Flammable fluid reservoir

An aircraft engine, comprising:

• a source of a flammable fluid which pressurizes the flammable fluid to a pressure during an operational condition of the aircraft engine;
• an air source that operates at a pressure that is lower that the pressure of the flammable fluid during the operational condition of the aircraft engine;
• and
• a heat exchanger comprising a reservoir, the reservoir containing the flammable fluid, the reservoir including;
• a wall circumscribing an inner chamber containing the flammable fluid;
• an inlet to the inner chamber, the inlet fluidly connected to the source of the flammable fluid and flowing the flammable fluid into the inner chamber;
• an outlet from the inner chamber, the outlet flowing the flammable fluid out of the inner chamber;
• and
• a valve selectively fluidly connecting the inner chamber to the air source, the valve being movable between a closed position in which the valve blocks air from the air source from entering the inner chamber during an operational state of the aircraft engine in which the pressure of the flammable fluid in the inner chamber acting on the valve exceeds the pressure of air from the air source acting on the valve, and an open position in which the valve allows the air to flow into the inner chamber and evacuate the flammable fluid from the inner chamber through the outlet during a shutdown state of the aircraft engine in which the pressure of the flammable fluid in the inner chamber acting on the valve is lower than the pressure of the air from the air source acting on the valve.