# How to calculate methane number

Written by ryan menezes
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An engine's spark plug should ignite fuel, but additional fuel pockets sometimes combust, creating "knocking" in the engine. A fuel's methane number describes how likely it is to combust uncontrollably. Hydrogen receives a methane number of "0," and methane receives a number of "100." Other fuels lie elsewhere on this scale. Engineers measure a fuel's methane number experimentally, using an adapted engine. But when a fuel has a carbon-hydrogen ratio of at least 2.5, you can use that ratio to calculate its methane number.

Skill level:
Easy

## Instructions

1. 1

Determine your fuel's H/C ratio. You can calculate this with the chemical formula by dividing the number of hydrogen atoms by the number of carbon atoms, but heavier fuels will more likely be labelled by H/C ratio than by chemical formula. This example will use a fuel with an H/C of 3.72.

2. 2

Multiply the H/C by 508.04. So 3.72 * 508.04 = 1,889.9

3. 3

Square the H/C ratio. So 3.72 * 3.72 = 13.84

4. 4

5. 5

Find the cube of the H/C ratio:

3.72 * 3.72 * 3.72

= 51.48

6. 6

7. 7

Add the answers from steps 2, 4 and 6. 1,889.9 + -2,401.93 + 1,038.35 = 526.32

8. 8

9. 9

10. 10

This answer is the methane number.

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