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An experimental, fuel-vaporization system has been designed and installed in the intake systems of three port-injected, gasoline engines. Baseline, cold-start testing was undertaken using manufacturers' calibrations, where appropriate, in conjunction with standard, production fuelling systems. When vaporized fuelling was used, fuel enrichment was reduced to the lowest levels consistent with stable operation. In some cases this was achieved by altering the input signals to the engine's control unit; in other cases a programmable fuelling control system was used. This paper presents details of the design of the fuel prevaporizers and the operating temperatures and power consumption required to achieve complete fuel evaporation. Reductions in HC emissions which can be achieved by using prevaporized gasoline during cold-cranking and warm-up phases of engine operation are also reported. The response of the fuel prevaporizer to sudden changes in fuel flow has also been investigated.