**3. Results and discussion**

## **3.1. Sauter mean diameter**

Sauter Mean Diameter (SMD) is the diameter of a sphere that has the same volume/surface area ratio as a particle of interest or can be defined as the diameter of the droplet whose ratio of volume-to-surface area is equal to that of the spray as stated [30]. The most accurate method to determine SMD of fuels is through the acquisition of a device called Phase Doppler Particle Analyzer (PDPA) system [1]. Due to cost constraints, a SMD formula generated is adopted to study the SMD size, for this research purpose [24]. The chemical properties of the fuels, namely viscosity, surface tension and density will directly affect droplet size of fuels, where viscosity is regarded to have the largest contribution to change the SMD. The correlation for SMD is:

$$\text{SMD} = 6156 \,\psi\_m^{0.385} \gamma\_m^{0.737} \,\rho\_m^{0.737} \,\rho\_A^{0.06} \,\Delta P\_L^{-0.54} \tag{1}$$

Where;

**Name Type** Air fuel inlet Velocity-inlet

Co-flow air Velocity-inlet

Pressure outlet Pressure-outlet

Atomizer wall Wall

Symmetry a Wall

Symmetry b Wall

Outer wall Wall

Default interior Interior

**Table 2.** Name of the boundary condition and types

226 Advances in Internal Combustion Engines and Fuel Technologies

**Type**

**Table 3.** Setting for mesh

**Figure 9.** Domain of the spray

Fluid Fluid

**Volume Volume 1 Volume 2**

Tet/Hybrid Tet/Hybrid Tgrid Tgrid Interval size = 1 Interval size = 0.1 *νm* = mixture viscosity (m2 /s)

γm = surface tension (N/m)

*ρm* = fuel density (kg/m3 )

*ρA* = air density (1.145 kg/m3 )

∆PL = liquid fuel injection pressure difference. (2 bar)

**Figure 10.** Chart of Sauter Mean Diamater (SMD) for various fuel blends.

Based on the fuel sample prepared, the SMD was calculated for all sample fuel and tabulated results are shown in Figure 10. Pure biodiesel fuel, B100 has the largest SMD, followed by B80, B50, B20 and diesel. The SMD of B100 fuel is derived from WCO in this research and it agree with the SMD of biodiesel fuel derived from palm oil [7]. Sauter Mean Diameter (SMD) of biodiesel blends are much larger when compared to diesel because of the higher value of viscosity and surface tension of biodiesel [26]. The equation used to calculate SMD is used to give a comparable trend between different liquid fuels instead of accurate SMD values which can only be obtained by a complete PDPA system. The higher viscosity and density are responsible for the larger SMD of biodiesels, where the viscosity is regarded to have the largest contribution to the change in SMD it is proved [24]. High viscosity suppresses the instabilities required for the fuel jet to breakup and thus delays atomization. An increase in fuel density adversely affects atomization, whereas high surface tension opposes the formation of droplets from the liquid fuel as discussed [30]. Biodiesel fuel with a high viscosity has fewer droplets due to the breakup frequency, which is relatively low compared to that of diesel fuel [39]. In other words, with the same amount of injected fuel through the atomizer this will produce larger SMD if the amount of droplets is less. Despite of biodiesel having larger SMD, the difference with diesel is small which about 3 microns as obtained from the experiment performed.

researchers due to different atomization pressure applied. The pressure was set at 1,2,3,4 and 5 bar which is 0.1, 0.2, 0.3, 0.4 and 0.5 MPa whereas other researches using a much higher injection pressure ranging from 20 MPa to 300 MPa. Therefore only the general patterns of results were compared instead of the values obtained. This project focused on the comparison of various injection pressure starting from 1 bar until 5 bar and constant injection pressure which is 2 bar. As discussed earlier, SMD will be affected by chemical properties even though the injection pressure is constant and the same result is shown in this project. The larger ratio of biodiesel in the fuel blend gives a larger SMD and vice versa. Thus, this also affects the spray angle, spray width and spray length whereby it resulted in bigger spray angle, spray width and longer spray length. Moreover, this will cause poor atomization for power generation. In the other side, various injection pressures with specific biodiesel blend are specified to compare the SMD result for each injection pressure with specific biodiesel blend. The higher injection the smaller the droplet size even for B100 fuel and this also cause the poor atomization. The

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best is blending the biodiesel fuel with diesel to get good atomization process.

