Airliner Engines: Pratt & Whitney + Physics

choi

Civilian jet engines | Gearing up for a fight; Pratt & Whitney hopes a high-tech engine will restore its former dominance.
www.economist.com/news/business/ ... ce-gearing-up-fight

Quote:

"Pratt & Whitney used to tower over the market for such engines [those of airliners] but these days it is third-placed in a business dominated by GE, another American company, and Rolls-Royce, of Britain. Pratt is now hoping to claw its way back to the top with its new generation of jet engine, the 'geared turbofan.' This has a gearbox that lets the fan at the front of the engine turn at a different speed to the compressors inside it. By allowing each to run at optimal speeds it makes the engine more efficient.

"Understanding the aero-engine business is made harder by the fact that as they compete ferociously in one part of the market, manufacturers work together in joint ventures in other parts. In all, about 70% of the world’s jetliner engines are made either by GE alone or by CFM International, GE’s joint venture with Snecma of France. CFM supplies all the engines for Boeing’s 737, its rival to the A320 [both 737 and A320 are 'narrowbody']. Buyers of A320s can currently choose between a CFM engine or one from International Aero Engines (IAE), a consortium including Pratt and Japanese and German firms. For bigger 'widebody' jets, Rolls and GE are the main contenders.

"But from 2016, when the first revamped A320 is scheduled for delivery, its [Pratt's] new geared turbofan engines, which it will make all by itself, will go head-to-head against CFM’s LEAP. This [LEAP] is a more conventional engine design, but uses sophisticated composite materials to achieve the same fuel-efficiency savings, of around 15%, that airlines are demanding. Pratt may eventually produce versions of its geared turbofan for wide-bodied jets, where profits are fatter. * * *  Chinese and Russian firms want to enter the fray [of making jet engines], though that may take even longer.

"In the meantime, Rob Morris of Ascend, an aviation consultancy, notes that the tendency towards having just one engine option per
plane is growing. For example, Rolls is the only engine supplier for Airbus’s new long-haul plane, the A350, which had its first test flight last year. GE declined to offer an engine because some variants of the A350 are in direct competition with Boeing’s 777, on which GE already supplies all the engines. Rolls and GE at least both offer engines for Boeing’s 787 Dreamliner, which will compete with other variants of the A350.


Note:
(a) names:
(i) CFM International
en.wikipedia.org/wiki/CFM_International
(The names of CFM International and the CFM56 product line are derived from the two parent companies’ commercial engine designations: GE's CF6 and Snecma's M56)
(ii) The English surname Rolls: son of Rollo of Rolf
(iii) The English surname Royce: "originally from a Germanic personal name. This is recorded in Domesday Book in the form Rothais and is composed of the elements hrod ‘renown’ + haid(is) ‘kind’, ‘sort’"

(b) Pratt & Whitney pins hope on "'geared turbofan.' This has a gearbox that lets the fan at the front of the engine turn at a different speed to the compressors inside it.
(i) gearbox (n):
"1: GEARING 2
2: TRANSMISSION 3"
www.merriam-webster.com/dictionary/gearbox
(ii) gearing (n): "2: the parts by which motion is transmitted from one portion of machinery to another; especially :  a train of gears"
www.merriam-webster.com/dictionary/gearing
(iii) transmission (n):
"3: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a live axle; also :  the speed-changing gears in such an assembly"
www.merriam-webster.com/dictionary/transmission
(iv) train (n):
"6:  a series of moving mechanical parts (as gears) that transmit and modify motion <a gear train>"
www.merriam-webster.com/dictionary/train
(v) For compressor, see next posting.

(c) "Pratt’s new [geared turbfan] engine * * * is the only choice on the CSeries, a jet whose Canadian maker, Bombardier, is seeking to bust a duopoly between Airbus and Boeing for narrowbodies. But the CSeries’s entry into service was this month put back until perhaps 2015, two years later than first planned."
(i) Richard DeLuca, The Early Years of the Pratt & Whitney Aircraft Company. ConnecticutHistory.org, undated.
connecticuthistory.org/the-early-years-of-the-pratt-whitney-aircraft-company/
(ii) History. Pratt & Whitney, undated
www.prattandwhitney.com/Content/History.asp

("1860   Pratt & Whitney Company is founded by Francis Pratt and Amos Whitney.  The founders started the company in Hartford, Connecticut")
(iii) Bombardier CSeries Delayed Again Until Late 2015. The Canadian Press, Jan 16, 2014.
www.cbc.ca/news/business/bombard ... late-2015-1.2498880

Quote:

"A delay of the CSeries delivery was widely anticipated due to the small number of test flights since Sept 16[, 2013], when the CS100 flew for the first time after years of preparatory work.

"Walter Spracklin of RBC Capital Markets * * * suspects the delay is prompted by issues with the aircraft's avionics and fly-by-wire system since it continues to fly under 'direct' mode.


