Rotary engine vs piston engine

[martint235]

This has been bugging me since I was stuck behind a Mazda the other day. Which is better: a rotary engine or a "normal" piston engine? And if one is better than the other why is the other one still in use?

Criteria for best: fuel economy; emissions; acceleration/torque; noise.

 

[Beebo]

I cant help you, but I can be the first to say Wankel.

Edit:@ the swear filter doesnt like it! here's a link which answers most of your questions

 

[GrasB]

The first thing you have to do before you answer any of your questions is to normalise the engine capacities... The flat torque curve & very smooth nature of the engine makes them very predicable & nice to drive. Why are they not so prolific is easy, technically they're a much harder engine to make.

 

[tyred]

Don't think any of them have been very fuel efficient either.

 

[GrasB]

Don't think any of them have been very fuel efficient either.

The RX8 I drove on track was surprisingly fuel efficient compared to similar output conventional engine. But that's hardly typical road driving conditions.

 

[twentysix by twentyfive]

IIRC the rotary engine has wear and tear issues too.

 

[KneesUp]

The capacity of rotary engines is difficult. From memory the one Mazda make has, at any one time, three 'chambers' that total about 1.3 litres - but the total swept area is much more (about 4 litres? can't remember) Anyway, nominally it's a 1.3 for tax purposes, but the fuel consumption is more like a 4 litre, so it's misleading.

A rotary engine can be more compact and rev faster and generally way less than a comparable piston engine. But the tips wear out and they burn oil.

 

[sight-pin]

It was trouble with the seals blowing with the Wankel engine iirc, I think that's why that design never really took off.
Oddly enough, one of the best engines for speed i know was a commercial engine, 'Roots two stroke diesel' they was a 6 opposed / 3 cyl piston engine.... boy did they go,
We out accelerated a Porche down the commercial road in a rigid with one..... Well, the fitter did, i was just an apprentice at the time. Trouble with them was they kept breaking the turbo shaft.

Ah!! it's deleted part on the engine name, so here's a link instead. http://en.wikipedia.org/wiki/****el_engine....ok! try this.
http://www.popularmechanics.com/car...w-it-works-the-mazda-rotary-engine-with-video

 

[Markymark]

The problem with this thread is that the filter keeps blocking out the main part of the discussion.

It would be a nightmare if the engines were made in S****horpe.

 

[Jody]

The main advantage of the wan kel engine is that they have very few moving parts to go wrong. There are no cams, valves, connecting rods. They are also light and keep the center of gravity low. All the problem comes from the tips wearing and the engine loosing compression.

One of the best things about these engines (apart from the sound) is that you can strap more than one together.

 

[Piemaster]

Part of the capacity problem is that although you can compare volumes, rotaries have 1 'power stroke' per revolution, normal 4 stroke engines only have one per cylinder. So a 2 rotor rotary is more comparable to a 4 cylinder 4 stroke.
Think the Mazda engine only has 2 rotors, but as Jody points out, more have been bolted on!

There are non wan kel rotararies available. A lot of them are fitted to aeroplanes.
@sight-pin. Doxford made opposed piston diesels too. Bit bigger than the one in your post though.

 

[jazzkat]

I think on paper the rotary engine is far superior design. The fact that no one could make one that lasts a decent mileage says quite a lot!

 

[Lanzecki]

Emissions are an issue as well. In Ireland they went from a capacity based Vehicle tax where the Mazda was rated as a 1.3 ltr, to an emissons based tax. The € per annum went from under €300 to over €2000 (approx numbers, T&C apply etc).

TL;DR They are dirty, ohh so dirty.

 

[Tim Hall]

The problem with this thread is that the filter keeps blocking out the main part of the discussion.

It would be a nightmare if the engines were made in S****horpe.

Cummins diesel have a similar problem in some parts of the intarwebs.

 

[Fnaar]

My wankel is high on emissions