Lean-Burn Natural Gas Engine

A natural gas engine burning fuel with excess air, meaning that its air-to-fuel ratio can run as lean as 65 to 1 (by mass). In contrast, the air-to-fuel ratio needed to stoichiometrically combust gasoline is 14.64 to 1. The excess of air in a lean-burn engine results in an emission of far less hydrocarbons than rich-burn engines.

Compare to Rich-Burn Natural Gas Engine.