Same Old; China fumbles with jet engines

choi

Siva Govindasamy, Not Top Gun yet: China Struggles with Warplane Engine Technology. Reuters, Jan 28, 2016.
http://www.reuters.com/article/u ... gines-idUSKCN0V7083

Note: "Among the issues, China's J-20 and J-31 stealth fighters cannot super-cruise, or fly at supersonic speeds like their closest rivals, Lockheed Martin's (LMT.N) F-22 and F-35 stealth planes, without using after-burners, said two industry sources who follow Beijing's military programs closely.  After-burners remove a warplane's stealthiness"

afterburner
(a) afterburner
https://en.wikipedia.org/wiki/Afterburner

section 1 Principle: "Jet-engine thrust is governed by the general principle of mass flow rate. Thrust depends on two things: the velocity of the exhaust gas and the mass of that gas. A jet engine can produce more thrust by either accelerating the gas to a higher velocity or by having a greater mass of gas exit the engine. Designing a basic turbojet engine around the second principle produces the turbofan engine, which creates slower gas but more of it. Turbofans are highly fuel efficient and can deliver high thrust for long periods, but the design trade-off is a large size [of het engine] relative to the power output. To generate increased power with a more compact engine for short periods, an engine requires an afterburner. The afterburner increases thrust primarily by accelerating the exhaust gas to a higher velocity. While the mass of the fuel added to the exhaust does contribute to an increase in exhaust mass, this effect is small compared to the increase in exhaust velocity.

* View only the first photo to see what afterburning looks to a naked eye. (Because most of the time, a fighter jet takes off without afterburning, most photos about it shows darkness in the nozzles.)  There is no need to read the rest of this Wiki page.

(b)
(i) Afterburning Jet Thrust, Glenn Research Center (at Cleveland, Ohio), NASA, undated
https://www.grc.nasa.gov/www/k-12/airplane/turbab.html
("In a basic turbojet [without afterburning], some of the energy of the exhaust from the burner is used to turn the turbine. The afterburner is used to put back some energy by injecting fuel directly into the hot exhaust. On the schematic, you'll notice that the nozzle of the basic turbojet has been extended [lengthened] and there is now a ring of flame holders, colored yellow, in the nozzle. When the afterburner is turned on, additional fuel is injected through the hoops and into the hot exhaust stream of the turbojet. The fuel burns and produces additional thrust [specifically: speed, not volume of the exhaust], but it doesn't burn as efficiently as it does in the [internal] combustion section ['burner' in the schematic] of the turbojet. You get more thrust, but you burn much more fuel. With the increased temperature of the exhaust, the flow area of the nozzle has to be increased to pass the same mass flow. Therefore, afterburning nozzles must be designed with variable geometry and are heavier and more complex than simple turbojet nozzles")

Hoops? (That is, what an aferburner look like?)  See the next two.
(ii) The following has the same text, written by the same agency (Glenn Research Center). The only difference is that now the schematic of a turbofan is oblique (view), rather than lateral (view). So you can see what an afterburner looks like in a cartoon.
https://www.grc.nasa.gov/www/k-12/airplane/aturba.html

(c) Damond Benningfield, How Things Work: Afterburners. Air & Space Magazine, July 2007.
http://www.airspacemag.com/fligh ... erburners-18481403/