Crazy idea, need help with proving/disproving it

[m1tch]

Hi all,

I have been thinking about this for a while and had a chat to prof about it as well.

I know that the Chrysler 300C Hemi (booo pistons!) has a nasty V8, but around town it can just run on 4 out of the 8 cylinders. Same with all piston cars if you leave it in gear and take your foot of the throttle, it won\'t use any fuel.

I know that if the engine runs lean on a rotary is BAAAAD, but it won\'t be running lean if there is no fuel injected into the engine, only if there isn\'t enough for combustion.

Even if there was no fuel injected into the engine, the OMP is still injecting oil as per revs so its still lubricated.

I was just wondering if it would be worth shutting down 1 of the rotors or maybe a few combusions strokes to increase fuel economy when you aren\'t in a hurry, ie going to a drag strip.

I know its on an E-shaft, so to keep it balanced it might just need to fire once in each rotor to keep the rotors spinning.

Would this idea work? it wouldn\'t be too difficult to \'tune\' it like this as I have an E-manage Ultimate, so a map could be set for it to come on when say the OEM O2 sensor kicks it into the cruise map.

Just an idea, but would it work?

[trotter]

Good idea in theory, but I have a reservation...

If you are running one rotor only, the e-shaft will surely keep moving the other as it rotates. In this case the shaft will be driving the rotor rather than the other way round.

Therefore, with no combustion \'push\' in time with the working rotor, this will be having to power both the car as well as the rear rotor round? I dont think its a massively efficient way of running - you\'ll be down on power even more. Unless you can disengage the rotor from the e-shaft somehow?


make sense?

[m1tch]

Yeah, which is why it might be an idea to perhaps fire just 1 of the 3 combustion cycles in each of the rotors, rather than just shutting 1 rotor down completly ie the rear rotor fires once, then 120 or 240 degrees later, the front rotor fires, so instead of having 3 combustion cycles in each rotor, there is only 1, but it would be in time opposite the other rotor, ie fire the front rotor when the rear rotor\'s exhaust stroke is happening from the combustion stage of the rear rotor, Then when the front rotor\'s combustion stage is then in exhaust, the rear fires, if you get what I mean? lol

[shaunwil]

Wouldn\'t you need the injectors to be direct fire ? If you are injecting fuel in the intake system then you can\'t simply switch the system off in a given cycle because the amount of air going through the system is still the same and if you reduce the fuel you will go lean.

What you would need it what matts 3 rotor has with one of the injectors direct fire. I think its been mounted in the OMP injection point with some machining.

Shaun

[m1tch]

Wouldn\'t you need the injectors to be direct fire ? If you are injecting fuel in the intake system then you can\'t simply switch the system off in a given cycle because the amount of air going through the system is still the same and if you reduce the fuel you will go lean.

What you would need it what matts 3 rotor has with one of the injectors direct fire. I think its been mounted in the OMP injection point with some machining.

Shaun

I will be running a triple rail setup and 2 fuel pumps, so I might be able to plumb the tertiary rail in as direct fire

[Prof]

The racelogic traction control does actually cut fuel on odd cycles to limit power - even on a rotary setup - but that is only for moments at a time. What you are describing is longer term cut - which may have implications on bearing throw, one rotor dragging the other and so on.
 
I think the engines are balanced on the basis that there are even power strokes to move the engine round.  If you think about the engine cycle - there is a load on the engine during the intake phase, which increases as the compression stage occurs.  Then when the plugs fire, the expanding gases are giving energy to move the rotors around.  So if you miss one of these firing events, you are relying on inertia to keep the engine running.
 
It would definitely have to be random power cutting, to avoid an uneven stressing of the eshaft and bearings.
 
I think you\'d be better off tuning for as close to stoich as you can in the cruise part of the map - you should be able to get mid to high 20\'s mpg for sure - getting intake / fueling and spark working as efficiently as possible.

[leon]

I seem to remember reading somwhere that the standard ecu cuts fuel to the rear rotor on deceleration as a way of improving economy and smoothness of the engine? I can\'t remember where i have read that as it was some time ago :Hammer (mazda fsm?)

[HaywardRotary]

Fuel injection is cut to both rotors on deceleration.
Compression is the main issue,you need to vent compression from the rotor not running in order to reduce pumping losses,on piston engines that is done by playing with valve timing,Mazda developed a miller cycle piston engine to reduce pumping losses and put it into production,and they played with it on the rotary too which helps.
You can be sure though that Mazda have tried just about everything including what you are thinking about to help economy,if it was viable they would have it in production by now.
If you look into Mazda\'s rotary development history they have really tried hard to get the engines to run leaner with many different ideas.
As for shutting down phases of combustion it would  make the engine run really rough so I think that is why it is not done.
Regards
Carl