Question 1Â
(a) In the field of aerospace propulsion, define the terms propulsive efficiency ηP, thermal efficiency ηT and overall engine efficiency ηO.
(b)
(i) From the definition of overall engine efficiency ηO, develop an expression for it in terms of aircraft velocity V0 and the TSFC. Show the steps clearly and
provide a glossary of terms used.
(ii) Using this expression, explain the effect of increasing aircraft speed on the
engine overall efficiency, assuming the engine is ideal.
(c) For an ideal turbojet engine, analyze how the overall engine efficiency and TSFC would change with compressor pressure ratio. Illustrate with relevant thermodynamic equation(s) and a graphical sketch.
Question 2
Consider an ideal turbojet engine operating under the following conditions:
Taking into consideration the effects of fuel mass flow on engine thrust, evaluate the following:
(a) Net thrust.
(b) Specific thrust.
(c) Power output of the engine.
(d) Engine thermal efficiency.
(e) Propulsive efficiency and overall engine efficiency
(f) Thrust-specific fuel consumption.
(g) Exhaust exit Mach number.
(h) Gas static temperature at exhaust exit.
(i) Exhaust nozzle exit area.
(j) From the above answers, deduce the cross-sectional profile of the core engine exhaust duct. Explain the rationale for your answer. Further calculations are not needed.
