Internal combustion engines emission calculations

This method may be used to develop an editable spreadsheet containing detailed emissions calculations for internal combustion engines. Each step in your calculation(s) needs to be clear and easy to follow.

Include the following information with your calculations:

  • AQ Facility ID No. – Include your Air Quality (AQ) facility Identification Number (ID No.). This is the first eight digits of the permit number for all permits issued under the operating permit program. If your facility has never been issued a permit under this program, do not include at this time.
  • AQ File No. – Include your AQ File Number, if known. This number can be found in the “cc” section of correspondence from the MPCA. If you do not know this, or can’t find it, do not include it at this time.
  • Facility name – Include your facility name.
  • Emission unit ID(s) – Include the identification number of each emission unit. Obtain this number from your Form GI-05B, or the appropriate form related to the permit you are applying for, or your existing permit. If you are applying for a Registration Permit Option D, just provide a description of the emission unit.
  • Stack/Vent designation number(s) – Include the designation number of the stack(s) or vent(s) through which the unit will exhaust into the atmosphere. Obtain these numbers from Form GI-04, or the appropriate form related to the permit you are applying for, or your existing permit. If you are applying for a registration permit Option D, you do not need to include this information.
  • Control equipment Include a description of the type of control equipment. Use either the identifying number from Form GI-05A, or the appropriate form related to the permit you are applying for, or your existing permit. If none, indicate no control equipment. If you are applying for a registration permit Option D, just provide a description of the control equipment.
  • Engine Type – Indicate the engine type (reciprocating, turbine, or, if another type, provide a description).
  • Purpose of Engine – Indicate whether the engine is used for routine operation or emergency use. Complete Screen Model for Ambient Air Impacts unless you are installing a generator to be used only for emergencies.  Microsoft Office document icon EC-03 IC Engine Screen Modeling, (revised 2/5/14).
  • Rated Heat Input – Include the rated heat input of the engine, in units of million British thermal units per hour (MMBTU/hr).
  • Rated Mechanical Output -- Include the rated output of the engine in horsepower (hp) at a specified rpm.
  • Fuel Type – Indicate fuel type (e.g., natural gas, diesel).  Indicate the weight percent sulfur content, if applicable. If more than one fuel is combusted in this unit, include emissions calculations for each fuel.
  • Rated Fuel Consumption – Indicate the manufacturer’s rated fuel consumption for the engine. This information can be obtained from the manufacturer. If the engine has been de-rated, attach supporting documentation. Indicate the appropriate units (gal/hr, cf/hr).
  • Source of emission factors – Indicate the source of your emission factors. Possible sources include those listed on the Emissions Calculations page and those described in Minn. R. 7005.0100, subp. 10. If the emission factor is from AP-42, cite the exact section or table used. If emission factor is from some other source, attach a photocopy of the information used, or provide an exact internet address, so the information can be verified.  
  • Formula/Equation – The formula and/or equation needs to be available in each spreadsheet cell for which there is a calculation (for example, Steps 3, 4, 6, 7, 8, 9 below.)
  • Operating limitations – Describe in detail any permit limits you plan to take to restrict your potential-to-emit (fuel type and/or usage, hours of operation, bottlenecks, etc. - seeProposing Synthetic Minor Permit Limits). Attach additional spreadsheets or other information, if needed. Describe the limiting factors, cite any rules that apply (e.g., Standards of Performance for Stationary Sources (NSPS, 40 CFR part pt. 60), Best Available Control Technology [BACT]). The associated limit must be used to calculate your potential-to-emit after permit limits in Step 8. If you used vendor certification or stack test data to limit your potential-to-emit, the factor you used will become your permit limit. Include all proposed limits on Form CD-01, and anywhere else as instructed in the application forms.

Emissions Calculations

Follow these steps for calculating emissions for each internal combustion unit at the Facility. Each step should generally correlate to a column in your spreadsheet. Additional columns can and should be included in the spreadsheet to indicate additional calculation steps or information specific to your process.

Step 1. Pollutant

For each pollutant listed below, calculate the unit’s emissions. 

  • PM = particulate matter
  • PM10 = particulate matter smaller than 10 microns in aerodynamic diameter
  • PM2.5 = particulate matter smaller than 2.5 microns in aerodynamic diameter
  • SO2 = sulfur dioxide
  • NOX = nitrogen oxides
  • VOC = volatile organic compounds
  • CO = carbon monoxide
  • HAPs = hazardous air pollutants – each individual hazardous air pollutant. See EPA's Web site for more information.
  • Total HAPs = All HAPs added together
  • Greenhouse Gas (individual greenhouse gases, and as CO2e) See Greenhouse Gas Emissions: Instructions for Emission Calculations Spreadsheets

Step 2. Emission Factor

For each pollutant, indicate the uncontrolled emission factor.  For PM10 and PM2.5, be sure your emission factor includes organic and inorganic condensable particulate matter.

