CyberPitz

This really isn't a "OMG I BOUGHT THE CAR I HATE IT!" Thread. I actually, being an enthusiast, would love to learn more and more about the engine. I would LOVE to know what exactly causes the fuel consumption issues, and if anybody has any ideas about how they can resolve it.

Obviously, it would be rather difficult to sift through all the usual mpg threads, so I gave up after the first page of searching. I'm sure this has been discussed, just wish I could find it

Through a google search, I've found a description that sounded like it made sense. How the engine doesn't burn all of the fuel, so it pushes some of it straight out the tail pipe *of course, the engine smells SOOO good though!*. Others said that the engine spins 3x's as fast then conventional piston engines, so that's another cause...

I would just love to see everybody's ideas.

Thanks in advance, and if I need my flame suit, just give me a few minutes to put it on before you turn the flamethrowers on

refugeefrompistons

a smaller percentage of the fuel consumed and combusted is converted into mechanical energy. Much of it is converted into heat. Was stated this was caused inherently by the design of the engine partly due to the high surface area/volume of the rotor housing.

rglbegl

You have to feed the ponies.

To get over 200hp out of a 1.3l engine . . you are gonna consume a lot of air, and a lot of fuel.

CyberPitz

Well, since the 16x is coming out soon, they are incorporating the direct injection fuel. *I'm so sorry for not being the most intelligent bean in the can...* but how will that help with the MPG as has been stated. Since it will be a larger engine *though lighter :D* will that inherently help anything, or will it probably keep around the same MPG..?

rglbegl

Who cares, it will be fast


To be honost, I know nothing about the 16x.
But for some reason I still want one in an FC

CyberPitz

You can have the 16x, I'll take the 20B... :p

Yeah, I'm unfortunately pretty clueless on the mechanics of the 16x as well. I read what Mazda has released, but that's about it.

Socket7

Rotarygod and others have posted some very informative articles on the physics of rotary engines, and why they are so inefficient. I recommend doing a bit more searching because i know they exist and are so info dense my eyes glaze over just thinking about reading them

shaunv74

The direct injection will allow it to run a leaner AFRs allowing for more power with less fuel while not detonating. There are two main reasons for poor fuel consumption.
1)gearing. You see this in your highway mileage. You cruise at 3500-4000 rpm you're going to burn more fuel then at 1500 or 2000 in a Corvette.

2)Volumetric efficiency. As stated above the volumetric efficiency of the rotary is not as good as a piston engine ~90% so you don't get as much power out of the same amount of air in a piston engine.

What you do get is a very compact, light weight, high reving, high specific hp/liter engine which is perfect for a sports car.

CyberPitz

Thanks Socket, I'll have to dig for RGs posts some more. I figured he's be the one to post something like that, haha.

@Shaunv: That helps a bit as well, thanks.

What about the low torque, is the same thing that plagues the MPG plaguing the torque?

daisuke

that it spins faster than other engines doesn't really explain it, the honda S2000 spins just as fast.

One of the main reasons is because you get 2 power strokes per turn of the engine shaft, that's also the reason why such a small engine can produce so much power. Also the new side exhaust port system has helped in keeping the unburned gasses from exiting the engine.

There have been a few things done to solve the fuel consumption, one was the 3 spark plug method per rotor used by the 787B Le Mans racer, compared to the cars it ran against, it got very competetive gas mileage. Direct injection will also help, but the main way to help is simply to make a smaller engine. Since the late 70s the only cars mazda has put the rotary in have been sports cars where fuel consumption isn't a concern. Make an engine with 2/3s the displacement or half the power of the renesis and slap it into something the size of a mazda 3 or 2 and you could easily break the 30 mpg barrier.

There is a recent article that Moller (the "maker" of the skycar) has developed a wankel engine where one rotor is powered and the other acts as a turbo/supercharger for the first one, the first rotor precompresses intake air and expands exhaust, the second one does the actual firing. They claim to decrease fuel consumption by 25% when they're done developing, it also decreases the noise made by something like 93%. I'd love it to be true, but given Moller's unimpressive track list in producing anything that ever hits the market I would be sceptical about it ever coming into production. We can only hope.

That said it will never ever be able to get the kind of mileage that a diesel can and there is little point in trying to make it very competitive in that sense. And before anyone asks... No you can't really make a diesel wankel, the current technology for sealing doesn't allow you to reach the compression ratios you need to be able to run diesel. Rolls Royce experimented with diesel wankels in the 70s and gave them up pretty quick.