Spray angle or spray cone angle, is another important atomization parameter in spray analysis. In fluid mechanics, spray angle is defined as angle formed by the cone of liquid leaving a nozzle orifice where two straight lines wrapped with the maximum outer side of the spray [21] and spray cone angle can be defined as the angle between the maximum left and right position at a half length of spray tip penetration from the nozzle tip [35]. Furthermore, according to another researcher stated that biodiesel gives narrower spray angle than diesel fuel [25] and the spray cone angle decreased as the ratio of the biodiesel blend increased [1]. Therefore, the author's experiment result is consistent with other researcher's results. In this research, spray images are captured using a high speed camera, when conducting fuels atomization experi‐ ment. Figure 11 shows two spray angles for the experimental and simulation analysis for constant injection pressure. Injection pressure were set to two bar to study the relationship between fuel properties and spray angle. Here, the spray angle for B100 and D100 were compared and it is obvious that the higher content of biodiesel resulted in a smaller spray angle. As the percentage of biodiesel increase, the spray angle with the increase pressure will increase the momentum of the fluid stream upon the activation of the jet spray. Furthermore, constant injection analysis shows that fuel properties will affect the spray angle whereby the higher content of biodiesel gives a smaller spray angle. This result is similar and it is said that B100 or higher content of biodiesel which is relatively viscous, dense and higher surface tension has the smallest spray angle [8]. Meanwhile, the results also concur with another researcher [39] and based on his paper it is reported that when surface tension is low, spray droplet are prone to quicker break up and wider of dispersion, because relatively larger spray angle could be observed. B100 spray angle is much smaller compared with D100 spray angle in this experiment. Fuel properties testing shows that the higher the ratio of biodiesel blend the higher content of viscosity and density. When both of it is higher, it shows that the surface tension

**3.2. Spray cone angle**

increased with biodiesel content in the fuel.

Biodiesel has more massive fragments and less fine droplets than those of diesel fuel due to its high liquid viscosity, resulting in high mean droplet size. Consequently, it can be postulated that the breakup characteristic is strongly dominated by not only the surface tension but also the friction flow inside a droplet [37]. To increase the poor atomization of biodiesel fuel compared to diesel due to the larger SMD, ethanol can be blended together with biodiesel to produce smaller SMD. This is because ethanol has lower kinematic viscosity with active interaction with ambient gas. In other words, blending ethanol with biodiesel will enhance atomization characteristics. Referring to the correlation for SMD, fuel mixture viscosity, fuel surface tension and fuel density has obvious impact for the change in SMD. Referring to Table 1, higher ratio of biodiesel in a fuel will correspond to the higher viscosity and density. A fluid's viscosity causes the fluids to resist agitation, tending to prevent its breakup and leading to a larger average droplet size. While density can cause a fluid to resist acceleration, so does other chemical properties such as viscosity, higher density. All this results in a larger SMD of the sample fuel.

In addition, SMD for both biodiesel blended fuels and diesel will be smaller when higher injection pressure is applied during atomization process. A research carried out by Kippax et. al. [20] shows that high injection pressure in the spray system will generate higher actuation velocity of the fuel particles and produce smaller droplet size from the nozzle orifice. More‐ over, higher injection pressure leads to an increase in the ambient gas density and the aero‐ dynamics interactions and so the breakup time occur earlier and thus decreases the SMD of the fuel. The general pattern is obtained whereby pure biodiesel (B100) records the highest value of kinematic viscosity and density. These high values recorded for B100 had caused poor atomization with long spray tip penetration, large spray cone angle, large spray width and also large SMD. Results obtained by author could not be directly compared with different researchers due to different atomization pressure applied. The pressure was set at 1,2,3,4 and 5 bar which is 0.1, 0.2, 0.3, 0.4 and 0.5 MPa whereas other researches using a much higher injection pressure ranging from 20 MPa to 300 MPa. Therefore only the general patterns of results were compared instead of the values obtained. This project focused on the comparison of various injection pressure starting from 1 bar until 5 bar and constant injection pressure which is 2 bar. As discussed earlier, SMD will be affected by chemical properties even though the injection pressure is constant and the same result is shown in this project. The larger ratio of biodiesel in the fuel blend gives a larger SMD and vice versa. Thus, this also affects the spray angle, spray width and spray length whereby it resulted in bigger spray angle, spray width and longer spray length. Moreover, this will cause poor atomization for power generation. In the other side, various injection pressures with specific biodiesel blend are specified to compare the SMD result for each injection pressure with specific biodiesel blend. The higher injection the smaller the droplet size even for B100 fuel and this also cause the poor atomization. The best is blending the biodiesel fuel with diesel to get good atomization process.

