At cruise conditions, air flows into a jet engine at a steady rate of 65 lbm/s.

Question

At cruise conditions, air flows into a jet engine at a steady rate of 65 lbm/s. Fuel enters the engine at a steady rate of 0.58 lbm/s. The average velocity of the exhaust gases is 1520 ft/s relative to the engine. If the engine exhaust effective cross-sectional area is 3.2 ft2, estimate the density of the exhaust gases in lbm/ft3.

p3 = lbm/ft3 At cruise conditions, air flows into a jet engine at a steady rate of 65 lbm/s. Fuel enters the engine at a steady rate of 0.58 lbm/s. The average velocity of the exhaust gases is 1520 ft/s relative to the engine. If the engine exhaust effective cross-sectional area is 3.2 ft^2, estimate the density of the exhaust gases in lbm/ft^3. p3 = lbm/ft^3

Explanation / Answer

From mass balance

The exhaust gas mass flow rate = sum of inlet mass flow rates

m = 65 + 0.58 = 65.58 lbm/s

Also

m = p3*A*V

65.58 = p3*3.2*1520

p3 = 0.013483 lbm/ft^3

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