Lynn,

 

    From your previous posts on this subject it seems that the Rotary does not react in the exact same way as a typical

piston engine to leaning and or timing changes...................William has used as reference a very detailed piece from

http://www.turborx7.com/fuel.htm (excerpt above) that he feels challenges previous info that you have posted and

that I mentioned from memory so I may not have related it accurately...........Would appreciate your additional thoughts

about this and any corrections if I misspoke.........(Tracy posted recently that his EC2-3 does retard ignition timing as

boost increases < up to12 degrees>)................

 

Thanks,

 

 Kelly Troyer

 

I just reread this and am having difficulty finding the differences between data. Except that I explain it much better.

 

It is nice to look back to my 14 year old motor head readings of anything published in any hot rod magazine.

 

It also points out that the systems used to establish long used methods of test in fuels have long ago been superceded by modern systems and practices. The two base systems (one from Kettering's labs in Dayton Ohio) are still referred to on fuel pumps everywhere. I would be surprized to find similar equipment out side of a museum.

 

You would think that we would know all there is to know about oil by now, but we know very little. For example, the discovery of Bucky balls. (Not a result of never washing you supporter). And Fullerines, both named after R. Buckminster Fuller, of dome fame. Carbon structures under our noses for billions of years and just now discovered.

 

 

Saying that 6 degrees of advance does one thing and 10 degrees does this other thing leaves a library of data left off the table. Those numbers are typical of initial advance settings for distributors clear back to points days. A valid statement if the full 600 parameters are also listed for each test.

 

Also, saying that 13:1 or 13.4:1 detonates more readily than 12:1 is accurate if all test conditions are duplicated exactly. I could drive my 14.4:1 compression racer all over the paddock on 97 octane fuel without detonation. But I know that inlet air temperature and cylinder filling are test parameters that I can control.

 

This is the type of generalization that just adds confusion. For example, a lightly loaded engine of any type running in the mid range of its parameters can be leaned from too rich to run all the way to lean cutoff with no damage of any kind.

 

Detonation requires lots of energy, so we need lots of fuel to make lots of heat, and that requires lots of air, so that means close to wide open throttle. Small throttle openings means poor cylinder filling and low effective compression ratio and almost no chance of detonation.  

 

The same system used to produce motor fuels is going on inside the combustion chamber on every ignition event. But we start with base stocks that are lighter and easy to light, instead of black goop.

 

So we light the fuel and a ball of fire starts at the plug tip, and radiant energy booms out from this event heating mixture ahead of the flame front. So the flame front accelerates (Hotter mixture burns faster) adding more energy to the unburned mixture and compressing that mixture at ever increasing rates into an ever decreasing volume. While this is going on

your little refining operation is cracking up brand new chemicals for the flame front to consume. Chemicals with long names and longer diagrams. Most of your new chemicals will last only Picoseconds, Some will exit the engine intact. Some will combine with oxygen and vanish adding heat, some will absorb heat and become bigger longer chains, that slow the flame front.

 

So if we start this process early (More advance) the results happen sooner in the crank rotation. The process will be hotter (Having burned longer) for each degree of crank rotation. All of the process will be hotter and move faster. So as far as mixture strength is concerned the closer to the fastest flame speed we get the more critical every operational parameter gets to detonation. When we say "lean it out" we have to start at some number and are then suggesting moving to another number with fewer parts of fuel per cubic foot of air.

 

So in the case where we are just one or two parameters away from detonation, and we then lean to a number that provides a higher flame speed, then we achieve detonation. But you need a large number of items to be in or near the red line before just one more change gets you to detonation.

 

So the wives tale is: I leaned it out just a bit, and it went soft (revs dropped off) and the apex seals are in the muffler. Or, in piston engines: the oil pump locked up from pieces of piston getting through the screen.

 

So leaning destroys engines, is that correct?  NO

 

Advancing the ignition does not in itself cause detonation. Leaning the mixture does not in itself cause detonation. Low octane fuel in itself does not cause detonation. High intake air temperatures do not alone cause detonation. Rapid throttle opening in itself does not cause detonation. High load, low RPM, wide open throttle alone does not cause detonation. High oil or water temperatures do not alone cause detonation.

 

The NA rotary has a large cold combustion chamber. It has no good squish areas, so fuel droplets tend to form near the apex seals, further cooling the chamber. And leading to poor BSFC and high HC. But this helps prevent detonation. The fire goes out because droplets do not burn worth a damn, and show up as high EGT as they find excess oxygen to join up with just about where your EGT probes are mounted.

 

So it is difficult to detonate a rotary. Unless you really want to. So, if you really want to, here are some tips.

Let the oil temperature get real high, well over 200 degrees. High rotor face temps and no more cold chamber (Ace in the hole) for you. Let the water temperature get well over 180 degrees, same as high oil temps. Add way more advance than is required. The rotor moves slowly over TDC, and needs very little ignition advance.

 

Use last years lawn mower gas. It has some kind of oil in it right?

 

Use rapid throttle movements on very hot days from low RPM. If it still won't detonate, as a last resort, add a turbo charger and do all of the above. Ouch, that worked didn't it?

 

Lean of peak EGT operation: once lean of Peak EGT, we have more oxygen than needed, and it absorbs energy so combustion temps start down along with less energy from the leaner fuel mixture. So leaning makes things cooler once past peak EGT. So, once again, Leaning does not alone cause detonation.

 

Rules is rules. Screw with mother nature, and she will screw with you. 

 

Lynn E. Hanover