Rotary Engines 101 - By Toyama Racing Spirit for http://www.importknights.co.za/

It's suprising when the topic comes up in conversation - not too many people actually understand the way it works at all. Most have an idea on the design, but start mentioning expectations of torque production vs rpm based on the technology, how much things differ from conventional engines, their efficiency and explanations start to get a bit thin to say the least.

So let's inform then :-) I'll start, by all means if you have anything to add, including comments or questions feel free.
    
The Rotary engine was designed by a German engineer Felix Wankel. The design hinges on the idea of converting pressure into a rotational movement on the 'rotor'  for lack of a better explanation. These motors are small and greatly differ from what we're used to. Some key differences:
    
No pistons
No valve-train (meaning no valves or camshafts)
No connecting rods
No crankshaft

Wankel motors, unlike Piston based setups, complete the four major stages of operation (air intake, compression, combustion and exhaust) within 1 action (view the flash demonstration courtesy of HowStuffWorks below for more information) of the rotor moving from current position on to the next position within the housing (1 of 3).  Lets looks at the parts within the design:

Rotor:

This is the three convex faced unit that for-fills the duty of a piston within Wankel design. Each edge of the rotor has a very small pocket, which allows for an increase in displacement (this is also how you can modify rotary displacement). The meeting point of each edge ensures a solid seal onto the housing itself (think of the housing as a oval cylinder if you must). As you can now work out, that tight seal encapsulates the pressure within that portion of the Housing allowing for the continuation of the combustion process.
    
Housing:

This is the oval 'cylinder' mentioned above. Actually not really oval either, the correct shapes name is an epitrochoid. The main design decision here is to ensure the rotor remains in contact with the housing at all times sealing the volume of gas within each 'pocket'. Each segmented 'pocket' allows for the intake of air moving to compression of the gas (heat generation), the ignition event and lastly the exhaust of the resultant gas. This literally happens all at once - a synergy of perfect timing. As you've figured by now the exhaust and intake ports have no valves, the only thing between these ports are the intake tract or the exhaust system itself. Strange isn't it ;-)

Power output shaft:

How do you get the power out? The rotor, sits over the output shaft, which has various lobes that the rotor pushes upon every revolution. This twisting motion drives torque down the shaft - resulting in power to the wheels.

You can see very clearly that the motor design really isn't the same at all. Think of the rotational masses being sheered off here, the kind of efficiency that results offering up high rpm power in a smooth fashion. These motors do not suffer from bad pre-ignition and will run low octane fuels without problems usually a few Ron less than the average piston engine. Combustion isn't as clean as a piston based motor, a fair amount of hydrocarbons are released as a by product from incomplete burn. With time design on the exhaust side of things have resulted in acceptable NOx levels meaning these motors run safe to the environment. The Renesis version (RX-8) brought about the best fuel economy and emissions ratings to date, meaning that the technology is still growing and acceptable as a working design in today's times where oil resources are becoming less and less. There are fewer moving parts - as a result more reliable. If you think back to what I mentioned above, for every turn of the output shaft, the rotor is 1/3 the speed, slower movement of these parts means less wear and increased reliability once more.

All good right? No pistons to worry about, no connecting rods, Not exactly.

By design, these motors consume a fair amount of oil. During operation the oil is trickled out in metered doses to keep the apex seals within operating standards. This means running costs on the oil side of things is something to consider, although it is very reasonable sometimes even comparable to some piston based motor oil usage. The motor is also less efficient  than piston based technology in terms of fuel economy, while the Renesis design made for acceptable economy, piston based motors still have the advantage (at time of writing). The other factor to consider when deciding on whether to try this technology for yourself is torque production and drivability. Think about it, the output shaft is spun, this translates in power, you have one cycle versus four, it all boils down to torque being produced later in the rpm range. You have to make these motors work to make them work for you. Cost is another key factor here, these motors cost more to produce upfront.
    
Lets see the process in motion:

<a href="http://static.howstuffworks.com/flash/rotary-engine-animation.swf" target="_blank">http://static.howstuffworks.com/flash/rotary-engine-animation.swf</a>

Amazing isn't it? So the next time the topic comes up in conversation, you know a little bit more.

Cheers.

Yes but it also runs on alot of magic and don't forget Hopes&Dreams and Heart&Spirit. I had to do a similar explanation on the Mazda forum lol, it's one of the reasons guys don't use this amazing engine much because they're afraid of anything that could happen inside. Yes they aren't engines to be repaired by ordinary mechanics. The stronger 2mm seals upwards do make the engine one of the smoothest most reliable engines producing a smooth power. I love rotaries, hence why I bought my series 6 RX7 because it's got the perfect balance handling wise, perfect balance weight wise, perfect rotary powerplant which in my eyes is the best so far besides the 20B, plus it's got the timeless looks of the best Efini sportscar ever made and modifications can only make this perfect car into something of greatness. wow what a car guys.