An internal combustion engine having a fuel injector, a piston chamber, a piston slidably disposed in the piston chamber having a piston crown along a top surface, a head assembly having at least one pre-chamber separate from the piston chamber and in fluid communication with the piston chamber via at least one connecting orifice, and an ignition device disposed in the pre-chamber for igniting a fuel air mixture within the pre-chamber, thereby producing an ignition jet being introduced into the piston chamber via the at least one connecting orifice to ignite a fuel/air mixture in the piston chamber. The fuel/air mixture is passively introduced into the at least one pre-chamber during at least a compression stroke of the piston.