Jet Engine Technology

JET ENGINE TECHNOLOGY

What is a jet engine?

A jet engine is a machine that turns energy-dense liquid fuel into a forceful pushing force known as thrust. The thrust of one or more engines propels a plane forward, forcing air past its scientifically formed wings to create an upward force known as lift, which propels it into the sky. That, in a nutshell, is how planes work—but how do jet engines work?

Jet Engines and Car Engines

Modern jet engines can be understood by comparing them to

piston engines used in early airplanes, which are remarkably similar to those used in vehicles today. A piston engine (also known as a reciprocating engine because the pistons move back and forth, or “reciprocate”) generates power in strong steel “cooking pots” known as cylinders. Fuel is squirted into the cylinders using atmospheric air. The piston in each cylinder compresses the mixture, raising its temperature until it either ignites spontaneously (in a diesel engine) or with the assistance of a spark plug (in a gas engine).

The burning gasoline and air explode and expand, forcing the piston back out and turning the crankshaft, which powers the car’s wheels (or the plane’s propeller), before repeating the four-step cycle. The problem is that the piston is only driven during one of the four phases, therefore it generates power for just a portion of the time. The amount of power produced by a piston engine is directly proportional to the size of the cylinder and the distance the piston travels; unless you utilize large cylinders and pistons (or a lot of them), you’ll only be able to generate moderate quantities of power. If a plane is powered by a piston engine, its speed, lift, size, and carrying capacity are all limited.

A jet engine operates on the same scientific premise as a car engine: it burns fuel and air (via a chemical reaction known as combustion) to produce energy that propels a plane, vehicle, or other equipment. Instead of using cylinders that go through four phases in turn, it employs a long metal tube that repeats the same four steps in a straight-line sequence. The simplest sort of jet engine, known as a turbojet, draws air in at the front through an inlet (or intake), compresses it by a fan, mixes it with fuel, and combusts it before firing out as a hot, fast-moving exhaust at the back.

Three things make a jet engine more powerful than a car’s piston engine-

According to the law of conservation of energy, a jet engine requires more fuel to generate more power per second. A jet engine is painstakingly engineered to collect large amounts of air and burn it with large amounts of fuel (about 50 parts air to one part fuel), hence the major reason it produces more power is because it can burn more fuel.

Jet engines deliver maximum power continuously due to simultaneous intake, compression, combustion and exhaust (unlike piston engines with a single cylinder).

Jet engines use many turbine “stages” to extract energy, unlike piston engines that only use one stroke. This significantly improves its efficiency.

Gas turbines

A gas turbine is a more technical term for a jet engine, and while it may not be immediately evident what it implies, it is a much better description of how this type of engine operates. A jet engine operates by burning fuel in air, resulting in hot exhaust gas. Unlike an automobile engine, which utilizes exhaust explosions to push its pistons, a jet engine propels the gas past the blades of a windmill-like rotating wheel (a

turbine), causing it to rotate. So, in a jet engine, exhaust gas drives a turbine, hence the name gas turbine.

Action and Reaction

When we think of jet engines, we typically see rocket-like tubes that fire exhaust gas backward. Newton’s third law of motion states that as the exhaust gas from a jet engine shoots back, the plane must move forward. It’s similar to a skateboarder kicking back on the concrete to propel themselves ahead; in a jet engine, the “kick” comes from the exhaust flow. In layman’s terms, the action (the force of the exhaust gas flying backward) is equal and opposite to

the reaction (the force of the plane moving forward); the action moves the exhaust gas, whilst the response moves the plane.

However, not all jet engines operate in this manner; some emit very no rocket exhaust at all. Instead, the turbine harnesses the majority of its power and the shaft connecting to the turbine powers a propeller (in a propeller airplane), a rotor blade (in a helicopter), a massive fan (in a large passenger jet), or an energy generator (in a gas turbine power plant).

Types of Jet engines

Because all jet engines and gas turbines operate in a similar manner (pulling air through an inlet, compressing it, combusting it with fuel, and allowing the exhaust to expand through a turbine), they all share five key components: an inlet, a compressor, a combustion chamber, and a turbine

(arranged in that order) with a driveshaft connecting them.

But that’s where similarities end. Different types of engines contain additional components (powered by the turbine), the inlets function differently, there may be more than one combustion chamber, two or more compressors and several turbines. In addition, the application (the task that the engine must perform) is critical. Aerospace engines are created by painstaking engineering compromise:they must produce the most power from the least amount of fuel (in other words, with maximum efficiency) while remaining as tiny, light, and quiet as feasible. Gas turbines used on the ground (for example, in power plants) do not have to make the same compromises; they do not need to be tiny or light, but they do require maximum power and efficiency.

Normal Aircraft vs. Jet Plane

Normal aircraft use light-weight piston engines or gas turbines, whereas advanced jet planes use turbojet, ramjet, and scramjet engines.

Normal airplanes move in the troposphere,whereas jet planes move very effortlessly and smoothly in the stratosphere. The stratosphere sits above the troposphere. The stratosphere reaches an altitude of 50 kilometers. The stratosphere’s airflow is substantially less turbulent than the troposphere’s.

Because the air does not flow up and down but rather parallel to the Earth in very fast moving air streams, this is where the majority of jet planes travel.

Types of Jet Plane

Jet engine technology is based on Newton’s third law of action and response. Any form of jet engine follows three principles: compression, combustion and expansion.

There are three forms of jet engine technology-

Turbojet,

Ramjet, and

Scramjet.

Turbojet

Turbojet engines are widely used in cruise missiles because of their small size, simplicity, and ability to maintain high speeds over long distances.

The turbojet can fly at approximately 40 kilometers altitude.

Ramjet

Jet engines draw in air at high speeds, thus if you constructed the entrance as a fast-narrowing nozzle, you could have it compressed the incoming air automatically, without the need for a compressor or a turbine. This type of engine is known as a ramjet, and because it requires quick air movement, it is best suited for supersonic and hypersonic (faster-than- sound) aircraft.

A ramjet employs the ram effect, or compression in an inlet, for all compression in an engine. As a result, it has no rotor or blades; instead, the inlet compresses the air (by a sequence of internal/external shocks), ignites it, and shoots it out the back through the nozzle.

Ramjets must run at high speeds due to the amount of flow energy required. They are unable to draw air at a stop. As air moves faster than sound into the engine, it is compressed and slowed considerably to subsonic speeds before being blended with fuel and ignited by a device known as a flame holder, producing a rocket-like exhaust similar to that of a classic turbojet. Ramjets are commonly employed in rocket and missile engines, however they are not suitable for use in space because they “breathe” air.

Scramjets are similar, but the supersonic air does not slow down nearly as much as it passes through the engine. By remaining supersonic, the air exits at a significantly higher speed, allowing the plane to travel far faster than a ramjet (theoretically up to Mach 15, or 15 times the speed of sound— in the “high hypersonic” range).

Scramjets

A scramjet (supersonic-combustion ramjet) is a ramjet engine that maintains supersonic airflow throughout its operation.

This allows the scramjet to go faster than a standard ramjet, which must decrease incoming air to subsonic speeds before entering the combustion chamber. Because the scramjet does not have to decelerate the air as much, the engine parts and materials can withstand significantly higher temperatures.

Scramjet-powered vehicles are expected to travel at speeds of at least Mach 15. Ground testing of scramjet combustors demonstrated this capability, but no flight tests have surpassed the Mach 9.6 X-43A flight.