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

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

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. However, spray width will be larger when fuel blends are tested at higher injection pressure during atomization process. This result agrees with a researcher [25] which discovered that the increase in injection pressure from 90MPa to 120MPa results in approximately 40% more ambient gas being entrained into the spray system in average. High injection pressure applied through spray system could mitigate undesirable atomization condition since the average particle size of fuel can be broken up into smaller partition and dispersed to larger area of coverage.

**Figure 15.** Spray length for fuel blends at different injection pressures based on the experimental results

area of spray dispersion (spray width) will results in shorter spray length.

**3.4. Spray pattern**

From Figure 13, spray length for B100 is higher compared to other biodiesel blended fuels and diesel (lowest spray length). Higher fuel viscosity develops a longer potential core and larger face area. This can increase the quality of the atomization by increasing the surface area. Meanwhile, spray length for every type of fuel will decrease when higher injection pressure applied during atomization process. From theoretical spray length formula, spray length is dependent on spray angle and spray width. Spray length is inversely proportional to spray angle and spray width. The larger the spray angle and spray width, the lower the spray length and vice versa due to gravity effect and ambient conditions. Ambient pressure has stronger effect or impact on spray tip penetration than injection pressure. An increase of the ambient pressure will decrease the spray length due to higher air resistance. Since amount or volume of fuel used for atomization process is considered constant, it is reasonable to state that larger

Biodiesel for Gas Turbine Application — An Atomization Characteristics Study

http://dx.doi.org/10.5772/54154

233

Spray pattern is the shape of the jet of spray leaving the atomizer or spray gun. The spray pattern can be obtained during atomization experiment by capturing the spray images using high speed camera. Different spray pattern obtained from different blending of biodiesel fuel. Spray pattern analysis is used to characterize types and quality of spray such as spray shape, color intensity of spray, spray speed and others. The photographs of spray pattern in this experiment were captured using an image processing procedure. As shown in Figure 16, spray pattern of diesel fuel is not very visible compared to spray pattern of B100 at injection pressure of 0.5MPa or 5 bars. Fuel with higher blending ratio of biodiesel will develop a longer, denser potential core and quality spray pattern. This is because relative‐ ly high viscosity fuel has larger SMD compare to lower biodiesel blended fuel. Presence of intact fuel core indicates that viscous and surface tension forces in biodiesel spray are high

**Figure 13.** D100 (left) and B100 (right) at 0.2 Mpa

**Figure 14.** Spray width for various fuel blends at different injection pressures

**Figure 15.** Spray length for fuel blends at different injection pressures based on the experimental results

From Figure 13, spray length for B100 is higher compared to other biodiesel blended fuels and diesel (lowest spray length). Higher fuel viscosity develops a longer potential core and larger face area. This can increase the quality of the atomization by increasing the surface area. Meanwhile, spray length for every type of fuel will decrease when higher injection pressure applied during atomization process. From theoretical spray length formula, spray length is dependent on spray angle and spray width. Spray length is inversely proportional to spray angle and spray width. The larger the spray angle and spray width, the lower the spray length and vice versa due to gravity effect and ambient conditions. Ambient pressure has stronger effect or impact on spray tip penetration than injection pressure. An increase of the ambient pressure will decrease the spray length due to higher air resistance. Since amount or volume of fuel used for atomization process is considered constant, it is reasonable to state that larger area of spray dispersion (spray width) will results in shorter spray length.

#### **3.4. Spray pattern**

However, spray width will be larger when fuel blends are tested at higher injection pressure during atomization process. This result agrees with a researcher [25] which discovered that the increase in injection pressure from 90MPa to 120MPa results in approximately 40% more ambient gas being entrained into the spray system in average. High injection pressure applied through spray system could mitigate undesirable atomization condition since the average particle size of fuel can be broken up into smaller partition and dispersed to larger area of

coverage.

**Figure 13.** D100 (left) and B100 (right) at 0.2 Mpa

232 Advances in Internal Combustion Engines and Fuel Technologies

**Figure 14.** Spray width for various fuel blends at different injection pressures

Spray pattern is the shape of the jet of spray leaving the atomizer or spray gun. The spray pattern can be obtained during atomization experiment by capturing the spray images using high speed camera. Different spray pattern obtained from different blending of biodiesel fuel. Spray pattern analysis is used to characterize types and quality of spray such as spray shape, color intensity of spray, spray speed and others. The photographs of spray pattern in this experiment were captured using an image processing procedure. As shown in Figure 16, spray pattern of diesel fuel is not very visible compared to spray pattern of B100 at injection pressure of 0.5MPa or 5 bars. Fuel with higher blending ratio of biodiesel will develop a longer, denser potential core and quality spray pattern. This is because relative‐ ly high viscosity fuel has larger SMD compare to lower biodiesel blended fuel. Presence of intact fuel core indicates that viscous and surface tension forces in biodiesel spray are high enough to suppress disintegration of the fuel core. It was claimed by a researcher [8] that "the vortex shape of biodiesel fuel with high viscosity is clearer than diesel fuel because the breakup frequency of biodiesel fuel is low". Lower break up rate for B100 produce larger droplet size and will cause the spray pattern to become clearer compared to diesel fuel. A clearer spray pattern or large droplet density is associated with overlapped images and fringes in arbitrary direction due to multiple scattering.

