Methanol
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longer than those of diesel fuel but had the same tendency as diesel fuel
(i.e., they decreased with increasing compression ratio). An increase in
delay period was obtained with increasing methanol amount in the fuel
mixture. However the difference between the delay times of the blend
fuels diminished for the compression ratios 16 and 14.8. They explained
this result by the lower temperature during the ignition period as a
result of the cooling effect of vaporized methanol. At the low compression ratios where the compression temperature is already low, this cooling effect becomes dominant. Although relatively higher pressures are
expected for the fuel blends due to the longer ignition delay periods, they
found that there was no significant difference between the peak pressures
of fuel types. This was attributed to the lower energy content of methanol
used in the fuel blends.
Canakci, Sayin, and Gumus (2008) also investigated combustion and heat
release characteristics of a single-cylinder diesel engine under different
injection timings when methanol-blended diesel fuel was used. The following part summarizes the combustion and heat release characteristics results
obtained in that study. The measured starts of combustion and ignition delay
for each fuel blend are shown in Table 4.3.
Figures 4.16 and 4.17 show the cylinder gas pressure, and Figures 4.19 and
4.20 demonstrate the rate of heat release (ROHR) for different fuel blends and
ORG injection timing at 20 and 10 Nm loads, respectively. Figures 4.18 and
4.21 illustrate the cylinder gas pressure and ROHR for M0 and M15 at different injection timing and 20 Nm load, respectively.
4.7.3.1 Peak Cylinder Gas Pressure
Figure 4.16 shows the cylinder gas pressure with respect to the crank angle
at 20 Nm load and ORG injection timing. As seen in the figure, peak cylinder gas pressure slightly decreased with the increase of the methanol
supplement rate. The researchers showed that the peak cylinder pressure
occurred at 7.96 MPa (at 3.20° CA ATDC), 7.86 MPa (at 3.28° CA ATDC),
7.78 MPa (at 3.32° CA ATDC), and 7.77 MPa (at 3.44° CA ATDC) for M0, M5,
M10, and M15 at 20 Nm load and ORG injection timing, respectively. They
claim that lowering the cetane number by methanol addition was responsible for the increase in the ignition delay. The increase in the ignition delay
would burn more fuel in the premixed burning phase. Because of this, the
rate of pressure rise increased and peak cylinder gas pressure diminished
(Heywood 1984).
When Figure 4.16 is compared to Figure 4.17, it is seen that the cylinder
gas pressure increased with an increasing engine load. Experimental results
showed that the increase in the cylinder pressure was approximately 5.5%
for M10 when the engine load increased from 10 to 20 Nm. The fuel consumption per unit time was measured between 0.42 g/s and 0.81 g/s at these
115
longer than those of diesel fuel but had the same tendency as diesel fuel
(i.e., they decreased with increasing compression ratio). An increase in
delay period was obtained with increasing methanol amount in the fuel
mixture. However the difference between the delay times of the blend
fuels diminished for the compression ratios 16 and 14.8. They explained
this result by the lower temperature during the ignition period as a
result of the cooling effect of vaporized methanol. At the low compression ratios where the compression temperature is already low, this cooling effect becomes dominant. Although relatively higher pressures are
expected for the fuel blends due to the longer ignition delay periods, they
found that there was no significant difference between the peak pressures
of fuel types. This was attributed to the lower energy content of methanol
used in the fuel blends.
Canakci, Sayin, and Gumus (2008) also investigated combustion and heat
release characteristics of a single-cylinder diesel engine under different
injection timings when methanol-blended diesel fuel was used. The following part summarizes the combustion and heat release characteristics results
obtained in that study. The measured starts of combustion and ignition delay
for each fuel blend are shown in Table 4.3.
Figures 4.16 and 4.17 show the cylinder gas pressure, and Figures 4.19 and
4.20 demonstrate the rate of heat release (ROHR) for different fuel blends and
ORG injection timing at 20 and 10 Nm loads, respectively. Figures 4.18 and
4.21 illustrate the cylinder gas pressure and ROHR for M0 and M15 at different injection timing and 20 Nm load, respectively.
4.7.3.1 Peak Cylinder Gas Pressure
Figure 4.16 shows the cylinder gas pressure with respect to the crank angle
at 20 Nm load and ORG injection timing. As seen in the figure, peak cylinder gas pressure slightly decreased with the increase of the methanol
supplement rate. The researchers showed that the peak cylinder pressure
occurred at 7.96 MPa (at 3.20° CA ATDC), 7.86 MPa (at 3.28° CA ATDC),
7.78 MPa (at 3.32° CA ATDC), and 7.77 MPa (at 3.44° CA ATDC) for M0, M5,
M10, and M15 at 20 Nm load and ORG injection timing, respectively. They
claim that lowering the cetane number by methanol addition was responsible for the increase in the ignition delay. The increase in the ignition delay
would burn more fuel in the premixed burning phase. Because of this, the
rate of pressure rise increased and peak cylinder gas pressure diminished
(Heywood 1984).
When Figure 4.16 is compared to Figure 4.17, it is seen that the cylinder
gas pressure increased with an increasing engine load. Experimental results
showed that the increase in the cylinder pressure was approximately 5.5%
for M10 when the engine load increased from 10 to 20 Nm. The fuel consumption per unit time was measured between 0.42 g/s and 0.81 g/s at these