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Statistically designed experiments were run in a single-cylinder engine to understand the reason for the decrease in exhaust mass HC emissions found in the Auto/Oil Program with decreasing 90% distillation temperature (T90) of gasoline. Besides T90, the effects of mixture preparation, equivalence ratio, and ambient temperature on emissions and fuel consumption were measured. HC emissions were higher with PFI than with premixed charge, but decreasing T90 decreased HC emissions with both premixed charge and PFI. Rich mixture and low ambient temperature increased HC emissions. Speciated exhaust HC measurements indicate that incomplete vaporization of heavy components of the gasoline (C8-C10 alkanes, C6-C9 aromatics and alkenes) was responsible for higher HC emissions.

A unique, temperature controlled, single-cylinder engine test facility was designed and constructed to simulate cold starting of a car engine. The temperature of the coolant, oil, fuel and air used by the engine can be individually controlled to -29°C. Moreover, the engine is enclosed in a temperature controlled insulated chamber. With this facility the conditions that occur in a car engine as it cranks and starts, can be quickly duplicated and maintained for detailed study. The supply equivalence ratio values for starting the engine were determined using either gasoline with port fuel injection or propane as a premixed charge. For gaseous propane, the supply equivalence ratio for starting was nearly constant at all temperatures studied. However, for gasoline the supply equivalence ratio for starting increased as the temperature was lowered. The significance of these findings is discussed.

Single-cylinder spark ignition engine experiments conducted at constant speed, fixed airflow, and using isooctane as the fuel, demonstrated the effects of fuel-air mixture preparation on lean operation. Mixture preparation was changed by varying the time of fuel injection in the induction manifold, near the intake valve port. For comparison, a prevaporized fuel-air mixture was also investigated. Emphasis was placed on determining the effects of mixture preparation on combustion characteristics. Based on the results from this study, the often favored prevaporized mixture of fuel and air may not be the best diet for lean engine operation.

Statistically designed experiments with a port fuel injected, single-cylinder engine were run to determine the effects of injector-, engine-, and fuel-related variables on exhaust smoke and hydrocarbon (HC) emissions. Among injector-related variables, targeting the fuel spray at the inlet valve centerline toward the valve head resulted in low smoke and HC emissions. These factors apparently help break up the fuel spray and they help subsequent vaporization of the fuel droplets. Among engine-related variables, high coolant temperatures and lean mixtures resulted in less smoke and HC emissions, probably because of better fuel vaporization. Gasolines with aromaticity and 90% point close to the maximum of the ranges of commercial gasolines significantly increased HC and smoke emissions compared with gasolines representing the average or minimum values, of these ranges.