Step 3. Emission Rate

Calculate the Emission Rate in lb/hr. Calculate the emission rate by using one of the following methods:

If the emission factor is in units of pounds per quantity of fuel (gallons or cubic feet):

  • Emission Rate [lb/hr] = Fuel Consumption Rate [unit/hr] x Emission Factor [lb/unit]

If the emission factor is in units of pounds per hp-hr power output:

  • Emission Rate [lb/hr] = Rated Mechanical Output [hp] x Emission Factor [lb/hp-hr]

If the emission factor is in units of pounds per MMBtu heat input:

  • Emission Rate [lb/hr] = Rated Heat Input [MMBtu/hr] x Emission Factor [lb/MMBtu]

Step 4.  Maximum Uncontrolled Emissions

(Skip this item if applying for Registration Permit Option D.)

Calculate the maximum uncontrolled emissions in tons per year.

If the engine is an “emergency generator” (a generator whose sole function is to provide back-up power when power from the local utility is interrupted), the U.S. Environmental Protection Agency (EPA) has stated in a memorandum dated September 6, 1995, that maximum uncontrolled emissions may be based on operating the generator 500 hours per year.  Use the following equation:

  • Maximum Uncontrolled Emissions [tons/year] = Emission Rate [lb/hr] x 0.25 [hr/year x ton/lb]

The September 6, 1995 EPA memo applies only to emergency generators as defined above. It does not apply to peaking units at electric utilities (peak shaving units); generators at industrial facilities that typically operate at low rates but are not confined to emergency use; or any standby generator that is also used during times when power is available from the utility.

If your engine is not an emergency generator, you must base maximum uncontrolled emissions on operating the engine 8,760 hours per year. Use the following equation:

  • Maximum Uncontrolled Emissions [tons/year] = Emission Rate [lb/hour] x 4.38 [(hrs/year) x (tons/lb)]

Step 5. Pollution Control Efficiency

The pollution control efficiency is the product of the capture efficiency and the destruction/collection efficiency indicated on Form GI-05A or the appropriate form related to the permit you are applying for, or your existing permit.

If you are applying for Registration Permit Option D, the control efficiency is indicated on Form RP-D2. Enter this number here and remember to include on Form CD-05 a plan to demonstrate and maintain the destruction/collection efficiency (unless you are applying for Registration Permit Option D - in that case, Form CD-05 does not apply). The control efficiency should be expressed for each pollutant. If there is no control for a particular pollutant, indicate “zero” as the control efficiency.

Step 6. Maximum controlled emissions rate [lb/hr]

This is the maximum controlled emissions rate in lb/hr required in the first column of item 3e on Form GI-07. Use this method for the calculation:

  • Maximum controlled emissions rate (lb/hr) = Emission rate (lb/hr) x ([100 - Control Efficiency] ÷ 100)

Step 7. Maximum controlled emissions

Calculate the Maximum Controlled Emission in tons/year (tpy). Use this method for the calculation:

  • Maximum controlled emissions (tpy) = Maximum Uncontrolled Emissions (ton/yr) x ([100 - Control Efficiency] ÷ 100)

Step 8. Limited controlled emissions

(Skip this item if applying for Registration Permit Option D.)

The limited controlled emissions are calculated by taking into account all limitations on operation of the source that you are proposing to comply with in this application. These limitations include limits on hours of operation, on the amount of fuel combusted, etc. You start the calculation of Limited Controlled Emissions by repeating the calculation of Emission Rate (Step 3) but taking into account the limits you propose.

If an emission unit is subject to an emission limitation specified in 40 CFR pt. 60, 40 CFR pt. 61, 40 CFR pt. 63 or Minn. R. ch. 7011, you must show this requirement in the calculation of Limited Controlled Emissions and take this into account in calculating the Limited Controlled Emissions. If you choose to propose to comply with more a stringent limit, you should state this clearly and show the resulting allowed emissions in this calculation.

Step 9. Actual Emissions

If this is an existing unit and historical records exist, calculate actual emissions using the average of the previous two calendar years of usage data, or average the previous two emission inventory reports if an inventory was submitted. (Note: If you are calculating actual emissions for Registration Permit Option D, you may base this calculation on the previous 12 months of operation.) 

If this is a new unit or no records exist, use a reasonable estimate of how many hours the unit will be operated, how much fuel will be used, etc. Report actual emissions in tons/year. Calculate actual emissions using one of the following methods:

If the emission factor is in units of pounds per quantity of fuel (gallons or cubic feet):

  • Actual emissions (tpy) = Emission Factor (lb/unit) x Actual Annual Fuel Use (unit) x ([100 - Control Efficiency] ÷ 100)

If the emission factor is in units of pounds per hp-hr power output or pounds per MMBtu heat input:

  • Actual Emissions (tpy) = Emission Rate [lb/hr] x Actual Operating Hours [hr] x 0.005 [ton/lb] x ((100 – Control Efficiency)/100)