Restricting exhaust flow causing temperature increase?

[IPog]

We have a situation.
Someone modified the exhaust pipe from a diesel fired equipment. Exhaust gas flows out through a 30mm internal dia pipe. The modification carried out was to reduce the diameter of the pipe to 20 mm internal dia.
The Exhaust outlet temperature from the equipment was 400 deg C. I calculate that at the constriction the temperature would be 553 assuming a gamma of 1.4.
Any comments appreciated.

 

[theOrange]

I found this website, it may be helpful for you. Just keep in mind that the temperatures are in Kelvin.

https://www.dieselnet.com/tech/diesel_exh.php

If this table is correct, you have to take a "k" value (gamma) of around 0.0466.

1.4 can only be assumed for air at a specific temperature because "k" changes depending on your temperature. However if the temperature change is relatively small, then you can assume it is constant.

I hope this helps...