jamesf

iTrader: (1)

Or we could ignite the exhaust and have some rx8 afterburners :D

Jethro Tull

iTrader: (6)

There is much more potential energy stored in piston engines than Wankels. Due mostly to the rest mass, but also because of the "moving mass". 6 or 8 pistons, combined witht the crankshaft, camshaft, and all the other moving parts equals quite a bit more moving mass than a couple of rotors and and an eccentric shaft.

Quite a bit more.

Rotors spin very close to the axis of the crankshaft. Thanks to Archimedes, we know that the further from the axis a mass moves, the more torque it generates. Pistons and cranks are much further off-axis than rotors, as well as being "heavier". Thus, more mass. Thus, more torque.

Q.E.D.

Jethro Tull

iTrader: (6)

BTW, I love you guys.

This is funner than hell.

I'll check back in a few days. Go for it dudes.

monchie

Nice thread to read.

RIWWP

iTrader: (2)

I agree that there is much more potential energy stored in piston engines than Wankels. We have a smaller lighter package after all. I see this exactly the same as "there is more potential energy in a heavy OEM flywheel than in a lightweight aftermarket one" or "more potential energy in a steel driveshaft vs a carbon fiber driveshaft"

I agree that the further from the axis a mass is, the more torque is applied to the axis when that mass moves.


However, the only real connection between the two that I can follow is when there is 'the amount of torque applied to the crankshaft by the mass of the components when not on the throttle.'

The only way I can think of to show how I see this connection is:
If you take a piston engine and a rotary engine, minus all the accessories, no liquids, no fueling, nothing else, and you accelerate their driveshafts at the same acceleration rate, it will take less torque to achieve that acceleration rate on the rotary than it will on the piston engine. It does not matter if this acceleration is achieved through applying this to the driveshaft at the shaft itself or through the pistons/rotors. Less mass requires less torque to accelerate at the same speed.


I still don't see how the higher mass of the piston engine GENERATES more torque from a combustion due to it's mass.


Every torque calculation description I can find states basically this:
Torque is defined as the amount of rotation an object experiences when a force is applied to that object. The object rotates on an axis, called the pivot point. The distance between the pivot point and the point where the force is applied is called the "moment arm" and is represented by "r." Torque is defined mathematically as the cross product of the moment arm and the force vector, expressed as T=r x F=r(F)(sin[a]), where "a" is the angle of the force

At no point in any of these calculations is mass a factor

olddragger

iTrader: (3)

the combustion generates the TQ by moving the mass In addition that combustion is using a longer lever to rotate some of the heavier mass. Mass does not generate tq in itself-- it only is a factor once something else has moved it. Remember Eisteins--an object in motion will remain in motion until blah blah. Its harder to slow down something that is heavier. That is the reason that a very light flywheel car requires more rpm to get going.
But yall are not comparing 1 important aspect. Our engine (by size) is only a 1.3. Take a 1.3 recip engine and compare the Tq of it to ours.

RIWWP

iTrader: (2)

It's a scientific debate, I don't think anyone is trying to state that we have more or less torque than we actually do.

I believe that a lightweight flywheel only "requires more RPM to get going" if the driver isn't paying attention. The mass of the inert drivetrain is acting as a resistance against the rotation of the flywheel as the clutch engages, causing an RPM drop. Hamfooting it and letting the RPM drop from this can cause a stall at "normal" RPM for a heavier flywheel, and so can be offset by increasing the revs so that the drop isn't severe enough to cause a stall. If the driver maintains the throttle so as to prevent this RPM drop, then no additional RPM is needed to get an inert drivetrain moving for a light flywheel vs a heavy one. Exactly as you noted, "it's harder to slow down something that is heavier", and the flip side of "easier to slow down something that is lighter".


If you take two wrenches of the exact same dimensions, one weighing 2 pounds and one weighing 30 pounds, and use them to torque down a bolt (moving horizontally so you can rule out gravity), which one is producing more torque due to it's mass? If mass in indeed part of the torque calculation, then the heavier one would require less effort from your muscles to apply the same amount of torque. I don't think you will agree with this however.

If anything, your muscles are using more energy to move around the heavier mass, though none of this energy has anything to do with the amount of torque being applied to the bolt.

olddragger

iTrader: (3)

exactly!! You hit the nail on the head but i dont think you relaized it. Yes you had to provide more energy to move the heavier wrench--but what I dont think you reliazed is that the heavier wrench took longer to slow down than the lighter one. The tq should not be measured at the bolt, but at the wrench in that case.
There is a big difference between "work" and "torque". You cant have HP without torque but you can have tq without hp---its called a dump truck

RIWWP

iTrader: (2)

No, I do recognize that since the heavier wrench has more mass, you actually have to use more energy to get it moving.

