vipeRX7

As many of you probably know, the engine from the Cadillac 16 concept has 16 cylinders and 1000 hp, but gets a whopping 20 mpg. I was surprised to see this statistic, but it is a result of GM's displacement on demand which (correct me if I'm wrong) stops sending gas to certain cylinders when little power is required. Could this be used on the Renesis? I see no reason why not. The only downside I could see would be that there might be some lag under hard acceleration before the computer acknowledges that maximum power is needed. Consequently, I would hope that, if implemented, Mazda would allow the user to turn DOD on for increased fuel efficiency, and off for better performance. Just imagine if the RX-8 had DOD! Someone posted an article in the OHV thread mentioning that DOD improves fuel efficiency by some 25 percent, meaning the RX-8 would get 25 mpg for city driving and 38 mpg on the highway! :D

neit_jnf

I was just thinking about this too!! I think this technology was first used in Cadillac's Northstar V8's, it worked as a 4 banger for fuel economy and also when the engine was overheating to help lower its temperature. The RENESIS with this technology would be awesome!!! It might not be too difficult, maybe just requiring some programming of the ecu??

Sputnik

GM has been trying this kind of thing since the '80s. So far, on production vehicles, it has caused more problems than it helped, so it was discontinued. If they've been able to make it over the hurdles, then cool. But since GM already put an "iffy" setup on production models in the past, then I'll wait a year or so to see that they've actually made it work well.

But there's no reason why the theory wouldn't work on a rotary.

---jps

zoom44

how would that work? just cut off 1 rotor all together or skip a combustion cycle in each rotor?

wakeech

exactly what i was thinking "how?"...
you'd have a massively unbalanced motor, or at least a super-choppy idle, if you cut one rotor off... but we've gotta remember that there aren't 2 combustion chamers, but six.

again, i'm just an econ major with a panache for engineering, so i'm probably wrong but i think the best way to run it would be to simply alternate one to the other... what'll end up happening is that per rotor rotation (which means every three revolutions of the e-shaft) you'll have one rotor firing twice out of three times, and one rotor firing only once... then on the next cycle (three revolutions of the e-shaft) the two rotors would trade firing duties: one firing once, then the other firing twice...

aw, wait, ****... this thing doesn't operate like a 4 stroke piston... i've gotta think hard on this one...

wakeech

oh oh oh... maybe i have it now?? i'm just trying to see it in my head...

each rotor would fire twice in succession, then miss two (letting the other rotor do the firing duty), thus each skipping one cycle per full rotation, and the motor would have smoothish transitions between the alternating cycles, as every other power stroke would overlap... hmmmm... man, i really like this stuff.

vipeRX7

This may be a stupid question, but why would the motor be unbalanced? Both rotors would still be spining even if only one was creating power. Is it because of the weight of the gas at one end and not the other? If so, then I would think a 3 rotor would be ideal. For better mileage, use the middle rotor. For maximum performance, use all 3. For a compromise, use the outside 2 rotors. That way you wouldn't have to be opening and closing valves all the time to let fuel into one rotor and then another, but you would still maintain a balanced engine. Yet another reason for a 3 rotor ... listening, Mazda? :p

zoom44

that's what i said isn't it?

but you are saying alternate the skipped one between the 2 rotors, to keep it balanced and smooth? you would have to cut the injectors wouldn't you, so that no fuel was going into the cycle that would be skipped?

once we get this figured out we should send a link to this thread to the mazda techs to see what they think of our solution:D

MikeW

Displacement on demand actually removes the cylinders from the intake/exhaust systems. GM does this by decoupling pushrod from the lifter. So the vacuum in the cylinder does negative and positive work on the crankshaft.

That 20 mpg is achieved on 4 of the 16 cylinders and at something like 40 mph.

