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A single-cylinder, two-valve engine was operated with independent cooling circuits for the engine block and cylinder head to investigate the effect of temperature distribution on HC emissions. The goal was to understand and quantify the mechanisms responsible for decreased HC emissions at elevated temperatures. Tests were run at a typical road load condition using two different fuels (a 97 RON blend and isopentane - to eliminate liquid fuel and oil layer absorption effects). The total HC emissions (97 RON fuel) decreased by 15-20% with an increase in either the cylinder head or engine block coolant temperature from 71 to 110 °C. When operating with isopentane the HC emissions decreased by 15-20% with an increase in the engine block temperature from 71 to 110 °C but were essentially unaffected by cylinder head temperature. This indicates that the cylinder head temperature primarily influenced the HC emissions from liquid fuel effects.

A 1990 Ford Taurus operated on reformulated gasoline was tested under three modes of malfunction: disabled heated exhaust gas oxygen (HEGO) sensor, inactive catalytic converter, and controlled misfire. The vehicle was run for four U.S. EPA UDDS driving schedule (FTP-75) tests at each of the malfunction conditions, as well as under normal operating conditions. An extensive set of emissions data were collected. In addition to the regulated emissions (HC, CO, and NOx), a detailed chemical analysis was carried out to determine the gas- and particle-phase non-regulated emissions. The effect of vehicle malfunction on gas phase emissions was significantly greater than it was on particle phase emissions. For example, CO emissions ranged from 2.57 g/mi (normal operation) to 34.77 g/mi (disable HEGO). Total HCs varied from 0.22 g/mi (normal operation) to 2.21 g/mi (blank catalyst). Emissions of air toxics (1,3-butadiene, benzene, acetaldehyde, and formaldehyde) were also significantly effected.

It is frequently useful to calculate the theoretical composition of the major components of vehicle exhaust. A software program has been written in Basic (or Quick Basic) which allows the convenient calculation of volume percents of CO, CO2, O2, H2, and H2O from fuel composition (H/C and O/C ratios), the water content (dew point) of the combustion air, and a chosen stoichiometry (air/fuel ratio). The program considers the Water Gas Shift reaction and the production of hydrogen under fuel rich conditions. The program is valid for both standard gasolines and oxygenated blends. Vehicle emissions data, collected to compare values calculated by the program with actual experimentally determined values from vehicle exhaust, show good agreement for measurements made at a series of air/fuel ratios ranging from lambda of 0.85-1.2.