**2. Research methodology**

## **2.1. Fuel properties**

ing fossil fuel with renewable energy is one of the main solution. Biodiesel is a renewable, biodegradable and oxygenous fuel with almost similar physical and chemical characteris‐ tic to diesel [1]. Biodiesel are ethylic or methyl esters of acids with long chain derived from vegetable oils and animal fats through a thermochemical process involving the transesteri‐ fication process [2]. In addition, biodiesel being an oxygenated fuel whereby it is environ‐ mentally cleaner than diesel with respect to unburnt hydrocarbon (UHC) and particulate matter (PM) emissions [3]. The success of biodiesel is proven as can be seen in its use as a secondary fuel for vehicle in Europe and followed by other developed countries. The reason for using biodiesel, is that it can increase engine performance and produces low emission compared with conventional diesel fuel [2,5,6,17]. Biodiesel can be obtained from various sources such as palm oil [7], rapessed oil [14-15], soybean oil [8,14-15], vegetable oil [9-10], waste cooking oil [11-12], oleaginous microorganisms [13] and sunflower seed oil [14-15]. An important effect that has to take into consideration is the fuel spray atomizer where‐ by it is the contributing factor that will affect the efficiency and performance of power generation. Spray tip penetration and mean droplet size of which are the atomization characteristics of biodiesel fuel play an important role in the emission characteristics and the engine performance [26]. Biodiesel is mostly applied in transportation like petroleum diesel. Biodiesel blended fuel can be used as fuels for diesel engines without any modifica‐ tion. Moreover, pure biodiesel can be used as well but with some minor modification. Biodiesel gives better lubrication compared to diesel fuel [27-28]. Biodiesel also provides

214 Advances in Internal Combustion Engines and Fuel Technologies

advantages on performance, engine wear, value for money and availability.

in the microturbine and gas turbine combustion system.

Despite the significant advance arising from definition of the regulatory milestone, there are still many issues relating to the production and use of biodiesel that need to be debated. Among the issues, the ones that stand out are those of a technical order, such as how the biodiesel specifications and its consequences for the performance, emissions and durabili‐ ty of the engine and its system. Therefore, further research on ideal atomization character‐ istics of biodiesel fuels should be carried on for progressive development of this potential source in combustion engineering. Various biodiesel blended fuel derived from waste cooking oil (WCO) are produced through the method of transesterification. ASTM stand‐ ards are used to identify and verify physical and chemical properties such as viscosity, density, flash point and cetane number of the biodiesel produced. Meanwhile, a fuel atomizer designed act as a device that convert the working fuel flow into a finely dis‐ persed flow of fuel droplets in the form of a spray. Fuel spray testing will determine atomization characteristics such as Sauter Mean Diameter (SMD), spray angle, spray width, spray length and spray tip penetration for different types of fuel under certain atomiza‐ tion conditions. Thereafter, a computer simulation using CFD Fluent software is used to compare the experimental results to ascertain the appropriate biodiesel blend to be applied

This project is to study the possible application of diesel and biodiesel blends in gas turbine and microturbine application. Research of this project involves testing several composi‐ tions of diesel and biodiesel blends. The produced diesel and biodiesel blends will be tested to understand the behavior and atomization characteristics such as spray tip penetration,

The production of biodiesel was completed by conducting transesterification of Waste Cooking Oil (WCO). Relevant method was selected in this project based on its economic factors to produce different biodiesel blended fuels. Biodiesel and diesel blends of B100, B80, B50 and B20 and D100 were obtained through conducting tests that meet the require‐ ments of ASTM D6751, Specification for Biodiesel Fuel Blend Stock for Distillate and ASTM D2880 Standard Specification for Gas Turbine Fuel Oil. This is to ensure that the pro‐ duced biodiesel blended fuels meet the minimum fuel properties standards. Table 1 shows the main fuel properties that were studied with respect to its effects on atomization. Transesterification is the simplest way whereby it uses alcohol (e.g. methanol or ethanol) in the presence of a catalyst such as sodium hydroxide or potassium hydroxide, to chemically break the molecule of the raw material into methyl or ethyl esters of the renewable oil with glycerol as by-product. The chemical reaction of transesterification is ethyl esters of fatty acids plus glycerol equal to triglyceride (animals and plants fats and oil). The triglyceride will have chemical reaction with alcohol that usually is methanol or ethanol with the presence of a catalyst to produce ethyl ester and crude glycerol.


