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The performance of three way and NOx catalysts was evaluated on vehicles utilizing non-feedback fuel control and electronic feedback fuel control. The vehicles accumulated 80,450 km (50,000 miles) using fuels representing the extremes in hydrogen-carbon ratio available for commercial use. Feedback carburetion compared to non-feedback carburetion improved highway fuel economy by about 0.4 km/l (1 mpg) and reduced deterioration of NOx with mileage accumulation. NOx emissions were higher with the low H/C fuel in the three way catalyst system; feedback reduced the fuel effect on NOx in these cars by improving conversion efficiency with the low H/C fuel. Feedback had no measureable effect on HC and CO catalyst efficiency. Hydrocarbon emissions were lower with the low H/C fuel in all cars. Unleaded gasoline octane improver, MMT, at 0.015g Mn/l (0.06 g/gal) increased tailpipe hydrocarbon emissions by 0.05 g/km (0.08 g/mile).

Octane number requirement mapping of an 8:1 CR Ford 2.3 liter engine was carried out under dynamic conditions at 1″, 3″ and 6″ vacuum accelerations. Equations were developed relating octane number requirements to engine rpm, manifold vacuum, spark advance, air-fuel ratio, and exhaust gas recirculation rate. These equations, together with Ford's extensive emissions and fuel consumption data, were used to determine whether octane number requirements constitute a limiting constraint in the optimization of engine-vehicle systems. In addition, steady-state and dynamic octane number requirements were compared at 9:1 CR. The results indicate that dynamic octane number requirements cannot be predicted from limited steady-state requirements data.

Continued studies with full-scale engines in the laboratory have provided additional information about the parameters that affect ORI in today's cars. Reduced coolant temperature studies showed an average decrease in ORI of about two units in two popular make engines and no effect in a third make. Coolant temperature had no significant effect on exhaust emissions from any of the engines tested. Tests conducted on gasoline “tail” end properties showed that gasoline endpoint had no effect on ORI, while an increase in polycyclic nuclear aromatics increased it. A manganese antiknock additive reduced ORI in one make engine. Lube oil metal additive type and type of viscosity index (VI) improver affected ORI whereas, sulfated ash content did not affect it. A shortened laboratory test cycle produces ORI comparable to our previous laboratory procedure