No abstract

A spark ignition engine was used to study the impact of fuel composition and of the air/fuel equivalence (lambda) ratio on exhaust emissions of alcohols and aldehydes/ketones. Fuel blends contained eight hydrocarbons (n-hexane, 1-hexene, cyclohexane, n-octane, isooctane, toluene, o-xylene, and ethylbenzene (ETB)) and four oxygenated compounds (methanol, ethanol, 2-propanol, and methyl tert butyl ether (MTBE)). Exhaust methanol is principally produced from fuel methanol and MTBE but also from ethanol, 2-propanol, isooctane, and hexane. Exhaust ethanol and 2-propanol are produced only from the respective fuel compounds. Exhaust formaldehyde is mainly produced from fuel methanol, acetaldehyde from fuel ethanol, and propionaldehyde from straight-chain hydrocarbons. Exhaust acroleine comes from fuel 1-hexene, acetone from 2-propanol, n-hexane, n-octane, isooctane, and MTBE. Exhaust crotonaldehyde comes from fuel 1-hexene, cyclohexane, n-hexane, and n-octane, methacroleine from fuel isooctane, and benzaldehyde from fuel aromatics. Light pollutants (C1-C2) are most likely formed from intermediate species which are quite independent of the fuel composition. An increase in A increases the exhaust concentration of acroleine, crotonaldehyde, methacroleine, and decreases these of the three alcohols for the alcohol-blended fuels. The concentration of methanol, formaldehyde, propionaldehyde, and benzaldehyde is a maximum atstoichiometry. The exhaust concentration of acetaldehyde and acetone presents a complex behavior: it increases in some cases, decreases in others, or presents a maximum at stoichiometry. The concentration of four aldehydes (formaldehyde, acetaldehyde, propionaldehyde, and benzaldehyde) is also linked with the exhaust temperature and fuel H/C ratio.

No abstract

A spark ignition engine is used to study the impact of fuel composition and of the air/fuel equivalence ratio on exhaust emissions of organic acids. Fuel blends are composed from eight hydrocarbons (n-hexane, 1-hexene, cyclohexane, n-octane, 2,2,4-trimethylpentane, toluene, o-xylene, and ethylbenzene) and four oxygenated compounds (methanol, ethanol, 2-propanol, and MTBE). Exhaust formic acid is slightly enhanced from aromatics and oxygenated compounds; acetic acid is slightly enhanced from the oxygenated fuel components; propionic acid comes from fuel aromatic compounds, and butyric acid originates from fuel o-xylene. Acrylic and isovaleric acids are also detected in lower concentrations. It is unlikely that oxygenated compounds are precursors to the formation of organic acids, but they facilitate their formation because they facilitate the oxidation of other fuel components. Exhaust concentration of formic acid is also related to exhaust oxygen and exhaust temperature. Air/fuel equivalence ratio increases the exhaust concentration of formic, acetic acid (for the fuels without oxygenated compounds), and acrylic acid and decreases the concentration of isovaleric acid. The acetic (for the oxygenated fuels), propionic, and butyric acids are at a maximum at stoichiometry.