the use of fuel with higher viscosity delays atomization by suppressing the instabilities required for the fuel jet to break up. An increase in fuel density adversely affects atomization whereby higher fuel surface tension opposes the formation of droplets from the liquid fuel and some researchers analysis show that less viscosity of biodiesel is good to improve fuel atomization. The analysis showed the contributions to the change or rather the increase in SMD by the kinematic viscosity, surface tension and density were 89.1%, 10.7%, and 0.2% respec‐ tively and by reducing the viscosity of biodiesel this will reduce usage of petroleum diesel. However, further research need to be conducted to achieve the optimum blend in terms of cost, environmental effect and availability. A brief commentary is provided on the principal influences of fuel properties on atomization quality and injector performance. The viscosity of the fuel, on the other hand is of great importance in controlling both the formation of the continuous film immediately after exit from the nozzle and of the subsequent ligament disruption into individual droplets. The viscous forces decrease the rate of breaking-up of distortions in the liquid and decrease the rate of disruption of the droplets formed initially and increase the final droplet size. Experiment may show that both droplet diameter and penetra‐ tion are directly related to fuel viscosity. An increase in fuel viscosity will also tend to increase spray penetration with heavier and more viscous fuels, the jet will not be so well atomized for a given injection pressure and the spray will be more compact. Consequently there will be a decrease in spray cone angle and in spray distribution/uniformity. The temperature relation‐ ships for kinematic viscosity shows that vegetable oils have viscosities higher than that of conventional gas oil (diesel) thus tending to produce larger droplets. Viscosity has by far the greatest effect on jet atomization with high viscosity fuels provoking deterioration in the quality of atomization. Of the relevant fuel properties, density is generally found to have relatively little influence on spray formation. Moreover, looking at the temperature relation‐ ships for relative density, the variation in specific gravity is also not appreciable. An increase in fuel density will have a small direct effect on spray compactness and penetration. Surface tension also has a direct effect on drop size but shows much less variation with temperature. Surface tension forces tend to oppose the formation of distortion or irregularity on the surface of the continuous jet and so delay the formation of ligaments and the disintegration of the jet. Hence, an increase in the liquid surface tension will generally cause deterioration in atomiza‐

Biodiesel for Gas Turbine Application — An Atomization Characteristics Study

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

217

The most important component in the atomization testing is an injector nozzle. An atomizer nozzle produces a fine spray of a liquid based on the venturi effect. When a gas is blown through a constriction it speed up, this will reduce the pressure at the narrowest point. The reduced pressure sucks up a liquid through a narrow tube into the flow where it boils in the low pressure and form thousands of small droplets. These theories apply to the experiment where the atomizer turns the fuel into thousands of small droplets. Besides producing fine droplets the atomizer is important for air fuel mixing. The function of air fuel mixing of an atomizer is important where a proper air fuel mixing of fuel atomization can increase the fuel combustion efficiency in the microturbine. In the microturbine there are three liquid fuel injectors, each housing a plain-jet air blast atomizer which is air-assisted with four orifices to introduce the combustion of air and a helical swirled to inject the fuel air mixture in a staged approach to facilitate engine turndown [33]. Figure 1 show the sample of fuel and air interact

tion quality.

