Peter
Thanks for the explanation. Write more!
tnx
73
Hank WD5JFR
----- Original Message -----
From: "Peter Frederick" <[EMAIL PROTECTED]>
To: "Mercedes Discussion List" <[EMAIL PROTECTED]>
Sent: Sunday, February 05, 2006 9:12 AM
Subject: Re: [MBZ] what IS the "diesel noise"?
Gasoline engines have a fairly rapid burn, so the fuel mixture must be
ignited after TDC, else you get spark knock. Diesel engines indeed
have fuel injected for a large portion of the power stroke (and in
fact, sometime after when people fiddle with the IP to get more power
-- also more black smoke).
However, the velocity of the fuel spray combined with the expanding
flame front does produce a supersonic pressure wave, just like an
airplane produced as pressure wave at supersonic speeds, and the
"crack" is unmistakeable -- ditto for a cracking a whip, by the way, or
noise from a lawn mower with the blades turning too fast.
Add that to the fact that most older American diesel engines run fixed
injection timing, set for high rpm operation, and you get lots of noise
since at idle the injection it too soon, sometimes before TDC.
Peter
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