Modeling and unsteady simulation of turbulent multi-phase flow including fuel injection in IC-engines

In internal combustion engine (ICE), researchers have to face with stringent environment regulations concerning pollutants while improving engine thermal efficiency, making the engine design a complex task. To meet these requirements, an understanding of the salient features of all the engine processes are very important. Being the primitive process of engine operations, fuel injection influences whole engine cycle via fuel-air mixture preparation, thereby the combustion behavior and subsequently the emission performance. The inhospitable environment inside a combustion chamber makes the experimental investigations more complex and expensive. In contrast, a CFD based investigation can provide comprehensive insight about in-cylinder flow field, spray injection phenomena as encountered in IC-engine. In the present study, a CFD tool that enables to investigate the real unsteady behavior of realistic engine configuration is developed by coupling Large Eddy Simulation (LES) together with a spray module using the KIVA4-mpi Code. It is based on an Eulerian-Lagrangian framework to describe the spray evolution including primary and secondary atomization. A linear instability sheet atomization (LISA) based sub-model is integrated to represent the primary atomization. The secondary atomization is modeled by an available Taylor analogy break-up (TAB) model. In dense spray region, the droplet-droplet interaction considerably influences the overall spray dynamics. The first novelty of the proposed methodology is to include droplet-droplet interaction processes via an appropriate collision sub-model that is independent of mesh size and type. Thereby, taking account of different regimes, such as bouncing, separation, stretching separation, reflective separation and coalescence. The formation of wall film on hot cylinder surface is a critical process in an IC-engine, since it largely influences the engine performance and emission characteristics. The second novelty of this spray module is the implementation of an improved wall film model that includes the combined effects of droplet kinetic energy and wall temperature into KIVA4-mpi code. To perform an IC-engine simulation, a good quality mesh generation in ICEM-CFD for an engine geometry is challenging task. The KIVA4-mpi is compatible only with block structured mesh without any use of O-grid. Due to this reason, only certain degree of mesh refinement is possible. This makes it difficult to achieve a good quality fine mesh required for LES simulation. In the present study, a new meshing strategy is proposed to generate suitable mesh for real IC-engine configurations. The new method clearly demonstrates the improvement in resolving the in-cylinder flow structures. First, the simulated results for motored case (no fuel injection and no combustion) are compared with the experimental data for a transparent combustion chamber (TCC) engine configuration from Engine Combustion Network (ECN). Second, to demonstrate the importance of fuel injection sub-models, further simulations are carried out including the evolution of evaporating fuel spray with wall impingement. Third, using the new meshing strategy, simulations are also performed for a real complex canted 4-valve engine configuration. Simulated results are compared well with available experimental data