1 rotor = half the gas consumption of two ?
 

I was wondering why they haven't considered using the rotary in a more economical and cheaper car, ...I'm by now means an engineer, but was wondering if a 1 rotor rotary would suffice for this ?

120hp and around 30mpg ? This would definitely do for most cars, ...and...maybe cheaper to produce?

Jarred...you got me!! Maybe if it was a 10 rotor we would have 2380 HP? Seriously, I think your though process is a little off.

- Irish

I know it's off, it has to be, :) I was jsut wondering if a one rotor was possible, and if maybe it would be better on the gas, and or cheaper to produce ?

In the sense that anything is possible, it's possible. As I recall, the Mazda rotary prototype was a single rotor.

Since Mazda is the only auto manufacturer building rotaries it is totally up to them whether another, smaller version ever gets built and sold.

IMHO, it isn't going to happen. Alternative (and yes sometimes quirky) powerplants are going to be very hard to market to the low end of the market. People who buying at the low end want cheap to buy, cheap to maintain, reliable transportation. they don't really care what's under the hood. The rotary is a selling feature in a high-end sports car. In an economy car it would be "so what".

I'll take out a rotor from my 8 tomorrow and report my gas mileage back to you. ;)

using your equation, would you want a 119hp, 78ft/lb single rotor coupe while a similarly priced (i'd guess) 2+2 entry coupe would feature a large displacement 4 cylinder engine making anywhere from 130-160hp, AND 120+ft/lb of torque??

the 2 rotor is already barely 'practical', would anyone looking in the 'value' class of cars even consider it??

you're barking up the wrong tree if you want economy with a rotary. It wouldn't make sense to do the R&D for it when a 4 cyc car would beat it hands down.

My understanding is that the dual rotor is far superior to the single in ways other than it uses double the gas. First, I believe the single rotor motors are not balanced like the doubles, and thus would need some sort of a harmonic balancer. Not to mention it wouldn't be nearly as smooth since it'd be firing half as often.

Ahh, a dreamer like me...LOL

A rotary weighs more than a I-4 yet less than some V-6 & probably all V-8's. So, for a small car it would probably not be a good choice. Also, as others have said, considering that the rotary is still not as efficient with fuel as I-4's, most V-6, and heck even a few V-8's why put it into another car other than a sports car?

The weight savings, layout, and HP per size is a good thing while us rotary owners can close our eyes to the fuel ecnomy because well...it's expected. I don't think I would build rotaries if I owned a car company (just not worth the money and effort needed) and that is why Mazda is alone in the rotary department.

Honestly, I wish more companies got involved so there could be a chance for a breakthrough with the old rotary...and I still hope and dream about it, but it seems it might always be just a special motor but not a common or efficient one.

One bright side, they (Mazda and some others) say Hydro fuel really works well with the rotary engine so maybe it's the "OLD" engine design of the future...LOL, maybe the rotary was just created before it's time...in cars that is.

btw, there were threads a few months back about getting the rx8 to turn off half of the engine for better fuel economy at crusing speeds. You'd have to do a search to find it.

4 cyl half the gas of V8? V8 2x HP than 4? Not quite.

Honestly, I believe if Mazda stays on it and gets more support on it, the rotary could very easily become a good choice for a motor. Sure it doesn't get good gas mileage, but that could easily be improved with some studies. I would take this motor and have some serious experiments done with it. I think it could be a great motor for all cars... maybe not trucks or SUVs due to the lack of low end, but definitely cars.

Ok, just realized I was a little off subject so just ignore this post. :D

Last summer I rigged my RX-7 up to run on 1 rotor at the flick of a switch because I had the same question. What I found was that it had far less than half the power of 2 rotor mode and it vibrated like crazy. Max speed floored was about 50 mph. My engine is ported too. If you tried to accelerate in 1 rotor mode, you'd lose a race to a Geo Metro who started out in 5th gear. It is that bad. I had postulated that even if a slightly rich a/f ratio was needed in 1 rotor mode to keep it running, that it would still be less fuel than for 2 rotors. I'm not sure how that worked out though since the car wasn't fast enough for freeway use and to shut a rotor off on any other form of road was for such a short time that it didn't do anything useful. The project was abandoned.

hmmm....thats interesting, ..you think if they designed the engine for one rotor from the ground up they could get different results ? my only reasoning is, ...that engine was designed for 2 rotors, ...maybe something could be different. ...

awsome test though...

