Three-dimensional numerical simulation of the turbulent jet ignition combustion process of a premixed methane-air mixture in a Rapid Compression Machine (RCM) was performed using the Converge computational software. Turbulent jet ignition is a prechamber initiated combustion system that can replace the spark plug in a spark ignition engine. The prechamber is a small volume chamber where an injector and spark plug are located and is connected to the main combustion chamber via one or multiple small orifices. Turbulent jet ignition is capable of enabling low temperature combustion, through either lean or dilute combustion. A RANS model, which included a k-ε turbulence model to solve the mean flow and the SAGE chemistry solver with a reduced methane mechanism to solve the chemistry, was used to model the turbulent jet ignition system.The novelty of this research is the investigation of the impacts of an auxiliary fueled prechamber on the burn rate and on the lean or dilute limit extension of the RCM. The numerical results are compared to data and optical images obtained from high speed imaging of combustion in the optically accessible RCM. The results show that the simulation accurately predicts the combustion process and also gives insight into the mean velocity of the turbulent jet and the density and temperature variation in the entire domain, which cannot be measured experimentally.