Transparent Engine Cylinder Lets You Watch Combustion As It Happens

If you’ve ever wanted to peek inside the combustion chamber, this is your chance.

byLewin Day|
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YouTuber Integzaa's latest video gives us a neat look inside the combustion chamber of a four-stroke engine, using a transparent cylinder to show us how the piston moves within it to create internal combustion.

The project starts with a small tabletop engine from Stirlingkit. The 1.6cc M16 four-stroke engine has a single-cylinder fed by a carburetor and is designed to run on 95 RON gasoline. It's built primarily using brass and aluminum and has a small battery-powered ignition system that is triggered magnetically.

To see inside the engine, Integza produced a clear version of the cylinder on a resin 3D printer. The first version has a smoky, hazy finish, but proves the concept that the plastic part can hold up to real use. It comes up nice and clear after some sanding and polishing.

With a slow-motion camera set up, the combustion inside the engine can readily be visualized. On the power stroke, the flame front can be seen to travel through the cylinder, before being exhausted on the next stroke.


The transparent cylinder also reveals some irregularities. When running the engine on gasoline or methanol, Integza noticed the engine was only firing properly on every second power stroke. The problem was worse when running on a nitromethane blend, with only every third power stroke firing properly.

As with most Integza videos, it's very much science-lite. No tuning is done to correct the fuel-air ratio for the different fuels used in testing. Each fuel's "power" is then compared by the RPM the engine manages to reach, with no real torque-based measurements taken.

Nor is the mystery of the missing power strokes solved. Multiple variables are changed at once when investigating the problem, from fuel to cylinder sealing, negating the chance of finding the real cause. Commenters speculate as to the cause, whether it's an excessively rich mixture due to the simplistic carburetor, poor ignition timing, or a poorly grounded sparkplug thanks to the now-plastic cylinder.

We've seen some other great transparent engine builds before, too. TRO Designs managed to get a comparatively-giant 75cc Honda motorcycle engine running with a transparent cylinder, with impressive results. Smarter Every Day's transparent carburetor was also very educational, showing us exactly how fuel flows in and vaporizes on its way to the combustion chamber.

Integza's video is fun to watch, and it's great to get a real visualization of the fuel combusting inside a small four-stroke engine. It's a shame the little engine didn't run better, but given it's using a plastic cylinder full of hot combusting fuel, it's impressive that it ran so well at all.

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