It looks to me that if you started spinning the rotors in the opposite direction, there's no realy reason why they wouldn't. So what determines the direction? And it also look like the combustion is perpendicular to the rotor face, so how do they make power if the combustion isn't directed in the direction of the rotation? Just some simple questions

 

direction is first determined by the direction the starter turns. If you were to run the starter in reverse it still wouldnt work because you would be trying to suck air out of the exhaust ports and force it back out through the intake ports.

 

That is a funny thought

Try checking out http://www.rotaryengineillustrated.com for some nice graphics on how the engine works.

 

I had considered the starter creating the initial rotation, but my main point was that the the fuel is ignited perpendicular to the rotor face, so it would seem that this would cause a lot of stress on the e-shaft. But looking at one of the animations it show the spark plus firing in an offset order, so I'm guessing the flame front moves in the direction of the rotor rotation. Then the second plug firesd downstream of the originial, after the rotor has rotated some, continuing the rotation. Does that sound about right? (Thanks for the link too, that site rocks!)

 

Yup. The rotor is already moving in that direction from the starter. Then the spark is fired at the right moment and it begins the combustion at the front of the pocket I guess you could call it. Things take a few moments, very short moments, to happen which is why we advance our timing. When the rotor is all of the way to the right, TDC (Top Dead Center), it is at 0 degrees ATDC or BTDC Since it is 0. When things start moving you need to advance the spark firing so it pushes the rotor at just the right moment. This is why you will hear people speaking of advancing their timing to 10, 20, even 30 degrees BTDC (Before TDC).

Imagine this:

You remember those tetherballs at recess when you were a kid? They spin around a pole? Now, if it is spinning slow you swing at a certain time. Now, spin it faster and if you swing at the same time you will miss the ball! Hence you swing sooner Just like baseball. If he chucks a fastball you swing earlier to catch up to it. This would be advancing

Now, what happens if you advance too much?? You get exactly what you are talking about, pushing the rotor the WRONG WAY. The spark fires too soon and hits the rotor as it is approaching causing serious damage.

Hope this helps.

 

Another reason it wouldn't work (which I think TOM91R1 was trying to say) What would it ignite if it was spinning the wrong way? All the petrol would be spewed out of the air intake, whilst the chambers would only be recieving air. If you changed over the exhaust and injectors/Carb, then in theory, it should work

 

Thanks for the informative response. I generally understood the order of air/fuel mixing and that it would only go one way, so I was really just trying to get a firm handle on the rotary. The theory obviously works!

 

The e-shaft does see quite a bit of bending force from combustion, although the force it sees doesn't have anything to do with which direction the flame front progresses during combustion. The pressure acting on the rotor peaks just after combustion is completed, but it doesn't just go away after that. It smoothly ramps down until the exhaust port begins to open (at which point it rapidly diminishes). The fact that high pressure continues to exist as the rotor rotates through a significant angle is what allows the engine to make power.

In short, the pressure in the combustion chamber *after* the fuel is done burning is what really produces power. This pressure is essentially uniform at all points in the chamber (at any point in time), including all across the face of the rotor, and it's this uniform pressure that is transmitted through the rotor as a force which turns the e-shaft.

 

There is frankly no difference between the rotary and a piston engine, in this respect.

None that I can think of, anyway.