**5. Conculsion**

Sauter Mean Diameter (SMD), spray angle and spray tip penetration are recognized as the three major atomization characteristics in fuel spray experimental analysis. Theoretical SMD results were obtained via a correlation SMD formula, which were mainly based on chemical properties of the fuels. From experimental analysis, the higher the ratio of biodiesel in the fuel, the higher viscosity, density and surface tension of the fuel. This will result in larger SMD and longer spray length but smaller spray angle and spray width with clearer vortex shape of spray pattern. Fast movement of air surrounding the dispersion of spray will cause movement of spray penetration and unable to reach its maximum tip penetration. The same goes to ambient pressure where higher surrounding pressure will cause the spray leaving the nozzle to disperse in a shorter spray tip penetration. With increment in pressure of air, this will also increase density of air and affects the spray tip penetration as well. Thus the resulting in increment of ambient air pressure [21]. Spray tip penetrations of biodiesel blended fuels showed a similar pattern regardless of the mixing ratio of the biodiesel [34]. The atomization process for biodiesel blended fuel was inferior to that of the conventional diesel fuel due to high surface tension of the biodiesel fuel [36]. In addition, the higher injection pressure applied in atomi‐ zation tend to break up fuel particles into smaller size, which will subsequently produce larger spray angle and spray width but shorter spray length with denser spray pattern. It shows the same result with other researchers and the result also shows the clearer vortex spray pattern, small spray angle and longer sprays length for higher content of biodiesel.

In general, spray cone angle for diesel is the largest and spray cone angle for biodiesel is smaller. Spray cone angle for biodiesel can further be described as the blending ratio of biodiesel increases, the spray cone angle decreases. This can be due to the higher density of biodiesel compared to diesel. Another physical characteristic that effects spray cone angle is the viscosity of the liquid fuel [10]. At a lower ambient pressure compared to atomization pressure, the spray cone angle produced is also smaller. Furthermore, the general pattern whereby diesel has the largest cone angle and pure biodiesel has the smallest cone angle and SMD for biodiesel fuel are higher compared to conventional diesel oil because of different physical characteristics such as higher viscosity and surface tension for biodiesel [1]. For different blend of biodiesel, as the biodiesel blend ratio increases this will also produce larger SMD due to the differences of viscosity and surface tension. Also SMD of any liquid fuel will also reduce as the atomization or injection pressure increase [38]. All results obtained on atomization characteristics agrees with results obtained by different researchers. Furthermore, fuel properties play an important role in atomization and include kinematic viscosity, density and surface tension. Due to higher kinematic viscosity and surface tension of biodiesel compared to diesel, poor atomization is exhibited by biodiesel. This can be solved by increasing injection pressure for biodiesel as breakup rate will increase.

In addition, results obtained shows that spray cone angle for diesel is larger than that of biodiesel due to the increased spray tip penetration of biodiesel. Larger spray tip penetration occurs with a smaller spray cone angle. Meanwhile, larger spray tip penetration of biodiesel is also due to the higher density and viscosity value that reduces breakup rate of the liquid fuel. Droplets produced are larger for biodiesel compared to diesel. B20 was proposed to be selected as the most ideal biodiesel and diesel blended fuel to be applied in microturbine and gas turbine engine due to its adoptability to replace diesel fuel without affecting much of the engine performance. B20 also promote effective atomization characteristics, which are critical to execute proper combustion process. Table 4 show the description of atomization character‐ istic for better understanding.

Further research works in this field will be concentrated on the implementation of heating the fuel prior to the spray. This will decrease the viscosity of biodiesel and may allow the atomi‐ zation to be superior for higher blends of biodiesel. Meanwhile, further efforts are being made to enhance the simulation results. Moreover, the PDPA system should be used to obtain the accurate result whereby it can obtain the size of Sauter Mean Diameter and determine the velocity of the spray. Meanwhile, injection pressure also have to be enhanced by increasing the injection pressure into actual injection that will be applied into gas turbine to simulate the actual injection process.


**Table 4.** The atomization characteristic
