rotarygod

I know what you are saying but I have a very nontechnically advanced car that I am trying this on. I am using a simple toggle switch and have no way to try this idea on my car. Someone with good ecu tuning skills can try it though. If I could, I would.

I don't think an air/fuel mixture is going to help cool the rotors at all. In fact a burned mixture will be much hotter. When the spark ignites the mixture, we have nearly 2000 degree air going out the bottom half of the engine which in turn transfers more heat to the housings. Also consider that an engine running at what is considered 100% volumetric efficiency is actually still burning 10% exhaust gasses from the last combustion cycle. Not many people know that. In truth 100% volumetric efficiency isn't quite as good as what it would logically seem to be. Since some of these hot gasses are carried back into the intake charge, it only serves to heat up that side before it combusts. If the rotor is just spinning, it is still pumping air through it. The difference is that this air is now only serving to pull heat out of the engine and into the exhaust. It would actually cool the engine some.

The rotor housings are already cooled by water. The rotors themselves, unlike pistons in other engines, are cooled by the oil flowing through them. Oil actually is responsible for about 30% of the cooling in a rotary engine. This is why oil coolers are an absolute necessity in these engines but not necessarily in other engines. The rotary is unique in this respect. If the air/fuel mixture were an important part of cooling in an engine, we wouldn't need any other cooling form. You can't cool something down but then at the same time heat the surroundings back up. It just doesn't work that way.

buzzwordenabled

Here's a nice article that includes a description of the evaporative cooling that takes place in a rotary engine:

http://www.sportcompactcarweb.com/ed..._technobabble/

rotarygod

That article mentions how evaporative cooling helps cool a piston engine. Remember that a piston engine has all of it's phases of combustion in the same place whereas the rotary has them in different sides of the engine. After the combustion phase heats up the cylinder and is expelled, the incoming mixture helps cool it back down. In the rotary the incoming mixture is on the passenger side of the engine, combustiontakes place on the driver's side of the engine and then is spun around the bottom of the engine to be expelled back on the passenger side. With the exception of the carryback volume, the heat in a rotary is mostly on the bottom side of the engine. The only reason that the incoming air/fuel mixture is at all responsible for cooling down the chamber is because the previous mixture heated it up. If there is no combustion, there is no heat generated. Therefore adding an air fuel mixture to the engine is only responsible for heating and not cooling the engine. The nonrunning rotor will not generate any heat on it's own like it would have if it were working. Instead the air traveling through it will help pull heat away from the engine cooling it down some. The engine and consequently the cooling system and oil will run cooler. This would be no different in a piston engine either as there is no charge being burned and therefore no hot gasses to heat up the chamber. The incoming mixture would only help to cool back down the heat from this cycle. If there is no combustion, there is no heat and therefore any air running through it on it's own is just moving air which will pick up some heat from the surroundings and carry it back out of the engine.

T-von

I understand that. I was just more of less elaborating on how this could "eventually" be set-up if your experiment proves to be successfull. Also my comments about both front & rear keeping equally warm and lubricated was to show IMHO that it would be better than to just have one chamber completely stut down since both could be running at the same time(just at half duty).

r0tor

iTrader: (1)

i'm not seeing where this is going to be of any use except possibly at idle... i've never neeb a fan of displacement on demand.

If your running a car at a constant 30mph, it takes a certain amount of hp to do this to overcome friction, drag, ect. Say this is 30hp. So either you are going to be producing 30hp with a fairly efficient 2-rotor design, or 30hp with a smaller engine with horrible efficiency draging a dead rotor around. The only time you really are wasting energy with all the cylinders/rotors firing is at idle - which is why hybrids shut off the engine completely at idle.

