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I came across the picture below and saw the hole near the centerline on the left which appears to have some carbon next to it. What is its purpose and where does the carbon come from?

Enter image description here

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  • $\begingroup$ Cartridge starter? $\endgroup$ – Anilv Oct 24 at 3:36
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The Auxiliary Power Unit (APU) exhaust

This is answered by the following image (taken from this question, color markings are unrelated to this answer):

Eurofighter

The item 72 is what you are looking for and it is labelled "APU exhaust". The black residue is soot from incompletely burned fuel.

The Eurofighter Typhoon can use its APU to start the main engine or to provide power when on the ground. From airvectors.net:

The Eurofighter is also fitted with an auxiliary power unit (APU) for self-starting and ground power.

See also:

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  • 2
    $\begingroup$ But what do Kwik-E-Marts have to do with jet fighters? $\endgroup$ – Hot Licks Oct 23 at 22:52
  • $\begingroup$ ... if that is, in fact, your name ... -- Chief Wiggum $\endgroup$ – Will Crawford Oct 23 at 23:59
  • $\begingroup$ why is it placed there like that instead of a backwards pointing nozzle somewhere else? $\endgroup$ – user1062760 Oct 24 at 16:36
  • $\begingroup$ @user1062760 You can see the APU itself (item 71) right below, so it would make sense to have the exhaust right next to it to save on additional tubes (and weight). I don't know why the APU is placed there, but I assume that was just a place where it could fit. $\endgroup$ – Bianfable Oct 24 at 17:11

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