What needs to be done is a comparision between the Mazda rotary and 4, 6, and 8 cylinder engines with similar horsepower and vehicle weights. I'm pretty sure you won't see a huge difference in fuel consumption. I've heard lots and lots of horror stories on here about the gas milage of the RX-8, but so far mine does between 19-23 in mixed driving.

When you say that you rigged it by the flip of a switch, what exactly did you do? Shut down the fuel injectors or shut down the ignition or both?

Remember, all the piston engines with variable displacement kill the compression in the dead cylinders by leaving the exhaust valves open so there is no compression (in addition to killing the fuel injection and ignition).

In a rotary (standard anyway) there's no way to kill the compression in the unused rotor so you are using half the power just to overcome the compression of the dead rotor.

Actually in the variable piston engines, they leave all the valves closed, not open so in essence it is like a spring. Unfortunately I can't simulate that. I just shut off fuel to that rotor. Ignition was pointless so no need to kill it.

Yea, but you're still swinging around all the extra weight while not producing any power doing so.. in a single rotor engine (designed to be 1 rotor), you could possibly use less gas and get 1/2 the power as you dont have that extra weight to sling around, but you also dont have the power 180 degrees apart from the second rotor.

I dont know if that lack of power 180 degrees out of phase would be overcome by the lack of rotating mass..

RG? that make sense?

In a variable displacement piston engine, the others still have to move the nonworking ones as well.

I do feel that a dedicated 1 rotor engine would work better than the way I tried it. I just don't feel it is feasible to shut down a rotor for economy reasons as with some piston engines. For economy, maybe a turbo 1 rotor??? You could still get over 200 hp out of it.

interesting point, but they also shut down pistons in pairs in the V engines so that they're never off balance like you would be in a 2 rotor engine.. They're still moving the dead weight around but they're also still producing 2/3 of the power and only slinging an extra 1/3 of the weight whereas we'd be producing 1/2 the power and slinging an extra 1/2 the weight..

In a 2 rotor, each rotor is 180 degrees out from the other. How is shutting one down throwing it off? This would be a problem in a 3 rotor.

50% of the power comes from that 1 rotor though and it's 50% additionaly weight to carry around.. It's still rotating mass no matter where it is in phase, right? so it still counts as extra work that one rotor has to do, plus the e-shaft was balanced to have 2 working rotors, wasnt it?

I think a 3 rotor would actually work better. You drop the center rortor, lose 1/3 the power, 1/3 the extra mass the other 2 would have to carry.. so they're still producing 66% of the power they would normally and saving maybe 25-30% of the fuel.

the rotors in a 3 rotor are 120 out of phase, right? so if you kill the middle, the 2 ends are like 240 out of phase.. that could be bad too, lol.

Nope - doesn't work that way.

Your car requires a certain amount of energy to move and maintain speed. That requirement doesn't change just because you have a smaller or bigger powerplant. I went into details in this thread (third last post, dated 01-04-2005), talking about the energy requirements.

Basically, you can run a more efficient engine to produce the required power, but you're only talking a few percent difference in efficiency, not 50% less. Further, acceleration requires different operating constraints, and history has shown that often the more powerful optional engine in a car gets better fuel efficiency than the less-powerful base engine because it spends less time at full throttle, so more time operating in a more efficient range.

Regards,
Gordon

You just need 2 throttle bodies and you're all set, otherwise you're running a giant air compressor for nothing.

It's not the extra weight that is a problem, it's the extra friction. (Slinging around weight doesn't require energy as long as it's kept at a constant speed.)

One rotor at high throttle setting requires less fuel than 2 rotors at low throttle setting, assuming both produce the same amount of power.
Also when you accelerate at full throttle in a high gear you need less fuel than when you accelerate at partial throttle in a low gear (same power).

However you still have to deal with that extra vibration. Another reason for the flywheel generator/motor that could reduce that vibration (that's what Honda is using it for too).

exactly right...

Say it takes 50hp to run down the road at a speady speed of 50mph. Its going to take 50hp no matter if you have 1 rotor or 2 rotors - so your banking that the 1 rotor engine with a lot of throttle and dragging a dead rotor will be more efficient then a 2 rotor engine with minimal throttle.

It really doesn't work out too well and that also the same reason that there are relatively few gains made by the current dOd engines on the market.

Any engine at full throttle is more efficient than at partial throttle (amount of fuel per power unit). Partial throttle causes a pumping loss (in piston engines) and it's a general restriction in the airflow. Also any combustion chamber (of a gasoline engine) requires a minimal amount of air/fuel mixture in order to ignite. The bigger the combustion chamber, the bigger the minimal amount of air/fuel mixture. The rotary engine has a relatively large combustion chamber and it's likely that that minimal amount of air/fuel mixture required is even higher than in a piston engine.

