Aircraft engines Flashcards
Piston engine
Most common type is the 4/piston engine
Older aircraft have cylinders arranged radially around the crankshaft
Operation of a 4/piston engine
Stage one intake : The piston lowers and the valves open releasing and if fuel into the chamber
Stage two compression: The cylinder compresses the air and fuel
Stage three power: The spark plug ignites the compressed mixture forcing the piston down and creating an explosion
Stage four exhaust: The exhaust valves open and the cylinder pushes the exhaust gases out of this opening
Turbocharging
Provides high pressure air to boost manifold pressure
No physical link to engine
Turbine driven by exhaust air
Supercharging
Compressor forces a greater mass of air into the engine
This is achieved by mechanically or belt driven compressor
And advantage is that engines can fly at greater altitude than naturally aspirated engines
Types of gas turbine engines
Turbo jet
Bypass turbo fan
Turboprop
Components and operation of turbo jet engines
Consist of an air intake, air compressor, combustion chamber, gas turbine and a nozzle.
Air is compressed into the chamber, heated and expanded by fuel combustion then allowed to expand through the turbine and into the nozzle where it is accelerated to high-speed as exhaust gases which provide propulsion
Advantages/Disadvantages/uses of turbo jet engines
Inefficient if flown below Mach 2 and noisy
Most modern aircraft use turbo fans instead for economic reasons
Still common in medium range cruise missiles due to high exhaust speed, low frontal area and relative simplicity
Types of turbo jets
Centrifugal turbo jet
Axial turbo jet
Operation/characteristics of centrifugal turbo jet
Air is forced outwards during compression (airflow changes direction)
Advantage: allows for a compact engine
Disadvantage: less efficient than axial flow
Operation of axial turbo jet engines
Compresses are in line with each other and drawers and into the engine where these compresses then increase the pressure.
Air then flows into combustion Chambers where it is mixed with fuel and ignited
Provides high temperature and high velocity air which is been expelled out of the chamber and through a series of turbines
after passing through the turbines exits through the exhaust module providing a reactive force which is thrust
Advantages of axial turbo jet engine
Minimal moving parts therefore high reliability
Hi thrust/weight ratio
Small frontal area
High thrust at high-speed
Disadvantages of axial turbojet engines
High initial expense
High noise levels
Prone to foreign object damage
More specialist maintenance required
Bypass turbo fan engines Operation
The core acts as an axial turbo jet
The rest of the airflow bypasses the core to provide cooling and later mixes with stream from the core to reduce noise
The bypass air produces more thrust efficiently than the high-speed air from the core reducing fuel consumption
Operation of a turbo prop engine
Has similar components twin axial turbo jet except primary thrust is not produced by exhaust gases
The turbine is connected to the propeller via gearbox the gearbox slows down the spinning and it’s connected to the propeller
The rotation of the propeller produces the primary thrust
Advantages of turboprop engines
Minimal moving parts
High reliability
High thrust/weight ratio
Small frontal area
Low noise levels
Free spinning power turbines allow optimum engine and propeller efficiency
