MadSci Network: Science History
Query:

Re: Why wankel engine is not famous?

Date: Tue Jan 25 14:41:09 2005
Posted By: Kevin Reed, Engineer
Area of science: Science History
ID: 1106661787.Sh
Message:

Paripurnachari,

That's a very good question: in theory, the Wankel rotary engine is a very 
simple, efficient machine that can produce a higher power output per unit 
engine weight than the more common Otto/Benz reciprocating-piston engine 
design, but the only major manufacturer of that design was the Mazda 
motorcar company.

Despite theoretical advantages, the Wankel design has several technical 
hurdles that have made it less attractive than the Otto.

First, the Wankel design requires rotating seals, both between the rotor 
faces and the rotor outputs. These are harder to design and to maintain, 
so Wankel engines have had a tendency to have lower compression pressures 
than Otto engines, which lowers the power available from the engine.

Second, while the Wankel design has better fuel-air mixing and more even 
combustion in the chamber, it has a larger fraction of unburned fuel after 
each power cycle than a reciprocating piston engine with the same 
combustion-chamber size. That unburned fuel reduces the efficiency of the 
engine.

Third, it is very difficult to make a Wankel engine with more than two 
rotors because they all have to synchronize directly with the rotating 
power shaft. Additional rotors mean additional power can be produced by 
the engine, just as additional pistons mean additional power in a 
reciprocating engine. Some racing car designers have managed to do this, 
but at the cost of additional sealing and coupling structures that 
dramatically increase the complexity and weight of the engine.

A good animation of a Wankel engine in action can be found at  http://www.keveney.com/Wankel.htm
l .

Discussion of the Wankel engine and its advantages and disadvantages can 
be found at http://www.monito.com/wankel/r
ce.html and also at  http://en.wikipedia.org/w
iki/Wankel_engine .

I hope you find these helpful.

Thanks again for the question!


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