jet engine in a jar experiment explanation

Jam Jar Rocket Engine

Introduction: Jam Jar Rocket Engine

I am presently a high school student with plans to major in Aerospace Engineering at MIT. Eventually, I want to work for NASA or one of its subcontractors (SpaceX, Boeing, Lockheed Martin, Raytheon, United Launch Alliance, etc.). In preparation for this future, I am beginning a journey of learning about rocket engines with plans to build several different types. In the future, I hope to have posted instructions through this account how to build chemical rocket engines, pulsejet engines, ramjet engines, and more.

The first step in this process begins with what has affectionately become known as the Jam Jar Rocket Engine (for obvious reasons as you'll see). This engine is just short of being a pulsejet engine. If you just added a tube over the hole and put some valves, it could be considered a full pulsejet engine. Before we get started building one, a few things:

1) This engine does not produce much (if any) thrust. Do not plan to use it to propel anything.

2) Building and operating this engine is dangerous. There are fire dangers, heat dangers, broken glass dangers, as well as heat-breaking-glass-and-causing-fire-dangers. Appropriate safety precautions (fire extinguisher, goggles, gloves, location, water bath, etc.) should be taken. I am not responsible if you burn down your house if you do not heed this warning.

3) I tried to be scientific about the design of the Jam Jar rocket, calculating ratios of jar diameter to hole diameter and such. It didn't seem to help. It's more of a trial and error thing. So, don't try to follow someone else's instructions exactly because your results will be a little different depending on the exact jar, lid, fuel, and lighter that you use.

Step 1: What Is a Jam Jar Rocket Engine? Materials

A Jam Jar Rocket is basically a rocket engine made out of a glass jar with a hole and some fuel. It ignites and blows out hot air, then extinguishes and sucks oxygenated air back in, ignites again, then repeats over and over (you hope).

Because it's made of glass, it uses liquid fuel, and it has a short run span, it's not very useful. But, it is a good introduction to rocket engines and is the first step on the way to building bigger, better engines.

To build the rocket engine, you'll need:

- A glass jar with a screw-on lid

- A small drill bit (~ 1/8 inch) and a large drill bit (~ 1/4 inch)

That's it. You'll need some more materials to ignite the engine, but that is it as far as building one.

Step 2: Drill the Hole

Before this step, please put on your eye protection!

The next step is to drill the hole. It is difficult to drill a large hole in one pass, so I recommend that you drill a smaller hole first and then switch to a larger bit and drill a larger hole or use a small bit and work it around.

That's it! You have officially built your first Jam Jar Rocket Engine. Now on to the hard part . . . getting it to work consistently.

Step 3: Prepare to Ignite

To prepare the engine to ignite, you'll need two things:

2) A waterbath to put it in to keep the glass from overheating

There are a number of things that you can use for fuel. Some people use Heet Gas Line Antifreeze. There are two colors. Yellow is methanol and red is isopropyl alcohol. Both should work, but methanol has more health risks. Drinking it can cause blindness and death.

If you can find very pure isopropyl alcohol at your pharmacy, then that's an easy way. The higher the percentage the better. I would not try any less than 75%. Amazon has 99% for less than $10.

Some use 50% or 60% RC Nitro Fuel . The videos with this stuff as the fuel seem amazing! But it's only available in large quantities and is expensive. Maybe at your local RC store?

I used denatured ethanol and it works ok, not spectacular.

Pour enough of the liquid in to cover the bottom about an eighth of an inch and swirl it around.

Now what you have is a jar full of alcohol vapors with a pool at the bottom. That will only work as a bunsen burner because there is no oxygen inside to burn. So, the alcohol vapors will come out and burn in the air, but nothing will happen inside.

Take the lid off and blow inside to get some oxygen in there. Trial and error will tell you how hard and how long to do this.

Put the lid back on and set the engine in your water bath.

Step 4: Ignite

Now, you'll need a barbecue lighter. The longer the neck is, the better. I don't recommend cigarette lighters. They put your hand too close to the action. Here is an Amazon link , but you can usually find them at a dollar store, too.

Now, you've swirled it around, blown in it, put the lid back on, and put it in your water bath. Now just light the lighter just above the hole.

In the videos, you can see one that is just a short Whoosh but never takes off. Be very careful of these because they can keep burning with an invisible flame and hurt you pretty badly. Always put something flat over the top before you put your hand near the lid. These also get very, very hot to the touch.

Another burns for a short time and stops. That is generally seen as an issue with the size of the hole not allowing the right amount of oxygen-laden air in.

Another burns slowly, for a long time. That is generally chalked up to a fuel with a low energy density.

