Pyrometers and Exhaust Gas Temperature



Exhaust gas temperature (EGT) is probably one of the most important leading indicators of engine failure. A pyrometer is a device that can indicate the temperature of gasses at different points along the engine’s exhaust system. Therefore, in order to get the best diagnostic information from pyrometers, they must be positioned or mounted at the proper locations along the exhaust system, since temperatures will vary along different points.

Pyrometers can help diagnose the following conditions, prior to severe engine damage:

  • Cooling system problems
  • Combustion problems (air / fuel mix)
  • Fuel system problems

Note that by “problems”, we mean catastrophic, replace the engine problems.

A good example of this temperature variance is with the turbocharger. Exhaust gas temperature can indicate problems with the turbocharger, so a pyrometer placed before and after the turbocharger will give an indication of potential for failure. Between intake and out, the temperature differential can be 300 degrees C or more.

However, MarineDiesel uses Variable Geometry Turbochargers (VGT) with its’engines. As the inlet varies in size, the temperatures will normally fluctuate as the aperture of the turbocharger changes shape. Therefore, how is change in temperature a leading indicator? Simple. What you are looking for is temperature anomalies, outliers, or changes over time. Your engine manual gives an indication of the proper temperatures and the levels that should be present. Actually, this becomes an issue more with experienced engineers. They have the knowledge of one or more engines, but every engine manufacturer designs their engines differently, and the ratings are different, meaning temperatures will be different between manufacturers make and model. Hence, the standard “refer to the manual” line, cliche though it may be. With most engines, the exhaust gas temperature should range, normally, from 500 to 700 degrees C. Again, this will vary.

Also important to note: Engines are tested and rated in factory test cells, where conditions are constant. In the real world, vessels operate in a wide variety of conditions, climates, and use. Heavy loads typically mean higher exhaust gas temperatures. These all have an impact on exhaust gas temperature, and adjustments to what is “normal” are required under differing conditions.

Another indication provided by pyrometers is that of emissions. Exhaust gas temperature can help diagnose incomplete combustion and non-compliance of emissions.