Friday, 13 November 2020

How Jet Engines Work?


Many of you must have wondered at sometime or the other, how does a plane fly. And you must have got an answer, the plane flies with the help of a jet engine. Have you ever wondered how does the jet engine work and flies the big aeroplane to far off distances at great speed. The jet engine is one of the most advance innovations of mankind that has helped in flying and became a game changer. It provided a big boost to the aviation industry. Now people can reach far greater distances in much lesser time. It has also made flying safe, comfortable and a good experience.

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As you know birds fly by pushing air. Mankind has developed machines that mimics this action,  that push air; but one of the greatest machines that push air is the jet engine.  Jet engine suck air in the front and push a jet of air out at the back. That force is called thrust and it moves an airplane through the sky. 

It works on a principle - simply put, a big fan at the front of the engine pulls air around the engine and sucks air into the core. The air in the core goes into a compressor something like many household fans join together each fan gets smaller and smaller because the blades squeeze the air into a tighter and tighter space compressing it there. Like you would squeeze a balloon until that squeezed air is mixed with jet fuel, a kind of super gasoline in the combustor that air and fuel mix, a flame fires out the back of the engine and the rush of hot air spin the turbine and the  turbine is like a windmill that scoops up energy from the heated air and spins the shaft connected to the fan at the front of the engine, the excess hot air from the combustor blows out from the back of the engine producing thrust.

Airplane wings are shaped to make air move faster over the top of the wing. When air moves faster, the pressure of the air decreases. So the pressure on the top of the wing is less than the pressure on the bottom of the wing. The difference in pressure creates a force on the wing that lifts the wing up into the air. The plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. The wings force the air downward and that pushes the plane upward.

The key difference between jets and propeller planes is that jets produce thrust through the discharge of gas instead of powering a drive shaft linked to a propeller. This allows jets to fly faster and at higher altitudes. All jet engines, which are also called gas turbines, work on the same principle. The engine sucks air in at the front with a fan. The blades spin at high speed and compress or squeeze the air. The compressed air is then sprayed with fuel and an electric spark lights the mixture. All jet engines, which are also called gas turbines, work on the same principle. The engine sucks air in at the front with a fan. The burning gases expand and blast out through the nozzle, at the back of the engine. As the jets of gas shoot backward, the engine and the aircraft are thrust forward.

At any given moment, there are something like 5,000 flights zipping through the sky over the United States alone and similarly around the world; we're so used to the idea of flight that we barely even notice all the planes screaming above us, hauling hundreds of people at a time to their homes and holidays. Most modern planes are powered by jet engines. What exactly are these magic machines and what makes them different from the engines used in cars or trucks?

A jet engine is a type of reaction engine discharging a fast-moving jet that generates thrust by jet propulsion. While this broad definition can include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an air-breathing jet engine such as a turbojet, turbofan, ramjet, or pulse jet. In general, jet engines are internal combustion engines.

Air-breathing jet engines typically feature a rotating air compressor powered by a turbine, with the leftover power providing thrust through the propelling nozzle - this process is known as the Brayton thermodynamic cycle. Jet aircraft use such engines for long-distance travel. Early jet aircraft used turbojet engines that were relatively inefficient for subsonic flight. Most modern subsonic jet aircraft use more complex high-bypass turbofan engines. They give higher speed and greater fuel efficiency than piston and propeller aero-engines over long distances. A few air-breathing engines made for high speed applications (ramjets and scramjets) use the ram effect of the vehicle's speed instead of a mechanical compressor.

The thrust of a typical jetliner engine went from 5,000 lbf (22,000 N) (de Havilland Ghost turbojet) in the 1950s to 115,000 lbf (510,000 N) (General Electric GE90 turbofan) in the 1990s, and their reliability went from 40 in-flight shutdowns per 100,000 engine flight hours to less than 1 per 100,000 in the late 1990s. This, combined with greatly decreased fuel consumption, permitted routine transatlantic flight by twin-engined airliners by the turn of the century, where previously a similar journey would have required multiple fuel stops.

The combustion efficiency of most aircraft gas turbine engines at sea level takeoff conditions is almost 100%. It decreases to nearly to 98% at altitude cruise conditions. For any type of combustion chamber there is a rich and weak limit to the air-fuel ratio, beyond which the flame is extinguished. Passenger aircraft fly at a good speed, Commercial jet aircraft cruise at about 400 – 500 knots (460 – 575 mph / 740 – 930 kph). The speed of a private jet ranges from 400 to 711 miles per hour. When compared to a commercial airliner with top speeds just over 500 miles per hour, it is easy to decide that a private jet is the speediest aircraft to get you from here to there.

In fact, modern planes are designed to be able to glide for long distances without using engines. Even if every engine fails, the plane should still be able to glide to a landing spot. There's no set time limit on how long a plane can fly with one engine as long as you have fuel.

