120
Alternative Fuels for Transportation
diesel fuel, which reduces ROHR. It is apparent from the figure that the LHV
of methanol was more significant than the heat of vaporization with regard
to ROHR (Ghojel and Honnery 2005).
Figures 4.19 and 4.20 show the ROHR for different fuel blends and ORG injection timing at 20 and 10 Nm loads, respectively. As seen in these figures, ROHR
increased with the rise in the engine load because of the increase in the quantity of fuel injected. Figure 4.21 demonstrates a comparison of the changes in
the cylinder gas pressures with respect to the crank angle obtained for M0 and
M15 at different injection timings and 20 Nm load. The ignition delay in a diesel
engine is defined as the time between the start of fuel injection and the start of
combustion. As seen in Table 4.3, the ignition delay was raised with advanced
injection timing for M0 and M15 because the fuel was injected earlier into the
combustion chamber. This led to greater accumulation of the fuel in the ignition delay period and an increasing premixed heat release. This is the reason
of increasing ROHR. Retarding injection timing led to a lower accumulation
of fuel and poor combustion. However, both physical and chemical reactions
must take place before a significant fraction of chemical energy in the fuel is
released. These reactions need a finite time to occur. However, as ignition delay
proceeds, the in-cylinder pressures and temperatures decrease and reduce the
favorable conditions for ignition. The most favorable timing for ignition lies
between these two conditions (Kumar, Ramesh, and Nagalinman 2003).
Fuel injection pressure is a significant operating parameter affecting
the performance and combustion characteristics in CI engine. When fuel
injection pressure is low, fuel particle diameters will enlarge and ignition
delay period during the combustion will increase. CO, UHC, and NO x emissions can increase since the combustion process goes to a bad condition.
When injection pressure is increased, fuel particle diameters will become
small. Since formation of mixing of fuel to air becomes better during the
ignition period, smoke level, and CO emissions can be less. But, if injection
pressure is too high, the ignition delay period becomes shorter. So, possibilities of the homogeneous mixing decrease. Therefore, smoke can be seen at
the exhaust of the engine. See Canakci et al. (2009), for further information
related the effect of injection pressure on the emission and combustion characteristics of a CI engine using methanol-blended diesel fuel.
4.8 Methanol Benefits and Challenges
Methanol is one of the most promising sources of hydrogen for fuel cell systems and synthetic fuel in the future with the advantages of high energy density, easy availability, and safe storage. The using of methanol is in the point of
view of its power and other characteristics similar to those using gasoline or
diesel. Methanol has some advantages and disadvantages in comparison with
Alternative Fuels for Transportation
diesel fuel, which reduces ROHR. It is apparent from the figure that the LHV
of methanol was more significant than the heat of vaporization with regard
to ROHR (Ghojel and Honnery 2005).
Figures 4.19 and 4.20 show the ROHR for different fuel blends and ORG injection timing at 20 and 10 Nm loads, respectively. As seen in these figures, ROHR
increased with the rise in the engine load because of the increase in the quantity of fuel injected. Figure 4.21 demonstrates a comparison of the changes in
the cylinder gas pressures with respect to the crank angle obtained for M0 and
M15 at different injection timings and 20 Nm load. The ignition delay in a diesel
engine is defined as the time between the start of fuel injection and the start of
combustion. As seen in Table 4.3, the ignition delay was raised with advanced
injection timing for M0 and M15 because the fuel was injected earlier into the
combustion chamber. This led to greater accumulation of the fuel in the ignition delay period and an increasing premixed heat release. This is the reason
of increasing ROHR. Retarding injection timing led to a lower accumulation
of fuel and poor combustion. However, both physical and chemical reactions
must take place before a significant fraction of chemical energy in the fuel is
released. These reactions need a finite time to occur. However, as ignition delay
proceeds, the in-cylinder pressures and temperatures decrease and reduce the
favorable conditions for ignition. The most favorable timing for ignition lies
between these two conditions (Kumar, Ramesh, and Nagalinman 2003).
Fuel injection pressure is a significant operating parameter affecting
the performance and combustion characteristics in CI engine. When fuel
injection pressure is low, fuel particle diameters will enlarge and ignition
delay period during the combustion will increase. CO, UHC, and NO x emissions can increase since the combustion process goes to a bad condition.
When injection pressure is increased, fuel particle diameters will become
small. Since formation of mixing of fuel to air becomes better during the
ignition period, smoke level, and CO emissions can be less. But, if injection
pressure is too high, the ignition delay period becomes shorter. So, possibilities of the homogeneous mixing decrease. Therefore, smoke can be seen at
the exhaust of the engine. See Canakci et al. (2009), for further information
related the effect of injection pressure on the emission and combustion characteristics of a CI engine using methanol-blended diesel fuel.
4.8 Methanol Benefits and Challenges
Methanol is one of the most promising sources of hydrogen for fuel cell systems and synthetic fuel in the future with the advantages of high energy density, easy availability, and safe storage. The using of methanol is in the point of
view of its power and other characteristics similar to those using gasoline or
diesel. Methanol has some advantages and disadvantages in comparison with