Why does the cabin air sometimes smell of kerosene? [duplicate]

Question

Why does the cabin air sometimes smell of jet fuel, although bleed air is tapped before it comes in contact with fuel ? How is this possible?

I have smelled this a couple of times in my life (twice extremely irritating), mostly during boarding/taxiing but at least once also during the flight (although in that case I don't remember if the smell was already present before take-off and merely lingered on).

Apparently a similar observation was reported in Q25405 but limited to the taxiing phase, whereas I witnessed the smell when the plane was still connected to the PBB (and also in-flight with the caveat above). The root cause may differ.

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EDIT:
Meanwhile, I have found a satisfying answer on the net, but cannot add it anymore since the question is closed:

« You’ll occasionally notice a strong odor when the plane is on the ground – a pungent smell similar to the exhaust from an old car or bus that fills the cabin shortly after pushback. Usually this happens when exhaust gases are drawn into the air conditioning packs during engine start. The wind is often to blame, causing air to backflow or blowing fumes through the pack inlets. It normally lasts only a minute or so, until the engine is running and stabilized. It’s unpleasant but little different from the fumes you occasionally breathe in your car while stuck in traffic. » (source)

(Notice that in my cases it lasted definitely much longer than "only a minute or so".)

Answer 1

You might have been smelling cooked turbo oil. Leaking seals can potentially allow oil traces into the compressor bleed discharge, especially on auxiliary power units. The other possibility is cooked deicing fluid, which is quite common.

Turbo oil and deicing fluid are the two major sources of petrochemical cabin stink.

Another possibility would be an APU with stalling/surging problems where there can be backflow into the compressor end of the motor from the burner can, which will admit burner can gasses into the air conditioning system. If it is really kerosene you are smelling, that is the probable source.

It could be coming from the main engine but there would likely have been audible rumbling or thumping sounds if it was stalling/surging while on main engine bleed.

Answer 2

If you're smelling it on the ground, it's because there's kerosene in the air around an airport and the plane's door(s) are open. Anything on the wind will blow in. If you don't notice the smell until you're taxiing, remember that the cabin air is recycled by using outside air bled through the engine compressor stages. If you happen to be 6th in a line of aircraft taxiing to the take off end of the runway, there's a lot of burnt kerosene headed your way for the engines to ingest & blow into the cabin of your plane.

If you're smelling it in the air, it's likely that the smell was there on the ground and you just didn't notice and the air inside the cabin hasn't been fully replaced yet.

If the airport is downwind from a paper manufacturing plant, you'll probably never notice the kerosene smell because the paper plant smell would totally overwhelm it, but it would prompt questions of "I was flying out of PAPR and the air smelled really bad, what happened at the airport to cause this?"