'Sitting in an ashtray' is not necessarily the best choice but at least conveys the correct meaning. 置き means 'left (behind)' or 'unattended'. In this case, the point is that the smoke output depends on whether cigarettes are "puffed" or not.

置く = to place, 置き = placed (adjective)
煙草 = tobacco
煙草入 (tabako ire) = cigarette case
煙草2本分 = 2 cigarettes

--- The adjective “placed” would make the cigarettes lit and emitting smoke but “inactive” in terms of movement. (They’re placed there but aren’t being waved around by a smoking individual.)

--- If it is a test for smoke that a device is putting out, perhaps it can be something like these:

Emits an equivalent to 2 placed lit cigarettes in 10 seconds."
Takes 10 seconds to emit smoke equal to 2 placed lit cigarettes

--- Here are some examples of “placed cigarettes” – one for a mattress test, the other for a crime:
http://ohsonline.com/articles/2010/11/02/10-cpsc-proposes-ne...
CPSC Proposes New Cigarette for Mattress Testing
Industry trade associations wanted a reduced ignition propensity, or fire safe, cigarette used, but the commission said using one could reduce the fire safety effectiveness of the testing standard.
The standard was enacted in 1972, before the commission existed. It specifies a pass/fail test of the ignition resistance of a mattress or mattress pad when exposed to “lighted cigarettes placed at specified locations” on the surface of the mattress or pad.

http://blog.cleveland.com/metro/2010/06/bath_man_charged_wit...
When police approached, they realized that he had removed the gas cap and “placed a lit cigarette” in the opening. When they went to arrest Wixcey, he ran. He was caught after a brief chase.


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Note added at 4 hrs (2010-11-03 00:00:51 GMT)
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Or instead of "lit": placed lighted cigarettes

http://www.superstock.com/stock-photography/smoking
http://www.freepatentsonline.com/6182669.html
http://www.mst.dk/NR/rdonlyres/1DBB5B30-34F9-4F9D-BD0E-D8EA4...

See: http://www.swissinfo.ch/eng/index/Fire-safer_cigarette_spark...