Edit: The torque problem stems from how short the moment arm of the rotor is, that is how far away the point that recieves the turning power of the engine is from the center of the shaft. A common problem with all high revving engines, especially F1 engines. The 16x is supposed to address the torque problem in some way, probably with the bigger rotors.

superglue

^^^^^

You can't possibly be the result of the California public school system. You make way too much sense

That was a very good and brief explanation.

dannobre

iTrader: (3)

If you look....compare the mileage to a 350Z and a M3...it's really not that out of line...the track mileage is about the same at WOT

Piston engines just do much better in some areas like idle and off throttle and low load areas...that makes the rotary have shitty mileage when driven around town...and they run pig rich when cold.....

Footman

iTrader: (2)

You can get more torque if you increase the eccentricity, which would also increase the volume and thus have higher compression engine, but the seals would have to be developed in a way that it can seal at very sharp angles...

Old Rotor

You can research and try to understand the Rotary MPG but if you don't fall in love with the thirsty rotary you will never get over it. I remember when I bought my first RX-2 in '71. It had 100hp and gas was $0.29 cents a gallon(I think). It got 12mpg in city and 18mpg on hwy. Man was it fast and the 7K red-line was FUN! The mpg bothered me but the fun and uniqueness made me forgive it. Now each model had improved horse power and mpg. The 13B(120hp) in my RX-4 was a killer and was faster then most V8's except the high performance ones. Again I did not care about the mpg, I was having too much fun. The RX-8 now years later has much more HP and gets more mpg and now that I've retired It's my Sunday driver and the mpg don't bother me as I love the sound of the high revving rotary engine and the excellent chasis . It's not for everyone and if my employer did not pay for the use of my car I would have probably never have enjoyed all my years of them. Yes it's development is years behind the piston engine and may never catch up because Mazda is one of the few working on it. It's just one of the few things I really enjoy in life and do for myself.

mysql

I seem to recall reading somewhere that the 26b had an advantage over the pistons in lemans due to fuel economy. When at WOT most of the time it didn't have to refill as much.

Footman

iTrader: (2)

Rotary engines actually have high volumetric efficiencies especially the peripheral port ones.

daisuke

I'm not actually. Born, raised and educated in chile, which most ppl in California would consider a 3rd world country

MazdaManiac

iTrader: (3)

Chile is a beautiful place.

The Renesis eats fuel proportional to its specific power output (it eats twice as much per rev as a similarly sized piston motor), minus its 10% lower BSFC and 15% lower thermal efficiency (due to the shape of the combustion chambers).
Though its overall Ve is better than most piston motors, you need to be at WOT for that to matter.

robrecht

No. There are three power pulses per rotor revolution, and since the rotors turn at 1/3 the speed of the eccentric shaft there's really only one power pulse per rotor per eccentric shaft revolution. This contrasts with one power stroke per two crankshaft revolutions for a conventional 4-cycle piston engine. Multiply this by the number of rotors or cylinders. But this comparison of power pulses per shaft revolution does not really directly explain the differences in fuel efficiency between rotary and piston engines. That really has much more to do with the shape of the combustion chamber and thermal inefficiency.

Brettus

iTrader: (2)

If you ever go to a track day with someone in a similar performing piston car it becomes obvious that the rotary has pretty good consumption in comparison under those circumstances .
It's really just around town tootling where it sucks .

MikeTyson8MyKids

iTrader: (1)

Actually, they have a pretty decent volumetric efficiency...better than a piston engine. Its the overall thermodynamic efficiency that is low.

MazdaManiac

iTrader: (3)

Uh?

CyberPitz

You people are teaching me, thank you!

Another question, though I am sure I know the answer...just want to be sure. When it says you're going at 4,000 RPMs, is that for every FULL revolution of the rotor (All 3 sides run through their cycle) or is it with ONE side. I'm sure it's when the 3 sides run through, but like I said, want to be 100% sure.

robrecht

Well, don't be so sure, the engine RPMs refer directly to the revolutions of the eccentric shaft, which is rotating 3x as fast as the rotors.

CyberPitz

^ That's one thing I've noticed when watching diagrams and such. The rotors spin slower than the E-shaft is. that always boggled my mind. I'm looking at an E-shaft in my head, and I don't see why/how. Is it the whole "Balance" portion of the shaft?