MB actually has DOD on their 5.0 V8 in europe, but since it is a V8 the firing order goes from L R L L R L R R to L x L x R x R x, so it sounds somewhat like a subaru boxing 4 L L R R

wakeech

good god man

...maybe then Mazda could do the same thing with the butterfly valves in the intake runner system??? but yeah zoomy, the same effect could be achieved with a fuel cut (as it's directly injected, it's a simple matter to get the timing correct)

so, Mike, 'cause the wankel's firing order is so bloody balanced (F R F R F R), would (using my idea of alternating the skipped cycle) RF (skip) FR (skip) RF (skip) FR be balanced enough??
hmmmmm :D i'm feeling a little smarter today.

zoom44

me too! thanks mike for the info. i 'm serious too, once we decide on a scheme we like we should see if the mazda techs like it:D maybe they have ideas we haven't thought of

MikeW

If mazda ran a complete dual exhaust on the wankel, and could completely close off the exhaust of the rotor to be shutdown, than maybe it is feasibly. So only 1 rotor would be firing (evenly) but the engine could not run like this for anything longer than 5 minutes because the offline rotor would cool off to much. MB cylinder shutoff on the V12 would only work for period of up to 3 minutes or so, and the V8 only goes up to about 2 minutes. GM is persuing this technology to raise it CAFE numbers, period. Ford says it isn't even on their map for raising vehicle efficiency.

But the reason that I would buy the wankel is that the engine alway make power, that isn't true for 4 cylinder engines.(sorry Honda S2000) This is like GM's new V6's with DOD that shut off 3 cylinders. The reason I drive a V6 now (and not a 4 cylinder) is that it makes continuous power and has virtually no crankshaft resonance(got dual mass flywheel), unlike Inline 5&6's.

zoom44

So rotarynews.com put the question to the newly appointed Senior VP of Marketing and Product Development, Robert Davis.

here is how it went:

" If a larger displacement twin rotor or triple rotor is in the future of the RENESIS and fuel consumption is a concern, can Displacement On Demand (expected in the C6 Vette) be implemented in the rotary engine?

No"

and my answer to that is: he is just plain dead wrong! now someone go ask the engineers :D

vipeRX7

I agree completely. There is no reason (as far as I can tell) that it wouldn't work. The engineers would *hopefully* agree

MikeW

As far as I can gather, DOD is off for the Corvette. They will just keep on using the CAGS system with the manual, and use the 5L50 automatic until the 6 speed automatic is available in cy 2005.

They don't want their corvette to sound like a Subaru (or closer to an air cooled beetle) boxing 4 . That is what a cross plane crank V8 would sound like with DOD engaged L R L L R L R R into L x L x R x R x.

babylou

As mentioned earlier by MikeW DOD works by reducing pumping losses associated with filling a cylinder and exhausting a cylinder. Producing double the power in half the cylinders is not on its own more efficient.

The reduced pumping losses is only accomplished by closing off the cylinder intake and exhaust ports. How is this gonna be done on a rotary? I do not see the butterfly valves sealing well enough. Also, the butterfly valves are not on the primary intake ports and then we have to seal off the exhaust ports.

So to get the rotary to have DOD we are gonna have to add a bunch of gadgets. Then we have a rotary engine that is heavier, more expensive and less reliable but is more fuel efficient. Ths path kinda defeats the advantages of the rotary. Might as well get a piston engine.

If the rotary lives I bet it goes towards high pressure direct injection. For this engine we can see improvements in efficiency, emmissions, torque and power. Little cost increase would be associated with DI because 6 injectors would be supplanted by two.

rpm_pwr

Many years ago I read an SAE paper by one of the Wankel license holders (not mazda I think) on direct injection rotaries. They used special injectors to create a stratafied charge (richer near the plug, leaner near the apex's. Anyway they got reasonable power improvement, but significant emissions reductions. I've always wondered why Mazda never pursued this. I assume they have, just never got the $ to put it into production.

More recently I read about a guy who modified a 12A turbo (semi-direct) to do a very crude version of this. All he did was have the injector open/close timing correspond with the rotor position to get a crude version of stratified charge and even he saw emissions improvements.

