# How pulsejet engines work

Today, I’m going to talk a little bit about how pulsejet engines work.

I’m gonna do my best to explain how pulsejet engines work to you

This is a typical pulsejet engine, is pretty much a long pipe.

In fact if I take the front off you see it’s a hollow tube. You can see right through the damn thing.

There’s nothing in there except what you see on the outside, but the shape of the tube and the length and dimensions are very critical because this is how the pulse jet works.

Take our engine, let’s look at the combustion chamber which is this piece in the front this round cylinder here in the front. This is filled with a highly combustible mixture of fuel and air.

Fuel can be gasoline propane, diesel, jet fuel. In fact, anything that will burn in the presence of air.

## A Detailed Explanation of How Pulsejet Engines Work

Let’s assume we’ve filled it up with a mixture of air and fuel in this case, that we’ve got a spark plug in there. We create a spark and boom, it ignites!

That means that the gas inside expands rapidly gets hot and when things get hot they expand. So, suddenly there’s a lot of pressure in this combustion chamber area. When you have a gas under pressure it tries to flow as quickly as it can to an outlet. At the outlet the pressure equalises with the air outside.

In this case that flow is from the combustion chamber through the taper which actually makes it go faster down the tailpipe, and out of the end.

How Pulsejet Engines Work – Science History

Isaac Newton was a smart guy. He figured that he’d look at the laws of nature. He discovered or observed that for every action there’s an equal and opposite reaction.

Just as our hot-gases are racing down the tailpipe, in that direction the same amount of force is applied to the engine.

In that direction the guesses go one way, and the engine tries to go the other way.

That attempt to go the other way is the thrust that creates the force on the engine, the motive force.

So, here we have it the fuels exploded. All the gases are rushing out the back. But, what happens next?

If that was it,  it would simply go “bang” and give a little push, and then it would stop…

So, how do pulsejet engines work, and continue operating?

It’s a really interesting article about pulsejets.

Now, as the hot gas is rushed down the tailpipe driven by the pressure in the combustion chamber and pushing on the front, eventually the pressure in the combustion chamber runs out.

Effectively, all the air and fuel has been burnt all, the gases have expanded now suddenly, the pressure in here is the same as the pressure outside.

But, the gas is in the tailpipe because the gases are still flowing down here very very quickly. So, this becomes what I like to think of as a a giant syringe, and in effect the gases in the tailpipe here will act like the plunger and a syringe. They’ll be going this way, pulling on the combustion chamber where the gases in the combustion area.

And, it’ll create what looks like a vacuum. Not a perfect vacuum, but a reduction in pressure. Now, instead of having more pressure than outside the chamber has less pressure than outside.

These gases because they are travelling so fast, and they have a weight or a mass, they continue to travel outwards towards the tailpipe end.

This means that the pressure here continues to fall, and eventually it falls so far that some little valves in the front of the engine are pushed open. Pushed by the air pressure outside the difference wing.

The pressure outside of the pressure inside, applies a force to those little valves and they open up now, when they open up the outside air. Air can rush into the chamber. It rushes in and it mixes with air  and with fuel, so suddenly that the chamber becomes filled with fuel.

Here again just like when we started the cycle repeats itself.

Now of course, because these guests in the tailpipe are also subjected to that partial vacuum that we’ve created in the chamber they slow down and they start to go backwards so explosive mixture hot gases flame when they meet boom.

It all starts again, and the pulse jet cycles constantly, sucking in the front, blowing out at the back.

There’s only one moving part in this engine and it’s the little valves in the front. They are very small, light valves, driven only by the air pressure from the outside of the engine.

Why doesn’t the hot gas rush in at the front when it can when the combustion occurs? That’s because because those little valves closed now one-way valves only let air in there won’t let anything out. That’s also how it works!0 Utter simplicity and it’s a simplicity that makes these engine so very very attractive to people who want to build them because all you need to do is create a tube like combustion chamber.

This with the right dimensions and a valve plate, like this which is not a particularly hard job. Stick to this MP and the two together add fuel and air and you’ve got yourself a real jet engine now. Obviously it’s not quite that simple and there are a few little things to think about and so what I’ve done is I’ve created an ebook an electronic book that you can download from the website polish.