(d) "Zafar Khan of Société Générale, a bank, suggests that since Rolls is relatively small and Pratt is part of a deep-pocketed conglomerate, United Technologies, Pratt might contemplate bidding for Rolls to ensure its return to the widebodied market. That would require the agreement of the British government, which has a 'golden share' in Rolls."
(i) Rolls-Royce Group PLC
en.wikipedia.org/wiki/Rolls-Royce_Group_PLC
(is headquartered in City of Westminster, London; founded in 1906 by Henry Royce and Charles Rolls in Manchester; section 1.2 Nationalisation and separation: Edward Heath nationalized it in 1971; Margaret Thatcher privatized it in 1987)
(ii) Foreign bosses for defence firms | CEO Wanted, English Not Required; The last bastion of corporate nationalism may finally be crumbling. Economist, Mar 19, 2008
www.economist.com/node/10881189
("The firms' [Rolls-Royce's and BAE's] hands are tied by the terms of their privatisation two decades ago. The government hung on to a single special share in each of them that conveys particular powers. Both companies may hire only British chief executives or executive chairmen (and most of their directors must be British too) unless the government agrees otherwise. And government approval is needed before a foreign shareholder may own more than 15% of the company. Such 'golden' shares were once common in privatised industries such as water and electricity utilities. Yet most have been allowed to expire or have been removed")

choi

From (4)(c) of the preceding posting:

"Low bypass ratio turbofans are still more fuel efficient than basic turbojets. Many modern fighter planes actually use low bypass ratio turbofans equipped with afterburners. They can then cruise efficiently but still have high thrust when dogfighting. Even though the fighter plane can fly much faster than the speed of sound, the air going into the engine must travel less than the speed of sound for high efficiency. Therefore, the airplane inlet slows the air down from supersonic speeds."

(1) afterburner
en.wikipedia.org/wiki/Afterburner

(2) supersonic aircraft
en.wikipedia.org/wiki/Supersonic_aircraft
("have been used almost entirely for research and military purposes. Only two, Concorde and the Tupolev Tu-144, were ever designed for civil use as airliners"/ section 2.3 Engines

(3) Learn vocabulary and concepts.

components of jet engines
en.wikipedia.org/wiki/Components_of_jet_engines
(section 1 Major components: "Air intake (Inlet)" only; section 1.1.1 Subsonic inlets: view schematic only, showing increased air turbulence as aircraft speed adds up; section 1.1.2 Supersonic Inlets: inlet cone and intake ramp)

(4) Diane Tedeschi, How Things Work: Supersonic Inlets. Air & Space (magazine), November 2002.
www.airspacemag.com/military-aviation/Supersonic_Inlets.html
  
two consecutive paragraphs:

"When a jet airplane is flying faster than Mach 1—beyond the speed of sound—the air entering the engines is moving supersonically as well. But no turbojet engine compressor—the rotating disks and blades at the face of the engine that compress the air before it is mixed with fuel—is capable of handling supersonic air flow. The job of an engine inlet is to slow incoming air to subsonic speeds before it passes through the engine.

"The inlet’s job is complicated by the fact that air moving supersonically behaves differently from subsonic air. An aircraft flying subsonically pushes through the air ahead of it, with each molecule of air having plenty of time to pass over its wings and fuselage. But as an airplane approaches Mach 1, it compresses the air ahead of it into shock waves—bands of air radiating from the airplane that are much hotter and denser than the ambient air.

(a) Lockheed SR-71 Blackbird
en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird
(section 2.5 Engines: "A unique hybrid, the engine can be thought of as a turbojet inside a ramjet. At lower speeds, the turbojet provided most of the compression and most of the energy from fuel combustion. At higher speeds, the turbojet largely ceased to provide thrust; instead, air was compressed by the shock cones [ie, inlet cone] and fuel burned in the afterburn [ramjet]")
(b) sonic boom
en.wikipedia.org/wiki/Sonic_boom
(The crack of a supersonic bullet passing overhead is an example of a sonic boom in miniature)  

Quote: "When an aircraft passes through the air it creates a series of pressure waves in front of it and behind it, similar to the bow and stern waves created by a boat. These waves travel at the speed of sound, and as the speed of the object increases, the waves are forced together, or compressed, because they cannot get out of the way of each other. Eventually they merge into a single shock wave, which travels at the speed of sound

choi

Turbofan is the most prevalent engine of airliners. Here are its parts and physics.

(1) turbofan
en.wikipedia.org/wiki/Turbofan
(a) View only animation --NOT schematics.
(b) Read legend of the ani.mation. Disregard, for this purpose, low-pressure, high-pressure--the text of this Wiki page has a third one: intermediate-pressure--compressors; these are a series of AXIAL compressors. See (c).

