Fuel Quality Calculator

Cummins Westport natural gas engines can operate on CNG, LNG or biomethane that meets Cummins published fuel specifications.

Pipeline natural gas fuel quality can vary on a regional and seasonal basis. LNG fuel quality may change if it is held in storage for extended periods of time. Check with your fuel provider regularly to ensure that natural gas fuel quality, in particular, the methane number, meets engine requirements.

Minimum Methane Number
The minimum methane number requirement for Cummins Westport engines is:

  • C Gas Plus, B Gas Plus, and L Gas Plus:  65 
  • ISL G, ISX12 G, ISB6.7 G, and all 2018 engines: 75 

History and Methodology
Before November 2015, Cummins Westport’s fuel quality calculator used a Methane Number (MN) calculation based on the Society of Automotive Engineers (SAE 922359 Eqn 4). In November 2015, this was changed to a Cummins Proprietary methane number calculation. The Cummins Proprietary calculation provides a more accurate representation of the true Methane Number of the fuel. We recognize that the two methods will result in different calculated methane numbers for a given fuel composition. However, we expect that this difference will be small and will not likely change the acceptability of most automotive natural gas fuel compositions.

If the calculated methane number of a specific fuel composition is just above or below the acceptable limit, please contact us to discuss. Hourly and daily variation in fuel composition may have a greater impact on the resulting methane number than the calculation method used. The Cummins proprietary methane number calculation is a numerical, regression-analysis based method using an extensive set of experimental test data. While neither this data or the resulting calculation can be shared, this fuel quality calculator can be used to determine methane number for a given fuel composition.

Using the calculator
This fuel quality calculator will help you check that your fuel meets the required specifications for use in the following Cummins Westport engines. 

ISX12N • L9N  B6.7N  ISX12 G • ISL G • ISB6.7 G  L Gas Plus • C Gas Plus •
B Gas Plus

Fill in the Fuel Composition values so that the total equals 100%. Results are calculated automatically. Methane Number, Lower Heating Value, and Sulfur Content criteria must be met to pass a given fuel for a specific engine.

Sample Name:
All values should be entered as mole %, unless otherwise noted
Methane, CH4 %
Ethane,C2H6 %
Propane, C3H8 %
i-Butane, C4H10 %
n-Butane, C4H10 %
i-Pentane, C5H12 %
n-Pentane, C5H12 %
n-Hexane, C6H14 %
n-Heptane, C7H16 %
n-Octane, C8H18 %
n-Nonane, C9H20 %
n-Decane, C10H22 %
Hydrogen, H2 %
H2S ppmv
Carbon Monoxide, CO %
Carbon Dioxide, CO2 %
Nitrogen, N2 %
Oxygen, O2 %
Siloxanes, Si %
Sulfur, S2 % weight
Sample Percentage
MN Rich Burn


  1. The minimum methane number requirement for the C, B and L Gas Plus engines is 65 or greater.
  2. The ISX12 G, ISL G, ISLG NZ, ISB6.7 G, ISX12N, L9N, and B6.7N require a minimum methane number of 75 or greater.
  3. The minimum Lower Heating value (LHV) for 2018 EPA/CARB certified
    Cummins Westport engines is 19,000 btu/lbm. This LHV is also recommended for engines manufactured prior to 2018, however the previous LHV of 16,100 btu/lbm may still be used.
  4. The maximum Hydrogen value is 0.03%.
  5. The maximum H2S value is 6 ppmv.
  6. The maximum allowable sulfur content is no greater than 0.001% in weight (10 ppm weight).
  7. The maximum allowable siloxane is 0.0003% volume.
  8. Gas with chlorine additives are not permitted.
  9. Fuel must not contain water, dust, sand, dirt, oils, or any other substance that can harm engine operation.

Green   Pass:  Fuel composition acceptable.

Amber   Pass:  Fuel composition acceptable, but methane number is close to minimum specification. Be aware of potential variations in fuel composition as described above.

Red   Fail:  Fuel composition does not meet Cummins Westport requirements.