The Insane Engineering of the GEnX

This real

engineering

episode is brought to you by Curiosity Stream. A nebula packet. Register now to watch the one-hour version of this video linked in the description. Jet engines are an

engineering

marvel because they precisely control the internal atomic structure of metals. From creating turbine blades that are actually a single crystal to delicate robotic machining that humans could only have dreamed of a decade ago today's jet engines are barely recognizable compared to those of the 1940s they are larger, They are more powerful and more efficient, the Dreamliner's engines are so large that they have the same diameter as the fuselage of the 737 and this is only part of the puzzle that has allowed the 787 Dreamliner to break world records in March 2020 in the midst of a global pandemic.

The United States government imposed travel restrictions on all European travelers, a measure that isolated France from one of its remote territories in French Polynesia. It was business as usual for Air Tahiti. It was no longer necessary to find a creative solution to replace its regular flights between Tahiti International Airport and Charles De Gaulle Airport, which under normal circumstances stopped in Lax due to the interruption, Air Tahiti began operating the longest flights in the world, a 16 and a half hour flight, 15,700 kilometers without stopovers between Tahiti and Paris, the longest scheduled flight in the world and technically it was a domestic flight the 787 made it possible and today we are going to learn how in our latest video we explore the incredible engineering that has been used to sculpt the plane structure of the 787, but all that work is useless without a power system to match.

Boeing transformed the way airliners are powered to create a plane like no other. The first step to powering a large plane is to start the engine at reaction and that in itself is an energy intensive process, we need to spin the compressor section to achieve proper compression to start the engine We have all seen pictures of people hand spinning old piston powered airplanes to start them. This is obviously not feasible for jet engines that need to spin at very high speeds to start. Engineers have devised many ways to complete this work. Some engines. use explosive cartridges that look like shotgun shells that will be fired by an electrical charge, the cartridge expels the hot gas and then drives a smaller turbine that is connected to the drive shaft through a reduction gear that allows the smaller turbine to accelerate Engines Cartridge starters were popular on older military aircraft that may need to take off on very short notice with limited ground support.

Some aircraft like the sr-71 had direct drive starter cars that connected two huge v8 engines directly to the j58 engine from below. the nacelle to make the powerful jet engines reach up to 4500 rpm; However, air starting is by far the most common method in which pressurized air is introduced directly into the turbine section to make the engine move. This can be done with an external cart called a float cart that connects hoses to the engine, but most commercial aircraft are capable of generating their own pressurized air with an APU or auxiliary power unit. These are smaller turbine engines located in the tail of the plane that are small enough to start with a battery and an electric motor.

People don't even know this mini turbine engine exists, but you can see the exhaust here on all modern commercial airplanes. The 787 APU, like other aircraft, is started with a small battery, but from here the system architecture of the 787 is very different from the 787 APU like others. The planes start with a small battery, but from here the architecture of the 787 system is very different. The 787 APU does not provide pressurized air to the engines, but instead provides electrical current to two electric motors connected to each engine that nevertheless act as your car's starter motors. These engines can act as generators to provide the 787 with unparalleled electrical power.

A traditional airplane has a generator in each engine and another in the APU, but the 787 is anything but traditional. There are a total of six generators on board with two pairs on each engine. main power, each capable of generating 250 kilowatts, with two more in the apu providing secondary power, each capable of providing 225 kw, if all six generators were running at the same time, there would be 1.45 megawatts of power available to the 787, four times more than a triple seven is capable of producing to put this in perspective, this is a 787 on a football field, if we needed to generate that electricity with solar panels in the middle of the day, we would need to cover about 10 fields of soccer with solar panels, this is a lot of power, so why did the 787 need so much power and where is it going?

The 787 uses a bleed-free architecture. Traditionally, many aircraft systems are powered by hot compressed air drawn from the compressor section of the jet engine normally provided by the APU. hot air to the engines to start them and then once the main engines start, the hot compressed air bled from the compressor section powers several important systems. Normally the air conditioning and cabin pressurization are handled by the bleed air system, the bleed air would be drawn from the engine at a temperature above 230 degrees Celsius, this would obviously quickly turn the cabin into an oven, so the Air would first pass through a complicated air conditioning and pressurization system where some of the air is cooled by a heat exchanger that uses outside air from a surface-mounted intake called ram intakes to remove heat from the engine's bleed air until reach a suitable temperature to distribute throughout the cabin, so we are working to remove energy from this valuable engine bleed air, this is obviously quite inefficient and all that.