#### **3.2. Spray cone angle**

Based on the fuel sample prepared, the SMD was calculated for all sample fuel and tabulated results are shown in Figure 10. Pure biodiesel fuel, B100 has the largest SMD, followed by B80, B50, B20 and diesel. The SMD of B100 fuel is derived from WCO in this research and it agree with the SMD of biodiesel fuel derived from palm oil [7]. Sauter Mean Diameter (SMD) of biodiesel blends are much larger when compared to diesel because of the higher value of viscosity and surface tension of biodiesel [26]. The equation used to calculate SMD is used to give a comparable trend between different liquid fuels instead of accurate SMD values which can only be obtained by a complete PDPA system. The higher viscosity and density are responsible for the larger SMD of biodiesels, where the viscosity is regarded to have the largest contribution to the change in SMD it is proved [24]. High viscosity suppresses the instabilities required for the fuel jet to breakup and thus delays atomization. An increase in fuel density adversely affects atomization, whereas high surface tension opposes the formation of droplets from the liquid fuel as discussed [30]. Biodiesel fuel with a high viscosity has fewer droplets due to the breakup frequency, which is relatively low compared to that of diesel fuel [39]. In other words, with the same amount of injected fuel through the atomizer this will produce larger SMD if the amount of droplets is less. Despite of biodiesel having larger SMD, the difference with diesel is small which about 3 microns as obtained from the experiment

228 Advances in Internal Combustion Engines and Fuel Technologies

Biodiesel has more massive fragments and less fine droplets than those of diesel fuel due to its high liquid viscosity, resulting in high mean droplet size. Consequently, it can be postulated that the breakup characteristic is strongly dominated by not only the surface tension but also the friction flow inside a droplet [37]. To increase the poor atomization of biodiesel fuel compared to diesel due to the larger SMD, ethanol can be blended together with biodiesel to produce smaller SMD. This is because ethanol has lower kinematic viscosity with active interaction with ambient gas. In other words, blending ethanol with biodiesel will enhance atomization characteristics. Referring to the correlation for SMD, fuel mixture viscosity, fuel surface tension and fuel density has obvious impact for the change in SMD. Referring to Table 1, higher ratio of biodiesel in a fuel will correspond to the higher viscosity and density. A fluid's viscosity causes the fluids to resist agitation, tending to prevent its breakup and leading to a larger average droplet size. While density can cause a fluid to resist acceleration, so does other chemical properties such as viscosity, higher density. All this results in a larger SMD of the

In addition, SMD for both biodiesel blended fuels and diesel will be smaller when higher injection pressure is applied during atomization process. A research carried out by Kippax et. al. [20] shows that high injection pressure in the spray system will generate higher actuation velocity of the fuel particles and produce smaller droplet size from the nozzle orifice. More‐ over, higher injection pressure leads to an increase in the ambient gas density and the aero‐ dynamics interactions and so the breakup time occur earlier and thus decreases the SMD of the fuel. The general pattern is obtained whereby pure biodiesel (B100) records the highest value of kinematic viscosity and density. These high values recorded for B100 had caused poor atomization with long spray tip penetration, large spray cone angle, large spray width and also large SMD. Results obtained by author could not be directly compared with different

performed.

sample fuel.

