Development of a novel gas turbine driven centrifugal compressor

The purpose of the paper is to provide design and operational information f or the conversion of small turboprop engines into land-based shaft power dr ives. These can provide economical solutions to individual power requiremen ts such as standby electrical generators, combined heat and power units, fa n drives or centrifugal compressor drives. Considerable numbers of ex-milit ary 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 modificat ion of a Dart RDa 12 engine to drive a centrifugal compressor from a smalle r RDa 7, Mk 552, engine for a compressed air facility on a university campu s. The modified engine has a power of over 2400 hp (1790 kW) at 15 000 r/min a nd the compressor was driven directly from the engine output shaft supplyin g 10.5 kg/s of air at a pressure ratio of 3.3.1. To achieve this, the turbo prop's main reduction gearbox was removed, the teeth on the engine drive pi nion ground down and a flexible coupling fitted to it to drive the RDa 7 co mpressor which was flange mounted on the engine gearbox-air intake casing. The removal of the main gearbox removed the drives to the lubricating oil p umps the fuel pump and the engine control system. The manner in which these problems were overcome and the method of operating the system are describe d. One of the most important considerations in starting such a direct drive sy stem 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.