The ducts are heavy and that is why the 787 does not use the system. Cabin pressurization is handled entirely electrically. We now have two inlets: the ram air inlet and the cabin air compressor inlet. The cabin air compressor leads to, you guessed it, the cabin air compressor. Electrically powered device that compresses air for the passenger cabin. This compression process heats the air too much for direct use in the cabin, so it requires some cooling using a heat exchanger cooled by the ram air inlet. You can see this small door open while the plane is on the ground and it serves to protect the entrance from the entry of foreign objects.

Another energy-intensive process that has been handed over to electric motors is the braking system, as you can imagine the energy required to brake a traveling 200-ton plane. at 270 kilometers per hour is no small thing, calculating the energy required is quite trivial, we only need to calculate the kinetic energy of the object, which we can do with this equation and that gives us the kinetic energy of 562 million joules, which is a lot of energy and the vast majority of that energy must be dissipated by the plane's brakes. Reverse thrusters can be deployed that redirect air from the bypass ducts through slots that open in the side of the engine, so the brakes must convert a large amount of kinetic energy into another. form of energy, thermal energy, you can actually see this in effect during the most extreme brake test of an airplane, an aborted landing test.

Here the plane flies at full load, including the weight of fuel, and has to abort at its speed v1, the absolute maximum speed. the plane can abort a landing beyond that point the plane has to take off when the plane comes to a complete stop the brakes are red hot normally the braking mechanisms of airplanes are actuated by a hydraulic system with a hydraulic piston that forces the brake pads against the wheel To slow the plane, the 787 eliminated this bulky hydraulic system and replaced it with brakes powered by electric motors. Each of the eight landing gear wheels features one of these units and together they helped remove between 62 and 111 kilograms of weight from the 787, while also much easier to maintain and install, the 787 has a hydraulic system, but two large bleed air-driven hydraulic pumps that are normally used to meet peak demand during takeoff and landing, where the landing gear is activated and high-lift devices such as slats and flaps are implemented, have been removed. other pumps that powered the hydraulic system during the cruise.

The 787 had the additional electrical power needed to get rid of these bleed air driven pumps and replaced them with more efficient electrically driven pumps to start. The 787 is capable of generating higher hydraulic pressures allowing it to use smaller hydraulic components, saving weight and space, so that covers most of the system architecture, but we haven't even touched on the revolutionary engines themselves, the Dreamliner is usually equipped with two general electric GE and X engines. Each of them is capable of producing between 310 kilonewtons and 360 kilonewtons of thrust, about the same reliability that General Electric's previous generation engines, the CF6 equipped on the 767, were capable of producing, but the GE NX produces this confidence while consuming 15 less fuel, which is an incredible leap in technology.

The ge nx achieves this primarily through two main design features that were not possible with older engines: the first is a gigantic bypass duct surrounding the main engine. The main components of modern jet engines are the fan, compressor, combustion chamber, turbine and nozzle. The ultimate goal of a jet engine is to draw in air and pressurize it as much as possible, which increases the energy potential of the air before mixing it with fuel and igniting it, causing rapid expansion and acceleration of the air. The work done by the compressor is then recovered in the turbine section which powers both the compressor and the fan, finally the air with its remaining kinetic energy travels through the nozzle where it is further accelerated and sent towards the rear of the engine to provide thrust to the engine core in this part of the engine. is what drives the engine but most of the air traveling through the

genx

bypasses this section entirely it just goes through the fan and through this bypass duct and this is one of the reasons why the engine It's so incredibly efficient.

Referral ratios have continually increased over the years. Which is one of the reasons engines continue to grow, the Genx engine has a 9 to 1 bypass ratio, meaning that for every kilogram of air that passes through the engine core, nine kilograms flow through. of the bypass duct, this is extremely high, the engine that the

genx

only replaced had a 5.7 bypass, which in its time was in itself a very high bypass ratio, while the core takes in a small volume of air and accelerates it quickly, the fan takes a huge volume of air and accelerates it just a little without the need to mix it.

With fuel and turning it on, this dramatically increases the aircraft's fuel efficiency. The fan essentially acts as a gigantic propeller. The industry has been aiming for ever-increasing bypass ratios for decades, but there are a couple of limiting factors that make it difficult to increase the size of the valves. fan blades, the compressor and the fan are driven by the same shaft, which means they rotate at the same speed, but because the fan is much larger than the compressor and turbine blades, the fan it experiences much higher centrifugal forces and if the fan blades grow too long. long, their tips could even break the speed of sound, causing shock waves and a massive increase in drag.

