The Effect of Fuel Composition, Equivalence Ratio, and Mixture Temperature on Exhaust Emissions

A single-cylinder research engine was operated on pure hydrocarbons (HC) and simple mixtures of pure hydrocarbons to study the effect of fuel composition, equivalence ratio, and mixture temperature on exhaust emissions. Used as fuel components were hydrocarbons-n-pentane, 2-methyl-2-butene, isooctane, and m-xylene.

Total hydrocarbon emission in terms of moles of exhaust HC/mole of fuel input was lowered by increasing the amount of xylene in the fuel when operating on the fuel-rich side of stoichiometric; total hydrocarbon emission was higher for higher aromatic fuels when air-fuel ratios approached the lean misfire limit; the effect of mixture temperature on hydrocarbon emission was insignificant.

1-Methyl-3-ethylbenzene was observed as a synthesis product of combustion in the exhaust from fuels containing m-xylene. With increasing m-xylene concentration in the fuel, the yield of 1-methyl-3-ethylbenzene increases, reaches a maximum, and then decreases. The effect of equivalence ratio is to shift this maximum point toward lower aromatic fuels as the fuel-air mixture is leaned out.