How to Determine Emissions From Engine Generators

Updated April 17, 2017

The U.S. Environmental Protection Agency defines emissions as "pollution discharged into the atmosphere from smokestacks, generator exhaust, and surface areas of commercial or industrial facilities." Emissions can contribute to the formation of ozone in the troposphere and to acid rain. Diesel engine generator emissions are a significant source of emissions, which are usually formed during high-temperature combustion inside the engine. The equation for calculating engine generator emissions is E = A x EF x (1-ER/100). In this formula, E stand for "emissions," A equals "activity rate," EF is "emission factor" and ER is "overall emission reduction efficiency."

Calculate the activity rate, which for a generator is how many hours it operates. Determine the hours of operation by timing the generator from the moment of start up until the moment the generator is shut down. Maintain a log of the hours of operation for the life of the engine generator.

Determine the applicable emission factor. The emission factor is the key component to any emissions calculation. The two main sources for engine generator emission factors are the U.S. Environmental Protection Agency's AP-42 document and the generator's technical data sheet. EPA's AP-42 document, "Large Stationary Diesel and All Stationary Dual-Fuel Engines," has emission factors on a variety of diesel engines. From that document you can pull the emission factor that best fits your generator type. The generator technical data sheet is specific to your diesel engine. The emission factor in the data sheet is directly related to that engine. This is by far the best emission factor data available.

Verify that the units correspond, then multiply the hours of operation by the applicable emission factor. The result is the emission. Once the activity data and emission factor are obtained, the calculation is straightforward, because in most cases emissions from engine emissions are emitted directly out of the stack. In cases where engine emissions are emitted directly out of the stack, ER becomes zero. Thus, if ER is zero, (1 - (0/100)) is equal to one, and anything multiplied by one is equal to itself.


Logging hours of operation into a spreadsheet can save time when adding up the total hours operated for the month or year.


In some states operating a diesel generator may require a permit. Check with your state and local environmental departments before operating a diesel engine.

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About the Author

Harry Jeudy is an environmental/mechanical engineer who has been writing technical reports and procedural manuals for over seven years. One of his major publications was a contribution to Delaware’s "Environmental State Implementation Plan.” Harry holds a Bachelor of Science in mechanical engineering with a minor in structural engineering. He also has 10 years of experience in the environmental industry.