Once you find a combination of jar, hole, and fuel that are perfect, you can get a Jam Jar Rocket Engine that burns well and sustains for a long time.

How To : Your Personal NASA Program from Garbage: How to Build a Pulsing Jar Jet Engine

Jet engines combine oxygen from the surrounding air with on-board fuel to burn at very high temperatures and create thrust in the direction of the flame. Rockets, which we will learn about in a later post, are similar but carry oxygen internally and can therefore function in space!

Contrary to popular belief, jet engines are not hard to make. In just a few minutes, you will be on your way to starting your own personal NASA program! It all begins with the glass jar jet engine!

Methanol (antifreeze is almost pure methanol)
Glass jar with a metal screw cap
Hammer and nail (or a drill)
Safety goggles
Long match (or a ruler to tie a small match onto)

Long matches will keep you a safe distance from the flame.

Step 1 Set Up the Lid

Begin by removing the screw-on lid from the glass jar and placing it onto a piece of junk wood, cardboard, or something else you don't mind drilling a hole into.

The wood will stop the drill from scratching the table, too.

Step 2 Drill a Hole

Drill a small hole at the center of the cap. It's better to start out really small than too large. Later on, you can experiment with different hole sizes to see how they affect the performance of your jar jet engine.

If you don't have a drill, a hammer and nail will work fine.

Step 3 Freeze the Jar

Place your jar in the freezer for a few minutes. This will decrease the likelihood of your glass jar cracking due to overheating.

Wait until the glass frosts, then remove the jar from the freezer.

Step 4 Prepare the Jar

Place the frosty glass jar in a safe, non-flammable environment. I set mine on the shell of an old VCR that I sacrificed to the scavenging gods.

The metal shell will keep heat and broken glass off of the table.

Step 5 Pour In the Methanol

Pour a tiny bit of methanol into the jar, as shown in the following photo.

Just a spoonful or two will be enough.

Step 6 Fasten the Cap

Make sure it is on really tight.

Step 7 Ignite the Jet Engine

Attach the match to the end of your ruler or stick. Light the match away from the jar. With the match extended away from your body, bring the flame to the opening in the cap.

Before lighting your jet, put on safety goggles and make sure all sentient beings are well clear of the jar.
Always have a fire extinguisher on hand when experimenting with fire.
Be sure to let the glass cool down for a few minutes before touching it again.

Step 8 Laugh Maniacally

Part of the methanol that's trapped inside the glass jar floats around as vapor. This vapor flows toward the opening at the top of the jar. When the match flame meets the vapor, it ignites the entire vapor cloud.

The combustion consumes the oxygen in the jar, while more oxygen is sucked in through the lid. This results in the upside-down tornado shape of the jet flame.

Afterthoughts

After the first run, the inside of the cap was burned in a circular pattern! If you look closely, you will see that the burn is slightly lopsided. The hole is likely off center, so the escaping fire oscillates around the opening.

The constant heat caused this jar to break after three uses.

Now, try making your own miniature jam jet engine at home and share your experience with the community! Make sure to post any pictures and videos that you take of your valveless jet engine onto the community corkboard , and if you have any questions, ask them below in the comments or in the forum . I am always here to help make your science dreams a reality.

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11 Comments

This looks like a fun (and not too dangerous) project. How big do you think the hole in the lid would have to be for this not to work? And would a pin-sized hole be too small?

Generally the hole should be about the size of a penny, depending on the size of the jar. Love the article! I made a giant metal one similar to this, that could run continuously off propane. They're so loud!

Pin-sized is too small. Mine was less than half an inch across. The really fun part is to experiment with different sized holes and see how much flame you get.

Hmm... ideas of using a larger jar and making a flame tornado!

That sounds amazing. Be safe and take video!

Yes, please do and post a video of it! :) Excellent article, look forward to future ones! (The flames look like they are going super fast, it reminds me of watching clouds with the speed turned way up? haha)

Glad you liked it! If you try it yourself please share with us in the forums =)

Quick question... you say that antifreeze is almost pure methanol. Is it just the Heet brand gas-line antifreeze then? When I think of antifreeze, I think of engine coolant. And most of today's engine coolant skips methanol in lieu of ethylene glycol. So, that wouldn't work, would it? What I need to get is fuel-line antifreeze that specifically states that it contains methanol, right? Which I guess would be a good thing anyway, since a small bottle of fuel-line antifreeze is way cheaper than a jug of engine coolant.

Yup! You are correct. Get the Heet. It's less than two dollars at my local hardware store.

Great, thanks!

I do not understand this : 'The hole is likely off center, so the escaping fire oscillates around the opening.' --> Why does the hole have to be in the center of the lid? Why does it have to be symmetrical? What's the physics behind it? Thanks

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