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

[Val Christian]

It's important to remember that there is a range of mixtures, for
a given pressure (and to a much less degree temperature), where
any fuel, gasoline or peanut oil, will burn.

A fundamental difference between Otto and Diesel cycles is that in
an Otto cycle, you burn the full charge.  In a Diesel cycle, you 
burn only the fuel injected.

Therefore, for the Diesel cycle, mixture and combustion parameters 
are affected at the flame interface.  Turbulence, compression temperature
and injection atomization and distribution are big factors.  

If Hagar is compressing to high intake manifold pressures, that will
affect efficiency.  Taken to an extreme, very high boosting, very 
little fuel injected into a big engine, can lead to inefficiency.

Crusing in a Rabbit, at 40 to 50 MPH doesn't really take allot of 
power.  Tooling along at 80 to 85 MPH, with a fully loaded vehicle, 
windows open, etc., is going to be  a different story.  That a TDI
Jetta will get 55 mpg under those circumtances amazes me daily.

>From a lean/rich standpoint, the mixture at the burn point is critical.
In the case of a Otto, the burn point is all over the cylinder.  In a 
Diesel, there is the ability to control it.

Val




> 
> 
> > Loren if you had read my threads carefully ---you wold understand that
> > Lean comes in many shades. ---I chose SUPERLEAN  for good reasons.
> > 
> 
>   Indeed I've read your threads, all of them.  Yet the way you change 
> speed on a diesel is to add more fuel where on a gas you add more 
> air AND more fuel yet in the same ratios, basically always.  You 
> can adjust that ratio and it then runs at THAT ratio.  In a diesel you 
> maintain the air (of course excepting turbo, air density and all the 
> variables) and change the fuel (A/F ratio) to change the speed.  
> Thusly the A/F ratio is ALWAYS changing any time speed or load 
> changes and you can't lean out that ratio and maintain speed and 
> load.  You CAN increase the efficiency with adjustments.
> Better injectors, light foot, higher pressures, dialing in the timing 
> although have the effect of "leaning" things out and using less 
> fuel isn't really running the engine lean, it's setting as many of the 
> paramaters and variables to as close to ideal as possible.  
>   Maybe it's just our definitions of the terms.
>      Loren
> _______________________________________________
> Vwdiesel mailing list
> Vwdiesel at vwfans.com
> http://www.audifans.com/mailman/listinfo/vwdiesel
>