In an HFO service system, what is the immediate destination of the fuel unconsumed by the main propulsion diesel engine?

Correct Answer: Option C — The unconsumed fuel is recirculated back to the mixing tank (if fitted) or to the day tank.

Heavy fuel oil systems circulate excess heated fuel through the engine injection headers to maintain stable viscosity. Unconsumed fuel returns directly to the day tank or mixing tank to prevent thermal shock and vapor binding in the booster circuit.