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Correction Factors

POWER CORRECTION FACTORS (DIN, SAE..)

To correlate the engine performance measured in dynamometer tests, to the engine performance at different ambient conditions, correction factors for the engine power delivery are proposed by institutions, such as:

  • DIN (Deutsches Institut für Normung)
  • SAE (Society of Automotive Engineers)
  • ISO (International Organization for Standardization)
  • ABNT(Brazilian Association of Technical Standards)
  • JIS (Japanese Industrial Standard)

These correction factors can be used to estimate some performance parameters, such as power, torque.

CONCEPTS

  • The power produced by an engine is directly linked to the mass of air introduced into the cylinders, in the unit of time. It also depend on the atmospheric pressure and temperature values; in fact, there will be a decrease in density as pressure decreases and temperature increases (and vice versa).
  • The release of energy in a combustion process only depends on the presence of oxygen.
  • Therefore, even the variation in humidity can lead to a significant variation in the power developed which, in an engine, is directly proportional to the dry air pressure, i.e. the total barometric pressure minus the partial pressure of the water vapor.

For example, the decrease in power that occurs in the mountains, is due to the fact that the air density progressively decreases. The aspirated air, therefore, will contain fewer oxygen molecules.

A smaller quantity of oxygen molecules, will decrease in the amount of fuel that can be burned and therefore in the amount of thermal energy that is released by combustion (= less engine power)

It’s so necessary to carefully measure the environmental conditions when carrying out the dyno test; then modify the detected power using a special “Correction factor”; so as to bring it back to the value that would be obtained in “standard” conditions (i.e. temperature, reference pressure and humidity). Although the general measurement conditions are very different.

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