Fuel, some Sadie selected (6)
I believe the answer is:
diesel
'fuel' is the definition.
(diesel fuel is a kind of fuel)
'some sadie selected' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'DIESEL' is hidden in the letters of 'sadie selected'.
(Other definitions for diesel that I've seen before include "Rudolf __ , French-born German engine inventor, d.1913" , "Eponymous German engineer" , "Fuel used by heavy vehicles" , "Fuel for heavy vehicles like lorries" , "Train perhaps" .)