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

[Nate Wall]

On the opposite side of the coin, temperatures increase as gasses (including air)
are compressed. We all know that.  Compression ignition!

--nate

Nate Wall wrote:

> 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.
> >
> >
> >
> >
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