Lean burn gas engines are gaining large attention in the marine sector thanks to the low emissions levels and high efficiencies. However, as the ignitability and combustion stability of leaner mixtures are reduced, ignition systems able to deliver high energy content are necessary. One the most effective approach for large bore marine engines involves the use of an active prechamber in which a small quantity of quasi-stoichiometric air/fuel mixture is obtained and then ignited through a spark plug. The corresponding jet, flowing from prechamber to main chamber, contains many wrinkled turbulent flames and active radicals enhancing the probability of successful ignition.