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 drill
- 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.