Quote:
Originally Posted by serialk11r
That's not correct, they run distinctly separated chambers with no fuel/air mix blowing into the exhaust from the intake.
Lubrication isn't even that much of a problem, because piston engines burn oil too. The rotary just has one hot area where combustion is always happening and oil gets burned a little faster there. Since there's no blowby contamination of the oil, you just slowly burn the oil off (which also happens in most piston engines). Premix is supposed to not hurt cats.
The problem is combustion efficiency. You get those pockets of air/fuel mix near the seals that don't ignite in a timely fashion. Again, there seem to be workarounds, like charge cooling the rotor (aka hot air intake, which reduces torque), adding more spark plugs (the 787B had 3 plugs, there are diminishing returns to adding more but the engine can definitely fit more plugs), using thermal barrier coating everywhere.
The biggest challenge is really the thermal management of the housing, you have one side always running hot, the other side always running cold. Aggressively cooling it down leads to unacceptable heat loss at low speed. Keeping it really hot means more oil consumption and requires ceramic insulation and high temperature coatings.
Efficiency won't ever be as good as a super high compression ratio long stroke piston engine because you can't get the compression ratio and the low surface area/volume ratio, but it works very well if you are always running at high power and weight is important. If you compare it to a motorcycle engine, which also has very little low end torque due to the crazy cam profiles, and also has low efficiency because there's a ton of friction, the rotary looks pretty good.
E.g. on a street car with a 4 cylinder engine, you might be able to shed 150lbs with a rotary, which isn't very impressive if you're hauling over 2500lbs. However if you can take 150lbs off a 1350lb Ariel Atom or 100lbs off a 900lb single seat race car, you probably would actually be using less fuel on the track. A hypothetical all aluminum triple-plug Renesis would be a very attractive engine swap option for track cars.
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I never said they were 2-stroke engines, nor did I say they mixed the intake and exhaust gases like 2-stroke engines. I said they are essentially like/similar/share-features of 2-stroke engines in that there are no valves and in that they rely on mixing oil into the combustion chamber.
Now, I don't know how bad it is for emissions to burn oil versus gas, but the Renesis motor recommends 1 qt of oil per 600-1000 miles. That's not an insignificant amount of oil to be burning, and it is no where near what a 4-stroke piston motor would lose across the piston rings. That can't be great for emissions. You mentioned premix. The use of 2-stroke premix oil is common and many use around 1-2 oz per gallon, which is 0.5-1 qt per tank of gas on top of what the engine is mixing into the air/fuel mixture.
I'm not going to get into the fluid dynamics of the rotary engine, except to say that a piston engine has better fluid dynamics for getting a complete burn, and it is easier to modulate because there are valves and because there is an ability to control valve timing and lift. It is even possible to alter effective compression ratio. I'm not saying improvements couldn't be made in efficiency. Here are some possible ways rotary engines could get more efficient, but they would still require burning oil to lubricate the chamber, and on a separate, but related note, the apex seals would still fail and lead to premature engine failure, so I could imagine regulators requiring smog inspections on rotary powered vehicles at shorter intervals like instead of an eight year law for the first smog, it could be at four years.
[ame]https://www.youtube.com/watch?v=vEMuOi0N2fQ[/ame]