How Jet Engines Work

Summary

In 'How Jet Engines Work,' Jake O'Neal explains the turbofan design of modern jet engines, detailing their core components: the compressor, combustor, and turbine. The compressor increases air pressure, the combustor mixes air with fuel for powerful combustion, and the turbine powers the engine. Turbofan engines use bypass air for efficiency and noise reduction, while afterburners provide short bursts of extra power. This overview highlights the complexity and efficiency of jet propulsion technology.

Takeaways

• 🚀 Most jet-propelled airplanes use a turbofan design, which is a high-tech propeller inside a duct called a diffuser, driven by a gas generator.
• 🔧 The core of a jet engine is a gas generator that creates high-pressure gas to power a turbine, consisting of compressor, combustor, and turbine sections.
• 🌀 The compressor increases air pressure in stages, using a spinning rotor and stationary stator vanes to swirl and compress the air.
• 🔥 The combustor mixes air with fuel and ignites it, releasing a jet of super high-powered gas in an annular design for even mixing.
• 🌀 Turbines at the rear of the engine are powered by exhaust gases, with most power used to turn the fan and a smaller percentage for the compressor stages.
• 🔥 Turbine fins get extremely hot, requiring cooling from diverted compressor air and special coatings to manage temperatures.
• 🌪 The exhaust cone is specially shaped to mix and accelerate exhaust streams, also protecting sensitive internal engine parts.
• 🌬 Early turbojets had all air flowing through the core, but modern turbofans have a bypass system where only a fraction of air enters the core, with the rest powering a fan.
• 🛫 High bypass engines are designed for large quantities of air at slower speeds, suitable for commercial airliners and military transport aircraft.
• 🔊 Exhaust velocity affects jet engine noise; high bypass engines reduce noise by surrounding fast-moving core exhaust with slower-moving bypass air.
• ✈️ Military fighter aircraft use low bypass engines for compact size, high power-to-weight ratios, supersonic capabilities, and afterburners, despite noise and fuel consumption drawbacks.
• 🔥 Afterburners provide a second stage of combustion by igniting additional fuel mixed with exhaust gas, used for short bursts in high-performance engines due to fuel inefficiency.

Q & A

What is the primary function of a turbofan engine in a jet airplane?

The primary function of a turbofan engine is to provide thrust by using a high-tech propeller inside a duct called a diffuser, which is driven by a gas generator.

What is the core of a jet engine and what does it do?

The core of a jet engine is a gas generator that creates high-pressure gas to power a turbine, consisting of compressor, combustor, and turbine sections.

How does the compressor section of a jet engine work?

The compressor section works by compressing air in stages, forcing incoming air into increasingly narrow chambers with the help of spinning rotor blades and stationary stator vanes, which increase air pressure for more powerful combustion.

What is the purpose of the stator vanes in a compressor?

Stator vanes slow the swirling momentum of air from the rotor blades in exchange for increased air pressure, preparing the air for the combustion process.

How does the combustor section of a jet engine function?

The combustor section mixes compressed air with fuel and ignites it, releasing a jet of super high-powered gas that powers the engine.

What is an annular combustor and why is it used?

An annular combustor is a ring-shaped design that allows for an even mix of fuel and air, which is swirled and ignited by ignitor plugs for efficient and uniform combustion.

What is the role of the turbine in a jet engine?

The turbine in a jet engine is powered by exhaust gases from the combustor and uses much of its power to turn the fan, with a smaller percentage powering the compressor stages.

Why is cooling important for turbine fins in a jet engine?

Cooling is important for turbine fins because they get extremely hot due to the high temperatures of the exhaust gases, so air from the compressor is diverted for cooling, and special coatings are used to keep temperatures down.

What is the purpose of the exhaust cone in a jet engine?

The exhaust cone is specially shaped to mix and accelerate exhaust streams, and it also covers sensitive internal engine parts.

How does a high bypass engine differ from a low bypass engine?

A high bypass engine moves large quantities of air at slower cruising speeds for high efficiency and is larger with massive fans compared to core size, suitable for commercial airliners or military transport aircraft. A low bypass engine is more compact, has a high power-to-weight ratio, and can achieve supersonic speeds and afterburner capabilities, used in military fighter aircraft.

What is an afterburner and how is it used in jet engines?

An afterburner is a feature in high-performance engines that allows additional fuel to be sprayed into a jet pipe section, mixed with exhaust gas, and ignited for a second stage of combustion. It is generally used in short bursts during takeoff, climb, or combat maneuvers due to its fuel inefficiency.