Emissions of regulated pollutants from a spark ignition engine. Influence of fuel and air/fuel equivalence ratio.

A spark ignition engine is used to determine the influence of fuel composition and air/fuel equivalence ratio on the exhaust emissions of regulated pollutants. Two specific fuel matrices are used: the first contains eight hydrocarbons and the second contains four oxygenated compounds. A specific experimental design is used for these tests. Fuel aromatics increase the exhaust CO, HC, and NOx at stoichiometry, lean and rich conditions. Lambda is more important than fuel composition in the case of CO and HC. At stoichiometry, the addition of oxygenated compounds can decrease exhaust CO, HC, and NOx up to 30%, 50%, and 60%, respectively. Under these conditions, the addition of 5% of 2-propanol is the most effective for the reduction of CO, the addition of 20% of ethanol forthe reduction of HC, and this of 5% of methyl tributyl ester (MTBE) for the NOx. The addition of oxygenated compounds can decrease CO by 30% at lean conditions, while no decrease is observed at rich ones; HC and NOx can decrease up to 30% and 80%, respectively, under lean conditions and 50% under rich ones. At all lambda tested, exhaust NOx increases with the addition of 20% of 2-propanol.