**2.3. Application of biodiesel in gas turbine**

A gas turbine comprise of an upstream rotating compressor coupled to a downstream turbine and a combustion chamber in between. The structure of fuel sprays in gas turbine combustors is complex and varies both temporary and spatially. Slight imperfections to the fuel nozzle lip can yield significant variations in fuel spray pattern. Non uniform spray patterns can result in poor mixing between fuel and air which lowers combustion efficiency and increases emitted pollutants. The actual conditions of spray injection, dispersion, vaporization and burning of the fuel with different stoichiometric proportions of air in a well mixed environment affect the combustion stability and efficiency and pollutants formation. Specifically fuel/air mixing and the time temperature dwell history of fuel droplets determine the quality of combustion and the levels of emissions generated. However, most systems are not well mixed and require controlled mixing which in turn affects combustion and emission characteristics. Furthermore, efficiency of the gas turbine itself plays a role to control the combustion and emission charac‐ teristic. Basically, gas turbine engine applied in two major sectors which are aircraft propulsion and electric power plant. Implementation of gas turbine since 19th century had been commer‐ cialized and developed year by year until now. At the early stage or beginning stage of gas turbine, efficiency of gas turbine is just around 17 percent due to its low compressor, turbine efficiency and low turbine inlet temperature. There are some developments that had been made to improve operation of gas turbine such as increasing the efficiency of turbomachinery component, modification to the basic cycle and increasing the temperature of turbine inlet. The advantage for choosing the gas turbine is that it can produce greater power for a given size, high reliability, weight, long life and convenient operation compared with steam turbine. It also gives an advantage for operation part. For example, gas turbine can reduce the engine start up from few hours (steam turbine) to just a few minutes (gas turbine) to start up engine/ start up turbine. Thus, gas turbine is more efficient and it can cut cost and time. Nowadays, fuel used to operate the gas turbine is diesel or natural gas whereby the efficiency and emission have to be improved even though the carbon capture had been used to reduce the release of *CO*2 to the air. In advance, new approach will be implemented in gas turbine fuel by replacing it with biodiesel fuel for combustion process. Therefore, biodiesel is a good option to be used as fuel in gas turbine because it is renewable and it can sustain for long term. Even though, biodiesel is not implemented in any of gas turbine for power plant but the similarity of diesel engine and gas turbine convince that gas turbine will be more efficient using biodiesel as a fuel for power generation due to biodiesel chemical properties [1,3]. Moreover, application of biodiesel as a fuel for diesel engine proved that diesel engine can work efficiently and produce less harmful emission [27-28].The simple actual flow operation is in gas turbine shown in Figure 2 [7].There are some study had been made by other researchers to study the feasibility of biodiesel in gas turbine application and a gas turbine is also called a combustion turbine, which is a type of internal combustion engine. In recent years, studies of atomization in gas turbines were performed to study the feasibility of using biodiesel in gas turbines application. Many studies were conducted by researchers from all over world.

in a complex manner for the length of the premixed. The fuel spray is injected adjacent to the combustion air in a confined area. The presence of the preheated combustion and swirling air is critical in promoting droplet evaporation and minimizing fuel impingement on the injector walls. Combustion occurs a short distance downstream of the exit of the fuel injectors. Each of the three injectors is inserted into bellows circumferentially around the combustor on the same plane of the cross section as the right side of figure below. The empty bellow on the right houses the igniters and the circular combustion flow phenomena with sites of ignition identified is

**Figure 1.** Air blast spray phenomena (left) and planar cross-sectional of injector configuration and combustor flow in

A gas turbine comprise of an upstream rotating compressor coupled to a downstream turbine and a combustion chamber in between. The structure of fuel sprays in gas turbine combustors is complex and varies both temporary and spatially. Slight imperfections to the fuel nozzle lip can yield significant variations in fuel spray pattern. Non uniform spray patterns can result in poor mixing between fuel and air which lowers combustion efficiency and increases emitted pollutants. The actual conditions of spray injection, dispersion, vaporization and burning of the fuel with different stoichiometric proportions of air in a well mixed environment affect the combustion stability and efficiency and pollutants formation. Specifically fuel/air mixing and the time temperature dwell history of fuel droplets determine the quality of combustion and the levels of emissions generated. However, most systems are not well mixed and require controlled mixing which in turn affects combustion and emission characteristics. Furthermore, efficiency of the gas turbine itself plays a role to control the combustion and emission charac‐ teristic. Basically, gas turbine engine applied in two major sectors which are aircraft propulsion

also represented in Figure 1 [1].

