j9fd3s

i reread an SAE paper (ive got 2 different ones) on the renesis the other day, and they were nice enough to publish the VE chart. SAE # 2004-01-1790 developed technologies of the new Rotary engine



ve peaks at over 105%, but at the hp peak 8500rpms, its around 103%



they also have the VE chart for the 89-91 non turbo engine, it peaks about 95%, at the hp peak its right around 90%



the r26B does not have a ve table, but they do give us output and bsfc, so a guesstimate is around 115% at 8000rpm. guess also says it holds 115% up to 9000...

C. Ludwig

Damn. Nice info.

mazdaspeed7

Nothing official, but I have heard bridgeports and PP's often get 120-130% VE, and streetports as much as 110-115%

C. Ludwig

So what is the thermal efficiency compared to a good piston engine? It's obvious the rotary is a hell of an air pump but how much of that potential gets blown out through the radiator and oil cooler?

mazdaspeed7

I imagine the thermal efficiency is pretty crappy on a rotary. In general, you want a high ratio of volume to to surface area for the combustion chamber to be the most thermally efficient. Its almost universal in piston engines that the engines that get good gas mileage(the most tangible result of thermal efficiency) are all small bore long stroke engines. Getting back to rotaries, the ratio of surface area to volume is exceptionally high because of the long, flat, and thin combustion chamber. In theory, you cant get much worse than that in a combustion chamber.



That explains the poor bsfc rotaries are known for. The large surface area of the combustion chamber absorbs a lot of heat energy from the combustion process, that could otherwise be converted into mechanical work. The large cooling system is needed to shed that excess heat, and the large injectors(for a given hp level) are needed to provide enough fuel. The bsfc on rotaries generally ranges from .50 to .60, while piston engines are usually .4 to .5. The lower the number, the less fuel it takes to make a given amount of power.

j9fd3s

Mr Hanover has posted the hp,rpm, afr and bsfc of his engines. 241hp 9000rpm 13.2afr .662 bsfc. this gives you a VE of 128.5% which is outstanding with 38mm venturies.



there is a thermal efficency graph in the other renesis papre 950454 "the charachteristics of fuel consumption and exhaust emissions of the side port exhaust rotary engine"



the graph is thermal distribution in % vs afr at 80kmh cruise. of course its not labeled in units.... at 12.5 afr power output is maybe 12%, chemical energy in the exhaust gas 20%, enthalpy in exhaust gas is maybe 18% and heat loss to coolant gets the rest.



at 15:1 its much different, power is up, chemichal energy in the exhaust is down, and the other two go up

j9fd3s

for bsfc numbers, i've seen the following



PP around the hp peak, bsfc is in the low 50's, 787B is .48, below the hp peak bsfc goes way high



BP, again Mr Hanover reports .662, my only data point, at least its a good one



stock S5 na is about .68.



rx8 is in the low .6's, mixture varies with these, and bsfc will vary with it. get a lean one and it'll be in the .61 area, rich one might be .65

Lynn E. Hanover

That bsfc, or Brake Specific Fuel Consumption (should be all caps) is reported in Pounds of fuel per Horse Power Hour.



So, the figure .662 BSFC just means that to produce one Horse Power for One Hour, it used .662 of a pound of fuel, or about 2/3 of a pound. To make it easy to see this, let us make the outcome one hundred HP and that would then be:



Six point six two pounds of fuel per hour. Or since fuel weighs about 6.10 to 6.30 pounds per gallon, a bit over on gallon per hundred HP per hour. Not all that bad.............



So a smaller number is better from a mileage standpoint. You can drag that out further if you like, and say that at 60 MPH it takes about 25HP to hold that speed, so now you can deduce your mileage at 60 MPH, if you have a BSFC number for 25 HP.



Detroit and all other manufacturers actually have to dyno at these very low numbers, because 99.8% of the fleet operates at these numbers. It is fun to have 500HP on tap, but to drive to Barstow sans a speeding ticket, what can you do with the extra (above 25 HP) power?. This is not entirely true because I just returned from California, and unless you are over 85MPH or actually hit a police car, they don't bother folks.



In aircraft use, where you go to full throttle and leave it there for hours on end, the rotary does a bit better. You can adjust runner lengths to get the best tune at cruise RPM. You can lean the mixture 200 degrees past peak EGT to reduce power and fuel consumption and heat. (Look at Renisis mapping) The smooth power pulses ease reduction design and reduce fatigue.



The poor combustion chamber shape also reduces the likelyhood of detonation in normally aspirated engines. You can run on lower octane fuel with no damage.



Once you have added a few turbos or ports or both, it is a bit pointless to go for low fuel consumption unless you are talking about aircraft engines, where this is very important. When the rear tires are turning to a liquid, who cares?



The new engine will cure some of this with the same formula as a piston engine, and that is more stroke and smaller combustion chamber surface. Also injection into the chamber after the intake port is closed for no losses to overlap.



A super high pressure piazeo injector between the plugs would be better but much more expensive. And if the fuel is coming in at the same time as the spark, it cannot detonate can it? And if it cannot detonate, how much boost can we use?



We're going to need lots of dowels.



Lynn E. Hanover

heretic

There's a guy in Texas who found good success with installing ultrasonic devices in the intake manifold downstream of the injectors... called them "singing" manifolds. Talk about good atomization.

Lynn E. Hanover

Wankel went through thousands of patent drawings, looking for a pure rotary motion device to produce or convert as an engine.



He produced a cardboard model of his design and NSU produced two very small versions of it in single rotor designs. When NSU attempted to patent the device they discovered that an engineer for a truck manufacturer had already patented the device as a compressor. That engineer gifted NSU with the rights to the design. The Wankel version was not usable, as it was far too complex. The NSU version not the Wankel is what you see today. So, not only would it work as a compressor, it is a compressor.



NSU built a land speed record motorcycle with the Wankel engine and another wankel acting as a supercharger (compressor).



Lynn E. Hanover



DKM-54 from Paul Lamars web site. Note the rotor housing is spinning inside a second housing.