Starting Characteristic Analysis of a Radial Inflow Turbine for the Re-Generative Brayton Cycle(Thermal Engineering)

Microturbines have been developed as compact gas turbines to be applied in the re-generative Brayton cycle. A typical microturbine is composed of a centrifugal compressor and a radial inflow turbine. As such, the microturbine has a characteristic peculiar to radial inflow turbines. An idling state known as the windage point for mass flow rate can be formed because of improper inlet flow conditions for turbine expansion flow. The present study looked at the relationships between the radius ratio of the radial inflow turbine to the centrifugal compressor and the starting characteristic, and at the effects of turbine inlet flow conditions on the starting characteristic. Fundamental equations for the relationships between the radius ratio and the starting characteristic were obtained. There was a limitation for the radius ratio of the turbine rotor to the compressor where stable operation without compressor surge could be obtained. Pressure loss and heat loss between the compressor outlet and turbine inlet where a recuperator is placed significantly affected the turbine starting characteristic. In particular, the heat loss had a considerable effect to increase starting pressure. Regarding stable operation near the limitation for the radius ratio of the turbine rotor to the compressor, operation with ignition at a low rotation speed was proposed and the effectiveness of the equations was compared with experiment results obtained with a 150kW class prototype microturbine.