The first problem we must address is how to handle those centrifugal forces. The magnitude of the centrifugal force can be found using this equation where m is the mass w is the angular velocity and r is the distance from the center of rotation, so our force will increase with the weight of the blade, the speed of its rotation and its diameter, we want to increase our diameter to increase our bypass ratio, so we need to find ways to decrease our weight or decrease our rotation speed, ge and x achieved the first requirement by using carbon fiber fan blades light.

Older fan blades were constructed of titanium and titanium was used for its excellent strength-to-weight ratio, but carbon fiber blades have an even higher strength-to-weight ratio and at the same time much stiffer than titanium, making which allows the compound leavescarbon fiber are longer and thinner than their titanium counterparts. This form factor even allowed General Electric to reduce the number of blades from 22 to 18. In total, this resulted in a 15% weight savings on the blades, allowing them to spin faster without worrying about damage, however , composites have a major drawback: their impact resistance. One of the tests that the engine must pass to achieve certification is the chicken gun test which, as you may have guessed, involves eating a dead bird in the engine and seeing how it holds.

The fan blades are the first part of the engine that any foreign object will encounter and therefore must be able to withstand the impact. The early development of composite fan blades by NASA and GE demonstrated that composite blades alone were simply not up to the task of solving the problem. The leading edge of the blades is reinforced with titanium. Bypass ratios are likely to continue to grow as our technologies develop speed-reducing gears between the main drive shaft and fan that can enable engine manufacturers. To further increase bypass ratios, Pratt Whitney employed this technology in its PW1000G engine to achieve the largest bypass ratio ever seen in a commercial airline turbofan engine.

They included a planetary gear between the main drive shaft and the turbofan drive shaft which applied a three to one reduction in This allowed the fan to grow in diameter as the forces the larger blades had to withstand were drastically reduced. with a lower speed, giving the engine a record bypass ratio of 12.5 to 1. General Electric considered designing its new jump engine currently used by the 737 Max, but problems with weight and Planetary gearbox maintenance deterred them and that hesitation may have been justified as the engines have had a history of turbulent operation with several engine shutdowns and failures. removals, although these problems were not directly a result of the planetary crisis.

However, as technology improves, we may see more gear designs being used to generate even greater fuel savings. The next design feature that helps the genx reduce fuel consumption is the extremely high compression ratio achieved through the compressor section of the engine. The compression ratio is the relationship found by dividing the pressure at the outlet of the compressor section by the pressure at the inlet. This variable has enormous implications for the fuel efficiency of an aircraft and just as we can see a clear upward trend for the bypass ratios over time, the same can be seen For pressure ratios, the reason for this is quite simple: by increasing the pressure ratio, we can maximize the energy we can extract from our fuel because there is more useful energy available for extraction in our turbine and nozzle than if we compressed the air less, but that is not the case.

As easy as simply increasing the pressure in our compressor to achieve higher compression, we may need to increase the number of compressor sections, which will increase the weight of the engine, which will increase fuel consumption and reduce the lead. Higher compression will also lead to higher temperatures which can cause failure of compressor blade materials and, perhaps most critically, increased temperature results in increased emissions of potent greenhouse gases, such as nitrogen oxides. Nitrogen oxide formation rates increase exponentially with flame temperature to break down nitrogen molecules in the air and allow them to combine. with oxygen to facilitate higher pressure ratios while meeting climate change goals, this issue had to be addressed and they did so through ingenious fuel injection technology.

The compressor feeds its high-pressure air to 22 fuel mixing nozzles located in a ring around the compressor outlet. Its job is quite simple to mix the fuel in the air and ignite it a simple job that began to be developed in 1995 with general electric and NASA the art of creating the perfect fuel injection nozzle is incredibly complex a delicate but violent process like an orchestra whose crescendo is a fiery explosion with the advent of 3D printed manufacturing, GE has been able to create a fuel injector with a complex internal labyrinth of air channels that traditional tools simply could not cause.

The fuel injector they developed is called double annular pre-turn injector or taps, so how? Do you avoid those dangerous nitrous oxide emissions by carefully controlling air-fuel mixture ratios to control flame temperatures? If we plot flame temperatures as a function of the air-fuel ratio, we get something that looks like this: The maximum flame temperature occurs in stoichiometric air-fuel mixtures, which is the mixture where air and fuel fuel are completely consumed in the reaction, this is the zone where nitrous oxide emissions are highest because the flame temperature is higher to minimize nitrous oxide emissions, we can aim to be on this side of the curve with an air-rich fuel. mixture, but that would result in a lot of wasted unburned fuel, so our goal here is to be on the lean side of the graph.

