[Vwdiesel] Why so noisy?

LBaird119 at aol.com LBaird119 at aol.com
Tue Dec 11 00:12:40 PST 2007

In a message dated 12/10/2007 9:25:32 PM Pacific Standard Time, 
jhsg at sasktel.net writes:

> The new ones are direct injection motors, so the combustion process 
> happens inside the motor, on top of the piston, where there is a 
> depression the injector shoots into that mimics the precombustion 
> chamber in the early motors.  COnsider it muffled.

  Not that I quite disagree with you James but I don't think 
prechamber vs direct quite fits it as a lot of the older direct 
engines were noisier than the prechamber engines.  
Prechamber engines ARE quieter at rpm than a direct but 
most of the rattle has to do with the rapid combustion of 
the fuel over a gasser which has a "flame front".  The two 
rattles don't quite compare since preignition knock has about 
as much to do with a quick ignition as it does being early.  
  Just minor points but hey...  :-)
  Most of the quieting comes from multiple injections as you 
stated, which creates a flame front and a slower rise in cylinder
pressures instead of such a rapid rise in pressure.
  Most cures for diesel knock are opposite of gassers from 
one source I read.  Less fuel instead of more, advance the 
timing instead of retard (I think that has to do with that 
NASTY knocking rather than the inherent rattle/knock.)

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