The latest DOD designs try to address the dead cylinder by keeping the valves closed. Basically in the deactivated cylinder, the valves are close, the piston shoots up and sucks power from the active cylinders to compress the air, then after TDC the valves are still closed and the compressed air acts like a spring and pushes the piston back down which gives you some of the energy you put into compressing the air back. However, you still loose a good amount of energy to heat in the process and the 8cylinder engine you turned into a 4cylinder still has all the inertia and frictional losses of a 8cylinder. Hence, you may under the best of circumstance get a 1mpg increase.

Now you may be able to get somthing similar from a rotary since it already has no valves in the compression and combustion positions. The cetripetal force caused by the engine spinning at say 3k rpms is going to do a good job at getting the apex seals to seal and create compression - much more compression then they create when you just try to turn the engine over by hand. However, with the awkward movement of the rotor I'm not so sure your really going to get the compressed air to give you significant usefull energy back. But, hopefully i'm wrong about that.

.... now if you find a way to cut the eccentric shaft into 2 smaller shafts and be able to deactivate the front rotor during light driving and enguage a clutch for the front shaft/rotor for more spirited driving, then you may have something! :p

Zoom2X

According to Jim Mederer at Racing Beat the ECU in the RX-8 shuts down the rear rotor under deceleration condtions. He demostrated this to the Focus Group attendees on his ECU simulator bench.

r0tor

iTrader: (1)

Good point. I believe most cars with EFI do that these days as it can aid in engine braking and decrease fuel consumption and brake wear which is a win win senario.

rotarygod

My GSL-SE also cuts fuel on deceleration.

I do have the crude switch wired into one of my fuel injectors. This car only has 2. I just installed it today. At the flip of a switch from the dash I can shut down the rear rotor. I haven't gotten around to killing spark in the rotor yet though but have done a few driving tests around my house. I must say that you definitely don't want to cut out one rotor at anyplace other than idle or cruising. The engine has less than half the power than it does as a working 2 rotor and becomes very sluggish. The car expectedly runs rougher. At idle you can get behind the car and feel each individual pulse from the engine. One thing that is happening that I didn't account for is the timing. Since I have a distributer with vacuum advance, when I shut the rear rotor off my timing changes on the front rotor which makes it even worse. I didn't expect this. I watched this with a timing light. I need to lock the timing and try this again. As of right now the car does run but it isn't terribly smooth. I only have less than 15 minutes of experimentation in it right now though and still have many things to try.

I did flip the switch on and off repeatedly to see what kind of effect it has on the engine so I could very crudely simulate the type of thing that T-von is referring to. It didn't make much of a difference if the engine occasionally skipped a pulse and it is definitely smoother than running on one rotor. It kind of sounds more like a Harley in one rotor form and it actually gets louder than in 2 rotor form.

At cruising speeds when the rear rotor shuts off, the car needs a little more gas but it isn't too bad. You just aren't going to accelerate at any decent rate in this mode. The faster you try to go, the less the single rotor becomes an option. This car also has about 75 horsepower less than the Renesis to begin with so it is much more sluggish.

If my little experiment were to end right now with this small amount of work, I would say not to do it. However I am not done trying things. I still need to work on timing quite a bit as I believe this will help some. I am intrigued by T-Vons recommendation and wish I could do this. It may actually be a more viable option.

As I said, this is just an idea and may or may not work. All I know is that some rotary aircraft people are making it work in planes so it seems logical that it could work in a car too. Those guys just use ecu tuning to take care of the other issues. That is something I can't do.

pr0ber: Normally I wouldn't have tried this either but gas prices are pissing me off. Besides I just like experimenting and saw it elsewhere on the net and said what the hell, I'll try it. The two piece eccentric shaft idea would be cool. Now we are really out of my league.

buzzwordenabled

Cool. Thanks for the update. It's always great to see a "skeptics be damned" attitude. I'm impressed.

Keep up the experimentation!

lafrad

Okay.. some people are missing a CRITICAL point to "gas savings" here. Any air pumped through the "disabled" rotor, will COMPLETELY screw up the OXYGEN sensors in the exhaust system. Also, the mention of oxygen helping with emissions... oxygen in the exhaust stream will INCREASE the temps, unless you are running lean. You might toast up your cat converter pretty quick there.

