EPR
 

What does EPR mean when applied to a FADEC system? Is it to do with measuring the torque/power output of a turbofan engine? Can I also confirm that N1 is fan speed and N2 is turbine shaft speed? Generally speaking.
Many thanks

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EPR=Engine Pressure Ratio

N1=Fan Speed RPM
N2=Second Stage RPM

What does EPR mean when applied to a FADEC system?"

Basically, EPR tells you how much thrust you have. The air pressure at the intake is sensed and the air pressure at the back of the engine is sensed and these two are combined to create a ratio (exhaust px / intake px). The expression, "EPR", is not limited to FADEC engines, by the way. EPR predates electronic engine control.

E.g. With the engine not turning, there is no air compression, no combustion, so no pressure rise. The difference between the front and back is zero. As a ratio, this is equal to an EPR of 1.0.

"Can I also confirm that N1 is fan speed and N2 is turbine shaft speed?

N1 does equal "fan" speed, but this is an oversimplification. It means the speed of the rotor the big fan is attached to. The rotor has many rows of blades. The rows of blades at the front end of the rotor are called "compressor stages". The ones at the back end of the rotor are called "turbine(or expansion) stages".

However, most jet engines have more than one rotor. On a multi-rotor engine, the big, visible blades at the front and back of an engine are usually N1 (fan) rotor blades. Smaller concentric rotors are usually labelled N2, N3, etc. They have compressor stages at the front and turbine stages at the back, just like the big N1 rotor.

Rgds.
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