Numerical Analysis of Mixing of Bio-Hybrid Fuels in a Direct Injection Engine with a Pre-Chamber Ignition System

Numerical analyses of the liquid fuel injection and subsequent fuel-air mixing for a high-tumble direct injection engine with an active pre-chamber ignition system at operation conditions of 2000 RPM are presented. The Navier-Stokes equations for compressible in-cylinder flow are solved numerically using a hierarchical Cartesian mesh based finite-volume method. To determine the fuel vapor before ignition large-eddy flow simulations are two-way coupled with the spray droplets in a Lagrangian Particle Tracking (LPT) formulation. The combined hierarchical Cartesian mesh ensures efficient usage of high performance computing systems through solution adaptive refinement and dynamic load balancing. Computational meshes with approximately 170 million cells and 1.0 million spray parcels are used for the simulations. The influence of a lateral ethanol injection on the tumble flow motion and the entrainment into the pre-chamber is analyzed for stoichiometric and lean fuel conditions for an early injection at 60 CAD. The injection into the main-chamber shows a strong impact of the fuel jets on the in-cylinder flow field with a sustained tumble-motion. For the stoichiometric condition and at 300 CAD, the fuel concentration in the pre-chamber lies 67% below the main-chamber fuel concentration. For the lean condition, the deviation from the target fuel concentration in the main-chamber is lowered by at least one order of magnitude compared to the stoichiometric fuel injection at the start of ignition.