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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.

Experimental studies have been carried out on a spark ignition engine with port fuel injection to examine the influence of injector type and to contrast this with the effects of fuel composition. Intake port fuel transport characteristics and engine-out emissions for fully-warm and warm-up engine operating conditions have been examined as indicators of performance. The investigation has encompassed four types of injector and five gasoline blends. Fuel transport has been characterised using the τ and X parameters. The influence of injector type on these is of similar significance as that of changes in gasoline composition between summer and winter grades. The latter will limit the in-service accuracy of open-loop mixture control during transients. Injector type has a small effect on engine-out emissions under fully-warm operating conditions but has a significant influence on emissions during the early stages of warm-up.