**4. Optimum fuel blend for microturbine engine**

With increased interest in emissions and reduction of the use of fossil based fuels, biodiesel fuel blends should be considered especially on ideal atomization for microturbine engine. Impact of effervescent spray characteristics should be taken into consideration. From experi‐ mental analysis, the higher the ratio of biodiesel in a fuel, the higher viscosity and density the fuel is. This will result in larger SMD or known as droplet size, smaller spray angle and spray width but longer spray length during atomization process. In order to substitute burning of diesel fuel in a microturbine engine, the viscosity of biodiesel blended fuel oil must be lowered to allow proper atomization and complete combustion process. High viscosity of biodiesel fuel tends to build up carbon on engine and ultimately damage the fuel injection system. A critical

17

factor to be considered in selection of suitable biodiesel fuel blend to be used in microturbine is its oxidation stability. Biodiesel fuels are methyl/ethyl ester oxygenates. The higher the ratio of biodiesel blended fuel, the higher the oxygen content of the fuel. The degree of saturation of fatty acid chains tends to correlate with its stability. Oxidative instability and fuel oxidation during storage not only affect fuel life, but also can lead to deposit formation on injector nozzles, inlet & exhaust valves and other potential engine problems such as premature wear of pistons, segment rings and cylinders, difficult when starting from cold, irregular ignition

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Another important factor to be considered in selecting the suitable alternative fuel is fuel consumption, which is directly related to economic factor. A study on the use of biodiesel in combustion engine state that the mixture of diesel oil and pure biodiesel in proportion of up to 10% will result in the reduction of the fuel consumption, and that for greater proportions, there was an increase in consumption of up to as much as 4.77% when pure biodiesel was used [31]. This increase in consumption is explained by the difference in the calorific power of biodiesel, which is generally less than the calorific power of diesel oil. The calorific value of biodiesel which is about 37.27 MJ/L, and thus biodiesel fuels have lower energy content, about 89% of diesel fuel. With respect to environmental consideration, it can be seen that significant reductions in the emission of carbon monoxide (CO), carbon dioxide (CO2), hydrocarbon (HC), sulphur dioxide (SO2) and other pollutants can be obtained by biodiesel because carbon, hydrogen, sulphur and nitrogen content of this renewable fuel is relatively lower than diesel fuel. However, smaller spray angle for biodiesel fuels during atomization process and higher injection pressure in internal combustion engine can leads to higher NOx emission. This is because fuels tend to overflow into high temperature region where abundance of oxygen in

With extra attention and consideration paid for various important aspects such as technical (atomization characteristics and fuel properties), environment, economic, and global energy issues, the blended biodiesel fuel should be selected due to its availability to reduce emission at certain level of pollutants. The recommended fuel must adhere to ASTM D2880 or similar requirements for gas turbine fuel oil. Experimental investigations showed that B20 is the most ideal alternative fuel to substitute diesel in a micro turbine engine. B20 has the fuel chemical properties very close to diesel especially viscosity which will directly influence spray charac‐ teristic such as SMD, spray angle, spray width, spray length and spray pattern. Smaller droplets size of B20 compared to other biodiesel blended fuel provide larger area of fuel air mixing and increase the time available for complete combustion in liquid fuelled combustion system. While smaller spray angle or narrow angle sprays of B20 compare to diesel during atomization could increase spray impingement in the microturbine engine. As a general rule, the narrower the spray angle, the greater the impact of ignition it gives over a given area. Combustion will first be confined for narrow angle spray; while spray penetration length is not the main concern in this selection analysis due to limited burning space of micro turbine

Oxygen content in B20 is at acceptable level compared to other higher blended biodiesel fuel and this will improve oxidation stability and the fuel life. Although calorific value for B20 is

and others.

engine.

this section readily oxidizes soot in faster rate.

factor to be considered in selection of suitable biodiesel fuel blend to be used in microturbine is its oxidation stability. Biodiesel fuels are methyl/ethyl ester oxygenates. The higher the ratio of biodiesel blended fuel, the higher the oxygen content of the fuel. The degree of saturation of fatty acid chains tends to correlate with its stability. Oxidative instability and fuel oxidation during storage not only affect fuel life, but also can lead to deposit formation on injector nozzles, inlet & exhaust valves and other potential engine problems such as premature wear of pistons, segment rings and cylinders, difficult when starting from cold, irregular ignition and others.

