the GE90 is the world's most powerful commercial jet engine in service the Boeing 777 the best-selling
wide-body aircraft of all time the combination of the engine and the airframe is nothing short of an engineering marvel in this comprehensive 777 engine series we will build up the engine from scratch and understand how all the components
function as we start and operate it the engine has two rotor shafts high
pressure shaft and the low pressure shaft a stator and a rotor combine to form
a single stage the N2 shaft has nine such stages of high pressure compressors and two stages of high pressure turbine the N1 shaft has six stages
of low pressure turbine four stages of low pressure compressors and ahead of them is the massive fan before we look at more engine components let's
do the aircraft configuration for engine start first the battery switch battery provides limited
power good enough to start the APU a small engine in the empennage of the aircraft rotate the
APU start switch hold for a second and release the APU is online now we can use the APU generator selecting the generator switch establishes
full electrical power of the aircraft during engine start electrical panels
will provide power to the electronic engine control installed on the engine fan case APU will also provide the
pneumatic power to start the engine make sure the bleed switch is in auto position next the fuel panel selections we only
require fuel from the left main tank so select the two left tank pump switches two boost pumps inside the
fuel tank transfer fuel to the engine spar valve in the wing aft spar section aircraft configuration is complete let's attempt an engine start on the engine the pneumatic
pressure reaches the start valve 777 has an auto start feature when used the EEC
takes over the entire engine start operation now turn the engine start switch to start position EEC gets the start signal and power to operate EEC commands the start valve to open the
pneumatic pressure reaches the air starter the air starter drives the accessories gearbox several torque requiring components are mounted on the gearbox one of them is the horizontal
drive shaft that connects to the transfer gearbox the transfer gearbox changes the axis of rotation and with the help of a radial drive shaft rotates the N2 shaft as N2 rises airflow is established
through the core of the engine due to the airflow N1 shaft has positive rotation fan rotation in
turn leads to bypass airflow through the engine at 7 percent N2 a small alternator
installed on the gearbox supplies power to the EEC and the airplane power
supply goes into standby mode since we are doing an auto start we
can use the fuel control switch and need not wait for the engine to reach
21 percent N2 which is the case in manual start let's select the fuel control switch to run and see how the fuel travels within the engine the fuel control switch opens the spar valve and the fuel rushes to the main fuel pump the pump driven by the gearbox increases the
fuel pressure and transfers it to the fuel oil heat exchanger where fuel picks up heat and
cools down the engine oil from the heat exchanger fuel travels to the fuel filter filter screens the
fuel for debris and transfers it back to the pump from here the fuel is sent to the hydro
mechanical unit the HMU now controls the fuel to the engine for combustion and any excess
fuel is bypassed back to the pump HMU waits for the EEC command to open the fuel shut-off
valve and EEC waits for N2 to reach 21 percent as N2 reaches 21 percent rpm EEC sets
up the engine for combustion out of two ignition exciters EEC commands
one to activate keeping the other as backup the ignition exciter converts
the input power to high voltage pulse and transfers it to the igniter plug three seconds after ignition activation EEC
commands the HMU to open the fuel shutoff valve before heading to the combustion
chamber fuel travels through the fuel flow transmitter and back into the HMU fuel
flow transmitter sends signal to the EEC to determine engine fuel consumption which is
crucial for engine performance monitoring fuel is now sent for combustion through two
manifolds to which are connected 30 fuel nozzles each fuel nozzle has two sprayer tip and each tip goes into the swirler slots in the combustion chamber the swirlers
diffuse the core airflow slowing them down ensuring proper fuel air mixture and
buying enough time for efficient combustion combustion gas forces directly affect the turbines since they are mounted on the same shaft increase in high pressure turbine rotation drives the
high pressure compressor at a faster rate likewise increase in low pressure turbine rotation drives the low pressure compressor and the fan as a result the rate of airflow through the engine
increases leading to steady increase in thrust temperatures inside the combustion
chamber is adequate for sustained combustion therefore at 56 percent N2 the
EEC deactivates the ignition system at about 64 percent N2 the EEC commands the start
valve to close and the pneumatic pressure to the starter is cut out disengaging
the air starter from the gearbox rotation as the engine reaches and stabilizes at
the idle power EEC sends a signal to the airplane systems that the engine
start procedure is now complete this allows the airplane systems to
de-energize the start switch latching solenoid so that it could return to normal position ready for next start attempt when required join us in the next part of the 777 engine series as we continue to put the engine through its paces thanks for watching