This article helps you to create and understand a mini pulse jet engine. Making pulse jet engines can be dangerous for beginners and experts alike. Pulse jets are one of the more simple jets to make. These jets are powered-controlled series explosions of gas and air from a chamber. This controlled series of explosions is the reason for the "pulse" in the name. As the explosion happens, the force of it closes valves that feed air into the combustion chamber. The explosion is forced out the back until it runs out of "oomph" and the force of the air at the front of the jet (as it flies) forces the valves to open in conjunction with the partial vacuum created by outward explosion from the tail end of the jet. The jet gets super-hot during operation and the metal expands. The back of the jet often shoots out long tongues of flame that sometimes have a ribbed appearance. This engine will be the valve-containing type.
- Skill level:
- Moderately Challenging
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Things you need
- Aluminium can
- Standard tin can
- Can opener (smooth-edge type)
- Small nail
- Metal file
- High temperature
- J-B Epoxy Weld
- Drill and bits
- Two heavy wooden blocks and screws to anchor the engine
- Oral syringe (available for free if you ask a retail pharmacist)
- Screwdriver and (if the screwdriver isn't flexible) a Pair of needle-nosed pliers
- Hair dryer
Take the can of food and open it using the smooth-edge opener. Empty it out into a bowl for later consumption. Clean and dry the can and lid. Cut a small hole in the lid for the flame to escape. Take a small nail and puncture some holes in the bottom of the can from the inside out (so that the inside of the can is smooth. Be careful not to get cut on the can. Make sure that the holes are in the middle of the can and not on or very near the concentric rings in the bottom of the can.
The original type of pulse jet consists of a metal tube that can withstand the heat of operation. It has two intake "holes" at the front. One is for usually fuel injection where the fuel is 'injected" but we will use this to light the engine instead. The other intake hole is much larger and is used to draw in air. The small holes you have put in the bottom of the can are the air intake holes, even though we will refer to it as the air intake hole. A second hole will be referred to as the fuel injection hole even though it is really used to ignite the engine. The fuel injection hole must be cut into the side and be made small (diameter of a small nail).
Cut a very small "fuel injection" hole using a drill into the side of the can. Put a block inside the can and clamp it down so that the can doesn't get away from you as you are drilling. Since the fuel is going to be limited to the liquid that we are providing and this version of the engine is designed to run only in short bursts of time to avoid burning itself up, this hole will be used for ignition only at this point though you can experiment later. Use a file to file down any sharp edges to avoid injury.
Cut a small piece of aluminium can that can cover the holes that you just put into the bottom of the can. Use the J-B Weld to affix it in a way that allows it to flap freely. This forms a type of valve that blocks the gas as a one-way valve so that when the gas expands in the can, it goes out the back and not the front. A partial vacuum will form after the gas cools slightly, sucking in more air from the front as needed.
Place the lid that you removed using the can opener back on the can. Tip the can on end and let it stick its exhaust up in the air. Make sure that you use the spare blocks at this point to sit under your can in a way that allows the air to enter the intake (the valve side of the can). Make sure that you affix the can to the two blocks using a screw in each block. You might do this by drilling into the sides of the can at the extreme front of the can and predrilling a hole into the blocks of wood where you want the screws to go in. The holes in the wood and can need to be the right size so that there is no leaking from the can and there is good "bite" into the wood. The difficult part comes in getting the screws into these holes and then into the blocks. If your screwdriver is short (or flexible) enough, you can potentially tighten the screws or instead opt to use needle-nosed pliers to tighten it. If you do a test run and are confident of the hole size in your lid, you can use the J-B Weld to make it permanent.
Light the engine after covering the openings to the engine and the engine is shaken to distribute the flammable liquid fuel. You will need to be careful that there is no leaking out the front. Additionally, if there is too much fuel vapour and the fuel air mixture isn't just right, the engine will be hard to start up. Shaking the can distributes the fuel which evaporates enough to supply vapour. Since you have a series of holes in the chamber, you have to be careful of any fuel that leaks out as it is a fire hazard. Use the oral syringe to draw the methanol and then gently squirt a small stream of liquid down around the inside of the can, allowing the chance for the liquid to form vapour as it runs down the insides of the can. Do not inhale the vapour; make sure that you can still keep the vapour in the can for combustion. The liquid that runs down the sides should be stopped by the concentric circles in the bottom of the can. Get your long-nosed lighter ready. The fuel injector hole is used in smaller engines mainly for ignition, rather than to inject more fuel. Light the lighter and put it up next to the hole so that the flame goes inside the can through the little hole for ignition. The engine may need a lot of fine tuning to get it working just right. You also have to use the hair dryer to force in hot air into air the intake past the valve so that the engine gets enough air into the fuel air mixture to run. Remember that this engine is only supposed to run for shot periods of time to avoid overheating of the parts but this should be enough to get you started. Be safe and always work under the supervision of an expert. Better yet, have an expert do this for you so that you don't get hurt.
Tips and warnings
- Do not do this at home. This article is for information/entertainment purposes only and by doing anything in this article, you acknowledge that you are doing so at your own risk and assume any and all responsibility. Jet engines are extremely dangerous and tricky to light.
- Methanol is highly flammable and toxic. Make sure to use the ethanol in a well ventilated location and wear gloves so you don't absorb it through your skin.
- Wear adequate ear protection as the engine gets loud.
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