Other than that.. it sounds like a very possible plan. Maybe, some method of *blocking* air entering the rotor... I know little of intake plenums on the rotories, but maybe you can rig up a "throttle body" in line with the rotor to be disabled. this could close and prohibit air from flowing into the rotor... and, provided there is very little port overlap, might help remove some of the "pumping" losses, while keeping the exhaust stream in stoich ratios.

rotarygod

I'm not overly concerned with the O2 sensor on my test vehicle only because I have another one. I also have a mid pipe so I'm not too concerned with the cat burning up. My only concern is if it can be made to work in my car or not.

I do need to try other things as well. I do intend to find a way to block off airflow to the other rotor so the intake pulses won't be messed up to the remaining rotor. I have also figured out pretty quickly that the exhaust system on my car which is designed to work for 2 rotors, isn't the best thing for only one. There is definitely more involved than just simply shutting one rotor down. This is probably why the airplane guys that do it can make it work better than I have so far. They treat their 2 rotor engines as 2-1 rotor engines. If my intake and exhaust were designed this way, things may be different. I don't have much time in it right now so I don't know for sure. I'm still going to try to make this work. It has in other vehicles. I just need to figure out how.

cerveza27

Thats the nice thing about doing this sort of thing in a regular 4 stroke engine. You can shut off the whole cylinder, valves etc, and completely remove the pumping losses associated with the piston. Basically all you have left is an air spring. I wonder how much you would gain by not being able to do this in a rotary engine.

lafrad

well.. I am not really worried about toasting the O2 sensor... i am just bringing up the fact that, when cruizing on the hiway, your entire fuel system is based off of the "closed loop" oxygen sensor feedback. If you pump extra oxygen into the exhaust, your computer will "think" its lean, and start dumping more gas in to get it back to "normal".... essentially, negating anything you just gained......

robertdot

I'm not an early rx-7 specialist, so I don't know how much of a crap the O2 censor really gives about stopping too much O2 coming through the pipes. It doesn't have an ECU like the rx-8. It might just tell you that it is running too much O2 and do nothing. RG already tested the system, and he didn't mention the sensor giving any problems. Since he has a pipe instead of a cat, he might have a "trick" sensor (forgot the proper name for them), so it wouldn't matter.

If you meant applying it to the rx-8, you have to remember that everything goes to the ECU first. So, if we can intercept the fuel map commands to change them (e.g. Canzoomer's piggy back unit), and/or cut off an entire rotor, we should also be able to trap for the O2 sensor, also. As long as it isn't reading abnormally high O2 levels (say, the headers came off or something weird like that), we could tell it to report as normal.

When I say we, I mean whoever does this, not necessarily me or anyone reading this.

r0tor

iTrader: (1)

Maybe it would pay you to do some research and find a flywheel that would fit the car but is heavier. The increased mass of the flywheel would give you more energy storage and should help smooth out your idle problems. If you can get something cheap from a junkyard it might be worth the effort.

TheDosDog

Back in 87 I put a 13b from an FC into a Mazda 4x4. In order to mate to the stock tranny I had to use the bell housing, flywheel and clutch from the FC turbo. The turbo flywheel was heavier than the one on the NA motor. It bolted right up with no mod required.

rotarygod

My old RX-7 ecu is extremely low tech compared to the RX-8 ecu. I've been thinking about it and I need to keep the air entering the front rotor. Since I have an air flow meter, if I block off air to one rotor, only half of the airflow would be available through the air flow meter. By letting the air flow meter sense airflow for both rotors, it still gives me the proper signal for each rotor's fuel injector. It won't do this if I block airflow to one of them.

My RX-7 ecu doesn't care if the O2 sensor is really there or not. I have actually gone for years without an O2 sensor for a long time and the car didn't care. The only time my car reads the O2 sensor is when cruising on the freeway at part throttle. Even then the car doesn't run any different than if it isn't there at all. Like I said, it's a low tech car. I still do have the O2 sensor though but only because I need something to fill in the hole in the exhaust pipe.

