Operation Manual Part 2

Aerosoft – Digital Aviation
CRJ-70 & CRJ-900
AOM PART 2
Systems Description
VOL
5
5-1-114
26-Jul-2017
POWER PLANT
Two General Electric CF34-8C5 engines provide 13,600 pounds of thrust each. In case one engine fails, the
automatic power reserve (APR) function will increase thrust on the remaining engine to 14,510 pounds. The
engine operation and thrust is controlled by the so called FADEC: full authority digital electronic control
system. Like all turbo-fan engines the CF34 is comprised of 6 sections:
- Intake
The air intake has a certain geometry which is supposed to optimise the air flow into the engine and
towards the fan.
- Fan
The fan works like a huge propeller and accelerates the air. After passing the fan, the airflow is
divided into two parts: one part is going through the core engine and the other part is passing the
core engine and reunites in the exhaust with the airflow from the core engine. The bypass ratio
indicates how much of the air-flow passes the core engine while the remainder passes the core
engine. The CF34’s bypass ratio is 5:1 – 5 parts pass the core engine and 1 part passes through the
core engine.
- Compressor
Several compressor stages are supposed to increase the pressure of the airflow to the possible
maximum. Stator vanes with variable geometry prevent the airflow from stalling. A compressor stall is
a serious incident which might destroy the engine and accordingly endanger the flight.
Normally bleed air is drawn from the compressor.
- Combustion chamber
The compressed air is injected with fuel and then lit. The following ‘explosion’ increases pressure
further and thus enables the engine to create thrust even though some of the energy is consumed by
the following turbine
- Turbine
The turbine section is very important as transforming the airflow into rotational energy which
basically makes the engine ‘run’ and propels the forward sections like the fan and compressor.
- Exhaust
The exhaust is important to optimize the airflow leaving the engine and hence creating thrust.
Usually the engine’s components are built on two shafts which are connected, that’s why the engine
instruments display two RPM values: N
1
and N
2
.
N
1
indicates the first stages ratio of the current RPM compared to the maximum RPM. The first stage
comprises the fan and the aft parts of the turbine section.
N
2
indicates second stages ratio of the current RPM compared to the maximum RPM. The second stages
comprise the compressor and forward parts of the turbine section. Several engine-subsystems are connected
to the second stage by means of a gearbox:
- Engine lubrication pump and integral oil reservoir
- FADEC alternator
- Hydraulic pump
- Engine fuel pump and metering unit
- Integrated drive AC generator
- Air turbine starter