This work aims to enhance fundamental and practical understanding of pre-chamber (PC) combustion engines, using computational fluid dynamics (CFD) simulations conducted with the software CONVERGE employing the Reynolds-averaged Navier-Stokes turbulence closure and the well-stirred reactor combustion model for methane oxidation. First, to help the design of the KAUST pre-chamber, the simulations were conducted to assess the impact of design parameters such as throat and nozzle diameters, and nozzle length in a passively operated pre-chamber at lean conditions. The geometrical parameters showed to affect the pre-chamber combustion characteristics, such as pressure build-up, radical formation, heat release, and the composition of the jets penetrating and igniting the main chamber charge. It was found that the narrow-throat pre-chamber is strongly influenced by the throat diameter, but weakly influenced by nozzle length. A flow reversal pattern was observed, promoting the accumulation of intermediate species in the PC, leading to a secondary heat release. Subsequently, the validation of the actively fueled pre-chamber systems was assessed under different fueling strategy and validated against experimental data. The last chapter analyzes the impact of enrichment and stratification of the pre-chamber on the main chamber combustion. An open-cycle simulation was conducted to describe the full interaction between both chambers. The influence of fuel enrichment in the PC was compared to the passive mode operation and found to greatly impact in the overall system performance. It was found that the excessively rich PC does not yield the optimal results; instead, a pre-chamber with stoichiometric composition at spark timing does. Although the fuel distribution inside the PC was not homogeneous, the active control of the PC was shown to enable a command of the pressure response. It was found that the upstream flame propagation forces part of the PC mixture to leak to the main chamber, creating localized fuel rich regions, which enhances the combustion of the MC charge. The overall MC combustion is found to be complex, influenced by the turbulent mixing and local cooling, and possibly local quenching events. The detailed interaction of mixing and combustion in the MC is not fully understood and is subject of future studies.
|Date of Award||Jul 2020|
|Original language||English (US)|
- Physical Sciences and Engineering
|Supervisor||Hong G. Im (Supervisor)|
- Clean combustion
- Computational fluid dynamics
- Large scale simulation