Fuel from a tank 1 and heated fuel returning from the engine fuel injection device 18 are maintained under pressure in a vessel 6 so that fuel components which would otherwise vaporise remain liquid. Fuel, e.g. at 130 DEG C, drawn through a mixer is pumped through a heater 16 to raise its temperature to 150 DEG C. The vessel pressure is maintained substantially constant by a pump bypass valve 11 and a valve 9 vents gas from the vessel 6 in response to a predetermined liquid level. IMAGE
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