# How to Calculate Methane Number

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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.

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 labeled by H/C ratio than by chemical formula. This example will use a fuel with an H/C of 3.72.

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

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

Multiply your answer by -173.55. So 13.84 * -173.55 = -2,401.93

Find the cube of the H/C ratio:

3.72 * 3.72 * 3.72

\= 51.48

Multiply your answer by 20.17. So 51.48 * 20.17 = 1,038.35

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

Subtract 406.14 from your answer. 526.32 - 406.14 = 120.18

Multiply your answer by 1.624. So 120.18 * 1.624 = 195.17

Subtract 119.1 from your answer. 195.17 - 119.1 = 76.07

This answer is the methane number.

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The passage provides a detailed method for calculating the methane number of a fuel based on its hydrogen-to-carbon (H/C) ratio, including a step-by-step example calculation.
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First, describe the content structure you found in 1-2 sentences.

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# How to Calculate Methane Number

••• gas pump image by jedphoto from Fotolia.com
Print

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.

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 labeled by H/C ratio than by chemical formula. This example will use a fuel with an H/C of 3.72.

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

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

Multiply your answer by -173.55. So 13.84 * -173.55 = -2,401.93

Find the cube of the H/C ratio:

3.72 * 3.72 * 3.72

\= 51.48

Multiply your answer by 20.17. So 51.48 * 20.17 = 1,038.35

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

Subtract 406.14 from your answer. 526.32 - 406.14 = 120.18

Multiply your answer by 1.624. So 120.18 * 1.624 = 195.17

Subtract 119.1 from your answer. 195.17 - 119.1 = 76.07

This answer is the methane number.

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The passage provides a detailed method for calculating the methane number of a fuel based on its hydrogen-to-carbon (H/C) ratio, including a step-by-step example calculation.

TYPE: SINGLE_QUESTION_WITH_ANSWER