Spray angle or spray cone angle, is another important atomization parameter in spray analysis. In fluid mechanics, spray angle is defined as angle formed by the cone of liquid leaving a nozzle orifice where two straight lines wrapped with the maximum outer side of the spray [21] and spray cone angle can be defined as the angle between the maximum left and right position at a half length of spray tip penetration from the nozzle tip [35]. Furthermore, according to another researcher stated that biodiesel gives narrower spray angle than diesel fuel [25] and the spray cone angle decreased as the ratio of the biodiesel blend increased [1]. Therefore, the author's experiment result is consistent with other researcher's results. In this research, spray images are captured using a high speed camera, when conducting fuels atomization experi‐ ment. Figure 11 shows two spray angles for the experimental and simulation analysis for constant injection pressure. Injection pressure were set to two bar to study the relationship between fuel properties and spray angle. Here, the spray angle for B100 and D100 were compared and it is obvious that the higher content of biodiesel resulted in a smaller spray angle. As the percentage of biodiesel increase, the spray angle with the increase pressure will increase the momentum of the fluid stream upon the activation of the jet spray. Furthermore, constant injection analysis shows that fuel properties will affect the spray angle whereby the higher content of biodiesel gives a smaller spray angle. This result is similar and it is said that B100 or higher content of biodiesel which is relatively viscous, dense and higher surface tension has the smallest spray angle [8]. Meanwhile, the results also concur with another researcher [39] and based on his paper it is reported that when surface tension is low, spray droplet are prone to quicker break up and wider of dispersion, because relatively larger spray angle could be observed. B100 spray angle is much smaller compared with D100 spray angle in this experiment. Fuel properties testing shows that the higher the ratio of biodiesel blend the higher content of viscosity and density. When both of it is higher, it shows that the surface tension increased with biodiesel content in the fuel.

**Figure 11.** B100 (left) is 30.24° (experiment),31.42 ° (simulation) and D100 (right) is 41.32° (experiment),37.51 ° (sim‐ ulation) at 0.2 MPa

**Figure 12.** Spray angle for various fuel blends at different injection pressures.

**3.3. Spray tip penetration (Spray width & spray length)**

Altercation about the effect of injection pressure on spray angle proved that spray geometries in particular penetration length and cone angle are sensitive to small changes in operating condition and injector geometry. Nozzle inlet condition, nozzle injection angle, nozzle hole dimension will give impact on various atomization characteristics. For instance, the smaller holes size and smaller injection angle of nozzles will produce smaller droplet size and spray angle. The nozzle is a critical part of any sprayer, used to regulate flow, atomize the mixture into droplets and disperse the spray in a desirable pattern. In short, spray angle produced during atomization is not absolutely dependent on fuel properties and injection pressure, but

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Spray tip penetration is significant atomization characteristic which is used to determine the size or area of atomization. Spray length, spray width and spray pattern are categorized as the three main parameters in spray tip measurement. Spray width is the atomization parameter used to observe area of dispersion of the spray. While spray length, also known as spray distance, measure the travel distance of the liquid fuel when it initiate the first spray from the nozzle orifice. The experiment results for spray width and spray length were collected and tabulated in Figure 14 and Figure 15 through the charts shown. Both these results are quali‐ tative in nature and are based on the drawing from the images captured. Meanwhile, Figure 13 show the length pattern of the spray. The spray penetration of diesel is the lowest for all chamber pressures. This is because the density and viscosity of diesel is lowest amongst all test fuels hence it atomizes more rapidly as compared to other test fuel [40]. Meanwhile, increase in injection pressure will increase flow rate through nozzle orifice, which will then

In Figure 13, the spray width for fuel with higher fraction of biodiesel is smaller than diesel at any injection pressure. There is a close relationship between spray angle and spray width. The larger spray angle will results in larger spray width. In addition, high percentage of biodiesel in a fuel (high viscosity and density) has larger droplet size which can causes poor atomization. This will cause the atomization pattern to have a smaller spray angle and spray width.

external factors such as the type of nozzle could also affect experimental results.

decrease the droplet size (SMD) of the fuel and facilitate evaporation [23].

