TURBO-PROP ENGINE

TURBO-PROP ENGINE (OR) TURBO-PROPELLER ENGINE

A turboprop engine is a turbine engine that drives an aircraft propeller. It is very similar to turbojet engine. In this type, the turbine drives the compressor and propeller. The world's first turboprop was designed by the Hungarian mechanical engineer Gyorgy Jendrassik. Jendrassik published a turboprop idea in 1928, and on 12 March 1929 he patented his invention.

Classification of Turboprop Engine

1. According to Spool
(a) Single Spool Turboprop Engine
(b) Double Spool Turboprop Engine
(c) Triple Spool Turboprop Engine

2. According to installation
(a) Pusher type Turboprop Engine
(b) Tractor or Puller type Turboprop Engine

Construction

It consists of:
(1) Diffuser
(2) Compressor
(3) Combustion chamber
(4) Exhaust nozzle
(5) Reduction gear and
(6) Propeller

Working

Air from the atmosphere enters into turbo prop engine. The air velocity gets reduced and its static pressure is increased by diffuser. Then the air passes through the rotary compressor in which the air is further compressed. So, the static pressure of the air is further increased. Then the high pressure air flows into the combustion chamber. In the combustion chamber, the fuel is injected by suitable injectors and the air-fuel mixture is burnt. Heat is supplied at constant pressure. The highly heated products of combustion gases are then enters the turbine and partially (about 80 to 90%) expanded. The power produced by the turbine is used to drive the compressor and propeller.

Propeller is used to increase the flow rate of air which results in better fuel economy. The hot gases from the turbine are then allowed to expand in the exhaust nozzle section. In the nozzle, pressure energy of the gas is converted into kinetic energy. So the gases coming out from the unit with very high velocity. Due to high velocity of gases coming out from the unit, a reaction (or) thrust is produced in the opposite direction. The total thrust produced in this engine is the sum of the thrust produced by the propeller and the thrust produced by the nozzle. This total thrust propels the air craft.

Advantages

1. High take-off thrust.
2. Good propeller efficiency at a speed below 800 km/hr.
3. Reduced vibration and noise.
4. Better fuel economy.
5. Easy maintenance.
6. It operates over a wide range of speeds due to multishaft arrangement.
7. The power output is not limited.
8. Sudden decrease of speed is possible by thrust reversal.

Disadvantages

1. The main disadvantage is, the propeller efficiency is rapidly decreases at high speeds due to shocks and flow separation.
2. It requires a reduction gear which increases the cost of the engine.
3. More space needed than turbojet engine.
4. Engine construction is more complicated.

Applications

The turbo prop engine is best suited for commercial and military air-craft operation due to its high flexibility of operation and good fuel economy.

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