Modern jet engines are based on the turbofan principle. Some of the air sucked i
ID: 1858912 • Letter: M
Question
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 time 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?
State all assumptions and show working.
Explanation / Answer
1000 km/hr = 277.77 m/s x + 3x = 360 x = 90 3x = 270 Momentum change of air through comb chamber = 90*(1200-277.77) = 83000 N Momentum change of air through bypass = 270*(720 - 277.77) = 119400 N Total Thrust = 83000 + 119400 = 202400 N = 202.4 kN
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