Lynn E. Hanover

Well, everyone seems to have a little piece of the puzzle.



The best milage you could normally find would be a diesel engine. Compression ratios up to 24:1 one. So the available oxygen is dozens of times more than in a NA gas engine. The other less obvious advantage is that the temperature of the oxygen is in hundreds of degrees, before the fuel is injected, at pressures that increase the fuel temperature even before it enters the chamber. This system works so well that the fuel need not very exotic at all. In fact anything that will burn can be used as fuel.



Even fluids that will not burn at sea level pressures will burn quite well in a diesel. So any gasoline engine seems a bit silly compared to a diesel. It is also true that the closer the gasoline engine gets to diesel like compression ratios, the more effiecient it becomes.



So why don't we just jack up the compression ration to the roof, and start from there? Well we are headed that way now. The new high pressure electrical injectors used in newer diesel engines can be used in gasoline engines as well. So injecting fuel later in the cycle, so it is not in the air being compressed, and less exposed to the heating of the air from compression, holds off the detonation normally connected to high compression and the gasoline engine begins to look more like a diesel each day.



So what?



Well the piston engine that has been well designed, has a large area of piston that will fit tightly against the cylinder head at TDC. this is called squish area. So, when the piston closes in on TDC the mixture burning near the spark plug is sprayed with fuel air mixture from the edges of the chamber most remote from the plug, because it is forced out of the squish areas where detonation would normally occur.



The rotary has nothing in the way of a squish area. The opposite is true. The rotor face is just close enough to the housing just about everywhere to cool the mixture but not close enough to drive it anywhere suddenly. So, the rotary has a big problem with unburned hydrocarbons (fuel) but not a big problem with detonation. The quenching effect is so prevelent that the flame front dies off before viable mixture near the apex seals burns. So you get a nice fireball out the exhaust pipe that shows you fuel that should have burned inside the engine.



With no squish area inside the engine and little turbulance to maintain a viable mixture, excess fuel is required to assure that the oxygen available is consumed. The fuel is flopping about in great clumps from lack of heat energy and there will always be an unhappy amount of fuel that is not finding oxygen to bond to. Note that the Lemans 4 rotor had 3 spark plugs in each housing.



So the ideal is only that, and is not attainable in anything but a 25CC test engine in a lab.



In racing there is not yet a demand for emissions control, so we can operate with only an eye to performance, and if HC and NOX are off the scale, it matters not. The rotary as we know it will not ever perform well with a liquid fuel. However, a fuel that has been excited mechanically and, or, with heat could make major improvements in effieciency.



These same mechanical short comings become (to some extent) advantages when the engine is boosted above atmospheric. The cold chamber surfaces allow for more compression (boost) without detonation. Higher compression means more energy in the mixture and more blobs of fuel finding oxygen to bond to. Along the same line of thinking, a low boost mechanical supercharger combined with very high pressure injection into the housing after port closing could make for a very viable emissions friendly package.



The point is, that ideal is not now available to anyone. Rich of ideal and much richer than ideal is the actual rule. In a very general truth, power increases (as you would think) as you lean toward the ideal, until all of these factors combine to stop you short of your goal.



Lynn E. Hanover

j9fd3s

http://www.pbase.com/mwphoto

boyrotor

Wasnt there a (US delivered only) rx7 model in the Gen 1 years somewhere with a 12a that ran extra lean for emmissions purposes? Something like 14 - 16 (maybe only on decel though) ????

BLUE TII

Lean burn 12A was available in late '79 in japan and late '80 in US in the new P815 model 1st gen. It ran at 14.8:1 AFR cruise using its high energy constant dual plug ignition system and used twin bed catalyitics and a split air system air pump. Sounds like all rotaries since except it had a carb :P



It was just called lean burn then because it was replacing the old rich running thermal reactor system.

boyrotor

Oh right. Yeah the old thermal reactor system must have run rich as. I was reading in my rx2 workshop manual that on thermal reactor models trailing ignition was cut at mid rpms so to allow a more unburnt mixture to burn properly in the TH - weird!

j9fd3s

yep its only lean burn compared to the thermal reactor system. in real life, it runs more like mid 13's