# Fuel-Water Emulsions as an Alternative Fuel for Gas Turbines: A Project Summary
## 2 Subject and Methodology of Research  
### Miniature Gas Turbine  
The research campaign that is the subject of this study was conducted on the test stand of the GTM120 miniature gas turbine engine manufactured by JetPol from Poznan (Poland). This is a type of gas turbine characterized by a system of evaporators replacing the injectors. Representatives of this type of structures include the miniature turbines P80-SE (JetCat, Ballrechten-Dottingen, Germany), Wren 180K Pro (Wren Turbines Limited, Norwich, UK) and Hawk 100R (Hawk Turbine AB, Vasteras, Sweden) and the entire series of GTM turbines [33; 34; 35; 36; 37]. The mentioned gas turbines are characterized by a similar structure in all cases. These are single-shaft units equipped with a single-stage radial compressor and a single-stage axial turbine located at the opposite end of the shaft. A characteristic feature of this type of turbine is their quasi-reverse flow--part of the air from behind the compressor flows to the end of the external engine channel and then flows through evaporators to which liquid fuel is applied; that is, to the primary combustion zone (Figure 1). For greater clarity, the diagram omits the shaft and shaft cover located in the engine axis.  
This type of engine is characterized by an open lubrication system. Part of the fuel pumped through the fuel pump is separated from the main flow that powers the turbine and is redirected through additional lines to the vicinity of two bearings with which these turbines are equipped. The front bearing is located in the plane of the diffuser disc (Figure 2a), and the rear bearing is in the plane of the turbine guide bar (Figure 2b). In order to improve its lubricating properties, the fuel is enriched with oil. In the case of the research conducted by the authors, this was Aerosoll Turbine Oil 500, which constituted 5% of the weight of the Jet A1 and oil mixture. 2.5% of the total fuel mixture flow is used to lubricate the bearings in the GTM120 turbine. The flow is divided using a separating orifice.  
The GTM120 miniature gas turbine has an anachronistic starting system. In more modern turbines of this type, starting is performed using liquid fuel and an ignition system adapted to it, which is able to evaporate the fuel before ignition (for a cold engine). In the case of the GTM120, which does not have this system, the cold unit is started using gaseous fuel. In this case, it is commercial propane-butane. In the first phase of reaching the idle speed, gas is fed into the combustion chamber and ignited by a glow plug. The burning gas fuel heats the combustion chamber, which allows the application of liquid fuel, which can evaporate and burn. During the start-up phase, the gas fuel supply is cut off and the  
Figure 1: Scheme of the quasi-reverse flow in a miniature gas turbine engine.  
Figure 2: Places of outlets of the lubrication system (GTM160) of the bearing: (**a**) front; (**b**) rear.  
gas turbine, after reaching idle speed, runs only on liquid fuel. Opening and shutting off the flow of each fuel is carried out via solenoid valves.  
The GTM120 gas turbine engine is characterized by the ability to achieve a shaft rotation of 120 krpm; at this rotational speed, it is able to generate 120N of thrust, while consuming just over 500 mL of fuel per minute. For the maximum shaft rotation speed, the mass flow of air flowing through the engine is approximately 0.35 kg/s. The average temperature behind the combustion chamber reaches approximately 720 \({}^{\circ}\)C, and at the engine outlet, to almost 600 \({}^{\circ}\)C. A single-stage radial compressor with a diameter of 70 mm is able to compress the flowing air to 2.2 bar (absolute pressure). The pressure mentioned is the static pressure measured behind the diffuser disk at a shaft rotation speed of 120 krpm. For these parameters, the measured temperature in the same plane reaches 120-130 \({}^{\circ}\)C. The weight of this unit is 1.5 kg, its maximum diameter is 110 mm and the total length is 265 mm [38; 39].