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Comment by hristov | Hacker News Reader

They did not talk about oil and how it lubricates itself. Only that it magically does not need oil changes. It is a two stroke engine and two stroke engines do not need oil changes, but that is for a very bad reason, environmentally-wise.

Two stroke engines do need oil changes because you are supposed to mix in the oil with the fuel and they just burn the oil and get new oil when new fuel comes in. This is very bad for the environment because burning lubricant is very bad for pollution. It is also costly because you have to pay for much more lubricant.

Perhaps Nokia figured out that it would be much cheaper for them to burn oil rather than occasionally send people to remote locations to service engines. This may be true but they should not pretend this is environmentally friendly. It isn't.

If you are older you may remember how gross and foul smelling two stroke lawn mowers used to be back in the times. We don't need to bring this back.

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I was also wondering about this claimed lack of oil from a different perspective.

Based on the article, the video embedded within it, and the Technology section of Aquarius' website, this is a double-acting uniflow two-stroke internal combustion engine. As it is double-acting, there is combustion on both sides of the piston, so I am wondering how the piston is cooled, especially given the high power density of this device.

In conventional IC piston engines, the piston is either cooled by the oil [1], or, in the case of small two strokes having a total-loss lubrication system (the sort that the parent post is concerned with) piston cooling is aided by the flow of the incoming mixture through the crankcase. Neither method seems to be feasible here. Has there been a breakthrough in materials (ceramics, perhaps?) which allow for a piston to work at high temperatures?

One other point that just occurred to me is that if you are using a total-loss, combustible lubricant design (which is what conventional gasoline two-strokes do), then the efficiency calculation must include the energy input of the lubricant as well as the gasoline (or whatever is being used purely as a fuel), as the lubricant is also a fuel.

[1] https://dieselnet.com/tech/combustion_piston-cool.php

In the video [0] it doesn't show combustion occurring on both sides of the pistons.

[0] http://www.youtube.com/watch?v=26PjRQmIoeE

That appears to be an earlier iteration, as (one of) the videos embedded in the article does show it to be double-acting, as does the one in the Technology section of the website [1], where it can be seen at 00:34 and 00:42.

[1] https://www.aquariusengines.com/technology/

This looks like video jacking. The description talks about acquarius, but the video is about a completely different free piston system being developed by a research group at newcastle university.

The article specifically states combustion is on one side only, the video's visual is a little misleading.

Not all two-strokes have "total loss" lubrication --- only crankcase-scavenged ones do. Larger ones, and notably two-stroke diesels, don't.

That said, this one may need minimal lubrication since in a free-piston generator, both ends are combustion chambers, the only place there is sliding friction is between the cylinder wall and the piston, and the "secret" to their success may be some sort of ultra-hard-wearing material for those surfaces.

Another possibility is using a magnetic bearing, i.e. using magnetic forces to hold the shaft without touching the cylinder.

Yup, two stroke engines are phasing out. Some places have banned them years ago, like Lake Tahoe. I grew up with dirt bikes, and two strokes were the most powerful and fun.

The Stanford version uses air lubricant seems much more advanced, and single combustion instead of dual.

https://www.youtube.com/watch?v=bSPRT1JAXj4

This video touts air bearings, but it says nothing about how the pistons rings (or equivalent seals) work without lubrication.

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