Question

What is the thrust of an engine if the inlet and exhaust mass flow rate are 150 kg/s and 190 kg/s respectively with the pressure difference between the exhaust and ambient air is 1.85 × 10^4? The exhaust area is 2m^2, the ambient and exhaust velocities are 280 m/s and 400 m/s.

(a) 50 kN

(b) 62 kN

(c) 71 kN

(d) 84 kN

This question was addressed to me during an online exam.

Question is from Jet Propulsion Engine Thrust in portion Integral Form of Conservation Equation for Inviscid Flow of Aerodynamics

Answer 1

The correct choice is (c) 71 kN

Best explanation: Given, \(\dot {m}\)i = 150 kg/s, \(\dot {m}\)e = 190 kg/s, pe – p∞= 1.85 × 10^4, Ae = 2m^2, V∞ = 280 m/s

Ve = 400 m/s.

The thrust equation is given by:

T = \(\dot {m}\)eVe – \(\dot {m}\)iV∞ + Ae(pe – p∞)

Substituting the values, we get

T = 190 × 400 – 150 × 280 + 2(1.85 × 10^4)

T = 76,000 – 42,000 + 37,000 = 71 kN