What would the Brayton cycle efficiency in Example 6.3 be if the pressure ratio was increased to 3.5?

Example 6.3

A jet engine needs to produce only enough net output power to drive the aircraft’s accessories (fuel pump, hydraulics, generator, etc.) and consequently it need not have a very high efficiency. The first successful Brayton cycle turbojet aircraft was the German Heinkel-178, which flew for the first time on August 27, 1939. The engine weighed 364 kg, produced a thrust of 1,100 lbf (4900 N) at 13,000 rpm, and had a compressor pressure ratio of 3.0. Determine its efficiency.

Need: The Heinkel WWII turbojet engine efficiency.

Know: The Brayton cycle efficiency is given by Equation (6.7).

How: The engine’s efficiency is given by Equation (6.7) as: η_Brayton = 1 – PR^-0.286