Most of us has often heard of ram
jet engine. If you are not aware of ram jet engine then it is recommended to
first study ram jet engine. You can read about ram jet engine in
my previous post.
Pulse jet engine is much similar
to ram jet engine. Main difference in pulse jet engine is of the combustion. In
ramjet combustion takes place continuously while in pulse jet combustion takes
place in pulse. First pulsejet engine was invented by Russian inventor N.
Teleshov in 1864 one Swedish inventor Martin Wiberg also claimed for patent.
The first working pulsejet was patented in 1906 by Russian engineer V.V.
Karavodin, who completed a working model in 1907.
Pulse jets are of mainly two
types
1) Valved
Pulsejets
2) Valve
less Pulsejets
Valved Pulsejets consists
of mechanical valve arrangement at inlet through which air enters in the pulse
jet. The valve has arrangement such that the flow is maintained in one
direction only (one way valve). This mechanical valve is reed valve.
Valve less pulsejets have
no moving part like valve but they uses their geometry to control flow
direction. This pulse jets expels gas in both direction inlet and outlet.
Valveless pulse jet engines is similar to valved pulse jet but the valve is
geometry of pulse jet. Today any valveless engine can be started through fuel
and spark. And once started the self sustaining cycle is maintained by
providing fuel and spark in combustion chamber. Valveless pulsejets come in a
number of shapes and sizes, with different designs being suited for different
functions.
We will learn valved pulse jet in
detail
Construction
Valved pulse jet is simple and
low cost construction type engine. It consists of a reed valve, tube,
combustion chamber, spark plug. This arrangement is shown in figure. There are
generally two type of valve A daisy valve which consists of thin sheet of
material to act as a reed and A rectangular valve grid which is more effective
than daisy valve.
Working
Pulse jet engines work on lenoir cycle
(Lenoir cycle is a cycle consists of 3 process or say it lacks compression
turbine in brayton cycle and other processes are same as brayton cycle). As it
lacks compression stage it has limited compression ratio of 1 to 1.5 .
The combustion cycle has five to
six phases depending on engine, generally Induction, Compression, (optional)
Fuel Injection, Ignition, Combustion, and Exhaust. In ignition high pressure is
raised by combustion of fuel-air mixture. This mixture cant exit from front due
to one way valve. The inertia reaction of this flue gas provide thrust to
engine. this force provide propulsion to airframe or rotor blade. The leaving
gas produces pressure drop in combustion chamber lower than require inlet pressure
hence valve is again opened and fresh charge enters in combustion chamber and
cycle repeats.
Animation image from wikipedia
will clear your all doubts.
Advantage
-Excellent thrust to
weight ratio.
-It
can start on its own, i.e. does not need starting velocity.
-Cheaper to build.
-Simple
in construction compared to turbojet engine.
Disadvantage
-Intermittent
combustion produces sever vibrations.
-Sometime valve wears
out and engine fails.
-Poor thermal
efficiency.
-As it is affected by
air density it has limited operating altitude.
Application
Today pulsejets are used in
target drone aircraft, fog generators, industrial drying and home heating
equipment. Sometimes it is used to
provide power in experimental helicopter.
V-1 flying bomb is powered by
pulsejet. Below is image of it.
You can find some interesting information on
ramjet from link given below.
I hope you have find
this article helpful. Please like and share (because sharing is caring) our
blog and check it for new articles.
Please like and share our facebook page for cool engineering
concepts:- Facebook
Comments
Post a Comment