"This thesis experimentally, computationally and analytically examines the transient jet used to ignite combustible mixtures during Turbulent Jet Ignition (TJI). The TJI system is a prechamber initiated combustion enhancement system that can be used in place of a spark plug in a spark ignition (SI) engine. In TJI the ignition source, which originates in the prechamber, enters the main chamber through a connecting nozzle(s) as a transient high temperature jet of reacted mixture, reacting mixture and active radicals. TJI is capable of enabling low temperature combustion, through either lean or dilute combustion. For this work, TJI experiments were performed in an optically accessible Rapid Compression Machine (RCM). High speed visualization was performed via an SA4 high speed color camera and the images were compared with Computational Fluid Dynamics (CFD) modeling results. Comparison was also made between the experimental and numerical pressure data. A significant portion of this work is dedicated to the CFD modeling of the TJI process and for the first time a theoretical study of the jet flow field, density gradients, turbulence intensity, and temperature fields in both the prechamber and the main chamber was performed. The influences of nozzle size and mixture stoichiometry on jet penetration speed and combustion performance were investigated. 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 f=0.67, 0.8 and 1.0. The hot jet velocity at the orifice exit was calculated, for the first time, using mathematical correlations. The Mach number and Reynolds number were also computed. The high speed imaging shows the influence of orifice diameter on 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 also a reduction in hot jet penetration speed with an increase in the equivalence ratio. Moreover, the jet was turbulent with calculated Reynolds numbers of around 20,000 or greater. Normalized transient results are presented that produce good agreement between the various model predictions. A discussion is provided of a new correlation model for the transient TJI process. In a separate set of experiments, the impact of an auxiliary fueled prechamber on the burn rate and on the lean or dilute limit extension of the RCM was investigated. Nitrogen was used as the diluent and the nitrogen dilution limit was found to be 35% of system mass. Both experimental and numerical results confirmed the idea of combustion enhancement of diluted mixtures by the prechamber auxiliary injection events. To model the turbulent jet of the TJI system, Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) turbulence models and the SAGE chemistry solver were used. To determine the effect of mechanism reduction, the pressure traces were computed using four (4) comprehensive chemical kinetic mechanisms (San Diego, Aramco, GRI, and NUI) and one (1) reduced chemical kinetic mechanism, which are all 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. The numerical iso-surface temperature contours (1200, 800, 2000, and, 2400 K) were obtained which enable 3-D views of the flame propagation, the jet discharge, the ignition and extinction events, and the heat release process."--Pages ii-iii.
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