density of the fuel, which can affect the initial spray velocity. This can be explained using fluids dynamic – Bernoulli equation, whereby velocity is inversely proportional to the square root of density. Hence, it can be concluded that atomization characteristics for fuels is not only dependent on experimental atomization factors. The studies on the relation‐ ship between ambient pressure and temperature, injection pressure, orifice diameter, nozzle

Biodiesel for Gas Turbine Application — An Atomization Characteristics Study

http://dx.doi.org/10.5772/54154

235

An open fire test was conducted as preliminary results for the combustion characteristics prediction. The photos captured in Figure 17 shows the test results for open fire test using five types of fuel that had been tested. They are Diesel 100% (D100), 100% biodiesel (B100), 80% biodiesel (B80), 50% biodiesel (B50) and 20% biodiesel (B20). Here, diesel obtained the largest flame structure as compared to B100. But B100 has the most intense and brightest burning capability, most likely due to the higher oxygen content that exist in the fuel. Heat of combus‐ tion is the thermal energy that is liberated upon combustion, so it is commonly referred to as energy content. As can be seen, as the biodiesel component in the fuel is increased from 0% to 100%, a concomitant decrease in energy content is observed. Factors that influence the energy content of biodiesel include the oxygen content and carbon to hydrogen ratio. For instance, fatty acid methyl esters (FAME) with 18 carbons in the fatty acid backbone include methyl esters of stearic (largest hydrogen content), oleic, linoleic and linoleic (smallest hydrogen content) acids. Biodiesel fuels with larger ester head groups such as ethyl, propyl or butyl are expected to have greater energy content as a result of their greater carbon to oxygen ratios.

The experiment result shows the same trends with CFD simulation. The spray angle result of experiment shows that the spray angle does not differ much for all five types of fuel. The pattern is maintained whereby D100 has the largest spray angle and BD 100 is the smallest spray angle. A comparison was done between CFD simulation and experiment spray angle result. The spray pattern of the atomization was done using CFD simulation and atomization testing experiment. Both CFD simulation and atomization testing have almost similar spray pattern of the fuel. From the spray pattern, the spray angle can be seen to be smaller from DF100, BD 20, BD 50, BD 80 and BD 100. The spray pattern of five types of fuel using CFD simulation is shown in Figure 18. From the comparison, it can be seen there are some differences in spray pattern between the CFD simulation and experi‐ ment result. In addition, spray geometry especially spray angle and spray length is sensitive to small change of operating condition and injector geometry such as nozzle inlet condi‐ tion, nozzle injection angle and nozzle hole dimension. The nozzle is a critical part of any spray, used to regulate flow, atomize the mixture into droplets and disperse the spray in a desirable pattern. Spray tip penetration of the tested fuels is similar as the spray cone, but B100 which is relatively viscous, dense and higher surface tension has the smallest spray angle [34-37]. Moreover, higher content of viscosity, density and surface tension will give a clearer picture of atomization spray or clear shape spray pattern. Although, the spray is clear but the spray angle is affected whereby it will give a small spray angle. The same situation happened in simulation result. Therefore, purpose of simulation is to compare

with the experiment result and other researchers result.

shape and biodiesel content in the fuels are also equally important to be studied.

**Figure 16.** Spray pattern for diesel (left) and B100 (right) at 0.5MPa

On the other hand, higher injection pressure increases the mass flow rate and will then increase the diameter of fuel core. This causes deposition of smaller droplets within the upper canopy near to the nozzle orifice. Therefore, a better quality spray pattern could be observed at higher injection pressure during atomization process. In short, fuel properties are the most important factor that affects spray tip penetration for atomization. Mixture of viscosity and density increase as the biodiesel ratio of fuel increase while the surface tension is relatively insensitive to the biodiesel proportion of the fuel. Dynamic viscosity of a fuel resists change in the shape or arrangement of its elements during flow. Fuel viscosity is the main factor that could affect spray pattern formation, and to a denser degree and capacity. Meanwhile, high viscosity fuel requires a higher minimum pressure to the begin formation of a spray pattern and provide narrower spray angles. Theoretically, higher viscosity of the fuel will cause the injector valve to move slowly due to the larger fric‐ tion. This will cause the initial spray velocity to decrease, resulting in shorter penetration. However, this concept cannot be completely accepted to evaluate experimental results obtained in this project because external factor such as ambient temperature has substan‐ tial impact on atomization characteristics. For instance, high ambient temperature tends to form a more volatile fuel (lower mixture viscosity, specific gravity and surface tension) and finally decrease SMD and spray length of the fuel at constant atomization viscosity and

density of the fuel, which can affect the initial spray velocity. This can be explained using fluids dynamic – Bernoulli equation, whereby velocity is inversely proportional to the square root of density. Hence, it can be concluded that atomization characteristics for fuels is not only dependent on experimental atomization factors. The studies on the relation‐ ship between ambient pressure and temperature, injection pressure, orifice diameter, nozzle shape and biodiesel content in the fuels are also equally important to be studied.

