Introduction
The invention of the aircraft was one of the most
revolutionary inventions in human history. The
various advancements in science and technology
have created a variety of engines but the basic
principle that drives them is very similar. All
the aircraft engines work on the Principle of
Newton’s third law of motion. Aircraft engines
require a system that can provide thrust so that
the aircraft is propelled forward. In most aircraft
engines the basic mechanism is to accelerate a
working fluid that pushes the aeroplane forward,
while the gas moves backwards with high force.
Analysis
Gas Turbine Engines
Most of the modern aircraft engines are powered
by the gas turbine engines which are also called
as the Jet engines. They are called Jet engines
because the take in a lot of air, compress it
and pushes it behind through a nozzle at high
pressure, which gives the aircraft the necessary
thrust to move forward. In a typical Jet engine,
the inlet sucks in air from the surrounding atmosphere.
The air from the atmosphere passes into the compression
chamber, where it is compressed to very high pressures.
The compressed air is mixed with highly inflammable
fuels like aviation fuel. The mixture is the pushed
into a combustion chamber where the air-fuel mixture
is ignited. The ignited fuel releases explosive
power that is allowed to pass through a set of
rotating fans called turbines. The turbines are
similar to the turbines that are used in hydroelectric
plants and rotate at a fast rate because of the
flow of the highly pressurized heated air that
passes through it. The turbines provide the mechanical
power to the aircraft. The turbines convey the
rotary energy to other parts of the engines with
the help of shafts that moves other components
in the engine. Part of the power is used to turn
the compressor, which sucks in a steady current
of air into the compression chamber. The remaining
hot gases are released from the combustion chamber
at high pressure, which gives the thrust to the
engine. The release of hit compressed gases provide
huge explosive power for the plane to get enough
power at takeoff and also to cruise at high speeds
[Glenn Research Center, 2004]
Jet engines are further classified Turbofans,
TurboShaft and TurboProp Engines. All these engines
use the same principle of Jet engines but they
are put to different uses. The Turboprop engine
uses energy from the engine to run fans mounted
on the outside of the plane. TurboShaft engines
are similar to Turboprop engines except that the
shaft is used to power a variety of additional
gadgets. The Turbofan engine has additional fans
located on the front of the aircraft that draws
additional air into the engine [GE, 2004]
Piston Engines
Piston engine are internal combustion engines
that burn a mixture of fuel and air inside a combustion
chamber. The chamber is provided with a piston
that moves within the compression chamber. The
energy for the movement of the piston is provided
by the air-fuel mixture. Piston engines operate
similar to the car and other automobile engines.
In its basic operation, a valve in the engine
permits air into the chamber (called the cylinder)
which is compressed by the moving piston. When
an appropriate compression is reached, fuel is
allowed into the compressed air through another
inlet as a fine spray. Finally, the compressed
fuel-air mixture is ignited with a spark provided
by a spark plug, which causes the mixture to explode
violently. The explosive power is used to move
the piston back, and remove the exhaust gases
from the compression chamber. The return movement
of the piston is conveyed to the wheel and fans
of the aircraft which causes it to rotate at high
speed. In a propeller powered aircraft, much of
the thrust is created by the propellers, which
creates the upward lift for the aircraft.
The piston engines were used to rotate the fans
at high speeds which provide the thrust for the
aircraft to move forward. Since the thrust that
could be developed by the piston engine is limited,
they cannot be used in aircrafts that need high
speed and thrust. Hence, piston engines are mostly
restricted to training flights and slow flights.
There were many modifications like the supercharger
that were added to the piston engine which provided
extras thrust to the existing engines. The supercharger
pumped in more air into the cylinder for better
compression and burn ratios. Many experiments
with water cooled engines, air cooled engines,
four stroke and two stroke engines were made before
they fell out of favor with the authorities who
were exposed to the explosive power of the Jet
engines. Piston engines are less costly, easier
to maintain and consumes lesser fuel. They are
a favorite with hobbyists and recreational users
who use such engines to power hand gliders and
miniature aircrafts. They are limited by the altitude
and speed to which they can climb because as the
sir gets thinner, lesser air enters the cylinder
thereby chocking their efficiency to burn fuel.
Rocket Engines
Rocket engines produce the most power in the class
of aircraft engines. They need so much of power
in order to push the aircraft outside the gravitational
pull of the earth. Rocket engines use a mixture
of oxygen and a very combustible material to produce
the thrust. The uniqueness of the rocket engine
is that it carries its own oxygen to ignite its
fuel. This is very different from the working
of the jet engine, which takes air from the surroundings
to ignite the fuel. Hence, a rocket engine can
go into space where there is no air. Rocket engines
use mainly two types of fluids. In a liquid fluid
rocket engine, liquid fluid and an oxidizer are
maintained in different chambers and they are
mixed in a combustion chamber when the need arises.
In solid fluid engines, the mixture of the fuel
and the oxidizers, which is inert at low temperatures
are maintained in a tank and is burnt when the
need arises to release the power. Solid propellants
provide higher range due to the lesser weight
and better efficiency of the fuels [Glenn research
center 1, 2004]
|