Specific air consumption equation?

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SUMMARY

The specific air consumption equation for a diesel engine is defined as the weight of air required to combust one pound of fuel, typically around 14.5 pounds of air per pound of fuel. This ratio is a pure figure and is independent of atmospheric pressure. Fuel consumption is often measured in pounds per horsepower hour, though the modern standard is kg/kW.hr. Diesel engines intake more air than necessary for combustion, with only the stoichiometric air counted in specific air consumption, while the excess air aids in achieving the required compression ignition temperature and ensures complete combustion.

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Webbd050
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what is the specific air consumption equation for a diesel engine?
 
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I believe it used to be specified as the weight of air required to combust one pound of fuel. The figure will depend on the fuel grade, if I remember correctly it is usually about 14.5 pounds of air per pound of fuel.

The value of 14.5 is actually a pure ratio, but the “pound” is often still referenced.
This is quite unrelated to the atmospheric pressure at sea level measured in psi.

Fuel consumption was often specified in pounds per horsepower hour. Now the more common units are kg / kW.hr

A diesel engine usually takes in more air than is needed to burn the injected fuel. Only the air needed for stoichiometric combustion is counted for the specific air consumption, the excess is used to achieve the required compression ignition temperature when idling, and to guarantee complete fuel combustion.
 

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