Emissions
Since hydrogen is not a fossil fuel, it contains no carbon molecules. Therefore, the products of combustion could not contain any carbon dioxide (CO2), carbon monoxide (CO), or other carbon compounds as seen in conventional internal combustion engines fueled by gasoline, diesel, or natural gas. The primary product of combustion for hydrogen would be water (H20) if stoichiometrically combusted. The stoichiometric air to fuel (A/F) ratio for hydrogen (H2) combusted in one molecule air is about 34. If the A/F ratio is less than this theoretical value the fuel/air mixture would be considered rich. If the the A/F ratio is greater than the theoretical value the fuel/air mixture would be considered lean. In both situations, other combustion products are possible because either the air or fuel quantity (or both simultaneously) involved in the combustion process is different than the theoretical amount needed. The only reactants for combustion are hydrogen (H2) and air which consists mainly of oxygen (O2) and nitrogen (N2). Therefore, the products of combustion can only contain compounds made up of the reactants. Nitrogen oxides (NOx) are another possible product from the combustion of hydrogen in air.
