Jet Propulsion

Overview and Mechanical Arrangement

• Sir Frank Whittle – 1930

• How does a Jet Engine work?

• - It is an internal combustion engine which produces power by controlled burning of fuel.

• - Air is compressed, fuel is mixed with it and the mixture is burnt.

• - The heat which results produces a rapid expansion of the gas and this is used to do work.

• Jet Engines work by reaction.

• Newton's law – To every action there is an equal and opposite reaction.

Layout of the a Jet Engine(Mechanical Arrangement)

• 3 main components – Compressor, combustion chamber and a turbine

Combustion

Chambers

(Cans)

Jet Pipe

(Exhaust)

Front

Engine

Mount

Compressor

Handling

Bleed ValveIntake Anti-

Icing Tube

Rear

Compressor

Case

Front

Compress

or Casing

Turbine

Section

Rear

Engine

Mount

Oil

Tank

Accessory

GearboxFuel, Oil, and

Hydraulic Pumps,

Electrical Generators, RPM

Governor.

Rotating Assembly

Compressor BladesTurbine

Blades

Shaft

Assembly

What is the problem with an engine?

• It’s Hot.

• Temperature changes cause the shaft and casings to expand and contract

• Solution?

• Bearings.

• The bearings are selected to allow this differential expansion (and contraction on cool down) without causing undue stresses

Front

Bearing

Chamber

Centre

Bearing

Chamber

Rear

Bearing

Chamber

Roller

Bearing

Ball Bearing

(Location

Bearing)

Roller

Bearing

Shaft

Casing

Casing

Hot

section

The bearings provide space to allow for the expansion and contraction.