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Evaporative and tailpipe emissions from a 1987 GM Corsica with adaptive learning closed loop control were measured with six fuels and four temperatures. Measured emissions were total (THC) and speciated hydrocarbons, aldehydes, ethanol, MTBE, benzene, 1,3-butadiene, CO, and NOx. Tests were also performed to determine the effect of air conditioning (AC) and oxygen sensor failure. In general, AC reduced Highway Fuel Economy emissions, increased FTP emissions, and reduced fuel economy for both test cycles. Oxygen sensor malfunction increased tailpipe emissions and fuel economy. Higher levels of regulated tailpipe emissions were generally produced at the low test temperature. None of the fuels tested appeared to offer a consistent reduction in tailpipe THC and CO emissions under the conditions tested.

Combustion of organic motor vehicle fuels produces carbon dioxide and water (H2O) vapor (and also products of incomplete combustion, e.g. hydrocarbons and carbon monoxide, at lower concentrations). The Constant Volume Sampling (CVS) system, commonly used to condition auto exhaust for sampling and analysis, provides for controlled ambient air dilution of the engine exhaust. Water condensation can be a problem during CVS system sample conditioning, depending upon vehicle fuel composition and fuel economy, and diluent air humidity and exhaust/diluent ratio. This paper describes a “spreadsheet” procedure for detailed, second by second, determination of diluted exhaust dew point and the necessary CVS system flow rates to avoid H2O vapor condensation.