The behavior of transient, compressible and combusting pre-mixed methane-air jets was experimentally studied with high speed imaging in a rapid compression machine. The jets were generated with a turbulent jet ignition system, which is a prechamber initiated combustion system. The absence of physical analyses of the characteristics of premixed turbulent jets was the motivation for the present study. Experiments were completed for turbulent jet ignition system orifice diameters of 2.0, 2.5 and 3.0 mm each at lean-to-stoichiometric equivalence ratios of phi = 0.67, 0.8 and 1.0. The hot jet velocity at the orifice exit was calculated using mathematical correlations. The Mach number and Reynolds number were also computed. The high speed imaging shows the influence of orifice diameter on the flame propagation and the shape and structure of vortices resulting from the turbulent jet. Results revealed a direct relationship between orifice exit area reduction and a decrease in hot jet penetration speed. There was a reduction in hot jet penetration speed with an increase in the equivalence ratio. For the orifice diameters and equivalence ratios tested here, results showed that the jet evolved downstream of the orifice exit in partial agreement with existing correlations. Moreover, the jet was turbulent with calculated Reynolds numbers of around 20,000 or greater. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.