218 Advances in Internal Combustion Engines and Fuel Technologies

engine (right)

**2.3. Application of biodiesel in gas turbine**

Atomization is a process where liquid fuel is forced through a nozzle under high pressure to form small particles in the form of spray. Atomization is highly dependent on the injection which includes the nozzle opening and also injection pressure. Studies were also performed on optimization of nozzle in order to produce well atomized fuel sprays. From atomization, various spray characteristics such as spray tip penetration, spray cone angle, spray width and Sauter Mean Diameter (SMD) can be studied. Over the years, atomization of various liquid fuels has been studied to evaluate fuel performance relationship with engine efficiency and pollutant emissions [37]. Studies of atomization performed is highly dependent on visual systems such as the Phase Doppler Particle Analyzer (PDPA). Viscosity that varies between fuels affects the atomization of various liquid fuels. To study the feasibility of biodiesel in gas turbine, sample biodiesel fuel used is jatropha oil and studies shows that jatropha biodiesel blend can be used as alternative fuel for gas turbine application. This oil has characteristics properties almost similar with diesel but need to undergo degumming or etherification to form its biodiesel fuel due to high viscosity. Another study was done on operation of a 30 kW gas turbine using biodiesel as primary fuel. The result were then compared with using diesel fuel distillate #2 and shows that biodiesel's fluid properties results in inferior atomization com‐ pared to diesel [33]. Flame structure in a gas turbine varies from that in a diesel engine. In

**2.5. CFD simulation**

characteristic and the calculation meshes. [8,21].

**Figure 3.** Experimental testing set up

In order to simulate the atomization process, the Computational Fluid Dynamics (CFD) model has to be constructed. The CFD model will be simulating the spray region of the fuel atomi‐ zation. Figure 4 shows a sample of simulated CFD model with square shape of the spray region using CFD preprocessor tools and Figure 5 is the axis symmetry constructed using the cylindrical shape of spray region. Both figures become the samples of the CFD model geometry simulating on spray region. Study in atomization and spray characteristic give an idea where the meshs of the atomization spray region can be created as cylinder shape or square shape [21]. Figure 4 is the computational grid for the numerical analysis and it also shows the size of the grid as modeled for atomizer [8,21]. Furthermore, different injection pressure will affect the spray length and angle. Figure 5 show the measuring points for analyzing the atomization

Biodiesel for Gas Turbine Application — An Atomization Characteristics Study

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

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Chemical properties and ambient pressure will affect the pattern and SMD of the spray. It is proved in Figure 6 and Figure 7 whereby after the injection the velocity increased due to droplet [34]. Thus, it is a high velocity and the relative velocity of droplets injected at later stage is decreased. Pressure and temperature can also affect the spray flow. In addition, chemical characteristics also will affect the spray length, spray angle, spray pattern and SMD. It depends on the various blend of the fuel whereby every blend of fuel consist of different amount of chemical characteristic such as density, viscosity, surface tension and others. Figure 6 shows the effect of pressure and Figure 7 shows the ambient pressure with different blend of fuel.

**Figure 2.** Simple actual flow in gas turbine

diesel engine, the flame is intermittent non-premixed reaction while the flame in gas turbine is more lean and premixed reaction. The study done on this gas turbine shows that biodiesel can be used for operation [33]. The structure of a gas turbine with injectors are placed at designated location. Fuel spray is injected adjacent to the combustion air in a confined area. The presence of the preheated combustion and swirling air is critical in promoting droplet evaporation and minimizing fuel impingement on the injector walls.

#### **2.4. Atomization test rig**

The atomization test rig was designed to achieve the atomization characteristics spray of biodiesel and diesel blends. The equipment comprise of a compressor, a timing control panel, pressure tank, solenoid valve, spray gun, test rig, and a high speed camera. Figure 3 shows the schematic diagram of the test rig. The fuel is injected into the atomizer under pressurized conditions channeled through the air compressor. An air-assist automatic spray gun connected to a high pressure pump or solenoid valve is used to atomize the fuel, using different tip size to achieve the desired atomization and spray pattern size. As the droplets are sprayed, the high speed camera is used to capture the images of the spray pattern. The atomization test was conducted for five blends of biodiesel and diesel fuel, under various pressure ranging from 0.1MPa to 0.5MPa.
