With the rise of usable electric cars in the marketplace, and markets around the world slowly phasing out the sale of fossil fuel cars, you could be forgiven for thinking that the age of the internal combustion engine is coming to an end. History is rarely so cut and dry, however, and new technologies aim to keep the combustion engine alive for some time yet.
One of the most interesting technologies in this area are hydrogen-burning combustion engines. In contrast to fuel cell technologies, which combine hydrogen with oxygen through special membranes in order to create electricity, these engines do it the old fashioned way – in flames. Toyota has recently been exploring the technology, and has announced a racecar sporting a three-cylinder hydrogen-burning engine will compete in this year’s Fuji Super TEC 24 Hour race.
The benefit of a hydrogen-burning engine is that unlike burning fossil fuels, the emissions from burning hydrogen are remarkably clean. Burning hydrogen in pure oxygen produces only water as a byproduct. When burned in atmospheric air, the result is much the same, albeit with small amounts of nitrogen oxides produced. Thus, there’s great incentive to explore the substitution of existing transportation fuels with hydrogen. It’s a potential way to reduce pollution output while avoiding the hassles of long recharge times with battery electric technologies. Continue reading “Toyota’s Hydrogen-Burning Racecar Soon To Hit The Track”→
The basic idea here is that you feed natural gas (though propane should also work) directly into the engine’s intake by way of a hose attached to the air filter box. While cranking the engine, a valve on the gas line is used to manually adjust the air–fuel mixture until it fires up. It’s an extremely simple hack that, in a pinch, you can pull off with the parts on hand. But as you might expect, that simplicity comes at a cost.
There are a few big problems with this approach, but certainly the major one is that there’s nothing to cut off the flow of gas when the engine stops running. So if the generator stalls or you just forget to close the valve after you shut it down, there’s the potential for a very dangerous situation. Additionally, the manual gas valve will be at odds with a generator that automatically throttles up and down based on load. Though to be fair, there are certainly generators out there that simply run the engine flat-out the whole time.
The idea of camless automotive engines has been around for a while but so far has been limited to prototypes and hypercars. [Wesley Kagan] has been working on a DIY version for a while, and successfully converted a Mazda Miata to a camless valve system. See the videos after the break.
There have been many R&D projects by car manufacturers to eliminate camshafts in order to achieve independent valve timing, but the technology has only seen commercial use on Koenigsegg hypercars. [Wesley] started this adventure on a cheap single cylinder Harbor Freight engine, and proved the basic concept, so he decided to move up to an actual car. He first sourced a junkyard engine head to convert, and use as a drop-in replacement for the head on the complete project car. An off-the-shelf double-acting pneumatic cylinder is mounted over each valve and connected to the valve stem with a custom adaptor. The double-acting cylinder allows the valve to be both opened and closed with air pressure, but [Wesley] still added the light-weight return spring to keep the valve closed if there is any problem with the pneumatic system.
The controller is an Arduino, and it receives a timing signal from a factory crankshaft and operates the pneumatic solenoid valves via MOSFETs. After mounting the new head and control box into the Miata, it took a couple of days of tuning to get the engine running smoothly. Initial tests were done using the compressor in his garage, but this was replaced with a small compressor and air tank mounted in the Miata’s boot for the driving tests.
Although the pneumatic system works well for short test drives, the compressor is quite noisy and adds a couple of points of failure. [Wesley] is also working on a solenoid actuated system, which would require a lot more current from the battery and alternator, but he believes it’s a better long-term solution compared to compressed air. However, he is still struggling to find solenoids with the required specifications. Continue reading “Deleting The Camshafts From A Miata Engine”→
If engineering choices a hundred years ago had been only slightly different, we could have ended up in a world full of steam engines rather than internal combustion engines. For now, though, steam engines are limited to a few niche applications and, of course, models built by enthusiasts. This one for example is built entirely in LEGO as a scale replica of a steam engine originally produced in 1907.
The model is based on a 2500 horsepower triple-expansion four-cylinder engine that was actually in use during the first half of the 20th century. Since the model is built using nothing but LEGO (and a few rubber bands) it operates using a vacuum rather than with working steam, but the principle is essentially the same. It also includes Corliss valves, a technology from c.1850 that used rotating valves and improved steam engine efficiency dramatically for the time.
