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Remove link to manualslib per WP:LINKVIO; they're not the original publisher of this manual, they don't own the rights, and they near-exclusively upload copyvios. (The spam blacklist folks are trying to clear these out so they can blacklist the entire site) |
Shonebrooks (talk | contribs) m →Combustion: I corrected the spelling of "system." WP:TYPO |
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File:Combustor diagram airflow.png|The engine combustor needs the high velocity air leaving the compressor to be slowed significantly, which is done with an increase in flow area (diffuser), to a low Mn before combustion takes place to ensure low combustion pressure loss. A recirculation zone (shown by the circular airflow paths) has to be maintained near the fuel nozzle for initial combustion of the entering fuel to take place. This zone (the primary zone) is maintained by the two primary air paths, the swirl flow entering through swirl vanes (depicted by grey squares) around the fuel injector and the first row of primary air radial inflow holes. Combustion is completed with the intermediate air and the gas temperature is reduced with the dilution air to the value required for long life of the turbine.<ref>"Gas Turbine Combustion" Third Edition, Lefebvre and Ballal, {{ISBN|978 1 4200 8605 8}}, pp. 15–16, Figure 1.16</ref>
File:FAILED COMBUSTOR LINER FROM J-85-21 - NARA - 17447966.jpg|J85 annular combustor, displayed rear-end up. When installed in the engine this open end is closed by the first stage turbine nozzle vane ring the flow area of which (together with the area of the exhaust nozzle) back pressures the compressor to control its pressure rise and flow rate as shown on a compressor map.
File:Core section of a sectioned Rolls-Royce Turboméca Adour turbofan.jpg|[[Rolls-Royce Turbomeca Adour]] military turbofan. There is a requirement to maintain a certain minimum pressure-loss in combustors, rather than reducing it as much as possible to minimize entropy production. It has to be maintained to prevent backflow in the turbine cooling circuits since cooling air from the HP compressor needs a lower pressure at the turbines in order to flow.<ref>https://patents.google.com/patent/US20150059355A1/en,"Method And
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Early tests on afterburning showed the pressure loss due to burning increased rapidly if the Mach number at entry to the combustion zone was more than 0.3. This is lower than the Mn leaving the turbine so a diffusing section is required to slow the gas before the flameholders where combustion begins and is maintained in the recirculation zone.<ref>"Exhaust Reheat for Turbojets - A Survey of Five Years' Development Work - Part 1", Flight magazine, 8 September 1949</ref> An early surprise in afterburner testing was that the fuel does not ignite of its own accord in the hot turbine exhaust so afterburners use various methods of ignition.
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