* nacelle (n; French, literally, small boat, from Late Latin navicella, diminutive of Latin navis ship — more at NAVE; First Known Use: 1904):
"a streamlined enclosure (as for an engine) on an aircraft"
www.merriam-webster.com/dictionary/nacelle

(2) Similar to a car or motorcycle engine, another energy source starts, including ignition of internal combustion "burner" inside the jet engine, a turbofan engine.
(a) auxiliary power unit
en.wikipedia.org/wiki/Auxiliary_power_unit
(section 1.1 Function: paragraph 1: two types of APU's (electric and pneumatic), depending on size of airplane
(b) Sarah Jense, How Do the Blades of a Jet Engine Start Turning? How Do the Blades of a Jet Engine Start Turning?  Ask an Engineer, MIT, Mar 19, 2013.
engineering.mit.edu/ask/how-do-blades-jet-engine-start-turning

Once the engine reaches the stage of self-sustaining, APU can turn to otehr chores, such as supplying electricity to lighting in the cabin.

(3) I will focus on compressor of a torbofan first, then zoom out to the entire engine in (4).

Compressor. Glenn Research Center (GRC), NASA, Sept 13, 2010
www.grc.nasa.gov/WWW/k-12/airplane/compress.html
(All turbine engines have a compressor to increase the pressure of the incoming air before it enters the combustor; axial compressor)

* Glenn Research Center
en.wikipedia.org/wiki/Glenn_Research_Center
(Formed 1942; in Ohio; In 1999 was officially renamed the NASA John H. Glenn Research Center at Lewis Field after John Glenn (American fighter pilot, astronaut and politician))

(4) Turbofan Engine. GRC, NASA, Sept 13, 2010
www.grc.nasa.gov/WWW/k-12/airplane/aturbf.html
(a) Click "parts" in paragraph 2, and the new Web page will tell you the deal functions of a nozzle: "Between the compressor and the turbine flow path is the combustion section or burner, which is colored red. This is where the fuel and the air are mixed and burned. The hot exhaust then passes through the turbine and out the nozzle. The nozzle performs two important tasks. The nozzle is shaped to accelerate the hot exhaust gas to produce thrust. And the nozzle sets the mass flow through the engine."
(i) nozzle (n; diminutive of nose):
"a short tube with a taper or constriction used (as on a hose) to speed up or direct a flow of fluid"
www.merriam-webster.com/dictionary/nozzle
(ii) There is no need to read the rest of this NASA page.
(b) "The rest of the incoming air passes through the fan and bypasses, or goes around the engine, just like the air through a propeller. The air that goes through the fan has a velocity that is slightly increased from free stream. So a turbofan gets some of its thrust from the core and some of its thrust from the fan. The ratio of the air that goes around the engine to the air that goes through the core is called the bypass ratio."
(i) In the quotation, the "engine" in sentence 1 is the same as the "core" in sentence 3. The "bypass" is the concentric space within the nacelle but surrounding the core.
(ii) The clause "just like the air through a propeller" meams the air stream, velocity increased by the fan by about 1.2 times, does not provide oxygen to burn fuel, someting the burner in the core does.
(c) "Low bypass ratio turbofans are still more fuel efficient than basic turbojets. Many modern fighter planes actually use low bypass ratio turbofans equipped with afterburners. They can then cruise efficiently but still have high thrust when dogfighting. Even though the fighter plane can fly much faster than the speed of sound, the air going into the engine must travel less than the speed of sound for high efficiency. Therefore, the airplane inlet slows the air down from supersonic speeds."

What does does this mean?  This topic digresses, but I will explain in the third posting of this series.
(d) Do not click "mathematics" in the last paragraph (paragraph 5), mainly because the new page does nor provide keys to subscripts in the equations. There is a better NASA page. See next, which is (5).


(5) We are going through physics of a turbofan.
(a) First and foremost, the meaning of m-dot.

mass flow rate
en.wikipedia.org/wiki/Mass_flow_rate
(introduction: The overdot on the m is Newton's notation for a time derivative)
(b) Jet Engine. Encyclopaedia Britannica, undated.
www.britannica.com/EBchecked/top ... or?anchor=ref135171
(BROWSE, not really read, section 1 The prime mover; section 2 The propulsor: formula one only, which is Newton's second law of motion)

Do not read the rest of section 2, whose formula uses subscripts different from those of NASA. See (c) below.

(c) Turbofan Thrust. GRC, NASA, Sept 13, 2010.
www.grc.nasa.gov/WWW/k-12/Virtua ... rplane/turbfan.html
(i) Formula 1 ("Thrust = Thrust of Fan  + Thrust of Core") should be more precise: not "Thrust of Fan" but "Thrust of Bypass."
(ii) "If we denote the exit of the core as station 'e,' the exit of the fan as station 'f,' and the free stream as station '0,' we can use the basic thrust equation for each stream to obtain the total thrust."
(A) station (n; ultimately from Latin stare to stand):
"1a:  the place or position in which something or someone stands or is assigned to stand or remain
* * *
6:  a place for specialized observation and study of scientific phenomena <a seismological station> <a marine biological station>"
www.merriam-webster.com/dictionary/station
(B) Again, in the clause "the exit of the fan as station 'f'"--the "fan" refer to the bypass. However, because "fan" is used (perhaps for historical reasons), the subscript is "f."
(C) Subscript 0 is zero, not letter o.
(D) Subscript "c" in formula 2 is "core."
(E) Thus (Vf-V0) is merely acceleration in Newton's second law of motion.