Therefore, another comparison can be made for various injection pressure to see the relation‐ ship between effect of the fuel injection pressure with spray angle. The experimental testing was conducted through various injection pressures and based on the spray cone angle test, the results are tabulated in Figure 12. It can be seen from this figure that the spray cone angle for diesel is the highest among all types of fuel at different injection pressures and decrease of spray cone angle is because of the increased of spray tip penetration and the biodiesel has the spray cone angle less than diesel. Spray angle decrease slightly when ratio or percentage of biodiesel in the fuel increased. B100 has the lowest spray angle compared to other types of fuel at any injection pressure. A fuel spray characteristics research proved that spray angle will decrease irregularly as the biodiesel fraction increase, but inversely with fuel surface tension [22]. When surface tension is low, spray droplet are prone to quicker break up and wider of dispersion, and cause a relatively larger spray angle. The experiment results were supported by researchers [8,21] whose work concentrated on spray biodiesel blended fuel. Axial spray tip penetration of the tested fuels were similar as the spray cone, but B100 which is relatively viscous, dense and higher surface tension has the smallest spray angle compared to diesel and other biodiesel blended fuels. Value of surface tension for all types of fuel provided was assumed constant, at 0.2616 N/m and therefore, the effect of surface tension to spray angle can be negligible in this research.

Meanwhile, the spray angle for all types of fuel increase when higher injection pressure is applied during atomization process. This statement is supported by a researcher [23], whose work emphasize on the injection characteristic using honge methyl ester. Increase in injection pressure will increase the flow rate through the nozzle orifice, which will then decrease the droplet size (SMD) of the fuels and facilitate evaporation. This will result in larger spray angle (larger dispersion area) and a significant increase of spray coverage.

**Figure 12.** Spray angle for various fuel blends at different injection pressures.

**Figure 11.** B100 (left) is 30.24° (experiment),31.42 ° (simulation) and D100 (right) is 41.32° (experiment),37.51 ° (sim‐

Therefore, another comparison can be made for various injection pressure to see the relation‐ ship between effect of the fuel injection pressure with spray angle. The experimental testing was conducted through various injection pressures and based on the spray cone angle test, the results are tabulated in Figure 12. It can be seen from this figure that the spray cone angle for diesel is the highest among all types of fuel at different injection pressures and decrease of spray cone angle is because of the increased of spray tip penetration and the biodiesel has the spray cone angle less than diesel. Spray angle decrease slightly when ratio or percentage of biodiesel in the fuel increased. B100 has the lowest spray angle compared to other types of fuel at any injection pressure. A fuel spray characteristics research proved that spray angle will decrease irregularly as the biodiesel fraction increase, but inversely with fuel surface tension [22]. When surface tension is low, spray droplet are prone to quicker break up and wider of dispersion, and cause a relatively larger spray angle. The experiment results were supported by researchers [8,21] whose work concentrated on spray biodiesel blended fuel. Axial spray tip penetration of the tested fuels were similar as the spray cone, but B100 which is relatively viscous, dense and higher surface tension has the smallest spray angle compared to diesel and other biodiesel blended fuels. Value of surface tension for all types of fuel provided was assumed constant, at 0.2616 N/m and therefore, the effect of surface tension to spray angle can

Meanwhile, the spray angle for all types of fuel increase when higher injection pressure is applied during atomization process. This statement is supported by a researcher [23], whose work emphasize on the injection characteristic using honge methyl ester. Increase in injection pressure will increase the flow rate through the nozzle orifice, which will then decrease the droplet size (SMD) of the fuels and facilitate evaporation. This will result in larger spray angle

(larger dispersion area) and a significant increase of spray coverage.

ulation) at 0.2 MPa

230 Advances in Internal Combustion Engines and Fuel Technologies

be negligible in this research.

Altercation about the effect of injection pressure on spray angle proved that spray geometries in particular penetration length and cone angle are sensitive to small changes in operating condition and injector geometry. Nozzle inlet condition, nozzle injection angle, nozzle hole dimension will give impact on various atomization characteristics. For instance, the smaller holes size and smaller injection angle of nozzles will produce smaller droplet size and spray angle. The nozzle is a critical part of any sprayer, used to regulate flow, atomize the mixture into droplets and disperse the spray in a desirable pattern. In short, spray angle produced during atomization is not absolutely dependent on fuel properties and injection pressure, but external factors such as the type of nozzle could also affect experimental results.