This build is an impressive recreation of the original machine, and can even run at extremely slow speeds thanks to a working valve on the top, allowing its operation to be viewed in detail. Maximum speed is about 80 rpm, very close to the original machine’s 68 rpm operational speed. If you’d prefer your steam engines to have real-world applications, though, make sure to check out this steam-powered lawnmower.
The inlet and exhaust valve timing of a piston engine plays a large role in engine performance. Many modern automotive engines have some sort of variable valve timing, but the valves are still mechanically coupled together and to the crankshaft. This means that there is always a degree of performance compromise for various operating conditions. [Wesley Kagan] took inspiration from Koenigsegg’s camless Freevalve technology, and converted a Harbour Freight engine to camless technology for individual valve control.
By eliminating the traditional camshaft and giving each valve its actuator, it is possible to tune valve timing for any specific operating condition or even for each cylinder. A cheap single-cylinder engine is a perfect testbed for the garage hacker. [Wesley] removed the rocker arms and pushrods, and replaced the stock rocker cover with a 3D printed rocker cover which contains two small pneumatic pistons that push against the spring-loaded valve stems. These pistons are controlled by high-speed pneumatic solenoid valves. A reference timing signal is still required from the crankshaft, so [Wesley] built a timing system with a 3D printed timing wheel containing a bunch of embedded magnets and being sensed by a stationary Hall effect sensor. An Arduino is used to read the timing wheel position and output the control signals to the solenoid valves. With a rough timing program he was able to get the engine running, although it wouldn’t accelerate.
In the second video after the break, he makes a digital copy of the engine’s existing camshaft. Using two potentiometers in a 3D printed bracket, he measured push rod motion for a complete engine cycle. He still plans to add position sensing for each of the valves, and after a bit more work on the single-cylinder motor he plans to convert a full-size car, which we are looking forward to.
The video posted by [Let’s Learn Something] is long, but watching it at double speed doesn’t take away much from the enjoyment. By using a piston-type compressor, a lot of the precision machining is already taken care of here. Adding the intake and exhaust valves, camshaft, timing chain, carburetor, and ignition system are still pretty challenging tasks, though. We loved the home-made timing chain sprockets, made with nothing more than a drill and an angle grinder. In a truly inspired moment, flat-head screws are turned into valves, rocker arms are fabricated from bits of scrap, and a bolt becomes a camshaft with built-up TIG filler. Ignition and carburetion are cobbled together from more bits of scrap, resulting in an engine that fired up the first time — and promptly melted the epoxy holding the exhaust header to the cylinder head.
Now, compressor-to-engine conversions aren’t exactly new territory. We’ve seen both fridge compressors and automotive AC compressors turned into engines before. But most of what we’ve seen has been simple two-stroke engines. We’re really impressed with the skill needed to bring off a four-stroke engine like this, and we feel like we picked up quite a few junk-box tips from this one.
One of the tricky parts of engineering in the physical world is making machines work with the available resources and manufacturing technologies. [Tom Stanton] has designed and made a couple of air-powered 3D printed engines but always struggled with the problem of air leaking past the 3D-printed pistons. Instead of trying to make an air-tight piston, he added a rubber membrane and a clever valve system to create a diaphragm air engine.
A round rubber diaphragm with a hole in the center creates a seal with the piston at the top of its stroke. A brass sleeve and pin protrude through the diaphragm, and the sleeve seals create a plug with an o-ring, while the pin pushes open a ball which acts as the inlet valve to pressurize an intermediate chamber. As the piston retracts, the ball closes the inlet valve, the outlet valve of the intermediate chamber is opened, forcing the diaphragm to push against the piston. The seal between the piston and diaphragm holds until the piston reaches its bottom position, where the pressurized air is vented past the piston and out through the gearbox. For full details see the video after the break.
It took a few iterations to get the engine to run. The volume of the intermediate chamber had to increase and [Tom] had to try a few different combinations of the sleeve and pin lengths to get the inlet timing right. Since he wanted to use the motor on a plane, he compared the thrust of the latest design with that of the previous version. The latest design improved efficiency by 366%. We look forward to seeing it fly! Continue reading “Diaphragm Air Engine”→