Laboratory and Vehicle Studies of Aldehyde Emissions from Alcohol Fuels

Laboratory and vehicle studies were carried out characterizing formaldehyde emissions from methanol fuels. Laboratory experiments focused on catalytic methanol oxidation activity and yield of formaldehyde as a function of temperature and feedgas composition. Pt and Pd catalysts gave the highest activity and lowest formaldehyde yield of a series of noble and base metal catalysts. Formaldehyde yields were lowest under stoichiometric or slightly rich conditions. Experiments carried out with thermally aged lead poisoned catalysts indicated at most about 5% conversion of methanol to formaldehyde, thus proving that catalytic partial oxidation of methanol is not a major source of tailpipe formaldehyde emissions. Nevertheless, FTP emission tests on a 3.0L FFV Taurus with production three-way converters showed significant mileage related increases in formaldehyde emissions from 14 mg/mile for a fresh catalyst (4,000 simulated miles) to 17 mg/mile for a 50,000 simulated mile catalyst and 30 mg/mile for a 100,000 mile in-use catalyst tested with 100,000 mile oxygen sensor. Additional laboratory experiments were carried out on a pulse flame combuster examining the effects of combustion temperature and air/fuel ratio on unburned methanol and formaldehyde emissions.