Development of a novel gas turbine driven centrifugal compressor

The purpose of the paper is to provide design and operational information for the conversion of small turboprop engines into land-based shaft power drives. These can provide economical solutions to individual power requirements such as standby electrical generators, combined heat and power units, fan drives or centrifugal compressor drives. Considerable numbers of ex-military engines are currently becoming available at economical prices. One such engine is the Rolls-Royce Dart turboprop gas turbine which, although there are over 2000 still in civil and military service worldwide, is now being phased out of Royal Air Force operation. This paper describes the modification of a Dart RDa 12 engine to drive a centrifugal compressor from a smaller RDa 7, Mk 552, engine for a compressed air facility on a university campus. The modified engine has a power of over 2400 hp (1790 kW) at 15000 r/min and the compressor was driven directly from the engine output shaft supplying 10.5 kg/s of air at a pressure ration of 3.3:1. To achieve this, the turboprop's main reduction gearbox was removed, the teeth on the engine drive pinion ground down and a flexible coupling fitted to it to drive the RDa 7 compressor which was flange mounted on the engine gearbox-air intake casing. The removal of the main gearbox removed the drives to the lubricating oil pumps the fuel pump and the engine control system. The manner in which these problems were overcome and the method of operating the system are described. One of the most important considerations in starting such a direct drive system is the complete closing off of the air intake to the driven compressor and the design of an annular valve to perform this duty is described. The operating parameters including the flow, pressure ratio and engine turbine entry temperatures for this system are given.