-pete

wakeech

...that is bloody brilliant.

kidmarc

neit_jnf wrote:
The RENESIS with this technology would be awesome!!! It might not be too difficult, maybe just requiring some programming of the ecu??

That is one method... another is to bypass the ECU.

zoom44 wrote:
i 'm serious too, once we decide on a scheme we like we should see if the mazda techs like it maybe they have ideas we haven't thought of

You don't need Mazda to take notice of and implement it; you can do so yourselves.

MikeW. wrote:
If mazda ran a complete dual exhaust on the wankel, and could completely close off the exhaust of the rotor to be shutdown, than maybe it is feasibly. So only 1 rotor would be firing (evenly) but the engine could not run like this for anything longer than 5 minutes because the offline rotor would cool off to much. MB cylinder shutoff on the V12 would only work for period of up to 3 minutes or so, and the V8 only goes up to about 2 minutes. GM is persuing this technology to raise it CAFE numbers, period. Ford says it isn't even on their map for raising vehicle efficiency.

You don't need it (the shutdown) to be continuous; only when power is of no use.

But the reason that I would buy the wankel is that the engine alway make power, that isn't true for 4 cylinder engines.

And that is the problem.

babylou wrote:
The reduced pumping losses is only accomplished by closing off the cylinder intake and exhaust ports. How is this gonna be done on a rotary? I do not see the butterfly valves sealing well enough. Also, the butterfly valves are not on the primary intake ports and then we have to seal off the exhaust ports.

So to get the rotary to have DOD we are gonna have to add a bunch of gadgets. Then we have a rotary engine that is heavier, more expensive and less reliable but is more fuel efficient. Ths path kinda defeats the advantages of the rotary. Might as well get a piston engine.

Not necessary to add gadgets that increase weight significantly to drastically. There are two methods - mechanical and electronic - to accomplish the end result which is to shut down the injectors.

Peace
marcus

babylou

Marcus,

You did not read my post carefully. It does no good to shut down the injectors. If DOD was this simple every engine would incorporate it. DOD is simply a method to reduce engine pumping losses and therefore increased efficiency is had a low loads. Not injecting fuel does nothing to reduce pumping losses. You gotta actually quit pumping. To quit pumping while the pumps (pistons or rotors) are still active they must be sealed. Imagine that.

P00Man

hmmmm every problem can be solved, even the ones that dont have solutions, and even those have solutions, which would be that they have none...

now to get displacement on demand in a rotary...
a rotary works by spinning a triangle...GOT IT!

of course it requires smart metals or some other exotic scheme...or...perhaps even just a band that actually changes the shape of the rotor mechanically. like a strip of titanium that would fit the controus of the oval housing, that is held off of the main rotor by rods of some sort that are controlled electronically. the problem is the wiring, and making titanium flexible, of course you could have a piece with a constant curve to match that of the housing, but since its oval it itself doesnt have a constant curvature, so you need something flexible...maybe a teflon coated polymer..., but the info transfer would have to be wireless and thats a major problem with all the metals because the electronics would have to be inside the rotor...youd need something like carbon fibre rotors...

in the end the cost of it is extroadinary at this point in time and will never come to market, much less be designed...

anyways, this would work by changing the open volume that can be "breathed" (ie, istead of one rotor breathing 1.3 litres, it would be breathing 1 or something like that) as you guys say and could be constantly adjustedm but the algorithms in the ECU would be pretty complex and then there again is the cost...


of course if DOD works by stopping the pumping...well, you WOULD have to seal stuff...but i dont know what, so when i learn more about the wankel, maybe ill try to solve it


edit:
back to my other idea, ive revised it and made it better:
it would require a maleable/smart outer wall of the rotor wich could be expanded by some means, depending on whether its a smart metal or simply maleable. a smart metal would do it itself, a maleable one would require poles to push it out towards the sidewall of the housing, ofcourse theyd have to be able to adjust their length for optimum contact, which would be th only kind of any use lol
________
milf Cam

