yay turbine engines!

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Utah Valley University *

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3300

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Mechanical Engineering

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Feb 20, 2024

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docx

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From four horizontal inline cylinders that ran the Wright brothers’ flyer in the early 1900’s, to the titanium fans rotating around the Rolls Royce Trent 900 turbine engines, aviation has seen so many advances in aircraft engine engineering over the last century. World wars, trade needs, and mail service helped push the aircraft further than any other piece of technology within such a short time frame. To better understand the system gauges that we diagnose in times of aircraft distress, pilots must understand the innerworkings of their jet engines. The gas turbine engines of modern day are all comprised of the same idea as piston engines. Intake, compression, combustion, and exhaustion are occurring in jet engines just the same as piston engines, except that the process is simultaneous instead of in “strokes”. Different engines have different methods to execute each stage in this process, but they all include these stages. Some engines have single, dual, or even three spool compressors that act independently to take in air and combust it within its combustor. Intake is comprised of air passing through the front of the engine housing and then, usually, through a large fan. This assembly comprises of numerous parts to protect the engine from the elements such as rain, dust, or debris. Compressors then handle the “squeezing” of the air and provide it at high pressure to the turbines. Within the combustor, fuel is introduced to the high-pressure air where it is responsible for controlling the even distribution of heat and air expansion. Finally, once the heated and expanded air has been able to pass through the turbine, it is expelled through the exhaust. In a single spool compressor, one compressor unit is connected to the turbine section by a single shaft. This means the entire spool is rotating as one assembly all together. The single spool pulls air through many stages within the single compressor and is not broken up into a high pressure and low-pressure compressor. In a dual-spool engine, the high-pressure compressor, or N2, and turbine spins independently from the low-pressure compressor, or N1, and turbine. The

shaft connecting the high-pressure compressor and its turbine is hollow leaving room for the shaft turning the low-pressure compressor. The two compressors in a dual-spool engine run at different pressures meaning they turn at different speeds. The high-pressure compressor requires more energy and turns at a faster speed, so it connects to the turbine closest to the exiting exhaust to take the initial blow or thrust from the combustion chamber. The low-pressure compressor requires less energy than its neighbor, therefore it is connected to the outer turbines, collecting the left-over exhaust from the first turbine. In both single and dual spool engines, all the air that enters the engine goes through the engine from intake to exhaust. The single and dual spool engines are best used for multiple combinations of axial and centrifugal flow compressors in many different aircraft, however, “dual-compressor engines deliver higher compression ratios than single-compressor models” (Brown & Holt, 2001). The Pratt & Whitney PW6000 is a popular dual spool jet engine that was used in the Airbus A318. An example of modern-day turbine engines is the turbofan. “ In the turbofan engine, the core engine is surrounded by a fan in the front and an additional turbine at the rear” (Hall, 2021) . The turbofan is unique from the previous examples due to its use of bypass air, or air that does not pass through the compressors or combustor. This cool air instead travels through its own chamber from the front fan blades of the intake to the exhaust opening in the back. The design of the fan blades allows the bypass air to produce thrust on its own without adding fuel to that air. This means that engines built this way are more fuel efficient and are in higher demand due to the ever-rising costs of fuel, and our ever-growing demand to travel. Some aircraft can obtain eighty percent of their thrust through bypass air at lower altitudes where the air is denser. The most popular, or most sold turbofan engine is the CFM56, becoming the “exclusive engine on

Boeing’s narrowbodies” (Morrison, 2019) delivering over 22,000 engines by 2019. These engines are typically used in commercial airliners as well as military transport operations. Other further advancements in the world of turbine engines include the engineering of the ramjet and the scramjet. Ram jets work on the principle that the “high pressure air is produced by ‘ramming’ external air into the combustor using the forward speed of the vehicle” (Hall, 2021) This means that the engine is incapable of creating any thrust whatsoever unless it is already at a speed high enough to execute this process. For a ramjet this speed is typically subsonic, and when the aircraft reaches a supersonic speed, the air must be slowed. Typically, this is done by shock waves that exist within the inlet that slow the air down. The newer technology of the scramjet allows the supersonic speed of air to enter the engine unchanged and continue to combustion. Both jets are used for high speed, or hypersonic speed, mostly in relation to military operations such as combat or reconnaissance. Having a clear understanding on all the systems that power an aircraft is a pilot’s responsibility and requirement to execute all flights as safe as humanly possible. The jet engine is actually a very simple machine that leaves no room for excuse understanding its basic functionality and defects. Whether flying corporate, part 121, military, or medical field operations, the use of the jet engine spans from small private jet to large cargo carriers. The pounds of thrust may differ, but the principles and functions remain mostly the same.

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References Brown, G. N., & Holt, M. J. (2001). The Turbine Pilot’s flight manual . Iowa State University Press. Hall, N. (2021a, May 13). Ramjet propulsion . NASA. https://www.grc.nasa.gov/www/k-12/airplane/ramjet.html Hall, N. (2021, May 13). Turbofan engine . NASA. https://www.grc.nasa.gov/www/k-12/airplane/aturbf.html Morrison, M. (2019, October 9). The power list: Top 10 delivered commercial turbofans . Flight Global. https://www.flightglobal.com/the-power-list-top-10-delivered-commercial- turbofans/116576.article