Estimation of Optimum Blend Ratios of Biodiesel for Diesel Engine
4.3 Results and Discussion
4.3.1 Analysis of Biodiesel-Diesel Blend Properties
In this study, POME/COME biodiesel diesel blends (vol. 10%−vol. 90%) along neat mineral diesel fuel (BD0) and neat biodiesel (BD100) were prepared and presented in Figure 4.3 to Figure 4.8.
The results are presented and disused in the following sections.
4.3.1.1 Effect of Blending on Cloud Point and Pour Point
The pour point is the lowest temperature used to characterize cold flow properties and the cloud point is the highest one. Figure 4.3 demonstrates the variations of the cloud point and pour point with the volumetric percentage of the COME and POME diesel blended fuel, respectively. It indicates that, biodiesel blends have higher cloud point and pour points than diesel fuel and this is one of the most critical obstacles against the wide- spread of biodiesel usage (Demirbas, 2008;
Morad et al., 2006). The fatty acid composition of biodiesel greatly influences the cloud point and pour point. Furthermore, the temperature gap between the cloud point and pour point is very narrow for COME due to the lack of chemical diversity in biodiesel fuels (Chiu et al., 2004). It is evident from these data that cloud point and pour point of the blends decrease with the increase quantity of diesel in the blend due to the synergistic interaction between fatty acid methyl ester and diesel molecules that affect the orientation of the molecular arrangement during crystallization
(Lim et al., 2009). The higher cloud point and pour point was found for CBD100 (14 and 12°C) and PBD100 (11 and 8°C). However, the blended fuels ratio 30% or less of cloud point and pour point was less than of the blended fuel standard requirements BIS (3 max for winter) at biodiesel blending ratios ( ≤ CBD30 and ≤PBD30). Thus, cloud point and pour point for biodiesel diesel blends (CBD10, CBD20, CBD30, and PB10, PBD20, PBD30) are suitable to be used and closer within the recommended specified limits for biodiesel diesel blending standards.
4.3.1.2 Effect of Blending on Flash Point and Fire Point
Flashpoint is the minimum temperature at which the vapor is given off by a fuel when heated will flash with a test flame held above the surface without the fuel catching fire. It plays a vital role when determining the fire hazard of the fuel. Figure 4.4 shows that the flash point and fire point of all biodiesel diesel blends are higher than diesel. The flash point and fire point increases on increasing the percentage of biodiesel in diesel, as shown in Table 4.4. It is observed that the increasing quantity of COME and POME biodiesel oil in the diesel-biodiesel blends, due to the higher value of flash point of biodiesel oil, flash point of the blend, is found to rise. It is seen in Figure 4.4 that, CBD10 and PBD10 have lowest flashpoint (67 and 64 °C) and fire point (78 and 72 °C). In contrast, CBD100 and PBD100 have highest flashpoint (168 and 155 °C) and fire point of (272 and 265 °C) which is relatively higher than the ASTMD7467 and BIS specified minimum of 52°C and 35°C, respectively. This shows that the main advantage of biodiesel diesel blends makes it possible to store and safer to handle for transportation sector. Therefore, the results of all biodiesel blends are considered to be safe to store for use in the engine (Agarwal and Das, 2001).
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Figure 4.3: Blending effect on cloud and pour point: (a) COME-diesel blends (b) POME-diesel blends.
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Figure 4.4: Blending effect on flash and fire point: (a) COME-diesel blends (b) POME-diesel blends.
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Figure 4.5: Blending effect on density: (a) COME-diesel blends (b) POME-diesel blends.
4.3.1.3 Effect of Blending on Density
The fuel density is an important parameter for various aspects of diesel engine performance, as the high biodiesel fuel density can influence the engine power output due to the difference in fuel injected mass, where the fuel is measured by volume in a fuel injection system (Alptekin and Canakci, 2009). The lower value of the density is desirable to obtain the maximum engine power through the fuel flow control in the injection pump. The density of a fuel influences its fuel consumption. Thus, it is preferred to have a less denser fuel whose consumption would be less.