**Table 1.** Important fuel characteristics of Biodiesel and its blend with Diesel.

## **2.2. Atomization**

Atomization is the breakup of bulk liquid jets into small droplets using an atomizer or spray [3]. Adequate atomization enhances mixing and complete combustion in a direct injection (DI) engine and therefore it is an important factor in engine emission and efficiency. This applies to microturbines and gas turbines as well as witnessed in the need for an atomizer in gas turbines when diesel is being used. Feasibility of biodiesel as a renewable fossil fuel replace‐ ment for power generation, must also consider emissions of pollutants including oxides of nitrogen (NOx), oxides of sulfur (SOx), carbon monoxide (CO), and particulate. This is true for both emergency (backup) power and base load applications. Fuel stability still remains an issue during storage, a hurdle which must be overcome in order to maintain fuel quality. Combustion systems for environmentally preferred alternative fuels like biodiesel have yet to be fully optimized for emissions. As a result, the feasibility of biodiesel as a low emission alternative fuel option is still being evaluated [33].

The atomization of fuel is crucial in the combustion and emission on engine but the atomization process in engine and in microturbine are completely different. Both microturbine and diesel engine have the same fundamentals where both operate through combustion but the principle of the atomization process in the both cases varies because the fuel injector for microturbine and diesel engine are not similar. For microturbine the combustion is continuous, so the fuel atomization in microturbine is continuous without any cycles or strokes. Atomization plays major role in combustion and emission in microturbine. By modifying the atomization process, the gas turbine can produce lower emission of nitrogen oxide (NOx) and carbon monoxide (CO). Adequate atomization enhances mixing and complete combustion in a direct injection gas turbine and therefore it is an important factor in gas turbine emission and efficiency. Otherwise, the properties of a liquid fuel that affect atomization in a gas turbine are viscosity, density and surface tension. For a gas turbine biodiesel injector at fixed operating condition, the use of fuel with higher viscosity delays atomization by suppressing the instabilities required for the fuel jet to break up. An increase in fuel density adversely affects atomization whereby higher fuel surface tension opposes the formation of droplets from the liquid fuel and some researchers analysis show that less viscosity of biodiesel is good to improve fuel atomization. The analysis showed the contributions to the change or rather the increase in SMD by the kinematic viscosity, surface tension and density were 89.1%, 10.7%, and 0.2% respec‐ tively and by reducing the viscosity of biodiesel this will reduce usage of petroleum diesel. However, further research need to be conducted to achieve the optimum blend in terms of cost, environmental effect and availability. A brief commentary is provided on the principal influences of fuel properties on atomization quality and injector performance. The viscosity of the fuel, on the other hand is of great importance in controlling both the formation of the continuous film immediately after exit from the nozzle and of the subsequent ligament disruption into individual droplets. The viscous forces decrease the rate of breaking-up of distortions in the liquid and decrease the rate of disruption of the droplets formed initially and increase the final droplet size. Experiment may show that both droplet diameter and penetra‐ tion are directly related to fuel viscosity. An increase in fuel viscosity will also tend to increase spray penetration with heavier and more viscous fuels, the jet will not be so well atomized for a given injection pressure and the spray will be more compact. Consequently there will be a decrease in spray cone angle and in spray distribution/uniformity. The temperature relation‐ ships for kinematic viscosity shows that vegetable oils have viscosities higher than that of conventional gas oil (diesel) thus tending to produce larger droplets. Viscosity has by far the greatest effect on jet atomization with high viscosity fuels provoking deterioration in the quality of atomization. Of the relevant fuel properties, density is generally found to have relatively little influence on spray formation. Moreover, looking at the temperature relation‐ ships for relative density, the variation in specific gravity is also not appreciable. An increase in fuel density will have a small direct effect on spray compactness and penetration. Surface tension also has a direct effect on drop size but shows much less variation with temperature. Surface tension forces tend to oppose the formation of distortion or irregularity on the surface of the continuous jet and so delay the formation of ligaments and the disintegration of the jet. Hence, an increase in the liquid surface tension will generally cause deterioration in atomiza‐ tion quality.

