[Vwdiesel] INCREASING AND DECREASING FUELING

[hwy9fergs at comcast.net]

Svend said
> Andrew please explain  "Pumping Losses" ---- You totally lost me 
> there.---BUT it sounds
> interesting to me.  ------------  TIA.
> 
Andrew said
There is a certain amount of energy loss with regard to pumping air into and 
out of the cylinders.  If you lean a turbo diesel out beyond the point where 
you burning more fuel you are merely pumping air into and out of the engine.  
That pumping action creates inherent losses due several factors.  Primarily to 
the added backpressure between the turbo and piston.  Granted there is some 
gain due to the added pressure of the intake air pushing onto the opposing 
piston on the intake stroke, but there are significant energy losses in just 
pumping air.  So, to sum up, just pumping more air into the cylinders consumes 
energy.  If you are not gaining more energy than you are losing from getting a 
better (more complete) burn then you are merely consuming energy and decreasing 
overall fuel economy.  Super-lean is not super-economical in a TD.

Andrew


OK, now you guys have got me started, bear with me for a minute.  Andrew I think I follow where you're going with the air pressure entering the combustion chamber from the action of the turbo. And the pistons having to compress that air. What I think needs to be clarified here (and you might not have considered) is that the amount of air being pushed into the cylinders from the turbo is DIRECTLY dependent on the amount of FUEL being supplied.  If you decrease fueling, you decrease the volume of hot exhaust gases spinning up the turbo, THE TURBO SPINS DOWN, and you in turn decrease manifold pressure.  The absolute most efficiency you will squeeze out of these engines has very little to do with whether or not (as you guys insist on putting it) if it's rich or lean.  Sure, you can overfuel the engine and produce a bunch of black smoke. Not efficient. A properly adjusted pump won't allow this. But that's probably the closest condition I could think of where calling it "rich" might work.  Again, I still prefer "overfueled".  The most efficient vw diesel engine will have good compression, unrestricted intake and exhaust, a healthy turbo (if applicable), GOOD NOZZLES, which are properly atomizing the fuel (critical), a healthy set of prechambers to properly swirl the fuel spray (Svend's "vortex" comes to mind")  and the injection must happen at the precise time and duration in the amount necessary to meet the demand. If the pump is weak and the various advance and metering mechanisms aren't working right, OK you might need to use a little Voodoo (hillbilly tuning), or you may just be kinda screwed. Anyway, given a healthy engine and fuel system, bottom line is, you put more fuel in, you get more power, and visa versa. It's not a matter of "rich" and "lean" with these engines. As for gas engines? yes yes yes.  With gas engines it's all about mixture- Aka-rich and lean.  Familiar with the word "stoichiometric"?.  Does any of this now make any more sense to anybody?  Thanks,  Doug Ferguson -------------------More on diesel efficiency may be forthcoming, unless I now get thoroughly shouted down.