Question

The stoichiometric ratio of methane is higher than gasoline or diesel fuel because 
1. methane has a lower percentage of hydrogen
2. methane has a higher percentage of carbon
3. methane easily mixed with air
4. methane has higher percentage of hydrogen

Answer 1

Correct Answer - Option 4 : methane has higher percentage of hydrogen

Concept:

For a general hydrocarbon with ‘A’ hydrogen atoms per carbon molecule, combustion with oxygen is given as

CH_A + (1 + 0.25A) O₂ → CO₂ + 0.5A H₂O

Now the stoichiometric ratio is ratio of air to fuel which is 1 + 0.25A

∴ Stoichiometric ratio is directly dependent on number of hydrogen atoms per a carbon molecule in a fuel.

The exact chemical composition of gasoline varies depending on its grade or octane rating, but generally speaking it is a mixture of combustible hydrocarbons. This octane rating describes the quality of the fuel, so octane itself is the highest quality of gasoline which is C₈H₁₈

The average chemical formula for common diesel fuel is C₁₂H₂₄, ranging approximately from C₁₀H₂₀ to C₁₅H₂₈.

Chemical formula for methane is CH₄

It is clearly evident that methane has the higher percentage of hydrogen hence higher stoichiometric ratio.