Maybe lower emission from flame than exhaust (7)
I believe the answer is:
methane
'maybe lower emission' is the definition.
The answer and definition can be both substances as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'from flame than exhaust' is the wordplay.
'from' says the answer is hidden in the clue.
'METHANE' can be found hidden inside 'flame than exhaust'.
Can you help me to learn more?
(Other definitions for methane that I've seen before include "compound" , "simplest hydrocarbon" , "Marsh gas - the name (anag)" , "Get fuel" , "Main constituent of natural gas" .)