Design and construction of a small gas turbine to drive a permanent magnet high speed generator

Abstract

Radial gas turbines engines have established prominence in the field of small turbomachinery because of their simplicity, relatively high performance and installation features. Thus they have been used in a variety of applications such as generator sets, small auxiliary power units (APu), air conditioning of aircraft cabins and hybrid electric vehicles turbines. The current research describes the design, manufacturing, construction and testing a radial type small gas turbine. The aim was to design and build the engine to drive directly a high-speed permanent magnet alternator running at 60000 rpmand developing a maximum of 60 W. This direct coupling arrangement produces a portable, light, compact, reliable and environment friendly power generator. These features make the generator set very attractive to use in many applications including emergency power generation for hospitals, in areas of natural disasters such as floods and earthquakes, in remote areas that cannot be served from the national grid, oil rigs, and in confined places of limited spaces. It is important to recognize that the design of the main components, that is, the inward flow radial UFR turbines, the centrifugal compressor and the combustion chamber involve consideration of aero-dynamics, thermodynamics, fluid mechanics, stress analysis, vibration analysis, selection of bearings, selection of suitable materials and the requirements for manufacturing. These considerations are all inter-linked and a procedure has been followed to reach an optimum design. This research was divided into three phases: phase I dealt with the complete design of the inward radial turbine, the centrifugal compressor, the power transmission shaft, the selection of combustion chamber and the bearing housing including the selection of bearings. Phase 2 dealt with mechanical consideration of the rotating components that is stress, thermal and vibration analyses of the turbine rotor, the impeller and the rotating shaft, respectively. Also it dealt with the selection of a suitable fuel and oil lubrication systems and a suitable starting system. Phase 3 dealt with the manufacturing of the gas turbine components, balancing the rotating components, assembling the engine and finally commissioning and then testing the engine. The current work in this thesis has put the light on a new design methodology on determining the optimum principal dimensions of the rotor and the impeller. This method, also, has defined the optimum number of blades and the axial length of the rotor and the impeller. Mathematical models linking the performance parameters and the design variables for the turbine and the compressor have been developed to assist in carrying out parametric studies to study the influence of the design parameters on the performance and on each other. Also, a new graphical matching procedure has been developed for the gas turbine components. This technique can serve as a valuable tool to determine the operating range and the engine running line. Furthermore, it would decide whether the gas turbine engine operates in a region of satisfactory compressor and turbine efficiencies