4 ms·

Having to stop production because you just got nuked and then turning around to become a major car manufacturer within a generation is remarkable. Too bad the

by pwaai 9y ago

Having to stop production because you just got nuked and then turning around to become a major car manufacturer within a generation is remarkable. Too bad the rotary engine never was reliable, practical or efficient but man are they fun cars. I fondly remember the RX-8 in 2004 my friend got for his birthday, that unique wailing rotary sound and go kart like experience is still in the back of my mind. RX-7 still has a ton of demand and held its value if not appreciated for spot clean low mileage cars. I prefer the older generation RX-7 but most of it is limited to Gran Turismo 2 experience.

djsumdog 9y ago
I had an RX-7 GSL-SE first gen. I never got it working well enough to race though. Damn vacuum tubes everywhere. I ended up selling it after University to some dude who wanted to put a V8 in it. :(
ansible 9y ago
... spot clean low mileage cars ... Because the rotary engine has serious wear issues above 100K miles, even with proper maintenance. Which is a shame, really, because piston engines can double or triple that before running into the same sorts of problems (if well maintained).
- pkroll 9y ago
  Is that inherent, or part of having so much more research and experience with pistons? (Will we ever know?)
  - ohazi 9y ago
    It's somewhat inherent to the design. In a piston engine, the cylinder walls and the sides of the piston form the seal that keeps the combustion contained. You have a lot of metal-oil-metal surface area to work with here, so it's relatively easy to get a good seal. On a rotary engine, you have comparatively thin apex seals. These wear out quickly, and make it more difficult to get a good seal. Additionally, combustion always happens on the same side of the engine housing, so you tend to get warping, which also makes the sealing problems worse. Reciprocating engines definitely have their own problems though (e.g. valves), and here I think you can safely argue that our longer history with them has helped a lot.
  - da_chicken 9y ago
    It's basically inherent. At there are apex seals at the ends of the triangular rotor that need to stay in contact with the sides of the combustion chamber to prevent blow by and get a complete and efficient burn, so they have springs in them that press them against the walls of the engine. However, metal (or ceramic) to metal contact like that means that they also need to stay lubricated. Unlike the a piston engine's piston rings, there isn't a real easy way to get oil to where the seal is, so you must inject oil into the engine where it will be swept into the combustion chamber. Even then, the apex seals eventually wear out. They basically require a complete engine rebuild to replace. The combustion chamber is quite long compared to a traditional piston driven engine, and that, combined with the apex seal blowby problem and oil burning problem, means the engine is actually quite inefficient. Rotary engines do not typically have good gas mileage. An RX-8 has a 1.3 L engine but only gets 18 mpg (13L/100km), although it produces 210–235 hp (157–175 kW). It's this poor efficiency that caused Mazda to cease production of Wenkel engines in 2012. They can't pass emissions tests. The Wankel rotary engine (https://en.wikipedia.org/wiki/Wankel_engine https://en.wikipedia.org/wiki/Wankel_engine) actually has comparatively poor fuel efficiency. It just also has a high power to weight ratio. Additionally, the combustion chamber is on one side of the engine, meaning the engine heats up unevenly. That makes it wear unevenly and can make it difficult to get a seal that will work on both the hot side and the cold side. So, the problems with the Wenkel engine: 1. Lubricate a part that you can't reach and is going to be constantly bathed in fire. 2. Make the combustion of a fuel/air mixture in a long, wide, narrow chamber as efficient as the same fuel/air mixture in a much more ideal cylindrical chamber.
    - da_chicken 9y ago
      The first paragraph above should begin "At the ends of the triangular rotor there are apex seals that...". I somehow transposed the words there while writing it.
    - dbosch 9y ago
      Thanks for the detailed explanation !
lloeki 9y ago
> wailing rotary sound Instant throwback to the legendary 787B: https://www.youtube.com/watch?v=az39eqLIbyU https://www.youtube.com/watch?v=az39eqLIbyU https://www.youtube.com/watch?v=OjwwV20iZYE https://www.youtube.com/watch?v=OjwwV20iZYE
- lloeki 9y ago
  That was the one I was actually looking for: https://www.youtube.com/watch?v=40CXVrMf8bs https://www.youtube.com/watch?v=40CXVrMf8bs

