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| All About Pulsejet Engines |
| To find out more about the history of valveless pulsejets click here to read the paper by Bruno Ogorelec |
More coming soon, including how valveless pulsejets work.
Copyright © 2005 Eric Beck
Mechanically speaking, pulsejet engines are a very simple type of engine. There are many
different pulsejet designs, and several different types. As with all jet engines, pulsejets use a
stream of high velocity exhaust gas to create thrust. Pulsejets are jet engines, not rockets.
Valved Dynajet Valveless Lockwood
Pulsejets can be made in a variety of shapes and sizes, but the two basic types are valved
engines, and valveless engines.
A valved engine uses a mechanical apparatus in order to control the flow of air in and out of
the engine. This can make an engine more advanced and able to produce much more power,
but it is also much more complex to design and make. Valved engines usually require a
considerable amount of machining, and very accurate work.
Valveless engines on the other hand use only their geometry to control the flow of air in the
engine. Valveless engines have zero moving parts, and are the simplest type of jet engine
capable of producing static thrust. Valveless engines can be made in a variety of shapes,
some looking quite odd in comparison to valved engines. Most valveless engines cannot
compete with valved engines, mainly because their design is much more complex and few, if
any design is really putting out as much power as it is capable of.
A valved engine consists of a few major parts:
The valve head is the major part of the engine. In a small engine it is designed to act as a
carburetor, which draws fuel and mixes it with air before it enters the tailpipe. The valve head
contains the fuel system, the valves, and the valve retainer system. In larger engines fuel may
be injected directly behind the valves, into the tailpipe.
The valve needs to open a very specific distance, and in order to keep it from opening too far,
a valve retainer is used. By adjusting the valve retainer you can adjust how much fuel and air
enter the engine.
The fuel system delivers fuel to the engine, and may use liquid fuel or gaseous fuel such as
propane.
The valve head is attached to the tailpipe with an airtight seal, it is very important that there
are no leaks in this area.
The valves themselves are made from thin tempered carbon spring steel. The thickness
usually ranges between .006” for small engines and .012” for larger engines. A pulsejet
engine will fire at up to several hundred times a second, and the valves really take a beating.
Because of this they do not last long, valves are easy to make and are considered disposable
parts, as they need to be replaced every 30 minutes or less.
Now lets take a look at what actually goes on inside the engine:
Compressed air pulls fuel into the valve head, and forces the valves open.
The fuel air mixture travels past the valves and into the engine where it can be burnt.
To start the engine air must be forced into the engine (BLUE) and mixed with fuel. The fuel
air mixture (GREEN) is then lit in order to start the pulsejets operating cycle. The easiest way
to start a pulsejet is to use a spark plug with a spark source that produces sparks many times
a second.
A small pulsejet is designed so that when forced air is applied, fuel is sucked up through the
fuel line, and sprayed through a fuel venturi so it can mix with the air. Larger engines may use
fuel pumps or use gaseous fuel like propane. It is possible to also run small engines on
propane.
When forced air is supplied from an air compressor gun, the fuel air mixture then forces the
valves to open, but only as far as the valve retainer will allow. Once the proper quantity of fuel
and air has entered the engine it reaches the spark plug and ignites.
The pressure increases inside the engine, and the valves slam shut.
The exhaust now can only go out of the exhaust pipe.
The fuel mixture will burn and cause the valves to slam shut. Because the valves close the
exhaust gas can only go out the back of the tailpipe, creating thrust in the process. After the
super hot exhaust gas has mostly left the tailpipe, the pressure in the combustion chamber is
below atmospheric pressure. The pressure in the valve head intake is now more than in the
combustion chamber, so the valves are forced open. When this happens a fresh charge of
fuel and air enter the engine.
The pressure falls and the engine takes in more fuel and air.
Returning exhaust gas ignites the fresh fuel charge.
As the combustion chamber is being filled with a fresh fuel charge, hot exhaust gas is also
being pulled back towards the combustion chamber. When the two meet it ignites the fresh
fuel air charge. At this point there is no need to use the spark plug, and the spark source can
be turned off. The engine will continue to operate until out of fuel, or until the valves fail.
Pulsejets burn the fuel air mixture very quickly, creating a loud bang. Because these engines
can operate at several hundred pulses per second, the quantity of noise is unbelievable.
