[Vwdiesel] Diesel octane or why can you run a diesel engine lean?

[LBaird119 at aol.com]

> ----BUT I have to downshift on the hills.   The turbo
> likes lots of RPM.----do not ask me why , that is another complex issue.
> 

  Not really.  It's a fan for the most part.  The more air you push through 
it
the faster it turns and then compounds the effect a bit.  More engine 
rpm = more turbo rpm.  More fuel = more heat = more turbo rpm.  
The faster the EGT can rise, the faster the turbo can spin up and 
the quicker you accelerate.  More volume or a smaller turbo is 
what will make it spin up faster. 
 
  I think most of us understand ignition delay.  It's a constant yet it's a 
variable.  ;-)  Same thing with a gas engine.  Setting the timing to 10BTDC 
does NOT make ignition happen at that point, to completion.  Neither does 
it in a diesel and none of us believe that, AFIK.  If it did we'd REALLY 
have a knock.  For basic purposes though, ignition DOES happen at 
injection.  Kind of like shooting skeet.  Sure you have to "lead" the 
target, speed varies and you take that all into consideration yet you 
time that all from the instant it leaves the thrower.  Piston speed 
changes the point at where the maximum pressure happens 
relative to rotation, the governor compensates so that peak pressures 
happen about where you want them. 
  For all intents and purposes, ignition happens at injection however 
peak pressure does not.  Getting peak pressure at the most efficient 
point of rotation is the key.  Only problem is that it can vary with 
temperature, humidity, engine speed, governor, etc, etc.  
  Always wanted to put mine on a dyno, set speed at 60mph, check 
fuel consumption and then rotate the pump to see if peak power happens 
at peak efficiency (it should, or very closely) and then set it there.  
After that, read the static timing and that's my setting from then on. 
No dynos in town.  :-P
     Loren