foxman

I noticed someone on RX-7 club said Mazda is working on a variable displacement rotary possibly for the RX-8 or future rotary powered vehicles.

Aseras

IIRC rotarygod tried it himself,and also tried to get mazda to officially do it and the pres himself said mazda wasn't looking at that right now.

RedFC3S86

I started thnking about this today...I did a search for "variable displacement" and stumbled upon this thread......I'm surprised mazda hasn't used some sort of rotor deactivation setup (much in the same way some of today's 6 and 8 cyl engines only use half the cyls under cruising conditions.) Couldnt u just simply cut fuel to one rotor under certain conditions to improve fuel economy? What are the dangers/drawbacks to doing this? Could the "working" rotor somehow be worn out prematurely by pulling the "dead weight" of the non working rotor? If there are no ill effects to shutting down one rotor under appropriate conditions, i think mazda should definitely look into it.

Razz1

You thought the RX8 was gut less.

You haven't seen anything yet. Running on one rotor

jasonrxeight

you need a valve to release the vacuum not just simply cut the fuel cuz that would even make things worse.

RedFC3S86

I see

Spin9k

A valve? That sounds easy. On-Off 1 rotor-2 rotor. How simple is that? Pretty darn simple I guess. Surprised it hasn't been tried.

jasonrxeight

its called engine braking.
all these engines with cylinder off stuff has some kind of valve-train design to release the vacuum to eliminate engine braking.

from Wikipedia
"Cylinder deactivation is achieved by keeping the intake and exhaust valves closed for a particular cylinder. By keeping the intake and exhaust valves closed, it creates an ‘air spring’ in the combustion chamber – the trapped exhaust gases (kept from the previous charge burn) are compressed during the piston’s upstroke and push down on the piston during its downstroke. The compression and decompression of the trapped exhaust gases have an equalising effect – overall, there is virtually no extra load on the engine. In the latest breed of cylinder deactivation systems, the engine management system is also used to cut fuel delivery to the disabled cylinders. The transition between normal engine operation and cylinder deactivation is also smoothed using changes in ignition timing, cam timing and throttle position (thanks to electronic throttle control). In most instances, cylinder deactivation is applied to relatively large displacement engines that are particularly inefficient at light load. In the case of a V12, up to 6 cylinders can be disabled.[1]
"

Spin9k

^Exactly - so put a valve to let air OUT OF one rotor during the compression cycle (no compression), while simulataneously cutting any fuel injection. Done deal, no engine braking.

jasonrxeight

why dont you do it?
its like saying having 800hp from a 13B just put a big turbo on it.

Spin9k

You're it. - You posted 1st, so you have to do it

zoom44

you can run a two rotor car on one rotor for cruise on the highway. there is plenty of power for that. RG has tried it.

Another way to do it to reduce pumping losses is to deactivate individual rotor faces to keep the combustion balanced as everything goes round. Wakeech and I and a couple others worked out a firing scheme that worked rather well 6 years ago. basically you skip every third firing so you fire face 1 rotor 1 face one rotor two skip face two rotor one fire face two rotor two etc etc .

But this discussion is all moot as far as Mazda is concerned. They have tried several permutations of the idea and rejected them all. as the president of mazda usa said "we are going in a different direction."

our engines already cut the combustion of at various times when decelerating to extend mileage. look at your AFRs when decelerating in gear

PhillipM

Most fuel injected engines have done that for the past 30 years though...

zoom44

yeah that part was just responding to one of the posts above suggesting cutting fuel at times.