Pre-chamber jet ignition, an alternative to traditional spark ignition, has been used in large-bore natural gas engines and F-1 racing cars. It has demonstrated the potential for enabling stable ultra-lean combustion, reduction in cycle-to-cycle variation, and extension of the lean operating limit of the engines. The concept of pre-chamber jet ignition is to burn a small amount of near-stoichiometric air-fuel mixture in a small volume called pre-chamber. The higher pressure resulting from pre-chamber combustion pushes the combustion products into the main chamber in the form of a hot turbulent jet, which then ignites the lean mixture in the main chamber. Compared to standard spark ignition, the hot jet has a much larger surface area leading to multiple ignition sites on its surface, which can enhance the probability of successful ignition and cause faster heat release and flame propagation due to the strong turbulence contained in the jet.