When running pulsejets you absolutely need hearing protection, and when running large
engines you absolutely need to wear both earplugs and shooting earmuffs!
different pulsejet designs, and several different types. As with all jet engines, pulsejets use a
stream of high velocity exhaust gas to create thrust. Pulsejets are jet engines, not rockets.
Valved Dynajet Valveless Lockwood
Pulsejets can be made in a variety of shapes and sizes, but the two basic types are valved
engines, and valveless engines.
A valved engine uses a mechanical apparatus in order to control the flow of air in and out of
the engine. This can make an engine more advanced and able to produce much more power,
but it is also much more complex to design and make. Valved engines usually require a
considerable amount of machining, and very accurate work.
Valveless engines on the other hand use only their geometry to control the flow of air in the
engine. Valveless engines have zero moving parts, and are the simplest type of jet engine
capable of producing static thrust. Valveless engines can be made in a variety of shapes,
some looking quite odd in comparison to valved engines. Most valveless engines cannot
compete with valved engines, mainly because their design is much more complex and few, if
any design is really putting out as much power as it is capable of.
A valved engine consists of a few major parts:
The valve head is the major part of the engine. In a small engine it is designed to act as a
carburetor, which draws fuel and mixes it with air before it enters the tailpipe. The valve head
contains the fuel system, the valves, and the valve retainer system. In larger engines fuel may
be injected directly behind the valves, into the tailpipe.
The valve needs to open a very specific distance, and in order to keep it from opening too far,
a valve retainer is used. By adjusting the valve retainer you can adjust how much fuel and air
enter the engine.
The fuel system delivers fuel to the engine, and may use liquid fuel or gaseous fuel such as
propane.
The valve head is attached to the tailpipe with an airtight seal, it is very important that there
are no leaks in this area.
The valves themselves are made from thin tempered carbon spring steel. The thickness
usually ranges between .006” for small engines and .012” for larger engines. A pulsejet
engine will fire at up to several hundred times a second, and the valves really take a beating.
Because of this they do not last long, valves are easy to make and are considered disposable
parts, as they need to be replaced every 30 minutes or less.
Now lets take a look at what actually goes on inside the engine:
Compressed air pulls fuel into the valve head, and forces the valves open.
The fuel air mixture travels past the valves and into the engine where it can be burnt.
To start the engine air must be forced into the engine (BLUE) and mixed with fuel. The fuel
air mixture (GREEN) is then lit in order to start the pulsejets operating cycle. The easiest way
to start a pulsejet is to use a spark plug with a spark source that produces sparks many times
a second.
A small pulsejet is designed so that when forced air is applied, fuel is sucked up through the
fuel line, and sprayed through a fuel venturi so it can mix with the air. Larger engines may use
fuel pumps or use gaseous fuel like propane. It is possible to also run small engines on
propane.
When forced air is supplied from an air compressor gun, the fuel air mixture then forces the
valves to open, but only as far as the valve retainer will allow. Once the proper quantity of fuel
and air has entered the engine it reaches the spark plug and ignites.
The pressure increases inside the engine, and the valves slam shut.
The exhaust now can only go out of the exhaust pipe.
The fuel mixture will burn and cause the valves to slam shut. Because the valves close the
exhaust gas can only go out the back of the tailpipe, creating thrust in the process. After the
super hot exhaust gas has mostly left the tailpipe, the pressure in the combustion chamber is
below atmospheric pressure. The pressure in the valve head intake is now more than in the
combustion chamber, so the valves are forced open. When this happens a fresh charge of
fuel and air enter the engine.
The pressure falls and the engine takes in more fuel and air.
Returning exhaust gas ignites the fresh fuel charge.
As the combustion chamber is being filled with a fresh fuel charge, hot exhaust gas is also
being pulled back towards the combustion chamber. When the two meet it ignites the fresh
fuel air charge. At this point there is no need to use the spark plug, and the spark source can
be turned off. The engine will continue to operate until out of fuel, or until the valves fail.
Pulsejets burn the fuel air mixture very quickly, creating a loud bang. Because these engines
can operate at several hundred pulses per second, the quantity of noise is unbelievable.
When running pulsejets you absolutely need hearing protection, and when running large
engines you absolutely need to wear both earplugs and shooting earmuffs!
