[Vwdiesel] Re: [Audi-VW-Diesels] EGT temps revisited

[Nate Wall]

What causes the temp drop? Being a former chemistry major, the ideal gas law
comes to mind. Its not just because the turbo acts as a big heat sink,
dissipating heat. Thge gases expand as they pass through the turbo, giving up
energy (doing work) against the turbine. As that expansion occurrs, the temp
drops. Sound correct?

Remember old steam locomotives? Some of them use a smaller cylinder under the
primary one to expand the steam a second time (the first cylinder exhausts into
the second) on each set of drive wheels to get greater effeciency.

BTW I read efficiency of old steam locomotives was 3 - 5% and maintenance was
horrendous (constant oiling/greasing, etc.) that's the big reason the switch to
diesel/electric. Using the electric motor/generator concept coupled to diesel
engines negated the necessity of a huge transmissions.

--nate

dieseltdi at earthlink.net wrote:

> Just wanted to pass on some wisdom that I picked up today.  I went over to
> Diesel Injection Service, the dieselpages people, they have an place over in
> Dallas.  Anyway, I spent some time talking to the guys that actually work on
> the engines and asked him what the difference in temperature one could
> expect between preturbo and post turbo.  To answer the question, he handed
> me two Isspro (sp?) pyrometers one to be installed post and one designed to
> be installed pre turbo.  The caution zone on the post turbo one started at
> 900 degrees F and extended to 1150 degrees where it entered the red.
> Preturbo had the yellow zone beginnig at around 1150 and the red at 1300.
> He said that for the pickups that he mostly works on, they have found a
> rather consistent 200-250 degree drop across the turbo.  However, after
> looking at the tdi set up, commented that the drop could be much less
> because the distances between head, manifold, turbo and downpipe are very
> small.  I mean the total distance between the head and where my thermocouple
> is located is not more that 12-16".  The same set up on a Ford Powerstroke
> can be as far as 3 feet.  He also told me that the general rule of thumb in
> automotive diesel engines for max preturbo temps is 1300 degrees.  I feel
> better now that I am not horribly exceeding max temps when I have seen 1000
> degrees post turbo only for a few seconds on a couple of times.
> BTW while I was there, I had them check a bag full of turbo injectors to see
> if I have 4 good ones for the turbo engine that I have in my garage.  No
> charge for the testing.  hayden
>
> -- Visit my homepage at http://home.earthlink.net/~dieseltdi
>     2002 Jetta Wagon GLS TDI
>     98 Jetta TDI (Silver Arrow)
>     98 Jetta TDI (daughter's car)
>     90 Corrado (son's car, gas :^P)
>     81 VW Rabbit Pickup (Caddy, Diesel of course, awaiting
>     a TD engine transplant)
>     And many, many water cooled and aircooled
>     VW cars now departed or sold.
>
> ------------------------ Yahoo! Groups Sponsor ---------------------~-->
> Plan to Sell a Home?
> http://us.click.yahoo.com/J2SnNA/y.lEAA/MVfIAA/gkiolB/TM
> ---------------------------------------------------------------------~->
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/