I read the first 5 pages of this stuff and my head hurts.. Im 16 and all this stuff is really really interesting.. this thread just has way too much knowledge for one sitting.. lets all go watch jack-***!

 

Exactly. A typical piston engine at highway speed (say 60mph) may be turning at 2500 rpm and getting 40 mpg--- but it's only producing 35% of it's rated power. Step it up to say, 5000 rpm in the same gear (now you're doing around 100mph) and it gets only 25 mpg--- but it's producing over 80% of it's rated hp.

This means that for a mere 37.5% increase in fuel burn the hp produced more than doubles. So the engine is more efficient at higher rpms than it is at lower revs. The same is true for a rotary.

But what confuses many people is that in the above scenario you don't really need anywhere near the full hp potential of the engine to travel at highway speed, so any excessive speed may result in more hp produced per fuel consumed, but this is wasted hp. It's very much like putting a V8 into a Toyota Corolla. The result is less DISTANCE covered per weight of fuel consumed.

So a gutless wonder 4-cylinder will get 40 to 50 mpg at a steady highway speed. This is one form of efficiency, known to most of us as fuel economy. But in the small, light-weight car it is in, only 30 hp is required to push the car down the highway at a given velocity.

If this same engine were installed in a full-sized pickup truck the mileage would drop to about 20mpg because the engine would now have to be revved higher to produce the 70 hp necessary to propel the heavier and less-areodynamic truck down the same stretch of highway. The penalty for this is of course poor acceleration on the order of zero-to-sixty in... the same day. And you'd still only be getting 20 mpg. This is where a larger and more powerful engine comes in handy. Your mpg wouldn't be as good, but your engines EFFICIENCY would be better, ie: less fuel consumed PER HP produced.

 

Rotaries require a lot of AIR and FUEL to make the power because they are horribly inefficient thermodynamically. There is a lot of surface/volume area for heat to be lost to the cooling system, and the combustion chamber has a very poor shape so incomplete combustion is the norm.

However, the "if they run lean they will explode"... where did you get that kind of information? I've driven literally for thousands of miles at a cruise A/F ratio that registered a 0.000 volts on the O2 sensor. I've hit that at the dragstrip and the road course, too, but it's not the way to go fast Speaking of road courses, all the jiniopr high kiddie winkies like to beat off over the 787B that won LeMans. Blah blah, 700hp from a 4 rotor. Chew on this, though... even though that is the equivalent of 350hp from a 13B, the car was running significantly leaner than best power in an effort to get fuel economy up, since at LeMans you are only allowed to use a certain amount of fuel in the 24 hours. You can't win if you go fast for 20 hours and then have to park the car because you've run out of your fuel allotment.

Now, it's true that TURBOCHARGED rotaries don't like to be lean under boost. But turbocharged rotaries are in the vast minority.

I've got upwards of 27-28mpg with a carbureted 12A, and have friends who've done 29mpg... in FDs.

 

peejay, would a little ceramic coating here and there cause fuel consumption to go down?

 

Seems like a good question, I've wondered what coatings might do for a rotary.

 

im not peejay, but the answer is yes, it would increase efficency, possibly dramatically.

the reason is that the caramic acts as a barrier to heat transfer from the combustion chamber to the coolant and block. the more heat that is retained in the air/fuel mixture, the more complete the burn, and also the more energy that can be extracted from its expansion.

another point is that ceramic surfaces typically have a lower coefficient of friction than steel, so that the frictional losses will be reduced.

companies that manufacture ceramic coated wankels and do add-on ceramic coatings for 13Bs claim an efficency increase of 20-40%, which is probably quite a bit on the optimistic side, but smaller increases are absolutely to be expected

pat

 

You'd have to coat the side housings and the rotor housing's inner surface to be the most effective. I'm not up on current thermal barrier (not just "ceramic") coating technology to know how well it can stand up to friction and high pressure, and what kind of lubricity it has compared to an oil-saturated chrome sponge.

It would provide a benefit, but it would still suck, and you'd still have the inefficient combustion to deal with.

Best thing to do is just roll with it, really. What the rotary lacks in efficiency it more than makes up in reliability and lack of expense.

