Abstract This paper analytically and computationally examines the transient jet used to ignite combustible mixtures during Turbulent Jet Ignition (TJI). In TJI the ignition source, which originates in the prechamber, enters through a connecting nozzle into the main chamber as a transient high temperature jet of reacted mixture, reacting mixture and active radicals. A Computational Fluid Dynamics (CFD) model is developed for the flow field, density gradients, turbulence intensity, and temperature fields in both the prechamber and the main chamber. None of these quantities are currently measurable. The pressure traces computed using four (4) comprehensive chemical kinetic mechanisms (San Diego, Aramco, GRI, and, NUI) and one (1) reduced chemical kinetic mechanism are compared with the experimental pressure data. Results indicate that none of the mechanisms are in complete agreement, however they are in good agreement with the experimental burn rate, peak pressure and ignition delay predictions. Comparison is made of the simulations with high speed chemiluminescence images of combustion and measured pressure traces in a Rapid Compression Machine (RCM). The influences of nozzle size and mixture stoichiometry on jet penetration speed and combustion performance are investigated. Normalized transient results are presented that produce good agreement between the various classes of model predictions. A discussion is provided of a new correlation model for the transient TJI process.