Restricting exhaust flow causing temperature increase?

AI Thread Summary
Modifying the exhaust pipe from a diesel-fired equipment by reducing its diameter from 30mm to 20mm can significantly increase exhaust outlet temperature, with calculations suggesting a rise from 400°C to 553°C at the constriction. The discussion highlights the importance of the specific heat ratio (gamma) in determining temperature changes, noting that a gamma value of 1.4 is only applicable under certain conditions. It is also mentioned that the "k" value varies with temperature, which could affect calculations. A referenced website provides additional insights into diesel exhaust technology. Understanding these factors is crucial for assessing the impact of exhaust modifications on temperature.
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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.
 
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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...
 

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