From the test results it is found that the density of the CBD100 and PBD100 are the highest 943 kg/m3 and 946 kg/m3 as shown in Figure 4.5. It is clearly shown that the rising of biodiesel content in the fuel blend will increase the density of the fuel. The density recorded for diesel is 838 kg/m3. It is obvious that the rise of the biodiesel content in the blended mixture increases the density of the blended fuel (Figure 4.5 and Table 4.4). It is seen that, the ratio blending up to 30% of COME and POME biodiesel diesel blending (CBD10, CBD20, CBD30) and (PBD10, PBD20, PBD30) were very close to diesel. There is no significant difference among the density of the blends with up to 30% of methyl esters. The maximum difference is about (0.24−2.27 %) and (0.48−2.86 %) for the density of biodiesel diesel blends, respectively. This result matches with (Alptekin and Canakci, 2009), which reported that the ratio blending up to 20% of biodiesel diesel blending.
However, the blended fuel density is out of the blended fuel standard requirements ASTM D7467 (820–860 kg/m3) and BIS (820−860 kg/m3) at biodiesel blending ratio more than 40% (BD40).
Thus, density for all biodiesel diesel blends must be closer within the recommended specified limits for biodiesel diesel blending standards.
4.3.1.4 Effect of Blending on Kinematic Viscosity
A viscous fuel has poor atomization characteristics and narrow spray angle, one with poor viscosity, leads to excessive wear and poor lubrication (Sarin, 2012). Thus, it is desired for a fuel to possess optimum value of kinematic viscosity. Figure 4.6 shows viscosity of the fuel samples measured using Red wood viscometer in Chemical Laboratory. The diesel fuel is less viscous than biodiesel, it clearly shows that the viscosity of CBD100 and PBD100 are 6.78 and 2.69 times higher than the mineral diesel, respectively. This because the free fatty acid (FFA) concentration in biodiesel. As a result, biodiesel diesel blends of all fuels have higher kinematic viscosities as the percentage of biodiesel was increase (Table 4.4and Figure 4.6). This result was in agreement with Benjemea et al. (Benjumea et al., 2008; Tat and Van Gerpen, 1999). The viscosity of mineral diesel is recorded as the lowest number at 3.23 mm2/s. The behavior at each blend level among the CBD10, CBD20, CBD30, CBD40, CBD50, CBD60, CBD70, CBD80, CBD90, and CBD100 blends did not vary significantly with regard to viscosity. The viscosity of CBD10 is recorded as the lowest number at 4.01 mm2/s and 5.18 mm2/s which greater than the mineral diesel viscosity but still meet the ASTM D7467 requirement, while, CBD20 is recorded as 5.18 mm2/s and close to BIS standard requirement. However, the behavior of each blend level of palm biodiesel-diesel blends (PBD10− PBD100) vary significantly with regard to viscosity. The viscosity of PBD10, PBD20 are recorded as the lowest number at 3.51 mm2/s and 3.98 mm2/s which greater than the mineral diesel viscosity but still meet the ASTM D7467 requirement, and PBD30 is recorded as 4.58 mm2/s that meets the BIS standard requirement. Thus PBD10, PBD20, PBD30 blends exhibited kinematic viscosities that were satisfactory according to diesel biodiesel blend (ASTMD7467) and BIS standards. Therefore, it can be noticed that CBD10, PBD10, PBD20 and PBD30 can be used in the diesel engine without any modifications.
4.3.1.5 Effect of Blending on Calorific Value
Calorific value is the amount of heating energy released by the combustion of a unit value of fuels.
