Rotary 'vs' Piston engines
Discussion
There have been 2.6 (quad rotor) versions of the Mazda engine, I believe a car powered by one won Le Mans a few years back. Rotary engines are rather inefficient at partial load so aren't really great for road cars. They also need rotor tips replacing regularly and tend to drink oil like other cars drink petrol. They are however, very light and compact for their power output.
Oh and rotary engines are combustion engines.
Oh and rotary engines are combustion engines.
Edited by kambites on Tuesday 30th October 13:59
They use oil by design though. Think of it like a consumable like wiper blades and cam belts. I also think the rotor tip issue has been banished in the latest Renesis engine.
I'm sure the cost of topping up the oil with not be all that different to periodic cambelt changes on a piston engined car, probably less.
I'm sure the cost of topping up the oil with not be all that different to periodic cambelt changes on a piston engined car, probably less.
I know a rotary engine still uses combustion so is regarded as so. Just had a thought about the point in which it would be better to use a normal engine over a Rotary one when it comes to supercar power. What's been said about the wear & oil useage of the rotary engine would highlight why it isn't used too much in endurance racing & supercars.
Rotary engined bikes have done so well in the past so wandered why this hasn't been exploited in cars.
Rotary engined bikes have done so well in the past so wandered why this hasn't been exploited in cars.
they arent wonderfully suited to "real world" driving...short journeys, traffic, cruise-controlled motorway driving (i.e. constant rpm), people who are used to Toyota four-cylinder levels of care and attention to their engine.
However, if someone were to make a hairy balls track-focussed sportscar with a big rotary, that, like a TVR, people bought expecting to have to look after it properly, a big triple rotor might work.
trouble is, as TVR found, the germans can offer 90% of the thrills with 300% of the reliability.
However, if someone were to make a hairy balls track-focussed sportscar with a big rotary, that, like a TVR, people bought expecting to have to look after it properly, a big triple rotor might work.
trouble is, as TVR found, the germans can offer 90% of the thrills with 300% of the reliability.
Mazda did the 787B, 4 rotor 700hp. It won LeMans, they banned it.
http://en.wikipedia.org/wiki/Mazda_787B
It should be rotor vs piston .. they are both combustion.
You multiply the displacement by 2, to compare it to a piston engine as most car piston engines are "2 stroke" so need to work twice as much.
The DVLA mark them down at 1.3 .. the RX7 is cheap tax
There was a tri rotor Cosmo, which is a comon swap.
The MPG and oil use are bad, and the rotor wear has been massively reduced with Ti rotor tips I believe.
http://en.wikipedia.org/wiki/Mazda_787B
It should be rotor vs piston .. they are both combustion.
You multiply the displacement by 2, to compare it to a piston engine as most car piston engines are "2 stroke" so need to work twice as much.
The DVLA mark them down at 1.3 .. the RX7 is cheap tax
There was a tri rotor Cosmo, which is a comon swap.
The MPG and oil use are bad, and the rotor wear has been massively reduced with Ti rotor tips I believe.
MK4 Slowride said:
I know a rotary engine still uses combustion so is regarded as so. Just had a thought about the point in which it would be better to use a normal engine over a Rotary one when it comes to supercar power. What's been said about the wear & oil useage of the rotary engine would highlight why it isn't used too much in endurance racing & supercars.
Rotary engined bikes have done so well in the past so wandered why this hasn't been exploited in cars.
conventional piston engines (as opposed to ratary piston engines) have had huge amounts of R&D thrown at them for a long long time.Rotary engined bikes have done so well in the past so wandered why this hasn't been exploited in cars.
The Rotary has, in comparison, very very little R&D.
On full-chat my rotary is pretty much comparable with any normal engine developing the same power - possibly slightly more economical. When not being puches (as said above) it's far less economical as the issues in overlap between input and exhaust ports becomes a big factor. Even more so on a car like mine that has enlarged porting
Because of the way the internal gearing of the engine works the output shaft and the rotations of the rotors are not 1-1 and the best equivalency really is 2.6 for a 1.3 rotary. There are a few good vids on youtube explaining how this all works.
Building a standard 3-rotor to produce 500 rwhp isn't all that hard. Achievable in turbo form at less than 1 bar of boost.
The 787b (Le Mans winner) was 4-rotor n/a:
* Engine capacity: 654cc x 4
* Fuel system: Nippon Denso electronic fuel injection
* Maximum Power: 700 hp/9000 rpm
* Maximum Torque: 448 ft.lb/6500 rpm
(from wikipedia)... This was built to last 24 hours at race pace so would probably have pushed more power closer to the edge I guess.
Gazillions of reasons why Rotaries aren't very good as engines for road vehicles. Apart from the ones listed above, they have the following drawbacks - mostly shared with two-stroke engines;
Heat. They generate a huge amount of power for relatively low input. This does mean they generate huge amounts of heat - both under bonnet and in the exhaust. Look at the scary tuned RX-7 TT from Japan, and most of them have huge amounts of bonnet missing.
Pressure Wave Tuned exhausts - they don't really have a stroke dedicated to expelling the left overs from combustion. Like two-strokes, they need an element of pressure wave tuning in the manifold and exhaust to achieve a clean chamber for a fresh mix. Pressure wave tuning is notoriously difficult to do well - it has a similar effect as cam profile in a four stroke, but the waves are affected by heat in the system, thickness and materials used in exhaust construction, as well as usual stuff like backpressure.
