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Previously reported studies of heat transfer between the intake port surface, gas flows in the port, and fuel deposited in surface films have been extended to examine details of the heat flux variations which occur within the engine cycle. The dynamic response characteristics of the surface-mounted heat flux sensors have been determined, and measured heat flux data corrected accordingly to account for these characteristics. Details of the model and data processing technique used are described. Corrected intra-cycle variations of heat transfer to fuel deposited have been derived for engine operating conditions at 1000 RPM covering a range of manifold pressures, fuel supply rates, port surface temperatures, and fuel injection timings. Both pump-grade gasoline and isooctane fuel have been used. The effects of operating conditions on the magnitude and features of the heat flux variations are described.

Surface heat transfer measurements have been taken in the intake port of a single cylinder four valve SI engine running on isooctane fuel. The objective has been to establish how fuel characteristics affect trends in surface heat transfer rates for a range of engine operating conditions. The heat transfer measurements were made using heat flux gauges bonded to the intake port surface in the region where highest rates of fuel deposition occur. The influence on heat transfer rates of the deposited fuel and its subsequent behaviour has been examined by comparing fuel-wetted and dry-surface heat transfer measurements. Heat transfer changes are consistent with trends predicted by convective mass transfer over much of the range of surface temperatures from 20°C to 100°C. Towards the upper temperature limit heat transfer reaches a maximum limited by the rate and distribution of fuel deposition.

Experimental studies of fuel utilisation during the early stages of engine warm-up after cold-starts are reported. The investigation has been carried out on a 1.81, 4 cylinder spark-ignition engine with port electronic fuel injection. The relationship between fuel supplied and fuel accounted for by the analysis of exhaust gas composition shows that a significant mass of fuel supplied is temporarily stored or permanently lost. An interpretation of data is made which allows time-dependent variations of these to be separately resolved and estimates of fuel quantities made. The data covers a range of cold-start conditions down to -5°C at which, on a per cylinder basis, fuel stored peaks typically at around 0.75g and a total of 1g is returned over 100 seconds of engine running. Fuel lost past the piston typically accounts for 2g over 200 to 300 seconds of running.

Fuel losses to the crankcase, fuel/oil interactions, and fuel return as unburned hydrocarbons in the breather flow have been investigated. Hydrocarbons in the breather flow have been measured during motored and firing engine operation over a range of temperatures. Fuel desorption from the sump oil accounts for a small proportion of this. The major source is hydrocarbons transported past the piston with blowby. After a cold start, around 85% of these are retained in oil films below the ring pack. The recirculation of oil from the films to the sump contributes to bulk oil dilution. This appears to be the prime mechanism by which fuel is lost to oil dilution during cold operation. The mechanism becomes less effective as engine warm-up progresses. At fully-warm oil temperatures (∼100°C), only about 5% are removed from the blowby.