Type your question here Modern jet engines are based on the turbofan principle.

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Modern jet engines are based on the turbofan principle. Some of the air sucked in by an intake fan then enters a set of compressors, is mixed with fuel in combustion chambers, and expands through the turbines that drive the fan. However, most of the air is accelerated by the fan through a bypass and exits together with the hot combustion exhaust.

In one type of engine, the ratio of the mass flow rate through the bypass is 3.0 times that through the combustion path. An aircraft fitted with this engine is in steady flight at 1000 km/hr. Air enters the jet engine at a rate of 360 kg/s. Bypass air exits at 720 m/s while combustion air exits at 1200 m/s. What is the thrust in kN of this engine?

Explanation / Answer

1000 km/hr = 277.8 m/s

Since amount of air going through bypass is 3 times the air going through comb chamber and total air is 360 kg/s, we get that air going through bypass is 270 kg/s and air going through comb chamber is 90 kg/s.

Momentum change of air through comb chamber = m*(Vout - Vin) = 90*(1200 - 277.8) = 83000 N

Momentum change of air through bypass = m*(Vout - Vin) = 270*(720 - 277.8) = 119400 N

Total thrust = 83000 + 119400 N = 202400 N = 202.4 kN

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