ENGINE FUEL SYSTEM

CFM 56-3 ENGINE FUEL SYSTEM

The fuel delivery system provides the energy required for the engine thermodynamic process, supplies hydraulic power to the VBV, VSV and HPTCC control systems, provides hydromechanical amplification to the MEC and cools lubrication oil.
Fuel passes through the pump LP stage and the main oil/fuel heat exchanger and fuel filter. It then flows through the HP stage and into the MEC to pass through a pressurizing valve, flowmeter, fuel manifold and nozzles for combustion.

FUEL PUMP

The fuel pump pressurizes the fuel required for combustion and fuel-operated servo systems. It is mounted on the aft side of the AGB at the 8 o’clock position. The housing provides mounting surfaces for the MEC and main oil/fuel heat exchanger




FUEL FILTER


The replaceable filter element is made of paper and has a filtering capability of 20 microns. Fuel circulates from the outside to the inside of the cartridge. There is a bypass valve installed on the pump in case of filter clogging.





SERVO FUEL HEATER



The servo fuel heater heats the fuel to eliminate ice particles that might damage sensitive control servos inside the MEC. It is mounted on the aft side of the main oil/ fuel heat exchanger and consists of a housing containing a heat exchanger core.

The servo fuel heater is an exchanger using engine scavenge oil as its heat source. The hot scavenge oil first goes through the servo fuel heater to heat the fuel going to the MEC servos. It then goes to the main oil/fuel heat exchanger to be cooled.

MEC (Main Engine Control)


The MEC is a hydromechanical device that is basically a speed governor with refinements to provide automatic speed adjustments. It is mounted on the fuel pump, at approximately the 8 o’clock position, on the aft end of the AGB.

The MEC is hydromechanical and uses fuel operated servo valves. Engine speed control is effected by controlling fuel flow to maintain flight deck speed settings and establishing the maximum safe fuel limit under any operating condition.

The MEC establishes a fule flow (P6) to the Compressor inlet Temperature (CIT) sensor with a return (Pb) to the control. The differential fuel pressure ( P6 - Pb ) is proportional to (T2.5) .

The MEC establishes schedules for VSV and VBV positioning.

The MEC establishes a schedule for the TCCV as a function of N2 speed. This then regulates the airflow of 5th and 9th stage compressor bleed air to the High Pressure Turbine (HPT) shroud support.
The MEC establishes a fuel flow (P7) to the (T2.0) sensor with a return (Pb) to the control. the differential fuel pressure (P7-Pb) is a proportional to (T2.0).

Reff : CFM56-3 Training Manual - CFM The Power Of Flight