See-through engine cylinder lets you watch combustion as it occurs
The project starts with a small tabletop engine from Stirlingkit. The 1.6 cc M16 four-stroke engine has a carburetor-fed single cylinder and is designed to run on 95 RON gasoline. It is constructed primarily of brass and aluminum and has a small battery-powered ignition system that is magnetically triggered.
To see the inside of 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 withstand actual use. It comes out nice and clear after a bit of sanding and buffing.
With a slow-motion camera set up, the combustion inside the engine can be easily viewed. During the driving stroke, the flame front can be seen crossing the cylinder, before being exhausted during the following stroke.
The transparent cylinder also reveals some irregularities. When running the engine on gasoline or methanol, Integza noticed that the engine only ignited properly every second power stroke. The problem was worse when using a nitromethane mix, with only one out of three power shots firing correctly.
As with most Integza videos, it’s very scientific. No adjustments are made to correct the fuel to air ratio for the different fuels used in the tests. The “power” of each fuel is then compared to the rpm the engine manages to reach, without any actual torque-based measurements being taken.
The mystery of the missing power shots is also not solved. Several variables are changed at once when investigating the problem, from fuel to cylinder sealing, negating the possibility of finding the real cause. Commentators speculate on the cause, whether it’s an overly rich mixture due to the simplistic carburettor, poor ignition timing, or a poorly grounded spark plug thanks to the now plastic cylinder .
Integra’s video is fun to watch, and it’s great to get a real visualization of the fuel burning inside a small four-stroke engine. It’s a shame the little engine didn’t perform better, but considering it uses a plastic cylinder full of hot fuel, it’s impressive that it performed so well.
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