I'm not going to get back into another flywheel debate since I've had every style and know what their effect is on the car but lets just say a heavier flywheel is the last thing I want.

If anything limits this experiment in my car, it will be the limited abilites of the stock 1984 ecu.

r0tor

iTrader: (1)

I'm a bit confused why a heavier flywheel is the last thing you want.
Flywheel designs revolve around keeping the engine running smoothly at idle. Your current flywheel is designed to store enough energy to account for power pulses from 2 rotors. You need something heavier since you have only 1 rotor firing and less frequent power pulses

screenshot from a software package i use to have in school which would calculate flywheel weights....


... you need to do something to dampen the pulses

rotarygod

This is why I go from personal experience rather than try to internet argue.

Regardless, it won't make the car run any differently. The 3 rotor engines do not come with a lighter flywheel because it is irrelevant for a different number of rotors. The custom built one rotor engines out there also typically use the same flywheels as the 2 rotor engines. I have never seen a heavier flywheel on the market on there is absolutely no need for them. This will have zero effect on this experiment.

rotarygod

I failed to add that when I shut one rotor off, I effectively do have a heavier flywheel. Remember that now I also have a 10.5 lb rotor spinning on the shaft and also it's counterweight. Add this to the 24 lb flywheel currently on the car and that is alot of weight to spin. Besides before we have 2 rotors spinning a 24 lb flywheel. Now we have 1 rotor spinning a 24 lb flywheel which means it feels twice the weight and also the added weight of the other rotor and counterweight. I don't think lack of weight is an issue. Regardless, the car is still much rougher than in 2 rotor mode. This is because no matter how much weight we add in the form of flywheels, a 1 rotor with its 3 pulses can never be as smooth as a 2 rotor with it's 6 pulses. All the added weight does is rob power and make the car slower. A heavier flywheel will not help. A lighter one will.

Omicron

I think this is a great experiment, RG, and if it works out it will be a big service to the rotary community. You have FORGOTTEN more things about rotary engines than most of us will ever learn, so I'm confident that if anyone can work this out, you can. Heck, maybe Mazda will come along and offer you a billion dollars for your idea. :D

Please keep us posted.

HollywoodHall

yea.. someone figure out something. my gas mpg is between 13-15.. always.. all city or all highway. its friggin horrible. i cry.. i complain to mazda. nothing happens. there is no fix. they just tell me to live with it.. well i tell them they need to live with dropping $27.00 every 3 days and then come talk to me when they dont have any money to buy beer or drugs.

Omicron

Yes, something CAN be done about it. I too used to get 13-15 MPG max in the city, then I got the "L" then the "M" ECU flash. I now get 19 MPG in the city with spirited driving.

In order to get this flash, your dealership has to have their "WDS" (service department) computers relatively up to date. If they do, it should be no problem to get it done. Read through this thread for all the gooey details.

Hope this helps.

Rotarian_SC

Sounds good RG. I hope that Mazda will hire you, then you could have all sorts of experiments. Using a stock eccentric shaft I would say this idea would be much better suited for Mazda if they made in the future a 3-4 rotor (maybe even a 1.3L three rotor) engine and then only shut off one rotor.

The first idea that came to my mind was to be able to "unattach" one rotor from the eccentric shaft, yet that would require high tech.

The alternating pulses sounds good as well. That could be something for Mazda to look into.

robertdot

While I know Rotarian_SC wasn't the first to mention it, and probably won't be the last, detaching a rotor will kill one of the beautiful things about the rotary engine: the lack of moving parts. To knock one rotor off of the eccentric shaft would require at least one more moving part, which is something I'd like to leave out. If the current design keeps me at 15 MPG, so be it. If it really mattered that much, I'd get a Prius or InSight (though if gas prices keep rising, I might get a new daily driver .