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A set of model fuels has been designed, using the Major-Component Fuel approach, to represent a range of gasoline mid-range and back-end volatilities. The thermo-physical properties of the model fuels have been used, together with a simple model of inlet system, to calculate liquid-vapour mass fractions in the inlet system, and the composition of the inlet port wall film. This has enabled the effects of gasoline volatility, speed, load and inlet port wall temperature to be studied systematically. The results indicate that, in cold start, only some 20-30% of the injected fuel is vapourised in the inlet port, leading to an accumulation of liquid fuel in the inlet port wall film reservoir. As the engine warms up, the mass of fuel in the reservoir decreases, and its composition changes, becoming progressively richer in heavy end species. Mid-range volatility affects the cold start behaviour, whilst back-end volatility affects the approach to fully-warmed up operation.

The effects of injection system design, air/fuel ratio, coolant temperature and fuel volatility on engine-out hydrocarbon emissions, NOx emissions and cyclic variability have been studied in a prototype 1.8l lean-burn SI engine. The results have been compared with ILIDS measurements of in-cylinder spray characteristics made under similar conditions, to establish the degree to which variations in fuel spray formation correlate with engine performance. The lean-burn engine and the methodology of the combined study are described. The engine was found to exhibit a different behaviour when running lean compared to stoichiometric. When running lean, there was a negative correlation between steady-state engine-out NOx emissions and cyclic variability (COV of IMEP), and a positive correlation between steady-state engine-out hydrocarbon emissions and cyclic variability.

The effects of injection system design, air/fuel ratio, coolant temperature and fuel volatility on engine-out hydrocarbon emissions, NOx emissions and cyclic variability have been studied in a prototype 1.8l lean-burn SI engine. The results have been compared with ILIDS measurements of in-cylinder spray characteristics made under similar conditions, to establish the degree to which variations in fuel spray formation affect engine performance. The engine was found to exhibit a different behaviour when running lean compared to stoichiometric. In lean-burn operation, there was a clear tendency for the best performance to occur under operating conditions which produced charge stratification in the cylinder, whereas when the engine was run with a stoichiometric air/fuel ratio, the best performance was achieved under engine operating conditions which gave the most homogeneous charge in-cylinder.