Lean Burn Gas Engine with a Pre Chamber Ignition System: Grid Independence Study and Design Optimization

Pre-chamber ignition systems are used in the lean burn gas engines to avail benefits of low emissions and high efficiency. Numerical investigations of these pre-chamber ignition systems are challenging due to the requirement of local refinement inside the pre-chamber, especially between the electrodes. In addition, high pressurized jets from the pre-chamber small holes require jet-directed fine mesh, which is quite challenging with the cylinder hexahedron coarse moving mesh. In the present work, a specialized mesh with the optimized spatial grid size distribution of the single cylinder engine with pre-chamber ignition system is generated and the influence of the pre-chamber geometry on charge motion and exhaust gas residuals inside pre-chamber is numerically investigated.
Firstly, grid independence study of a single cylinder engine and pre-chamber ignition system is conducted respectively and validated with experimental data of the open cycle at motored operation for reference geometry. Afterward, a study of pre-chamber ignition system geometry is conducted using an open-cycle mesh (valves and piston motion are included), to optimize the charge motion and exhaust gas residuals inside the pre-chamber. ... mehrSubsequently, charge motion inside the pre-chamber from open cycle simulation before ignition is mapped with closed-cycle mesh (no valves included) using Star-CD SMAP feature, to initialize the similar flow conditions inside the pre-chamber ignition system, which in turn is used to study the flame kernel development. The mapping process drastically reduces overall grid size and consequently time and computational power required by simulation without affecting the accuracy of results. Several pre-chamber designs were evaluated and the influence of pre-chamber geometry on flow velocity, TKE and exhaust gas residuals inside the spark gap and their subsequent effects on the flame (kernel) development were studied.