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This paper describes an emissions study of two vans powered by compressed natural gas (CNG). One van was relatively new, while the other had been driven more than 120,000 mi. The purpose of the study was to obtain emissions information which could be used to predict the impact of CNG use on ambient air quality and air toxic concentrations, and to develop a better understanding of the effect of ambient temperature variations on CNG emissions. Using four different driving cycles, emission tests were carried out at 20°F, 75°F, and 105°F. Test results agree with previous findings that document low emissions of nonmethane hydrocarbons from CNG vehicles. Results also confirm the expectation that CNG emissions are not significantly affected by ambient temperature variations, although an increase in formaldehyde emission was noted for the 20°F cold-start tests.

In-use, light-duty vehicles were recruited in Cary, North Carolina for emissions testing on a transportable dynamometer in 1999. Two hundred forty-eight vehicles were tested in as received condition using the IM240 driving cycle. The study was conducted in two phases, a summer and winter phase, with half of the vehicles recruited during each phase. Regulated emissions, PM10, carbonaceous PM, aldehydes and ketones were measured for every test. PM2.5, individual volatile hydrocarbons, polycyclic aromatic hydrocarbons, sterane and hopane emissions were measured from a subset of the vehicles. Average light-duty gasoline PM10 emission rates increased from 6.5 mg/mi for 1993-97 vehicles to 53.8 mg/mi for the pre-1985 vehicles. The recruited fleet average, hot-stabilized IM240 PM10 emission rate for gasoline vehicles was 19.0 mg/mi.

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.

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.

A procedure using a porous polymer resin as a trapping medium, was developed and verified as a viable means for collecting gas phase hydrocarbons in the diesel fuel (C10 +) range. The method was then used in a series of diesel and gasoline powered passenger car studies aimed at comparing the gas phase with the particle-bound hydrocarbon mutagenic activity. A second objective was to compare the dilute exhaust polymer trapping method with the cold water raw exhaust trapping system. The VW Rabbit diesel studies showed the gas phase activity to be less than 11% that of the particle-bound with the activity relationship depending upon the test cycle. The gasoline studies showed the gaseous hydrocarbon activity to be at or near background level. A comparison of the particle-bound activity from the diesel and gasoline engines showed the gasoline emissions activity, reverents per mile, to be less than 12% that of the diesel emissions.