There’s A Wrinkle In This 3D Printed Wankel

February 10, 2022 by Matthew Carlson 10 Comments

Rotary engines such as the Wankel have strange shapes that can be difficult to machine (as evidenced by the specialized production machines and patents in the 70s), which means it lends itself well to be 3D printed. The downside is that the tolerances, like most engines, are pretty tight, and it is difficult for a printer to match them. Not to be dissuaded, [3DprintedLife] designed and built a 3D printed liquid piston rotary engine. The liquid piston engine is not a Wankel and is more akin to an inside-out Wankel. The seals are on the housing, not the rotor itself, and there are three “chambers” instead of two.

The first of many iterations didn’t run. There was too much friction, but there were some positive signs as pressure was trapped in a chamber and released as it turned. The iterations continued, impressively not using any o-rings to seal, but instead sanding each part down using a 1-2-3 block as a flat reference, within 25 microns of the design. Despite his care and attention to detail, it still couldn’t self-sustain. He theorizes that it could be due to the resin being softer than other materials he has used in the past. Not to be left empty-handed, he built a dynamo to test his new engine out. It was a load cell and an encoder to measure speed and force. His encoder had trouble keeping up, so he ordered some optical limit switches.

This engine is a follow-on to an earlier 3D printed air-powered Wankel rotary engine, and we’re looking forward to part two of the liquid piston series. Video after the break.

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How Can 335 Horses Weigh 63 Pounds?

February 9, 2022 by Al Williams 110 Comments

Koenigsegg, the Swedish car company, has a history of unusual engineering. The latest innovation is an electric motor developed for its Gemera hybrid vehicle. The relatively tiny motor weighs 63 pounds and develops 335 horsepower and 443 lb-ft of torque. Dubbed the Quark, the motor uses both radial and axial flux designs to achieve these impressive numbers.

There is a catch, of course. Like most EV motors, those numbers are not sustainable. The company claims the motor can output peak power for 20 seconds and then drops to 134 horsepower/184 lb-ft of torque. The Gemera can supplement, of course, with its internal combustion engine — a 3 cylinder design.

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The Air Multiplier Fan Principle, Applied To A Jet Engine

January 28, 2022 by Jenny List 26 Comments

Many readers will be familiar with the Dyson Air Multiplier, an ingenious bladeless fan design in which a compressor pushes jets of air from the inside edge of a large ring. This fast-moving air draws the surrounding air through the ring, giving the effect of a large conventional fan without any visible moving parts and in a small package. It’s left to [Integza] to take this idea and see it as the compressor for a jet engine, and though the prototype you see in the video below is fragile and prone to melting, it shows some promise.

His design copies the layout of a Dyson with the compressor underneath the ring, with a gas injector and igniter immediately above it. The burning gas-air mixture passes through the jets and draws the extra air through the ring, eventually forming a roaring jet engine flame exhaust behind it. Unfortunately the choice of 3D print for the prototype leads to very short run times before melting, but it’s possible to see it working during that brief window. Future work will involve a non-combustible construction, but his early efforts were unsatisfactory.

It’s clear that he hasn’t created the equivalent of a conventional turbojet. Since it appears that its operation happens when the flame has passed into the center of the ring, it has more in common with a ramjet that gains its required air velocity with the help of extra energy from an external compressor. Whether he’s created an interesting toy or a useful idea remains to be answered, but it’s certainly an entertaining video to watch.

Meanwhile, this isn’t the first project we’ve seen inspired by the Air Multiplier.

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Running Methanol RC Engines On Gasoline

January 22, 2022 by Lewin Day 33 Comments

Methanol is a popular fuel for small engines used in radio-controlled models, but comes at a higher price than gasoline. It’s also harder to source and can be a mite corrosive, too. Gasoline comes with some benefits, but running it in a methanol engine usually requires some mods. [David] and [Bert] worked together to build a mixture controller for just this purpose.

The controller uses a solenoid to control the flow of gasoline to a conventional methanol-tuned carburetor for a small RC engine, allowing it to be accurately tuned to run gasoline well across the whole RPM range. Having gone through many revisions, all documented in a big forum thread, the latest version uses a Seeduino Xiao controller and a BMP280 pressure and temperature sensor for determining the right fuel/air mixture for the conditions. A small OLED screen can optionally be fitted to help with configuration of the mixture controller.

The system has worked well in testing, with [David] and [Bert] reporting that they have “converted engines as small as 0.3 CID up to large radials with this system.” It’s a promising tool that could be handy to have in the RC modeller’s arsenal.

These tiny engines have other applications too; they can make for one crazy power drill, that’s for sure!

