Restricting exhaust flow causing temperature increase?

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SUMMARY

The modification of a diesel exhaust system by reducing the internal diameter from 30mm to 20mm significantly impacts exhaust gas temperature. The initial outlet temperature of 400°C rises to approximately 553°C at the constriction, based on a gamma value of 1.4. However, it is crucial to note that the specific heat ratio (k) varies with temperature, and a more accurate value of 0.0466 should be considered for precise calculations. This discussion highlights the importance of understanding thermodynamic principles in exhaust system modifications.

PREREQUISITES
  • Understanding of thermodynamics and specific heat ratios
  • Familiarity with diesel engine exhaust systems
  • Knowledge of temperature measurement in Celsius and Kelvin
  • Basic principles of fluid dynamics and gas flow
NEXT STEPS
  • Research the impact of exhaust diameter on diesel engine performance
  • Learn about the calculation of exhaust gas temperatures using the ideal gas law
  • Explore the significance of specific heat ratios in thermodynamic processes
  • Investigate methods for measuring and monitoring exhaust temperatures accurately
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Engineers, mechanics, and technicians involved in diesel engine maintenance and modifications, as well as students studying thermodynamics and fluid dynamics.

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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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