Over the years [Integza] has blown up or melted many types of jet engine, including the humble pulsejet. Earlier improvements revolved around pumping in more fuel, or forced air intakes, but now it’s time for a bit more refinement of the idea, and he takes a sidestep towards the more controllable detonation engine. His latest experiment (video, embedded below) attempts to dial-in the concept a little more. First he built a prototype from a set of resin printed parts, with associated tubing and gas control valves, and a long acrylic tube to send the exhaust down. Control of the butane and air injection, as well as triggering of the spark-ignition, are handled by an Arduino — although he could have just used a 555 timer — driving a few solid state relays. This provided some repeatable control of the pulse rate. This is a journey towards a very interesting engine design, known as the rotating detonation engine. This will be very interesting to see, if he can get it to work.
Detonation engines operate due to the pressure part of the general thrust equation, where the action is in the detonative combustion. Detonative combustion takes place at constant pressure, which theoretically should lead to a greater efficiency than boring old deflagration, but the risks are somewhat higher. Apparently this is tricky to achieve with a fuel/air mix, as there just isn’t enough oomph in the mixture. [Integza] did try adding a Shchelkin spiral (we call them springs around here) which acts to slow down the combustion and shorten the time taken for it to transition from deflagration to detonation.
It sort of worked, but not well enough, so running with butane and pure oxygen was the way forward. This proved the basic idea worked, and the final step was to rebuild the whole thing in metal, with CNC machined end plates and some box section clamped with a few bolts. This appeared to work reasonably well at around 10 pulses/sec with some measurable thrust, but not a lot. More work to be done we think.
We hinted at earlier work on forced-air pulsejets, so here that is. Of course, whilst we’re on the subject of pulsejets, we can’t not mention [Colinfurze] and his pulsejet go kart.
When we think of a typical four stroke internal combustion engine, we think of metal. And for any type of longevity or performance, that’s certainly the right choice. But [Integza] wanted to see what happens inside a 4 stroke engine, and it wasn’t enough to see it from a transparent cylinder head. No, he wanted to see it in the cylinder itself. Thanks to advances in material sciences, he got his wish as seen in the video below the break.
While researching possible transparent materials to use as a cylinder on his model engine, he learned about resin polishing. Combining his newly learned resin polishing knowledge with his knowledge of 3D printing, [Integza] printed a new cylinder and polished the resin until it was transparent. The engine ran, but misfired terribly.
The experiment progressed into trying different fuels and learning the differences between them, as well as uncovering a new-to-him mystery: Why was the engine misfiring, and why did the different fuels act so dramatically different? Indeed, more learning and more experimenting is needed. But if you want to see the great sight of watching combustion take place in slo-mo, you have to check out the video below.
Have you ever wished you could peer inside a complex machine while it was still running? We sort of can with simulations and the CAD tools we have today, but it isn’t the same as doing IRL. [Warped Perception] made a see-thru jet engine to experience the feeling. The effect, we dare say, is better than any simulation.
[Warped Perception] has a good bit of experience with jet engines and previously mounted them to his car. The first step was balancing, and while he didn’t use an oscilloscope, he could get it within a few thousands of a gram balanced. Then, after some light CAD work, it was all machining. Brackets were fabricated, and gaskets were laser cut to hold the large thick clear cover together. There are a few exciting things to see (and hear). The engine expands and contracts significantly due to pressure and heat, but it’s interesting to see it move physically as it ramps up and down.
Additionally, the sound as it goes through the various thrust levels is quite impressive. But, of course, what’s a jet engine test with an airflow test? Surprisingly, the engine didn’t pull in as much air as he thought. Eighty pounds of thrust doesn’t mean eighty pounds of air.
You don’t happen to own and operate your own turbojet engine, do you? If you do, have you ever had the urge to “kick the tires and light the fires”? Kicking tires simply requires adding tires to your engine cart, but what about lighting the fires? In the video below the break, [Tech Ingredients] explains that we will require some specialized hardware called a re-heater — also known as an afterburner.