Fuel consumption - whilst everyone falls over themselve about the specific output, it is balanced by it's specific consumption. They generate a huge amount of energy, but they take a huge amount of fuel in doing so. They're not strictly comparable to four-stroke engines as a rotary is theoretically a one-stroke (IIRC) - so you get into hugely complex and baffling calculations based on stroke differential. But basically a 2.6 inline six producing 260bhp at 6,000rpm is more efficient than a rotary 2.6 producing the same amount at 6000rpm - argument is that 6000rpm in a fourstroke is 1500 ignitions are generating that 100bhp per litre, against 6000 (or whatever it is) in a rotary.
They're an engineers engine. Brilliant, but with massive implications in application.
That said, I've never understood why they're not used in F1 - after all, a pure rotary only has one moving part.
If you really want to get a headache, do a trawl of the web for the theory behind the other rotary design - the one where the crankcase revolves around a fixed rotor...
Heat. They generate a huge amount of power for relatively low input. This does mean they generate huge amounts of heat - both under bonnet and in the exhaust. Look at the scary tuned RX-7 TT from Japan, and most of them have huge amounts of bonnet missing.
Pressure Wave Tuned exhausts - they don't really have a stroke dedicated to expelling the left overs from combustion. Like two-strokes, they need an element of pressure wave tuning in the manifold and exhaust to achieve a clean chamber for a fresh mix. Pressure wave tuning is notoriously difficult to do well - it has a similar effect as cam profile in a four stroke, but the waves are affected by heat in the system, thickness and materials used in exhaust construction, as well as usual stuff like backpressure.
Fuel consumption - whilst everyone falls over themselve about the specific output, it is balanced by it's specific consumption. They generate a huge amount of energy, but they take a huge amount of fuel in doing so. They're not strictly comparable to four-stroke engines as a rotary is theoretically a one-stroke (IIRC) - so you get into hugely complex and baffling calculations based on stroke differential. But basically a 2.6 inline six producing 260bhp at 6,000rpm is more efficient than a rotary 2.6 producing the same amount at 6000rpm - argument is that 6000rpm in a fourstroke is 1500 ignitions are generating that 100bhp per litre, against 6000 (or whatever it is) in a rotary.
They're an engineers engine. Brilliant, but with massive implications in application.
That said, I've never understood why they're not used in F1 - after all, a pure rotary only has one moving part.
If you really want to get a headache, do a trawl of the web for the theory behind the other rotary design - the one where the crankcase revolves around a fixed rotor...
MOD's please change title to :- Rotary 'vs' Piston engines.Bibbs said:
You multiply the displacement by 2, to compare it to a piston engine as most car piston engines are "2 stroke" so need to work twice as much.
No they aren't, they're 4 stroke. One chamber of a normal piston engine will be on its power stroke 1/4 of the time. A rotary chamber is on its power "stroke" roughly half the time (I think). As such, I guess rotary engines are directly comparable to 2-stroke piston engines.
Edited by kambites on Tuesday 30th October 14:28
They're not widely used in motorsport because when they have been, they won, and were promptly banned
It's a four stroke engine (intake, compression, expansion, exhaust). It's Otto cycle as I understand it (four phases, intake and expansion volumes equal). It differs from a piston engine in that the four phases are separated in space as well as time. So the combustion chamber moves and changes shape during a cycle.
The fuel efficiency suffers relative to a piston engine because it loses more heat to the walls of the combustion chamber because the combustion chamber effectively has a larger surface area. It's also difficult to optimise the shape of the combustion chamber. Issues of incomplete combustion and blow-by of unburnt fuel into the exhaust tract have now largely been resolved, as have issues of rotor tip wear.
Calculating nominal capacity is a source of argument. DVLA doubles the swept volume, so my V5 document reads 2616.
Here's someone's 590bhp naturally aspirated quad rotor engine.
http://videos.streetfire.net/video/e92eae11-ddea-4...
It's a four stroke engine (intake, compression, expansion, exhaust). It's Otto cycle as I understand it (four phases, intake and expansion volumes equal). It differs from a piston engine in that the four phases are separated in space as well as time. So the combustion chamber moves and changes shape during a cycle.
The fuel efficiency suffers relative to a piston engine because it loses more heat to the walls of the combustion chamber because the combustion chamber effectively has a larger surface area. It's also difficult to optimise the shape of the combustion chamber. Issues of incomplete combustion and blow-by of unburnt fuel into the exhaust tract have now largely been resolved, as have issues of rotor tip wear.
Calculating nominal capacity is a source of argument. DVLA doubles the swept volume, so my V5 document reads 2616.
Here's someone's 590bhp naturally aspirated quad rotor engine.
http://videos.streetfire.net/video/e92eae11-ddea-4...
mackie1 said:
I guess it's because Mazda alone have the rights to the design.
Thats not true, they licence it just like everyone else. I guess NSU had the original patent, which I suppose must mean VAG actually own the patent?Quite a lot of companies were working on rotary powerplants back in the 60s and 70s, perhaps most notably GM had a rotary powered Covette program and Mercedes had the C111 concept 'supercar' amongst others.
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