One of the most important determinants of the heating value is the moisture content of the feedstock oil (Cecrle et al., 2012). The heating value is not specified in the biodiesel standards ASTM D6751 but is prescribed in EN 14213 with a minimum value of 35 MJ/kg (Rashid et al., 2009). Figure 4.7 presents the calorific value of the fuels measured by Bomb Calorimeter. It decreases as the amount of biodiesel increases in the blends. This is mainly due to the higher oxygen content of biodiesel than that of diesel. Thus hydrogen and carbon contents in the blend decrease which is the source of thermal energy (Rao, 2011). It is shown in Table 4.4 that, the calorific value of ranges from 38.412 MJ/kg (CBD100) to 44.874MJ/kg (CBD10) for COME biodiesel diesel blend, and from 39.794 MJ/kg (PBD100) to 44.982 MJ/kg (PBD10) for POME biodiesel diesel blends which are slightly lower than diesel (44.69 MJ/kg). The calorific value does not indicate in the ASTM D7467 standard; all fuel samples meet the EN14213 requirement for the calorific value (minimum 35 MJ/kg). Hence, lower blends of biodiesels (CBD10−CBD40), and (PBD10−PBD40) have higher calorific value than other blending. The heating value for COME biodiesel/diesel blends is approximately by (1.13−14.05%), and POME biodiesel/diesel blends by (1.03−10.95%) lower than the heating value of mineral diesel (44.69 MJ/kg), respectively.
4.3.1.6 Effect of Blending on Cetane Number
The Cetane number of the biodiesel is significantly high when compared to mineral diesel. Figure 4.8 illustrates different Cetane number of the tested blends of fuels. It can be seen from the figure that the diesel fuel has the lowest Cetane number at 51°C while the blends of biodiesel CBD100 and PBD100 have the highest at 52.83°C and 60.84°C , respectively. The Cetane number is found to be increased when the percentage of biodiesel blend increase (Figure 4.8). This is because the Cetane number of biodiesel depends on the distribution of fatty acids in the original oil or fat. The longer the fatty acid carbon dioxide (CO2) chains and the more saturated the molecules, the higher the Cetane number. The Cetane number all fuel samples meet the in the ASTM D7467 standard (min. 40) and the BIS requirement (minimum 51).
4.3.1.7 Effect of Chemical Bonds of Fuel on its Properties
The percentage of unsaturation in biodiesel is in reference to the fuel properties, engine combustion. The degree of unsaturation of an alkyl ester molecule is an indicator of the average number of double bonds present in its fatty acid chain, with a higher number of double bonds representing a higher degree of unsaturation. There exists a strong correlation between the degree of unsaturation and the properties of alkyl esters. The unsaturation in biodiesel affect the fuel properties. Increasing percentage of degree of unsaturation decreases the kinematic viscosity, improves the cold flow properties and increases moderately the heating value, increases density but also lowers the cetane number. The density of the test fuels increased with the degree of unsaturation. The density of biodiesel fuels increases with increase in percentage of unsaturation.
An increase in density could be expected for every single percentage increase in unsaturation. The density increases with the increase in the number of double bonds, which means that themore unsaturated the originating oil, the higher the density of the derived methyl ester, and the greater the fuel mass that will be injected if a diesel-tuned engine is run on biodiesel. The density of biodiesel purely depends on the free space between the molecules, which in turn depends on the number of double bonds in the structure. Whereas, kinematic viscosity of biodiesel fuels decreases with increase in degree of unsaturation, due to the existence of double bonds reduces viscosity. It purely depends on the raw material and distribution of fatty acid ester composition. The cetane number of biodiesel fuels increases with chain length and decreases with increase in degree of unsaturation. Thus, each percentage increase in unsaturation could reduce in cetane number, which represents the ignitability of the fuel. Therefore, an increasing the percentage of unsaturation of biodiesel did not significantly affect oxygen content, heating value, and viscosity of biodiesel, which means it has insignificant effect of fuel atomization, but it may have a noticeable influence on combustion characteristics, via its effect on the cetane number. Since a higher degree of unsaturation of biodiesel fuels led to a longer ignition delay and, consequently, a more retarded start of combustion. This may also have attributed to the density variation of biodiesel due to the presence of double bonds. Ignition delay increases with increase in percentage of unsaturation and density. An increase in ignition delay may be predicted for an increase in each percentage of unsaturation.
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Figure 4.6: Blending effect on kinematic viscosity: (a) COME-diesel blends (b) POME-diesel blends.
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Figure 4.7: Blending effect on calorific value: (a) COME-diesel blends (b) POME-diesel blends.
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Figure 4.8: Blending effect on cetane number: (a) COME-diesel blends (b) POME-diesel blends.