A certain natural gas has the following volumetric analysis:...

A certain natural gas has the following volumetric analysis: 65 percent $\mathrm{CH}_{4}, 8$ percent $\mathrm{H}_{2}, 18$ percent $\mathrm{N}_{2}, 3$ percent $\mathrm{O}_{2},$ and 6 percent $\mathrm{CO}_{2} .$ This gas is now burned completely with the stoichiometric amount of dry air. What is the air-fuel ratio for this combustion process?

Key Concepts

Fuel Composition Analysis

Fuel composition analysis involves identifying and quantifying the reactive and inert components present in a fuel. In multi?component fuels, the reactive parts (such as hydrocarbons or hydrogen) determine the amount of oxygen required for combustion, while inert or non?combustible components do not participate directly in the combustion reaction but can influence the overall combustion process. This analysis is essential for accurately evaluating the stoichiometric requirements and calculating parameters like the air?fuel ratio.

Dry Air Composition

Dry air is primarily a mixture of oxygen and nitrogen, with oxygen accounting for roughly 21 percent and nitrogen about 79 percent by volume. In combustion calculations, it is important to consider dry air because the nitrogen, although inert under typical combustion conditions, dilutes the oxygen and must be factored into the overall mass and volume of the air needed for stoichiometric combustion.

Stoichiometric Combustion

Stoichiometric combustion is the ideal combustion process in which the fuel reacts completely with the exact amount of oxygen required, producing only the combustion products expected under complete combustion, without any leftover fuel or oxygen. This concept is crucial because it determines the amount of air or oxygen needed to achieve complete burning and is the basis for calculating combustion parameters such as the air-fuel ratio.

Air?Fuel Ratio

The air?fuel ratio is defined as the mass or volume of air needed per unit mass or volume of fuel for combustion. In combustion processes, this ratio is pivotal because it directly influences combustion efficiency, emissions, and overall energy release. Calculating the stoichiometric air?fuel ratio involves determining the exact amount of oxygen required to completely oxidize the fuel and then accounting for the inert components present in air.

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