Fail Of The Week: 3D Printed Parts That Burn Like NASA’s Rocket Fuel

January 9, 2022 by Dave Rowntree 21 Comments

[Integza] is on a mission to find as many ways as possible to build rockets and other engines using 3D printing and other accessible manufacturing techniques. He had an a great idea – is it possible to 3D print a solid fuelled rocket, (video, embedded below) specifically can you 3D print the rocket grain itself? By using the resin as a fuel and mixing in a potent oxidiser (ammonium perchlorate specifically – thanks for the tip NASA!) he has some, erm, mixed success.

Effective thrust vs grain cross-sectional profile

As many of us (ahem, I mean you) can attest to, when in the throes of amateur solid-propellant rocket engine experimentation (just speaking theoretically, you understand) it’s not an easy task to balance the thrust over time and keep the combustion pressure within bounds of the enclosure’s capability. Once you’ve cracked making and securing a nozzle within the combustion chamber, the easiest task is to get control of the fuel/oxidiser/binder (called the fuel grain) ratio, particle size and cast the mixture into a solid, dry mass inside. The hard part is designing and controlling the shape of the grain, such that as the surface of the grain burns, the actively burning surface area remains pretty constant over time. A simple cylindrical hole would obviously increase in diameter over time, increasing the burning surface area, and causing the burn rate and resulting pressure to constantly increase. This is bad news. Various internal profiles have been tested, but most common these days is a multi-pointed star shape, which when used with inhibitor compounds mixed in the grain, allows the thrust to be accurately controlled.

[Integza] tried a few experiments to determine the most appropriate fuel/binder/oxidiser ratio, then 3D printed a few fuel grain pellets, rammed them into an acrylic tube combustion chamber (obviously) and attached a 3D printed nozzle. You can see for yourself the mach diamonds in the exhaust plume (which is nice) due to the supersonic flow being marginally over-expanded. Ideally the nozzle wouldn’t be made from plastic, but it only needs to survive a couple of seconds, so that’s not really an issue here.

The question of whether 3D printed fuel grains are viable was posed on space stack exchange a few years ago, which was an interesting read.

We’ve seen some more sophisticated 3D printed rocket engines lately, such as this vortex-cooled, liquid-fuel engine, and over on Hackaday,IO, here’s a 3D printed engine attempting to use PLA as the fuel source.

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Turbocharger Jet Engine Relies On Wood Pellet Ignition

December 22, 2021 by Lewin Day 14 Comments

Turbochargers as used on cars bear some similarities with jet engines. Fundamentally, both contain a turbine that harvests energy from hot gas, using it to spin a compressor which sucks in fresh air for combustion. Thus, turning a turbocharger into a jet engine is entirely possible, and [HRom] decided to have a crack at it.

The build starts with a turbo that appears to have been used on a diesel engine from the Volkswagen group. The first step was to cut the integral exhaust manifold off the turbo housing. A combustion chamber is then added which takes in fresh air from the compressor housing, and delivers hot combustion products to the turbine inlet. The homebrewed jet engine burns propane as fuel, introduced into the chamber via a nozzle.

The initial test failed as combustion was occurring at the turbine exhaust rather than in the combustion chamber, likely due to the lack of a proper ignition source inside the combustion chamber. A redesign employed a bigger combustion chamber built out of a fire extinguisher, with smouldering wood pellets inserted inside to get the injected propane burning.

The redesign works, and the turbocharger jet engine releases a thunderous scream as it turns at ever-increasing speed. However, with no oiling system or any way of controlling air or fuel flow in the engine, it eventually stops in a huge puff of smoke. Regardless, the engine did run in a sustained manner even if the ignition method was rudimentary.

We’ve seen similar builds before, and the rudimentary construction means they’re typically nowhere near being flight-weight engines. They are incredibly cool, however, and a great way to learn the basic principles of how jet engines work. Video after the break.

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You Can 3D Print A Working Reciprocating Steam Engine

December 22, 2021 by Lewin Day 12 Comments

3D prints aren’t typically known for their heat resistance. However, [Integza] noted that using the right techniques, it was possible to 3D print parts that could handle steam heat without failing. Thus, the natural progression from there was to build a piston-type steam engine.

The sliding valve alternately feeds steam to each side of the piston.

Resin prints are key here, as the melting point of such parts is much higher than that of those turned out by typical FDM printers. Try this same build using PLA for the hot parts, and you’ll quickly end up with a pile of molten goo.

To make such an engine work, valves are required to allow steam to flow into alternating sides of the piston to let it reciprocate continuously. A simple slide valve is used, allowing steam to flow to one side of the piston and the other alternately, as driven by an arm coming off the flywheel attached to the engine’s output shaft.

Tested on compressed air and steam, the engine ran continuously, chugging away enthusiastically. However, steam performance was compromised by the low pressure output of just 1.5 bar from [Integza]’s pressure cooker. Similarly, the cooker’s steam capacity was low, so the engine ran for just 15 seconds.

However, it suggests that with a better supply of steam, the printed steamer could indeed run for some time. If you’re not into the wetter engines out there, though, consider extruding a Stirling engine instead. Video after the break.

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