🚀 go-pugleaf

In article <dq0i5g$rh7@u1.netgate.net>, geoffm@u1.netgate.net 
says...
> 
> 
> Keith Williams  <krw@att.bizzzz> writes:
> 
> : That vapor condenses as the result of the exhaust pipes being cold,
> : not the engine.  It's the same principle as that of contrails: hot
> : gases containing water vapor pass into a cold environment, where 
> : the vapor condenses.  As more and more warm exhaust passes through 
> : the exhaust pipes, they warm up down their length until at some 
> : point, no more visible vapor comes out. 
> 
> > If that were the case there wouldn't be contrails. 
> 
> Why?  The tailpipes of jet engines are proportionately shorter than
> those of automobiles, the exhaust gases are much hotter, and the 
> surrounding air at altitude is typically much colder than at ground 
> level. Given the greater temperature difference, it makes sense that
> high-flying aircraft put out visible water vapor in the form of con-
> trails while cars stop putting out visible vapor once their exhaust
> systems warm up.  

Except they don't (stop).  Cars won't stop producing a contrail 
when the exhaust system warms, as long as the outside temperature 
is below the dew point of the exhaust.  The temperature of the 
exhaust pipe has little to do with it (other than liquid water will 
stop running out of the heated pipe).  Perhaps there is an 
intermediate temperature where the exhaust remains above the dew 
point until it is dispersed enough to avoid noticable condensation.    

> > The water's not from the intake air, rather a combustion byproduct.
> 
> Noted.

-- 
  Keith