Turbulent jet ignition (TJI) is a novel ignition enhancement method, which facilitates the combustion of lean and ultra-lean mixtures in complex propulsion systems and engines. Here, a comprehensive study of TJI in different combustion systems is conducted with direct numerical simulation (DNS) and large eddy simulation (LES) methods.DNS of TJI-assisted combustion of lean hydrogen-air is performed in a three-dimensional planar jet configuration for various thermo-chemical and flow conditions. Fully compressible gas dynamics and species equations are solved with high order finite difference methods and a detailed chemical kinetics mechanism. Several interesting phenomena involved in TJI-assisted combustion including localized flame extinction/reignition and simultaneous premixed-diffusion flames are investigated by considering flow/combustion variables like the heat release, temperature, species concentrations, vorticity, Baroclinic torque, and a newly defined TJI progress variable.Numerical simulations of TJI-assisted combustion in a rapid compression machine (RCM) are also conducted by a hybrid Eulerian-Lagrangian LES method based on the filtered mass density function (FMDF) model. An immersed boundary method is developed and used in the LES to facilitate morphing the complex geometries and decrease the Monte Carlo (MC) particle search and locate operations in FMDF. It also helps to properly handle finite difference grids and MC particles at the boundaries while maintaining the high accuracy of the simulator. In the TJI-RCM system, a hot product turbulent jet rapidly propagates from a pre-chamber (PCh) to a main chamber (MCh). Three main combustion phases of TJI-assisted combustion in a RCM are delineated as i) cold fuel jet, ii) turbulent hot product jet, and iii) reverse fuel-air/product jet. The effects of various parameters on these phases are studied numerically, including the igniter timing and location, lean/rich/N2-diluted mixtures, and adiabatic vs. non-adiabatic walls. It is found that the turbulent jet characteristics and the MCh combustion are highly affected by the PCh turbulence intensity as well as the ignition parameters. For example, igniting the PCh at the lower locations close to the nozzle forces the PCh charge to fully participate in the PCh ignition/combustion processes and prevents the unburned fuels leaking to the MCh. It also enhances the MCh combustion by generating lower velocity hot product jets for a longer time. The pressure traces predicted by LES/FMDF are found to be in good comparison with the available experimental data. The temperature contours are also well comparable with the experiments.
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