I don't understand...is this rotary design wasting power this way?
When I look at a picture of a rotary engine, there is something I don't understand.
http://upload.wikimedia.org/wikipedi...ne_diagram.png At the ignition, the gas expands, but it looks to me as though some of the energy is directed perpendicular to the desired direction, some of the force looks as if it is traveling straight left from the spark plugs. It looks to me as if much of the useful energy is being absorbed by the shaft and the rotors only turn with the resultant power that has nowhere else to go. I have a feeling there is something I'm missing, can anyone tell me? |
Have you seen MM's video? Understanding takes more than a simple picture.;)
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im sure inertia helps combat the leftward push you are talking about.
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Originally Posted by kersh4w
(Post 2467695)
im sure inertia helps combat the leftward push you are talking about.
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This geometry isn't all that different from a piston engine near TDC, when the crank is pointing straight up. Not much leverage right then, and it's not the point where power is transmitted to the output. The air/fuel mixture is burning and building pressure, not expanding much right at that time.
Power is transmitted to the shaft during the stroke as the volume of the burned mixture expands. The Wankle never has a position with great leverage, like a piston engine at 90 degrees after TDC, which is why they're not known for torque. (Just like short stroke piston engines aren't torque monsters.) But the power that you get out them is still the energy associated with the burned mixture expanding through its volume, just like in a piston engine. The Wankel's inefficiency comes from the surface areas involved with the combustion chamber and the separate intake and compression regions. Ken |
Originally Posted by ken-x8
(Post 2467727)
This geometry isn't all that different from a piston engine near TDC, when the crank is pointing straight up. Not much leverage right then, and it's not the point where power is transmitted to the output. The air/fuel mixture is burning and building pressure, not expanding much right at that time.
Power is transmitted to the shaft during the stroke as the volume of the burned mixture expands. The Wankle never has a position with great leverage, like a piston engine at 90 degrees after TDC, which is why they're not known for torque. (Just like short stroke piston engines aren't torque monsters.) But the power that you get out them is still the energy associated with the burned mixture expanding through its volume, just like in a piston engine. The Wankel's inefficiency comes from the surface areas involved with the combustion chamber and the separate intake and compression regions. Ken |
Originally Posted by Falken
(Post 2467748)
I see what you're saying. But if that's true, than couldn't the problem be solved by designing an engine with elongated rotors for more leverage? OR by placing the spark closer to the bottom seal of the rotor?
You really need to consider the entire power stroke, not just what happens at one position. Think about Diesels, where all the combustion takes place close to TDC. Ken |
Originally Posted by Falken
(Post 2467748)
I see what you're saying. But if that's true, than couldn't the problem be solved by designing an engine with elongated rotors for more leverage? OR by placing the spark closer to the bottom seal of the rotor?
Due to the necessary geometry, elongated rotors would simply mean a larger rotor housing, and a larger engine. Very large rotary engines have been built, but they suffer the same fundamental issue -- the combustion zone is moving. The larger the rotary engine the lower the rpm because otherwise the air/fuel mixture moves faster than the flame front can propagate. From your last question I get the feeling that you are thinking of force being directed outward from the spark plug. The plug simply begins the combustion process. The location and timing of that initial spark have to take into account the movement that occurs. This is already timed in such a way as to optimize the energy transfer as the rotor continues its movement and the gasses burn and expand. |
Originally Posted by Nubo
(Post 2468104)
The force that is perpendicular has nowhere to go because the rotor can't move that way. Work only occurs if there is movement -- i.e., force through a distance. The rotor does move, and the energy of combustion drives that movement. Consider a piston. There's plenty of force against the cylinder walls trying to expand the cylinder. That energy is not wasted when the cylinder refuses to expand. :)
Due to the necessary geometry, elongated rotors would simply mean a larger rotor housing, and a larger engine. Very large rotary engines have been built, but they suffer the same fundamental issue -- the combustion zone is moving. The larger the rotary engine the lower the rpm because otherwise the air/fuel mixture moves faster than the flame front can propagate. From your last question I get the feeling that you are thinking of force being directed outward from the spark plug. The plug simply begins the combustion process. The location and timing of that initial spark have to take into account the movement that occurs. This is already timed in such a way as to optimize the energy transfer as the rotor continues its movement and the gasses burn and expand. |
makes sense to me:)
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