Houdini

iTrader: (3)

Yes, each combustion chamber is .65l. And yes, there's 3 sides per rotor. And yes, there are 2 rotors. So if you multiply that out, you get 3.9l for every full rotation of both rotors. But, you have to remember that the planetary gear system makes the eccentric shaft spin 3 times faster than the rotor. So for every revolution of the eccentric, you only get 1/3 of a revolution on the rotor. That means you divide by 3 to get to displacement per revolution of the eccentric shaft, so you're back down to 1.3l. But, you have to remember that the piston engine takes 2 revs of the crank to complete it's full displacement so if you want to compare a rotary to it, you multiply the the rotary by 2. So in summary:

13b =
3.9l if you use 1 rev of the rotor as a complete cycle
1.3l if you use 1 rev of the eccentric as a complete cycle
2.6l if you compare it to a 4 stroke piston engine

You pick what makes you sleep better at night, I'm partial to the last. Plus it makes more sense for a turbo charged 2.6l to make 255HP and 217lb.Ft of torque, than a 1.3l or 3.9l. That would be a lot of power out of a 1.3l with only 10lbs of boost and really weak for a 3.9l.

ERAUMAZDA

calling it a 2.6l makes no sense 1.3l or 3.9l makes sense.

Depends on if liter is considered all combusting surfaces or completing a 4 stoke event.

Crionics

I wasn't trying to discredit your background or anything, especially since I am about to graduate with a degree in Electrical Engineering (I also took thermodynamics at some point...lol). However, I still think that people are wrong when they say that a 4-stroke engine displaces it's entire volume in 2 crank revolutions.

Now just hear me out, and then you can tell me I'm wrong.

First, don't make the mistake of calling the rotary a 4-stroke engine. It is a 4-cycle engine, but stroke is a reciprocating engine term.

During 1 crank revolution in a 4-stroke engine, every piston moves either up and down, or down and up. there is no denying this. While each piston moves up, it is in fact displacing it's entire volume. Since each piston does this at some point during that one crank revolution, the entire engine overall displaces it's entire volume. the point where everyone seems to hang up on is the power strokes. Half of the pistons make 1 power stroke during the 1 crank revolution, and the other half make their power stroke during the next crank revolution.

Now, if you want to compare this engine to another engine, it makes no sense to call it 2.6L. You can't just say that because a 4-stroke engine makes all of it's power strokes in 2 revolutions, then we must compare a rotary after 2 revolutions. Each rotor makes 1 power stroke after 1 revolution, so we should compare 1 revolution. You don't compare 2-stroke and 4-stroke engines based on the same crank rotations, so you shouldn't try and do that with rotaries either.

Crionics

Sorry, I missed the second page, but this is exactly what I am talking about. This is wrong.It takes 2 revolutions for a 4-stroke engine to make 1 power stroke per piston, but the engine actually displaces it's entire volume in 1 crank revolution.

paw140

This is completely wrong... I think you're not understanding the term 'displace'. It might be easier to understand if we use the term 'pump' instead. An engine makes power by oxidizing hydrocarbons. The chemical reaction is Hydrocarbon + Oxygen -> CO2 and H20. This reaction is exothermic, and this engergy powers the motor. So to increase the power of a motor, you can need to increase the amount of fuel and oxygen.

One way to change the amount of oxygen is to change the engine's displacement. If it is able to draw in, or pump, or displace, more oxygen, then you can make more power.

So a measurement of the amount of air that an engine pumps is related to it's displacement. A piston motor pumps it's entire volume every two crank revs.

If you have understood everthing up to this point, you will realize that per crank rev, a 2.6L piston motor pumps the same amount of air per rev as a 1.3L rotary. Make sense?

Each cylinder in a 2-stroke motor pumps it's entire volume for each crank rev. Thus, roughly speaking, a 2-stroke motor is equal to a 4-stroke of twice it's displacement. That's why 2-strokes are usually so much more powerful than a 4-stroke of equivalent displacement. Notice, I said 'generally', because the technology of the 4-stroke engine is bringing it up to the same power level of the 2-stroke, without all the emissions problems.

TOUGHGUY

The rotary should be rated per one rotation of the e shaft just like a two stroke piston engine. The four stroke is the odd-man-out so to speak because it is the only one that needs two crank revolutions to complete it full displacement.

When you compare motocross bikes you don't say that the 250cc two stroke is really a 500cc motor because it competes against 500cc (450cc really) four strokes. If someone asks then why they make about the same amount of power, you explain that it is due to fundamental differences in design that they compare favourably. We EQUATE a 250cc two stroke with a 500cc four stroke but we DO NOT call it a 500cc motor! Why then would you call the 13B a 2.6L engine? Because that's how much four stroke piston displacement you need to compete with one? It should be rated at 1.3L just like you would rate a two stroke.

I can hear the screams already, "but it' has four cycles so it's a four stroke!!!" Absolutely correct! The four phases or cycles can be observed in the opperation of a Wankel rotary. They can also be observed in the opperation of a two stroke as well. The design condenses the cycles within one crank rotation (half as much as a four stroke) so it was called a two stroke. In actuality, it is just another form of internal combustion engine with four cycles.

Also, for those who might not have thought about it, the Wankel shares much more in common with a two stroke than with a four stroke. It has very few moving parts, uses ports instead of valves and opperates in a multitasking way. While intake is occuring in one chamber, combustion is occuring in another and exhaust in still another. The chamber experiencing the intake cycle is directly comparable to the volume below the piston in a two stroke. It is simply the next charge waiting for its turn to be in the combustion chamber. In the two stroke, while the combution process is driving the piston downwards, the bottom of the piston is forcing that charge up through the ports into the combustion chamber. Like the two stroke piston engine, the rotary uses the same principle of one dynamic part to complete the four cycles, only instead of having two chambers,(volume above the piston and volume below the piston) it has three. Also if you think about it, the characteristics of the power delivery are similar to the two stroke. Not much power at low RPMs and suddenly it gets into its "powerband" where the power curve climbs very quickly.

Why should the rotary be rated in two crank revs like the four stroke when we don't even do that for the two stroke. The fact that the four stroke requires two crank revolutions to complete its four cycles is the tradeoff it makes for being more fuel efficient. It seperates the four cycles much better than the two stroke or rotary so it is a more fuel efficient design but the extra crank rotation is wasted time that ALSO incures pumping and friction losses and that is why it is not as powerful as the other types of IC engines for the same amount of displacement.

The accepted standard for rating Wankel rotary engines is per 1 rotation of the eccentric shaft. That means the 13B is a 1.3L engine. If you have to compare one to a four stroke, then it should be compared like the two stroke, and that is by saying the 13B is 1.3L but because of fundamental design differences, it makes approximately as much power as a 2.6L four stroke.

Toughguy

paw140

Right. This is exactly what I've been saying the whole time. The 13B pumps as much air per rev as a 2.6L piston, thus they are roughly equivalent. And as I also said before, a 1.3L (or 3.9L) designation makes sense, whereas 2.6L does not, except for comparison purposes.