
1) Engine technology
Found on
https://www.crosswordclues.com/clue/lean-burn

Lean burn refers to the burning of fuel with an excess of air in an internal combustion engine. In lean burn engines the air:fuel ratio may be as lean as 65:1 (by mass). The air:fuel ratio needed to stoichiometrically combust petrol, by contrast, is 14.64:1. The excess of air in a lean burn engine combusts more of the fuel and emits fewer hydrocar...
Found on
http://en.wikipedia.org/wiki/Lean_burn

Lean-burn is the ability to ignite air and fuel mixtures that contain higher amounts of air than normally used.
Found on
https://www.encyclo.co.uk/local/20849
No exact match found.