3 ms·

Very interesting. No mention in the article if this has better fuel efficiency than existing rotaries, though their FAQ blames the poor efficiency and emission

by elihu 6y ago

Very interesting. No mention in the article if this has better fuel efficiency than existing rotaries, though their FAQ blames the poor efficiency and emissions issues of the Wankel on the weird shape of the combustion chamber[1], so if this design resolves those issues maybe we'll see these in cars eventually. (They'd better act quick if they want to get in on that market; I expect it'll be essentially all electric sooner than most people think.) They seem to think the apex seal wear issue will be better with the apex seals stationary. In addition to that, I wonder if it might also be possible to design the engine such that you can just slide the apex seals out sideways through a slot in the engine housing (sealed off in normal operation) without disassembling the whole engine? That by itself could be a pretty big improvement even if the seals wear down the same as they do in other rotaries. I also wonder if they have a good solution to having more than two rotors? Mazda made a 3-rotor but due to the way the engine fits together the eccentric shaft had to be in two pieces that bolt together. I hope as soon as this company makes a car-sized engine someone swaps one into a Mazda RX-7 or RX-8 just for fun. Maybe see if they can beat these guy's record [2] for longest RX-8 trip on a single tank of gas. Or swap one into one of the old Mazda rotary pickups. [1] https://www.liquidpiston.com/faq https://www.liquidpiston.com/faq [2] https://www.youtube.com/watch?v=PfiQu3XH2Pg https://www.youtube.com/watch?v=PfiQu3XH2Pg

hwillis 6y ago
Sliding friction is an issue with efficiency, I suspect. The flat sides of the rotor are holding back hot, compressed, abrasive gas. That means the faces need to be very flat and very rigid. Unlike the face of an engine block, you can't get away with a gasket to mask imperfections. You need a hard, smooth bearing surface. That means expensive materials, which makes them even harder to flatten. Then you need the actual sealing elements, and they'll be at the worst spots possible- far away from the shaft. The sealed edge is in fact the fastest-moving part of the engine. Bearing surfaces are rated on their PV- pressure times velocity. Both pressure and velocity create heat, and the life of a bearing surface is very roughly inversely proportional to the 4th power of the PV it's run at. Naturally, you want to put bearings as close to the shaft as possible. > They seem to think the apex seal wear issue will be better with the apex seals stationary. They're almost certainly right, although the actual details of implementing the seal are very complicated. They have to seal the corners as well as the sliding edge, so you need multi-part seals that are cut so that spring tension pushes them all outwards, and they still have to seal against each other[1]. They also need to be pressed sideways into their groove and kept from being dragged diagonally. However, normal Wankels burn oil to keep the seals lubricated. Since these are stationary, they can be fed from oil in the crankcase. They can also be fenced in with scraper rings like a normal piston has, which keeps oil on the bearing surface and prevents it from being burnt off. Normal Wankel rotors lift off too much to keep the oil contained. [1]: https://i.ebayimg.com/images/g/gRYAAOSw8-tWVSxv/s-l1600.jpg https://i.ebayimg.com/images/g/gRYAAOSw8-tWVSxv/s-l1600.jpg > I also wonder if they have a good solution to having more than two rotors? Mazda made a 3-rotor but due to the way the engine fits together the eccentric shaft had to be in two pieces that bolt together. IIRC they'll have pretty bad second-order vibration, but either way the exhaust/intake is in the way to a significant degree.

by elihu 6y ago

hwillis 6y ago

Sliding friction is an issue with efficiency, I suspect. The flat sides of the rotor are holding back hot, compressed, abrasive gas. That means the faces need to be very flat and very rigid. Unlike the face of an engine block, you can't get away with a gasket to mask imperfections. You need a hard, smooth bearing surface. That means expensive materials, which makes them even harder to flatten. Then you need the actual sealing elements, and they'll be at the worst spots possible- far away from the shaft. The sealed edge is in fact the fastest-moving part of the engine. Bearing surfaces are rated on their PV- pressure times velocity. Both pressure and velocity create heat, and the life of a bearing surface is very roughly inversely proportional to the 4th power of the PV it's run at. Naturally, you want to put bearings as close to the shaft as possible. > They seem to think the apex seal wear issue will be better with the apex seals stationary. They're almost certainly right, although the actual details of implementing the seal are very complicated. They have to seal the corners as well as the sliding edge, so you need multi-part seals that are cut so that spring tension pushes them all outwards, and they still have to seal against each other[1]. They also need to be pressed sideways into their groove and kept from being dragged diagonally. However, normal Wankels burn oil to keep the seals lubricated. Since these are stationary, they can be fed from oil in the crankcase. They can also be fenced in with scraper rings like a normal piston has, which keeps oil on the bearing surface and prevents it from being burnt off. Normal Wankel rotors lift off too much to keep the oil contained. [1]: https://i.ebayimg.com/images/g/gRYAAOSw8-tWVSxv/s-l1600.jpg https://i.ebayimg.com/images/g/gRYAAOSw8-tWVSxv/s-l1600.jpg > I also wonder if they have a good solution to having more than two rotors? Mazda made a 3-rotor but due to the way the engine fits together the eccentric shaft had to be in two pieces that bolt together. IIRC they'll have pretty bad second-order vibration, but either way the exhaust/intake is in the way to a significant degree.