by pwaai 9y ago

djsumdog 9y ago

I had an RX-7 GSL-SE first gen. I never got it working well enough to race though. Damn vacuum tubes everywhere. I ended up selling it after University to some dude who wanted to put a V8 in it. :(

ansible 9y ago

... spot clean low mileage cars ... Because the rotary engine has serious wear issues above 100K miles, even with proper maintenance. Which is a shame, really, because piston engines can double or triple that before running into the same sorts of problems (if well maintained).

pkroll 9y ago
Is that inherent, or part of having so much more research and experience with pistons? (Will we ever know?)
- ohazi 9y ago
  It's somewhat inherent to the design. In a piston engine, the cylinder walls and the sides of the piston form the seal that keeps the combustion contained. You have a lot of metal-oil-metal surface area to work with here, so it's relatively easy to get a good seal. On a rotary engine, you have comparatively thin apex seals. These wear out quickly, and make it more difficult to get a good seal. Additionally, combustion always happens on the same side of the engine housing, so you tend to get warping, which also makes the sealing problems worse. Reciprocating engines definitely have their own problems though (e.g. valves), and here I think you can safely argue that our longer history with them has helped a lot.
- da_chicken 9y ago
  It's basically inherent. At there are apex seals at the ends of the triangular rotor that need to stay in contact with the sides of the combustion chamber to prevent blow by and get a complete and efficient burn, so they have springs in them that press them against the walls of the engine. However, metal (or ceramic) to metal contact like that means that they also need to stay lubricated. Unlike the a piston engine's piston rings, there isn't a real easy way to get oil to where the seal is, so you must inject oil into the engine where it will be swept into the combustion chamber. Even then, the apex seals eventually wear out. They basically require a complete engine rebuild to replace. The combustion chamber is quite long compared to a traditional piston driven engine, and that, combined with the apex seal blowby problem and oil burning problem, means the engine is actually quite inefficient. Rotary engines do not typically have good gas mileage. An RX-8 has a 1.3 L engine but only gets 18 mpg (13L/100km), although it produces 210–235 hp (157–175 kW). It's this poor efficiency that caused Mazda to cease production of Wenkel engines in 2012. They can't pass emissions tests. The Wankel rotary engine (https://en.wikipedia.org/wiki/Wankel_engine https://en.wikipedia.org/wiki/Wankel_engine) actually has comparatively poor fuel efficiency. It just also has a high power to weight ratio. Additionally, the combustion chamber is on one side of the engine, meaning the engine heats up unevenly. That makes it wear unevenly and can make it difficult to get a seal that will work on both the hot side and the cold side. So, the problems with the Wenkel engine: 1. Lubricate a part that you can't reach and is going to be constantly bathed in fire. 2. Make the combustion of a fuel/air mixture in a long, wide, narrow chamber as efficient as the same fuel/air mixture in a much more ideal cylindrical chamber.
  - da_chicken 9y ago
    The first paragraph above should begin "At the ends of the triangular rotor there are apex seals that...". I somehow transposed the words there while writing it.
  - dbosch 9y ago
    Thanks for the detailed explanation !

lloeki 9y ago

> wailing rotary sound Instant throwback to the legendary 787B: https://www.youtube.com/watch?v=az39eqLIbyU https://www.youtube.com/watch?v=az39eqLIbyU https://www.youtube.com/watch?v=OjwwV20iZYE https://www.youtube.com/watch?v=OjwwV20iZYE

lloeki 9y ago
That was the one I was actually looking for: https://www.youtube.com/watch?v=40CXVrMf8bs https://www.youtube.com/watch?v=40CXVrMf8bs