P00Man

"You did not read my post carefully. It does no good to shut down the injectors. If DOD was this simple every engine would incorporate it. DOD is simply a method to reduce engine pumping losses and therefore increased efficiency is had a low loads. Not injecting fuel does nothing to reduce pumping losses. You gotta actually quit pumping. To quit pumping while the pumps (pistons or rotors) are still active they must be sealed. Imagine that."

what must be sealed? the pumps or the rotors/housings? i really have no idea what youre talking about lol, maybe im an idiot
________
Recall Zoloft

kidmarc

If the rotary (Wankel) engine was/is as good as many enthusiasts say, then every car manufacturer (at the very least more than just Mazda) would be using it. :D Because people don't use it does not justify its use (worthiness). Another example: The drop kick in US football through the goldposts accounts for 3 points, however its use has not been part of the game for a few decades. The explosiveness of the straight ahead toe-kick (on a place kick) is far more powerful than the wheel/swing kick (using the instep) of fussball/football/soccer player, yet the toe-kickers have gone the way of the Dodo bird. :D
Engine pumping losses is a bit more in-depth than GM is letting on. Displacement-on-demand closes the valves, resulting in no flow, pumping, compression of fluids and gases. Yes you cannot compress a fluid, but you are compressing around it, pumping and flowing it. Unless the pistons are disconnected from the crankshaft, you are also moving them (added weight as there is no full vacuum); you are pumping. Thus a reduction in the so-called pumping losses and not an elimination. In doing this, GM has shut off fuel flow.

Once an object is in motion the energy to sustain that motion is less than the energy needs to to put it into motion given the frictional forces playing on the object. If you apply even less energy than needed to sustain the motion at a given rate, then frictional forces take over. The object comes to rest (in this case). You have generated an engine brake where the engine is the object. The usefulness is in deceleration.

Shut off/down the fuel on deceleration and you use less fuel; you are not fighting the engine; less brake wear; engine runs cleaner; shorter stopping distances; less tire wear...

Simply put... there are more ways to accomplish efficiency (emissions and fuel consumption) than the one discussed here, displacement-on-demand.

Peace
marcus

babylou

Marcus,

Before posting need to read and comprehend the other posts. Your last two posts are based on miscomprehension.

In response to your last post: I said if DOD where so easy to implement it would be on all vehicles, nothing about Rotary Engines.

I then mention that the GM system reduces pumping losses and you go into a long and treatise of how the pumping losses cannot be eliminated but only reduced.

Finally, a drop kick was worth two points, not three. And the socccer style kick is much more powerful than the straight ahead kick. Why do you say such BS?

kidmarc

Yes sir, that is correct. I also did not refer to the DOD and rotaries. I made the same comment as you only I substituted the rotary for 'DOD' and 'car manufacturers' for 'all vehicles'. In other words, if you can make your statement (If the DOD were so easy it would be on all vehicles), then you can make this one (about rotaries being so great... all car manufacturers would make them) as well.
Not a 100% on that interpretation... I spoke of the pumping losses in one paragraph. The following paragraphs (3 in total) covered what happens when you do not inject fuel, which you said "... It does no good to shut down injectors... Not injecting fuel does nothing to reduce pumping losses."

You may correct me if I am wrong, but I believe I was addressing the 'shutting down of the injectors' comments you made. The drop kick came from rugby which is 3 points. In the genesis of US Football and up until the non-use of the drop kick, it was (and still is) 3 points.

The straight-ahead kick is a snap kick. It has a long follow through. The soccer-style kick is a sweeping kick with a short follow through. The former explodes through the ball while the latter pushes through. Force=Mass x Acceleration. The mass being the same (the leg and foot)... the acceleration of the former is greater than the latter. Bruce Lee demonstrated this often.

Jan Stenerud of the Kansas City Chiefs continually belted the ball into the bleachers with the straight-ahead kick that soccer players were taxed to copy.

However this 'BS' as you say, was mainly for analogous purposes; it was never meant to be the 'science'.:D

Peace
marcus