Introduction and Motivation
In internal combustion engines (ICE), researchers have to face with stringent regulations concerning pollutants while improving engine thermal efficiency, making the engine design a complex task. The rapid depleting fossil fuel reserve has put engine developers attention towards alternative bio-fuel fuels that can be used with existing engine configuration without any major changes. To meet these requirements intense effort is being put at various stages of engine operation, such as intake change motion, fuel injection and mixing, combustion, and exhaust after treatment. While the emission target is combined effort in-cylinder design and exhaust after treatment. To carry out complete and robust engine design, an understanding of the salient features of all the engine processes are very important. Being the primitive process of engine operations, fuel injection influences the whole engine cycle via air-fuel mixture preparation, thereby the combustion behaviour and subsequently the emission performance. The inhospitable environment inside a combustion chamber makes the experimental investigations become 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
Method and Theory
In ongoing research is mainly focused on developing 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 with KIVA-4 Code. It is based on an Eulerian-Lagrangian framework to describe the spray evolution including primary and secondary atomization with preliminary combustion model based on simple Arrhenius equation. The major task associated are: (1) Devising new meshing strategy for realistic IC-engine (2) Development of comprehensive fuel injection model (3) Extension of existing fuel injection models for bio-fuel such as butanol blended with conventional fuels (gasoline, diesel) by incorporating appropriate multi-component evaporation model (4) Modeling spray dynamics of Urea-water solution (adBlue) in the context of SCR NOx reduction.
To perform an LES in realistic IC-engine configuration, a good quality mesh generation in ICEM-CFD for an engine geometry is challenging task. A new meshing strategy is proposed to generate suitable mesh for real IC-engine configurations which has already been successfully applied for various engine configuration.
For a hollow-cone injector, a combined linear instability sheet atomization (LISA) and Taylor analogy break-up (TAB) model based sub-models are integrated to represents the primary atomization and secondary atomization, respectively. While for circular orifice injector, Kelvin-Helmholtz (KH) and TAB is used. In dense spray region, the droplet-droplet interactions considerably influences the overall spray dynamics. The proposed methodology also includes 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 spray module is therefore incorporated with improved wall film model that includes the combined effects of droplet kinetic energy and wall temperature is into KIVA4-mpi code. The multi-component evaporation model is very important when liquids with different evaporating behavior are mixed together, especially in case of bio-fuel blending with conventional fuels (gasoline, diesel) and during the injection of Urea-water solution (adBlue) for SCR NOx reduction. This has to be done by putting relevant thermo-physical properties accurately inside the CFD code.
In order to understand extact behavior of bio-fuel and various blending, it important to carry out detail validation study of spray dynamics of bio-fuel then evaporation study with fuel blending. Then incorporate it into the real engine configuration and perform comparative study with conventional fuel. While in case of Urea-water solution (adBlue) injection, the evaporation dynamics is complicated as urea tend to solidify before evaporating and hence necessary model is required pyrolysis of solidified urea. In such a scenario a spray wall interaction becomes even more complicated, an appropriate wall-film model is required to address the impingement of liquid, semi-solid, solid urea-water solution.