Another important factor to be considered in selecting the suitable alternative fuel is fuel consumption, which is directly related to economic factor. A study on the use of biodiesel in combustion engine state that the mixture of diesel oil and pure biodiesel in proportion of up to 10% will result in the reduction of the fuel consumption, and that for greater proportions, there was an increase in consumption of up to as much as 4.77% when pure biodiesel was used [31]. This increase in consumption is explained by the difference in the calorific power of biodiesel, which is generally less than the calorific power of diesel oil. The calorific value of biodiesel which is about 37.27 MJ/L, and thus biodiesel fuels have lower energy content, about 89% of diesel fuel. With respect to environmental consideration, it can be seen that significant reductions in the emission of carbon monoxide (CO), carbon dioxide (CO2), hydrocarbon (HC), sulphur dioxide (SO2) and other pollutants can be obtained by biodiesel because carbon, hydrogen, sulphur and nitrogen content of this renewable fuel is relatively lower than diesel fuel. However, smaller spray angle for biodiesel fuels during atomization process and higher injection pressure in internal combustion engine can leads to higher NOx emission. This is because fuels tend to overflow into high temperature region where abundance of oxygen in this section readily oxidizes soot in faster rate.

With extra attention and consideration paid for various important aspects such as technical (atomization characteristics and fuel properties), environment, economic, and global energy issues, the blended biodiesel fuel should be selected due to its availability to reduce emission at certain level of pollutants. The recommended fuel must adhere to ASTM D2880 or similar requirements for gas turbine fuel oil. Experimental investigations showed that B20 is the most ideal alternative fuel to substitute diesel in a micro turbine engine. B20 has the fuel chemical properties very close to diesel especially viscosity which will directly influence spray charac‐ teristic such as SMD, spray angle, spray width, spray length and spray pattern. Smaller droplets size of B20 compared to other biodiesel blended fuel provide larger area of fuel air mixing and increase the time available for complete combustion in liquid fuelled combustion system. While smaller spray angle or narrow angle sprays of B20 compare to diesel during atomization could increase spray impingement in the microturbine engine. As a general rule, the narrower the spray angle, the greater the impact of ignition it gives over a given area. Combustion will first be confined for narrow angle spray; while spray penetration length is not the main concern in this selection analysis due to limited burning space of micro turbine engine.

Oxygen content in B20 is at acceptable level compared to other higher blended biodiesel fuel and this will improve oxidation stability and the fuel life. Although calorific value for B20 is

17

**B80**

**B100**

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

**4. Optimum fuel blend for microturbine engine**

With increased interest in emissions and reduction of the use of fossil based fuels, biodiesel fuel blends should be considered especially on ideal atomization for microturbine engine. Impact of effervescent spray characteristics should be taken into consideration. From experi‐ mental analysis, the higher the ratio of biodiesel in a fuel, the higher viscosity and density the fuel is. This will result in larger SMD or known as droplet size, smaller spray angle and spray width but longer spray length during atomization process. In order to substitute burning of diesel fuel in a microturbine engine, the viscosity of biodiesel blended fuel oil must be lowered to allow proper atomization and complete combustion process. High viscosity of biodiesel fuel tends to build up carbon on engine and ultimately damage the fuel injection system. A critical

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

**B20**

**Diesel**

236 Advances in Internal Combustion Engines and Fuel Technologies

**B50**

lower than diesel, the consumption of B20 fuel in combustion engine is reduced [31]*.* Hence, B20 fuel is the most suitable biodiesel blended fuel to replace diesel fuel in a micro turbine engine, where the atomization characteristics and engine performance are the main factors to be considered in this research-based selection.

compared to diesel, poor atomization is exhibited by biodiesel. This can be solved by increasing

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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‐

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

> **Increase in Surface Tension**

, Muhammad Anwar, R. Adnan and M.A. Idris

\*Address all correspondence to: eesann@uniten.edu.my

Spray Angle Decrease Decrease Increase Negligible Increase Spray Width Decrease Decrease Increase Negligible Increase Spray Length Increase Increase Decrease Negligible Decrease Spray Pattern Improves Negligible Improves Negligible Improves Spray Velocity Decrease Negligible Increase Decrease Increase SMD Increase Increase Decrease Negligible Decrease

Department of Mechanical Engineering, Universiti Tenaga Nasional, Kajang, Selangor, Ma‐

**Increase in Injection Pressure**

**Increase in Specific Gravity** **Increase in Fluid Temperature**

injection pressure for biodiesel as breakup rate will increase.

istic for better understanding.

actual injection process.

**Table 4.** The atomization characteristic

**Author details**

Ee Sann Tan\*

laysia

**Increase in Mixture Viscosity and Density**

**Atomization Characteristics**