The Lockheed SR-71 Blackbird is the fastest jet aircraft in the world, reaching speeds of Mach 3.3, that's more than 3,500 kph (2,100 mph) and almost four times as fast as the average cruising speed of a commercial airliner. Key elements of the SR-71's design made this possible. Depending on the seat layout, the plane can carry as many as about 850 passengers, but the typical is closer to around 575. The plane entered commercial service in 2007, representing Airbus' gamble that a "hub-and-spoke" model would be the future of commercial air travel.

The ‘sweet spot’ of flying is regarded as between 35,000 and 42,000 feet – too high and the oxygen becomes too sparse to fuel the engines, too low and the air resistance is greater. This optimum height is linked to the usual weight of a commercial jet – that is, heavier planes fly lower, and lighter higher.

Airline engines (for example the Rolls Royce Trent series) usually have TBOs of over 15000 hours. The record for maximum time for an engine on wing (use in aircraft before removal for overhaul) is well over 40,000 hours. The life of an engine is given by the manufacturer and are different for different engines. It may take up to 2 months to complete, and is usually only performed 2 to 3 times per aircraft lifetime, as it is performed every 6 to 10 years. Often, airlines will opt to scrap, or sell off, older aircraft that are nearing their ‘D’ checks, simply because of the ridiculous amount of time, people and money required.

Generally, there are no scheduled oil changes for jet engines. During engine maintenance, however, oil filters and seals are checked and changed if necessary. Typical ‘top-ups’ are done on a daily basis, so jet engines always have some fresh oil but rarely need a complete oil change. The three items needed to keep a jet engine operating are fuel, air, and a source of heat to make them burn. While rain can have an influence on the function of a jet engine, but does not have a significant effect. The majority of storms produce light rain or snow that has little if any impact on an engine.

In an emergency, the aircraft will glide perfectly well even if all its engines fail. If both engines fail, the aeroplane is no longer being pushed forward, therefore in order to keep the air flowing over the wings, the aircraft must exchange energy through losing altitude to maintain forward airspeed. Jet engines are expensive. They are highly optimized machines containing thousands of parts. The parts used are made of expensive, exotic materials, which are often very expensive. The  engine has to be assembled by skilled mechanics over many hours.

Gas turbine aircraft engines such as turbojets, turboshafts and turbofans often use air/pneumatic starting, with the use of bleed air from built-in auxiliary power units (APUs) or external air compressors now seen as a common starting method. Often only one engine needs be started using the APU (or remote compressor). The compressed kerosene-air mixture then ignites, after which the motor then operates independently. This operation is carried out for each engine, generally one after the other, and takes about one minute. This jet engine automatic start procedure is the most common.

Who makes the best jet engines in the world? - General Electric. GE Aviation, part of the General Electric conglomerate, currently has the largest share of the turbofan engine market. Next is Rolls-Royce, Pratt & Whitney, CFM International, Engine Alliance, International Aero Engines,Williams International and Honeywell Aerospace.

Jet fuels are typically made by blending and refining various crude oil petroleum distillation products such as naphtha, gasoline, or kerosene in order to meet specific military or commercial specifications (Air Force 1989b).

One of the first engine makers Pratt and Whitney recently designed a new jet engine that lets the fan push air more slowly than the turbine by putting an amazing gear between them, Pratt & Whitney called this the pure power engine because it uses less fuel and makes more thrust at the same time with less fuel, saving money and cuts back on pollution which is better for the environment and all living things and when the fan moves slowly the noise drops so much you can barely hear the airplane in the sky it's a new design for jet engines and a new era for jet airplanes that we all can enjoy.

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Ancient caves in Mumbai:

In the western suburb of Mumbai, on the outskirts, are the Kanheri caves, which date back to more than 2,000 years. The caves – 140 in total are in good condition, all carved out of a single black rock, contain many ancient Buddhist sculptures, carvings, paintings and inscriptions dating from 1st century BCE to 10 th century CE.

The Kanheri Caves are a group of rock-cut monuments formed from a massive basalt rock in the forests of the Sanjay Gandhi National Park on the western outskirts of Mumbai. They contain Buddhist sculptures and relief carvings, paintings and inscriptions. Kanheri comes from the Sanskrit name, Krishnagiri, which means, black mountain. Each cave has a stone plinth that functioned as a bed. A congregation hall with huge stone pillars contains a stupa (a Buddhist shrine). Rock-cut channels above the caves fed rainwater into cisterns, which provided the complex with water. Once the caves were converted to permanent monasteries, their walls were carved with intricate reliefs of Buddha and the Bodhisattvas. Kanheri had become an important Buddhist settlement on the Konkan coast by the 3rd century CE. Most of the caves were used as the Buddhist viharas, meant for living, studying and meditating. The larger caves, functioned as chaitvas, or halls for congregational worship. The Avalokiteshwara is the most distinctive figure.

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