r0tor

iTrader: (1)

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.

globi

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?

Vaillant

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

rotarygod

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

globi

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.

army_rx8

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

globi

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

beachdog

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.

globi

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.

beachdog

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.

AvatarQAZ

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.

Dark8

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.

Vaillant

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

globi

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.

rotarygod

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