[Tech Ingredients] does a deep dive into the engineering behind turbojets, and explains how the very thing that keeps the turbines from melting also allows an afterburner to work. Also explained is why it can also be called a re-heater, and why there are limitations on the efficiency.
Moving on to the demonstration, two different homebrewed afterburners are put to use. The second iteration does exactly what you’d think it should do, and is a mighty impressive sight. We can only imagine what his neighbors think of all the noise! The first iteration was less successful, but that doesn’t mean it isn’t useful, and we’ll let you view the video below to see what else an afterburner can do. We’ll give you a hint: Worlds Biggest Fog Machine.
Does the thought of thrust turn your turbines? You might enjoy this motor-jet contraption that looks almost as fun as the real thing, but 3D printable!
There’s an old saying that says “Anything is possible with enough Time, Money, or Brains. Pick two.” For [Mr HỒ Thánh Chế], the choice was obvious: Time, and Brains. This is evident by the impressive DIY boat build shown in the video below the break.
[Mr HỒ] starts with an Isuzu marine diesel engine that was apparently found on the beach, covered in barnacles and keel worms (and who knows what else). A complete teardown reveals that the crankcase was miraculously spared the ravages of the sea, and somehow even the turbo survived. After a good cleaning and reassembly, the engine rumbles to life. What’s notable is that the entire engine project was done with only basic tools, save for a lathe. Even generally disposable parts such as the head gasket are re-used.
Moving onto the hull, half of an old damaged boat is used and a new top is built. Car seats out of a Toyota sit behind a steering column also from a car, while the deck is built from scratch out of square tubing, foam board, and fiberglass.
What we liked about the project isn’t so much the end result, it has some build quality issues and it looks like the steering is far too slow, but what project of our own hasn’t been knocked together for fun with some obvious flaws? In fact, that’s very often the epitome of the Hacker spirit- doing it quick, dirty, having fun, and iterating as we go. For that, our hat is off to [Mr HỒ].
We’ve all been there. You see a cool gadget on the Internet to 3D print and you can’t wait to fire up the old printer. Then you realize it will take 8 different prints over a span of 60 hours, chemical post-processing, drilling, exotic hardware, and paint to get the final result. [Peter Holderith’s] carburetor design, however, looks super easy.
If you have experience with real-world carbs, you might wonder how that would work, but as [Peter] points out, carburetors are very simple at the core — nothing more than a venturi. All the extra pieces you think of are for special cases and not necessary for basic operation. We doubt, though, that you could really use the thing in its current form in your car. There are no mounts and since he printed it in PLA, it seems like a hot engine would be a bad idea. However, it does work well with water and an electric blower.
[Peter] mentions that with some more work and the right material, he has no doubt he could create a working practical carb. We think he’s right. But even in this form, it is a great educational project for a budding car enthusiast — like the old transparent V8 engine models, maybe.
Speaking of transparent, we’ve seen — or maybe not seen is a better phrase — a see-through carburetor that is also a good demonstrator. If you could perfect a 3D printed carb, it would make conversion projects a lot easier.
When you think of ethanol, you might think of it as a type of alcohol, not alcohol itself. However, in reality, it is the primary ingredient in adult beverages. Which means humans have gotten quite good at making it, as we’ve been doing for a long time. With this in mind, [Sam Barker] decided to make ethanol out of apples to power a small engine to charge his phone.
The steps for making pure ethanol is quite similar to making alcoholic cider. A friend of [Sam’s] had an orchard and a surplus of apples, so [Sam] boiled them down and stored the mush in jugs. He added activated dry yeast to start the fermentation process. A dry lock allowed the CO2 gas that was being created to escape. Over a few weeks, the yeast converted all the sugar into ethanol and gas. In the meantime, [Sam] sourced a chainsaw and adapted the engine to run on ethanol, as ethanol needs to run richer than gasoline. The video below the break tells the story.