If we mapped the combustion process for the older GE injector installed on 56 engines over 22,000 cfm, we would see air. The fuel mixture is initially injected into this zone with a rich air-fuel mixture, then goes through a dilution process to reach a lean mixture where the fuel is completely consumed. The problem with this is that the fuel passes through the stoichiometric region between these two phases. By creating a large amount of nitrous oxides, the tap fuel injector looks like this with a central main pilot surrounded by a ring-shaped main injector that creates two rotating air streams that look like this, which uses a large amount of nitrous oxides. air in the premix phase to ensure complete mixing and a lean air-fuel mixture.

If we map the combustion process of the taps, it starts in the lean zone and becomes even leaner in the combustion chamber, never approaching the maximum region of nitrous oxide production. This may seem like a simple device, but it took generations of design iterations with computer simulations that gradually brought engineers closer to their goal and none of their designs would have been possible without current generation metal 3D printing that could manufacture complex parts. with materials capable of resisting the enormous heat inside the combustion chamber. 26 years of development bore fruit with 60 reductions in nitrous oxide emissions. A record 58-1 pressure ratio compatible fuel injector used on the gen-x ge managed to increase the pressure ratio even though they reduced the number of compressor stages in each of these.

The turbine discs are one stage, the Genx contains 10 stages, four fewer than the CF6 engine it is replacing. Ge managed to do this through a new improved blade design, which is a lot less information than I wanted to share, but finding information on this topic was incredibly difficult. A testament to how advanced and secretive the technology is, the compressor includes three blisk stages, which are perhaps the most impressive feats of machining I have ever seen. Traditionally, compressor stages are manufactured by attaching the blades to a separate disc with dovetail connections, which reduces manufacturing complexity, but the dovetail connection is less durable, increases assembly and maintenance costs, and allows allow some air to escape through the connections.

Blisks are compressor stages that are manufactured from a single piece of metal, making them stronger and easier to install, while improving aerodynamic efficiency. Improving aerodynamic efficiency was the name of the game for improving compression ratios, and of course that had to be applied to the section of the turbine that powers the compressor. It also benefited from cutting-edge aerodynamic modeling. The turbine also made use of new advances in materials science, being the first commercial engine to use gamma. Titanium Aluminum An advanced titanium-aluminum alloy that combines the heat resistance of titanium with the weight savings of aluminum replacing the nickel alloys of the past.

It took three decades to bring this material from the laboratory to commercial use and the Dreamliner was the first aircraft to use it. Paving the way for the acceptance of the materials in the industry, all of these factors combined to allow the Dreamliner's GE and X engines to reduce fuel consumption by 15% over previous generation engines, which is a astronomical leap and, in addition, the engine is 60 times quieter than aircraft of similar size, in part thanks to the most distinctive feature of the engine, this sawtooth pattern on the fan housing and engine exhaust, these features are called engine chevrons and are not just a futuristic cosmetic design, but functional engine parts that significantly reduce engine noise.

The question is what difference can a simple change in shape in the outlet of a nozzle have on the overall noise pollution produced by the aircraft because turbofan engines expel air from their bypass chambers and turbines at speeds much higher than the engine speed? Ambient air, the air interacts with the free air stream, causing it to mix. This mixture causes uncontrolled vortices which in turn generate excessive noise for both passengers and the community on the ground. Think of it as water speeding up a waterfall and hitting the water below, that turbulence can be extremely noisy, chevrons aim to control the vortices that are released from the engine nozzle by creating smaller vortices in each of the chevron teeth to allow hot, fast air exhausted from the engine to mix with ambient air more smoothly.

It is said to reduce the plane's explosion noise by up to 30 percent and allowed Boeing to use substantially less sound insulation in the plane's fuselage walls, which helped reduce the plane's weight. The 787 truly lives up to its name. Providing a passenger experience that is nearly incomparable to that of other commercial aircraft with advances in noise reduction, fuel efficiency and passenger comfort, this series is usually reserved for aircraft and technology that most of us will never set foot on, but the 787 might be the most advanced piece of engineering we've ever covered. and it's a plane that many of us will have the opportunity to fly and marvel at the decades of engineering advances that made it possible.

This nearly half-hour long video is only half the story, but the full director's cut. , an hour long, has been available on Nebula for over a week combines the two halves of this video posted on YouTube into one seamless, ad-free experience that you can sit back and relax to watch. I removed a section of this video that details the complicated thermodynamic explanation for why compression ratios actually increase. efficiency because it seemed too academic for YouTube, but I think die-hard fans of this channel might enjoy listening to a 10-minute explanation of temperature entropy diagrams. The director's cut also includes explanations of the 787's ingenious electronic display screen in the cockpit. and electrochromic blinds I felt like none of these themes really fit anywhere in the larger script.

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