A turbofan jet engine has a large fan that sucks in air. Some of this air enters

Question

A turbofan jet engine has a large fan that sucks in air. Some of this air 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 2.5 times that through the combustion path. An aircraft fitted with this engine is in steady flight at 300 m/s. Air enters the jet engine at a rate of 300 kg/s. Bypass air exits at 600 m/s while combustion air exits at 1000 m/s. What is the thrust in kN of this engine?

Explanation / Answer

Let the airflow rate through the combustion path be x kg/s. Then airflow rate through the bypass = 2.5*x kg/s

We have x + 2.5*x = 300

This gives x = 85.714 kg/s

Hence, airflow rate through bypass = 2.5*85.714 = 214.286 kg/s

Rate of Momentum of incoming air = mv = 300*300 = 90,000 kg-m/s2

Similarly, Rate of outgoing momentum = 85.714*1000 + 214.286*600 = 214,285 kg-m/s2

Thrust = Rate of outgoing momentum - Rate of incoming momentum = 214,285 - 90,000 = 124285 N

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.