[PCW] Diesel load and related questions

[2elnav at netbistro.com]

----- Original Message ----- 
From: "Dennis Raedeke" <dennis at wildmountain.com>
 > The idea that diesel engines have to be under a certain load to survive 
to long life is questionable.  My men leave  our diesel snow cats run to 
keep them warm and I see truckers keep their rigs running all night while 
sleeping. We have not seen any trouble related to this. The engine should be 
run fast for a little after a long idle period.

REPLY
That  notion is the result of mixing apples and oranges.  It is gensets 
that  must be run  at a certain load  when they are run at  1800 RPM.  Fast 
speed means   the fuel dielivery is set at so muchvolume.  If the  generator 
engine is not loaded fully,  it runs cool.  This in turn means   the fuel 
condenses on the cylinder walls instead of being burnt as a vapor.  Now it 
leaks down the cylinder walls   forming glaze  and in extreme cases dilutes 
the lube oil.
When you slow down to idle, the fuel metering is also reduced.  This pretty 
much eliminated much of the wet stacking.  As you so rightly indicate  a 
fast  run after prolonged idling  tends to burn off any residue and  the 
engine  is back to normal.
Admittedly a high power, high speed engine  is likely  not going to be  very 
happy if idled for prolonged periods of time. Especially in cool weather. 
If turbo charged, the turbo is  not spinning very quickly  but the bearing 
housing is still full of hot oil   which is not circulating quickly in the 
bearing.  That may cause cabonizing of the oil in the turbo bearing. 
Eventually such deposits build up to a point it impairs the bearing s 
rolling resistance.  I sucessfully cleaned up a clogged bearing  which had 
fouled  for that reason.


Dennis wrote
> With CPP's you are able to load the engine any way you like. With proper
> instrumentation you are able to fine tune your operation.


REPLY
Correct.  The trick is to bring  the combustion  chamber walls up to a point 
which  leads to complete  combustion all  the time. We sometimes forget 
that a diesel is a compression ignition engine and  the compression  creates 
the necessary heat.  If the heat removal system of the engine  removes the 
heat   too fast  or if the loading  is not sufficient to bring up the heat 
enough, we get poor running.  Lightly loaded engines tend to run cooler. 
That leads to less than optimum combustion efficiencies.  In propulsion 
engines this does not necessarily lead to  engine damage except for some 
carbon build up.

Arild