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 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.

[Emiel] aka [The Practical Engineer] makes all kinds of fun projects in his fully-featured shop, and one of his tangents has been building a series of solenoid engines. These engines mimic the function of an internal combustion engine, with each solenoid acting as a piston. The only problem with [Emiel]’s concept engines, though, was that he never actually put them into a vehicle to prove their effectiveness. This build finally proves that they can work at powering a vehicle.

The project starts with a new engine. [Emiel] chose a V4 design using four solenoids and an Arduino-based controller. After some trouble getting it to operate properly, he scavenged a small circuit board he built in his V8 solenoid engine to help with timing. With that installed, the solenoids click away and spin the crankshaft at a single constant speed. The vehicle itself was mostly 3D printed, with two aluminum tubes as support structures to mount the engine. Even the wheels were 3D printed with a special rubber coating applied to them. With a small drive train assembled, it’s off to the races for this tiny prototype.

While the small car doesn’t have steering and only goes at a constant speed, the proof of concept that these tiny electric engines actually work is a welcomed addition to [Emiel]’s collection of videos on these curious engines. Of course they’re not as efficient as driving the wheels directly with an electric motor, but we all know there’s no fun in that. If you haven’t seen his most intricate build, the V8 is certainly worth checking out, and also shows off the timing circuitry he repurposed for this car.