing decreased by 14%, 24%, and 40% for M5, M10, and
M15, respectively, at 10 Nm load and retarded injection timing, as seen in
Figure 4.13c. When methanol was added to the diesel fuel, it provided more
oxygen for the combustion process and led to the improving combustion.
In addition, methanol molecules are polar and cannot be absorbed easily
by the nonpolar lubrication oil, and therefore, methanol can lower the possibility of the production of UHC emissions (Alla et al. 2002). UHC emissions lessened reasonably with increasing load, which was the same trend
as with CO. For example, in comparison of Figures 4.13a through 4.15a, it
was observed that the change in UHC emissions diminished by 7% for M10
as the engine load increased from 10 to 20 Nm constant loads at advanced
injection timing. Figures 4.15a through c shows the change in UHC emissions with different methanol blends at different injection timings for 20 Nm
load compared to M0. From these figures, it was found that advanced injection timing caused a reduction in UHC emission by 9% and retarded injection timing boosted the UHC emission by 3% compared to ORG timing for