Crossword Genius

Ignited some fires with a quantity of petrol (5)

Ross

I believe the answer is:

litre

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'a quantity of petrol' is the definition.
(I've seen this in another clue)

'ignited some fires' is the wordplay.
'ignited' becomes 'lit' (synonyms).
'some fires' becomes 're' (I can't justify this - if you can you should give a lot more credence to this answer).
'lit'+'re'='LITRE'

'with' acts as a link.

Can you help me to learn more?

(Other definitions for litre that I've seen before include "Mcc?" , "quantity of drink" , "Metric liquid measure" , "One cubic decimetre" , "It's equal to about 1.75 pints" .)

I've seen this clue in the Evening Standard.
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