 

Of course, I too would get great MPG if my GTU had a V4 engine and was an Automatic Transmission like yours.

 

heres a little more food for thought. they run rich in order to cool the motor down. think about it how many selas are there in contact with the housings? 6 apex seals, 12 side seals, 8 oil seals, 12 corner seals, etc.... and they are all made of some metal... metal to metal contact = friction blah blah blah....getting it now? boingers are more effiecient because for each pistion there is only 3 seals, some of theam are lubed with oil squirters that shoot up the bottom of the skirt and come out the sides of the oil control ring. so in effect rotaries rely on gas to help cool the internals down and rely on oil to cool down the rotating friction on the e-shaft bearings and such. boingers only rely on oil to cool the engine down, not unless you count for tuners who tune cars somewhat richer to cool the cumbustion chambers down to prevent detonation and/or run higher boost and what nots....im no expert but thats what i have learned from talking rotary to fellow rotor heads at my local car wash every fri through sunday night from 7pm to 4am. not always talking about cars but talking in general, ya know, havin good times and such.

oh and my bone stock GSL-SE(Roxanne) with factory exhaust gets me 260miles in the city and 390 miles on highway. translates to 16 city and 23 highway. can someone chack those numbers for me my mental math may be off

 

[QUOTE=cptpain]

heres a little more food for thought. they run rich in order to cool the motor down. think about it how many selas are there in contact with the housings? 6 apex seals, 12 side seals, 8 oil seals, 12 corner seals, etc.... and they are all made of some metal... metal to metal contact = friction blah blah blah....getting it now? boingers are more effiecient because for each pistion there is only 3 seals, some of theam are lubed with oil squirters that shoot up the bottom of the skirt and come out the sides of the oil control ring. so in effect rotaries rely on gas to help cool the internals down and rely on oil to cool down the rotating friction on the e-shaft bearings and such.

Uh, interesting theory and it actually makes sense, but not quite accurate. While running leaner will cause rotaries and boingers to run hotter (and running too hot can contribute to pre-ignition, which is very bad for both engine types) the reason for the hotter temps in rotaries is not heat generated by seal contact. These seals are very effectively lubed by oil injection into the intakes, otherwise the engine would crater in short order.

The real villian here is the approximately 400F hotter (than that of boingers) exhaust temps. The engine cycles through the four sequences (strokes in boingers) so fast in the rotary that the exhaust is still on fire as it exits via the exhaust ports. Also, the power sequence is 50% longer in crank angle travel than that of a boinger. Not all of this excessive heat gets dumped out the exhaust--- much of it is absorbed by the cooling system.

With more effective heat exchangers this problem can be alleviated to the point where rotaries could be leaned out as much as (if not more) than boingers. Don't believe me? Check out www.rotaryaviation.com and read up on the reports during Tracy Crook's development of his 13B installation in his RV4 sport plane.

Once his cooling system was optimized (and also unencumbered by cooling-efficiency-robbing factory emissions systems) he was able to lean the engine out farther than he could have with a conventional boinger aircraft engine because he didn't have to worry about burning up valves in a rotary. At a steady 5500 rpm in cruise (170 mph) his coolant temps were around 185F and oil temps were around 195F. Fuel burn was around 6 gallons per hour, about 1/2 to 1 gallon less than that of the boinger it replaced.


thats what i have learned from talking rotary to fellow rotor heads at my local car wash every fri through sunday night from 7pm to 4am. not always talking about cars but talking in general, ya know, havin good times and such.


LOL, sounds like your buddys are definitely enthusiasts who know way more about rotaries than most auto mechanics do, but in this instance they're leading you down the garden path to boinger hell. Forty lashes with a metering pump oil line for all of 'em.


oh and my bone stock GSL-SE(Roxanne) with factory exhaust gets me 260miles in the city and 390 miles on highway. translates to 16 city and 23 highway. can someone chack those numbers for me my mental math may be off.

Actually that sounds about right for US gallons. Up here north of the 49th parallel our imperial gallons are slightly larger, giving us around 19 city and 29 highway--- but only if we don't drive excessively hard and only if the car is bone stock and in top running order.