An alternative to shutting off one rotor would be an overdrive or a 7th gear. This would also increase the throttle setting and not only that it would reduce the amount of friction per time unit and therefore improve fuel consumption.

What does the RX-8 need to drive 55 mph? 30HP or even less?

What about shutting off the fuel for every other cycle on both rotors? Would that work? I wonder what sort of balancing issues there would be?

~ Matt

So how is that principle any different from a variable displacement piston engine?

I guess that would work too. But the problem is that you still compress that intake air which requires power (unless you have a very fast valve that controls the airflow). If you have 2 throttle bodies you can shut off the airflow to one rotor and won't compress any air for nothing.

ahhh if only mazda had mad amounts of money to throw around..they coudl get to work on all the things we babble about:p hehe aw well i can dream i guess

I'm sure Mazda has considered this, but people that buy this car usually don't care much about fuel efficiency. How many would want to pay an extra $1000 if the car would make 10% more miles on a tank?

For those who don't know: The very first production car with Wankel engine was the NSU Spider and it did have a one rotor rotary engine.
http://www.der-wankelmotor.de/Fahrze...kelspider.html

ok, so you add a throttle body and close it off. So you think that will improve efficiency because there is no air to compress on the compression cycle. Might be true, but it is just going to be offset by the energy required trying to suck in nothing on the intake cycle. Closing the throttle body won't create a perfect vacuum for the rotor to operate in. This is a port engine, no valves, so, with no intake, no compression, no ignition, no expulsion of exhaust, it would probably suck exhaust in through the exhaust port. You want variable displacement, get a piston engine.

I'd rather see Mazda work on increasing the eccentric offsets so the engine gets more torque.

That sucking power is much less than the compressing power. In the worst case it needs to overcome 1 atm. On the other hand if the throttle is at WOT it needs power to compress it to 10 atm.

You're right it could suck exhaust gases into the engine, which might or might not be a problem (piston engines have EGR). You can always leave the throttle somewhat open in order to avoid this or you could add a valve on the exhaust side.

Anyway it wouldn't be my first choice either.
There are many other ways to reduce fuel consumption:
* overdrive
* flywheel motor generator
* maybe a third sparkplug
* lean combustion with fuel direct injection
Mazda could try something like Honda did with its CVCC. With fuel direct injection its conceivable to generate an ignitable air fuel mixture within a very small volume/area. An alternative way to reduce the minimal amount of fuel required.
http://world.honda.com/history/chall...o03/index.html

And in order to increase torque, I'd prefer an electric assisted turbo.

Agreed. I have written elsewhere on this forum about overdrive. My 1969 Fiat 124 Spyder had a 2 speed rearend. Nicest way to go for overdrive. Normal 5 speed and a little button on the shifter put it into overdrive. Technically it would work in any gear but you didn't want to leave it on in first.

I believe that the CVCC used a precombustion chamber where the spark plug ignited a lean mixture which expanded into the main combustion chamber like a flame thrower. Don't know if Mazda has ever experimented with this but it would seem like a good idea. Designed right you could send a flame front wherever it was needed.

Some company actually MAKES overdrive kits (7th gear for 6 speeds, 6th for 5 speeds). They simply bolt on after your tranny and require a second shifter. If I remember correctly, they are relatively cheap. Primarily, they are used for older cars (3 speeds... 4 speeds) that didnt have an overdrive.

I apologize greatly, but I can not for the life of me, remember the name of that company.

So with a 10% increase in fuel efficiency it would take me around 25 tanks of fuel to make back the $1000 at today's fuel prices. Let see, I've had the car for over 9K miles and put in roughly 32 tanks of fuel. I think I could live with the extra $1000 cost. :rolleyes:

What I'd like to see is *just* a taller 6th gear. I wonder if anything like that is out there?

Exactly and like Volvo did it on some of its cars in the seventies and eighties.

It would definitely reduce fuel consumption at very low power settings, since you wouldn't have to deal with an uneven fuel distribution due to the moving combustion chamber (less production of unburnt gas and lower overall fuel to air ratio). At higher power settings it would still require a second injection nozzle to more evenly distribute the fuel in the entire combustion chamber.

However at lean mode it might produce a lot of NOx, which they somehow need to get rid of again.

Yep they've tried it. They experimented with this on the rotary in the early '90's.