**Fuel Blend**

**2.2. Atomization**

**ASTM D445**

**Mixture Viscosity @ 40 Celcius (m2/s)**

**ASTM D4052**

216 Advances in Internal Combustion Engines and Fuel Technologies

**Fuel Density (kg/m3)** **ASTM D482**

**Ash Content %wt**

**Table 1.** Important fuel characteristics of Biodiesel and its blend with Diesel.

alternative fuel option is still being evaluated [33].

**Method**

**ASTM D4294**

**Sulphur Content %wt**

**ASTM D1796**

**Water & Sediment %volume**

**ASTM D5291**

**Carbon % wt**

**ASTM D5291**

**Hydrogen % wt**

**ASTM D5291**

**Nitrogen % wt**

**ICP-OES**

**Sodium mg/kg**

**Diesel** 3.88 x 10-6 842 0.004 0.15 0.241 0 85.37 13.27 0.14 **B20** 4.16 x 10-6 847 0.004 0.8 0.106 0.03 82.24 13.16 0.12 **B50** 4.28 x 10-6 855 0.004 0.8 0.063 0.05 81.33 13.01 0.11 **B80** 4.60 x 10-6 865 0.005 0.9 0.026 0.08 77.79 12.56 0.10 **B100** 4.76 x 10-6 872 0.006 0.8 0.003 0.1278 76.05 12.72 0.08

Atomization is the breakup of bulk liquid jets into small droplets using an atomizer or spray [3]. Adequate atomization enhances mixing and complete combustion in a direct injection (DI) engine and therefore it is an important factor in engine emission and efficiency. This applies to microturbines and gas turbines as well as witnessed in the need for an atomizer in gas turbines when diesel is being used. Feasibility of biodiesel as a renewable fossil fuel replace‐ ment for power generation, must also consider emissions of pollutants including oxides of nitrogen (NOx), oxides of sulfur (SOx), carbon monoxide (CO), and particulate. This is true for both emergency (backup) power and base load applications. Fuel stability still remains an issue during storage, a hurdle which must be overcome in order to maintain fuel quality. Combustion systems for environmentally preferred alternative fuels like biodiesel have yet to be fully optimized for emissions. As a result, the feasibility of biodiesel as a low emission

The atomization of fuel is crucial in the combustion and emission on engine but the atomization process in engine and in microturbine are completely different. Both microturbine and diesel engine have the same fundamentals where both operate through combustion but the principle of the atomization process in the both cases varies because the fuel injector for microturbine and diesel engine are not similar. For microturbine the combustion is continuous, so the fuel atomization in microturbine is continuous without any cycles or strokes. Atomization plays major role in combustion and emission in microturbine. By modifying the atomization process, the gas turbine can produce lower emission of nitrogen oxide (NOx) and carbon monoxide (CO). Adequate atomization enhances mixing and complete combustion in a direct injection gas turbine and therefore it is an important factor in gas turbine emission and efficiency. Otherwise, the properties of a liquid fuel that affect atomization in a gas turbine are viscosity, density and surface tension. For a gas turbine biodiesel injector at fixed operating condition, The most important component in the atomization testing is an injector nozzle. An atomizer nozzle produces a fine spray of a liquid based on the venturi effect. When a gas is blown through a constriction it speed up, this will reduce the pressure at the narrowest point. The reduced pressure sucks up a liquid through a narrow tube into the flow where it boils in the low pressure and form thousands of small droplets. These theories apply to the experiment where the atomizer turns the fuel into thousands of small droplets. Besides producing fine droplets the atomizer is important for air fuel mixing. The function of air fuel mixing of an atomizer is important where a proper air fuel mixing of fuel atomization can increase the fuel combustion efficiency in the microturbine. In the microturbine there are three liquid fuel injectors, each housing a plain-jet air blast atomizer which is air-assisted with four orifices to introduce the combustion of air and a helical swirled to inject the fuel air mixture in a staged approach to facilitate engine turndown [33]. Figure 1 show the sample of fuel and air interact 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 also represented in Figure 1 [1].

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.

Biodiesel for Gas Turbine Application — An Atomization Characteristics Study

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

219

Many studies were conducted by researchers from all over world.

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

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