Correct Answer - Option 1 : It is the ratio of thrust power and propulsive power
Explanation:
Propulsive efficiency (ηp)
- The propulsive efficiency is the fraction of total mechanical power output that is imparted to the working fluid and converted to the thrust power (as opposed to how much is wasted).
- For jet propulsion engines (turbojet and turbofan engines), the total mechanical power output is simply the rate of increase in kinetic energy of the working fluid (jet), also known as the jet power (Ẇjet).
For jet propulsion engine
\({\eta _p} = \frac{{thrust\;power}}{{total\;power}} = \frac{{{{\dot W}_F}}}{{{{\dot W}_{jet}}}} = \frac{{{{\dot W}_F}}}{{\frac{1}{2}{{\dot m}_{air}}\left( {V_e^2 - V_o^2} \right)}}\)
where ẆF = thrust power, Ve = exit velocity, Vo = entrance velocity, ṁair = mass flow rate of air
∴ For jet propulsion engine,
\({\eta _p} \propto {\dot W_F}\;and\;{\eta _p} \propto \frac{1}{{{{\dot m}_{air}}}}\)
