The PW200 Turboshaft
By Serge Richer
In the late 1980’s, Pratt & Whitney Canada (P&WC) launched the PW200, a new line of helicopter turboshaft engines. Today, the PW200 series engine is installed in a broad range of new generation, light-twin helicopters around the world, including the Agusta A109E, Bell Model 427, Eurocopter EC135P1, MDHI MD Explorer and the Kazan Ansat.
The PW206 engine family, rated at a nominal 600 shaft horsepower (shp), evolved to the PW207 engine, with a nominal 700 shp. The PW207 engine delivers increased power through component and material improvements and by incorporating compressor treatment for enhanced handling capability. In addition, its digital engine control system incorporates built-in engine condition monitoring system (ECMS) functions. P&WC certified the first helicopter with a full authority digital engine control (FADEC) system on the PT6B-36, and with the first integrated ECMS on the PW207. This evolution is in keeping with the maintenance approach promoted by P&WC, and used effectively over the years, which is based on a philosophy of preventive maintenance through engine condition monitoring.
Principles of operation
The PW207 is a lightweight, free turbine turboshaft engine incorporating a single stage centrifugal compressor driven by a single stage turbine. A single stage power turbine drives a reduction gearbox comprised of two stage helical gear train (6,000 RPM).
Metered fuel from the fuel control is sprayed into a reverse flow annular combustion chamber through 12 individual fuel nozzles mounted around the gas generator case. A high voltage ignition unit and dual spark igniters start combustion. A single channel, digital electronic control system, with a mechanical backup fuel control, ensures accurate control of engine output speed and fast response to changes in power demand. An electrical torque motor located within the fuel metering module (FMM) works in conjunction with the electronic engine control (EEC).
Inlet air enters the engine through a radial inlet plenum chamber, formed by the compressor inlet case, and is directed rearward to the centrifugal impeller. High-pressure air from the impeller passes through diffuser tubes, which turn the air 90 degrees in direction and convert velocity to static pressure. This high-pressure air surrounds the combustion chamber liner.
The combustion chamber liner consists of two annular weldments bolted together at the rear dome-shaped end and an outer liner, which incorporates an integral large exit duct. The liner assembly has perforations of various sizes that allow entry of compressor delivery air. The flow of air changes direction 180 degrees as it enters and mixes with fuel.
Fuel is injected into the combustion chamber liner through 12 fuel nozzles arranged evenly around the gas generator case for ease of starting. The nozzles are supplied with fuel by a flow divider and fuel manifolds. The air/fuel mixture is ignited and the resultant gases then expand from the combustion chamber, reverse direction in the exit duct zone, and pass through the compressor turbine stator vanes to the single stage compressor turbine.
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