That doesn't change the amount of torque at the bolt (crankshaft) though.

In fact, I'd say that the lighter wrench is superior, since the same amount of force through your muscles (combustion) moves the lighter wrench that much easier, wasting less force just moving the mass, and more force to the bolt at the other end.

Galen Darkmoon

And another.

http://editorial.autos.msn.com/blogs...3-3bb5ca189d26

Chibana

Einstein? I think you mean Newton. Einstein was all about relativity and, later, quantum mechanics to some degree.

http://csep10.phys.utk.edu/astr161/l...wton3laws.html

Chibana

Torque = r (vector) x F (vector)

simplified, with constant mass, it is

T = rma

r = radius
m = mass
a = acceleration

There will definitely be more mass in a heavier rotating object, and if the radius is longer, that will also result in more torque. However, given the same explosion from combustion, the heavier, longer object will accelerate more slowly. How does it all work out in the end? I don't know. I doubt it's a simple calculation given a complex engine.

Why are we going off on this in this thread?

olddragger

iTrader: (3)

it was one of those brain guys! Thanks for the correction and yes--back on subject.

Jake33

iTrader: (2)

cmon mazda! bring us what we REALLY wanna hear!

BJP

iTrader: (2)

I know i'm a bit biased toward the rotary engine but I get pissed when people dis the RX cars!
My thinking towards why no one else wanted to use the rotary engine in any of their cars is because they didnt get it! Mr. Wankel probably stood before a panel of engineers and corporate presidents and explained his design and they probably sat there and went *uh...what?*

Yes it doesnt make much torque but neither does Honda VTEC motors...I'm not a huge VTEC fan but dont they only make 140ft/lbs+- of torque? Same thing there, you have to rev them up to make High RPM HORSEPOWER.

As explained before the rotary engine doesnt have much for a "power stroke", that's why there is small amounts of torque. Think of a Semi diesel engine. Their piston stroke is massive...making tons of torque and that's why most of them redline in the 3-4000 rpm range. I'm not comparing rotaries to diesel engine just using it as an example for the power stroke scenario.

Anyways, I'm really glad to see Mazda try to keep the soul of their company alive. I hope they can pull it off.

Die Rotary Haters!

Footman

iTrader: (2)

Chibana,

The torque formula's mass is with reference to the force applied, not with reference to the object the torque is being acted upon.

Endgame

Well, I will jump in here. I was sitting in an airport yesterday chatting with a Mazda tech in a 'city' which I will not name doing training on the new Sky Active tech stuff. He told me he heard the next rotary car will be a 3 rotor.

That is all I got. Do not want to say anything else that may get him in trouble. Flame me if you want, but I thought I would toss that out there....

olddragger

iTrader: (3)

I dont doubt it. Rotors will be smaller in displacement than ours, bearings etc will also have less friction area. That with semi DI, electric water pump ( either primary or a booster pump) and ceramic seals will go a long way toward improvements.

RIWWP

iTrader: (2)

^


That's about as solid as my mailman's claim that Hyundai's next Sonata will top 400hp and dodge accidents for you.

Footman

iTrader: (2)

If they go with all electrical water pump, OMP, A/C pump.... and beef up the alternator to support those things, then the only "belt" required would go between the ES and the Generator!

That would be awesome! Simple to look at too. Plus when the A/C turns on, no longer physically "drags" the motor revs down and shake the car at idle.

alnielsen

iTrader: (4)

Talk about blowing smoke.....
I can't see how that can happen. And yet, you've been in the game (no pun intended) for a little while.

ShellDude

iTrader: (12)

3 rotor 20b?

RIWWP

iTrader: (2)

The only way I could see a 3-rotor happening is if they downsized the dimensions itself. Think instead of two 654cc rotors for a 1.3L 2 rotor, make it three ~436cc rotors. Instead of just straight down scaling, they could make the rotors ~66% of the current width to keep the current stroke to avoid losing any more torque, fit the 3 rotors into the same overall block size at that point. If you used the same size air / exhaust routing through the side/end plates, with each rotor needing 33% less flow, it would really open up the power production possibilities compared to the exhaust-flow limited MSP.


Interesting in theory, but seriously doubt Mazda would do it.

A production three rotor for consumer purchase with 2.0L of displacement will not be happening.

Spin9k

The three rotor I envision uses one rotor as a pre-charger (probably the center one) forcing compressed mixture into the other two rotors, IOW, a systemic supercharged rotary engine. That boost may allow a smaller fired chamber size to achieve current or better output levels.

alnielsen

iTrader: (4)

I don't see any change in the volume of an engine. The amount of engineering would be cost prohibitive. They've already spent a lot of money getting a 1.6 together.