Jet engines revolutionized air travel over half a century ago, propelling humanity to new heights of speed, efficiency, and accessibility. Understanding the intricate workings of these powerful engines can be a daunting task, but with the right guidance, it becomes an intriguing exploration of modern aviation technology. In this article, we will demystify jet engines and delve into their inner workings, from gas turbines to their incredible material science.

The Gas Turbine: The Heart of Jet Engines

The gas turbine serves as the driving force behind jet engines, using the Brayton cycle process to create pressurized gas for generating electricity or supplying kinetic energy to aircraft. In all modern gas turbines, combustion of fuels like natural gas, kerosene, propane, or jet fuel generates heat that expands air, propelling the turbine into action.

Key Components of Gas Turbines Although gas turbines may seem simple in theory, they consist of three primary components:

1. Compressor: Captures air from outside the turbine and amplifies its pressure.
2. Combustor: Burns fuel, producing high-pressure and high-velocity gas.
3. Turbine: Harvests energy from the gas flowing out of the combustor, as illustrated in the diagram below:

a. Compressor Functionality:

As shown in the diagram above, the compressor pulls in air from the left, and numerous fan blades compress the gas. Some turbines can achieve air pressure up to 30 times greater than the initial input pressure.

b. Combustor Operations:

High-pressure air enters the combustor, where a constant fuel injection maintains a steady flow of energy throughout the turbine.

c. Turbine Performance:

The turbine, linked to the compressor blades by a shaft, rotates independently. The hot gas passing through the turbine allows it to reach remarkable speeds. The turbine connects to an output shaft, generating an impressive amount of horsepower—large airplane turbines, for example, can generate nearly 110,000 hp, which is double the power output of the Titanic.

Read also: The Marvelous Complexity of Jet Engines: How Many Parts Do They Consist Of?

Turbofan engines, which power most modern commercial aircraft, belong to a family of engines called gas turbines. This family also includes engines used in helicopters, small power plants, and even certain types of tanks. The term “turbine” provides insight into how these engines function. Like wind or steam turbines, gas turbines rely on spinning to generate power, with pressurized air driving the rotation.

Fuel and Pressurized Air

Gas turbines need to produce highly pressurized air to maintain a continuous flow of power to the engine. To accomplish this, they burn energy-dense fuels like jet fuel, kerosene, or natural gas. Combusting these fuels expands the air, creating a rush of hot gas that spins the turbine.

The Four-Step Process: Suck, Squeeze, Bang, Blow

Before delving into the detailed workings of gas turbines, it’s essential to understand the basic four-step process that drives these engines: suck, squeeze, bang, and blow. This simple process helps explain how gas turbines harness the power of pressurized air and fuel combustion to generate energy for aircraft propulsion.

1. Sucking Air In
   • Air is sucked into the engine from the front using a large fan, typically visible when looking at a plane head-on.
2. Compressing the Air
   • The air is then compressed in the next stage of the engine, referred to as the “squeeze” phase. A second fan increases air pressure by approximately eight times, significantly raising its temperature in the process.
3. Igniting the Fuel-Air Mixture
   • Fuel mixes with the compressed air and ignites, producing the “bang” and generating power. The hot, high-pressure air rushes past a set of turbine blades, causing them to spin. The turbine connects to the compressor and fan via an axle, so as the gases turn the turbine, the inlet fan and compressor fan also spin.
4. Creating Thrust
   • The rapidly moving air propels the aircraft forward. Military jets and select passenger planes may use afterburners, which inject fuel directly into the exhaust jet for additional thrust. However, for most passenger planes, the force generated by the moving air is sufficient to provide adequate forward motion for the wings to create lift.

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Designing Jet Engines: Challenges and Innovations

High Pressures and Temperatures

Though the basic principles behind jet engines may seem simple, designing them involves overcoming numerous challenges, particularly the extreme pressures and temperatures involved. Combustion chambers, where compressed air mixes with fuel, can reach temperatures exceeding 900°C (1,650°F).

The Quest for Suitable Materials

Traditional materials like steel proved unsuitable for withstanding the intense heat and pressures within jet engines, leading manufacturers to search for alternatives. Nickel-chromium alloys emerged as an ideal solution, offering lightness, affordability, strength, corrosion resistance, and the ability to retain integrity at up to 85% of their melting point (1,455°C or 2,651°F).

Cooling Strategies and Ceramic Coatings

To maintain the integrity of turbine components operating in temperatures exceeding their melting points, engine manufacturers employ ceramic coatings and cooling mechanisms. The coatings reduce heat penetration, while cool air is channeled to the blade surfaces from further up the engine and distributed through tiny holes. Neil Glover, Rolls-Royce chief of materials, explained in an interview with The Engineer that these measures keep the metal from melting, despite the extreme temperatures in the surrounding environment.

Advanced Materials Technology

Materials technology has progressed even further, manipulating the metal’s atomic structure to enhance its integrity. The tiny crystals comprising metals are engineered to grow in the same direction, eliminating weaknesses typically found at crystal boundaries. As a result, turbine blades are essentially gemstones, featuring a single atomic lattice throughout their structure.

Refining Nickel Alloys

Over time, manufacturers have refined nickel alloys by creating new mixes and adding different elements. This innovation allows turbine designers to tailor the perfect blend for each engine component, significantly enhancing overall performance.

READ ALSO: The Process of Attaching Aircraft Engines

The Balancing Act: Engine Size, Bypass Ratio, and Materials

1. The Bypass Ratio:
   • Turbofan engines have generally increased in size as designs have evolved and improved. A significant portion of the thrust generated is due to incoming air being diverted around the compressor and turbine. The difference in the volume of air delivered to the turbine compared to the air bypassed is known as the “bypass ratio.” Engine efficiencies improve by increasing the bypass ratio, which typically involves creating a larger diameter engine.
2. The Weight Conundrum
   • However, enlarging the engine also increases the weight of the fan sections, leading to heavier engines. For every additional kilogram of weight in the fan section, an extra 2.25 kg of support structure is required in the engine and wing.
3. Composite Materials: The Solution
   • To counteract the increased weight from larger, more fuel-efficient engines, manufacturers have turned to composite materials as substitutes for metals. Ceramic matrix composites (CMCs) are as durable as metals but weigh only a third as much as nickel alloys.
4. The GE9X: A Modern Marvel
   • The GE9X, currently the world’s largest engine for the Boeing 777X, utilizes composite materials in its fan blades and casing, as well as CMCs in the turbine and combustor. This powerful, lightweight, and resilient engine boasts a 10% improvement in fuel efficiency compared to its predecessor, the GE90, and is also the quietest engine ever produced by General Electric.

Read also: The Purpose Of Jet Engine Spirals

The Bottom Line

Jet engines have come a long way since their inception, with constant innovations and improvements in design, materials, and efficiency. This fascinating exploration of jet engines reveals the incredible engineering feats and cutting-edge materials science that enable us to travel the world in record time. As aviation technology continues to advance, we can only imagine what the future holds for jet engines and air travel.

What other innovations do you think the future holds for jet engine technology? Share your thoughts in the comments below!

Sources

• Simple Flying
• Energy Education