The hydrogen in the hydrocarbon fuels

It is natural for us to compare hydrogen to other hydrocarbon fuels with which we are more familiar. All hydrocarbon fuels are molecular combinations of carbon and hydrogen atoms. There are thousands of types of hydrocarbon com-pounds, each with a specific combination of carbon and hydrogen atoms in a unique geometry.

The simplest of all hydrocarbons is methane, which is the principal constituent of natural gas. (Other components of natural gas include ethane, propane, butane and pentane as well as impurities.) Methane has the chemical formula CH₄, which means that each molecule has four hydrogen atoms and one carbon atom.

Other common hydrocarbons are ethane (C₂H₆), propane (C₃H₈) and butane (C₄H₁₀). These are all considered light hydrocarbons since they contain less than five carbon atoms per molecule and therefore have low molecular weight (a carbon atom is almost 12 times as heavy as a hydrogen atom).

Gasoline is composed of a mixture of many different hydro-carbons, but an important constituent is heptane (C₇H₁₆). Gasoline, diesel, kerosene, and compounds found in asphalt, heavy oils and waxes, are considered heavy hydrocarbons as they contain many carbon atoms per molecule, and therefore have high molecular weight.

Other chemical fuels include alcohols whose molecules combine an oxygen/hydrogen atom pair (OH) with one or more hydrocarbon groups. Common alcohol fuels are methanol (CH₃OH) and ethanol (C₂H₅OH). These may be blended with hydrocarbons for use in internal combustion engines.

Hydrogen is a nearly ideal fuel in terms of smog reduction when combusted. Hydrogen contains no carbon or sulphur, so no CO, CO₂ or SOx or soot is produced during combustion (although the combustion of lubricating oil may result in trace amounts). Hydrogen allows for leaner combustion, resulting in lower combustion temperatures and very low NOx emissions. Hydrogen is non-toxic so uncombusted hydrogen does not pose a direct health risk.

Hydrogen is an ideal fuel in terms of smog reduction.