enough to suppress disintegration of the fuel core. It was claimed by a researcher [8] that "the vortex shape of biodiesel fuel with high viscosity is clearer than diesel fuel because the breakup frequency of biodiesel fuel is low". Lower break up rate for B100 produce larger droplet size and will cause the spray pattern to become clearer compared to diesel fuel. A clearer spray pattern or large droplet density is associated with overlapped images

On the other hand, higher injection pressure increases the mass flow rate and will then increase the diameter of fuel core. This causes deposition of smaller droplets within the upper canopy near to the nozzle orifice. Therefore, a better quality spray pattern could be observed at higher injection pressure during atomization process. In short, fuel properties are the most important factor that affects spray tip penetration for atomization. Mixture of viscosity and density increase as the biodiesel ratio of fuel increase while the surface tension is relatively insensitive to the biodiesel proportion of the fuel. Dynamic viscosity of a fuel resists change in the shape or arrangement of its elements during flow. Fuel viscosity is the main factor that could affect spray pattern formation, and to a denser degree and capacity. Meanwhile, high viscosity fuel requires a higher minimum pressure to the begin formation of a spray pattern and provide narrower spray angles. Theoretically, higher viscosity of the fuel will cause the injector valve to move slowly due to the larger fric‐ tion. This will cause the initial spray velocity to decrease, resulting in shorter penetration. However, this concept cannot be completely accepted to evaluate experimental results obtained in this project because external factor such as ambient temperature has substan‐ tial impact on atomization characteristics. For instance, high ambient temperature tends to form a more volatile fuel (lower mixture viscosity, specific gravity and surface tension) and finally decrease SMD and spray length of the fuel at constant atomization viscosity and

and fringes in arbitrary direction due to multiple scattering.

234 Advances in Internal Combustion Engines and Fuel Technologies

**Figure 16.** Spray pattern for diesel (left) and B100 (right) at 0.5MPa

An open fire test was conducted as preliminary results for the combustion characteristics prediction. The photos captured in Figure 17 shows the test results for open fire test using five types of fuel that had been tested. They are Diesel 100% (D100), 100% biodiesel (B100), 80% biodiesel (B80), 50% biodiesel (B50) and 20% biodiesel (B20). Here, diesel obtained the largest flame structure as compared to B100. But B100 has the most intense and brightest burning capability, most likely due to the higher oxygen content that exist in the fuel. Heat of combus‐ tion is the thermal energy that is liberated upon combustion, so it is commonly referred to as energy content. As can be seen, as the biodiesel component in the fuel is increased from 0% to 100%, a concomitant decrease in energy content is observed. Factors that influence the energy content of biodiesel include the oxygen content and carbon to hydrogen ratio. For instance, fatty acid methyl esters (FAME) with 18 carbons in the fatty acid backbone include methyl esters of stearic (largest hydrogen content), oleic, linoleic and linoleic (smallest hydrogen content) acids. Biodiesel fuels with larger ester head groups such as ethyl, propyl or butyl are expected to have greater energy content as a result of their greater carbon to oxygen ratios.

The experiment result shows the same trends with CFD simulation. The spray angle result of experiment shows that the spray angle does not differ much for all five types of fuel. The pattern is maintained whereby D100 has the largest spray angle and BD 100 is the smallest spray angle. A comparison was done between CFD simulation and experiment spray angle result. The spray pattern of the atomization was done using CFD simulation and atomization testing experiment. Both CFD simulation and atomization testing have almost similar spray pattern of the fuel. From the spray pattern, the spray angle can be seen to be smaller from DF100, BD 20, BD 50, BD 80 and BD 100. The spray pattern of five types of fuel using CFD simulation is shown in Figure 18. From the comparison, it can be seen there are some differences in spray pattern between the CFD simulation and experi‐ ment result. In addition, spray geometry especially spray angle and spray length is sensitive to small change of operating condition and injector geometry such as nozzle inlet condi‐ tion, nozzle injection angle and nozzle hole dimension. The nozzle is a critical part of any spray, used to regulate flow, atomize the mixture into droplets and disperse the spray in a desirable pattern. Spray tip penetration of the tested fuels is similar as the spray cone, but B100 which is relatively viscous, dense and higher surface tension has the smallest spray angle [34-37]. Moreover, higher content of viscosity, density and surface tension will give a clearer picture of atomization spray or clear shape spray pattern. Although, the spray is clear but the spray angle is affected whereby it will give a small spray angle. The same situation happened in simulation result. Therefore, purpose of simulation is to compare with the experiment result and other researchers result.

**Figure 17.** Open fire testing for five type of fuel

**Figure 18.** Comparison between experiment and simulation result at 0.2MPa
