Optically Accessible Direct-Injection Spark-Ignited (DISI) Engine – Experimental Analysis and 3D-CFD Simulation

Nowadays, the growing importance of human emissions on the environment has led to decreasing emissions from internal combustion engines, and consequently reducing consumption, with ever more stringent regulation. For this region, the study of lean combustion spark-ignited engines was improved, but this type of combustion is less stable than the stoichiometric one, different researchers are studying what causes this Cycle-to-Cycle Variability (CCV) and how to solve the problem. In this thesis, the kernel formation was investigated in an optically accessible Direct-Injection Spark-Ignition (DISI) engine to correlate its formation with CCV. The work is divided into two main parts, in the first one was reported the thermodynamic analysis of the engine parameters (Indicated Mean Effective Pressure (IMEP), Covariance of the previous parameters (COV_IMEP), Peak of pressure and its covariance (P_MAX and COV_(P_MAX )), Mass Fraction Burned (MFB), Net Heat Release Rate (NHRR) etc...); two different spark plugs were used (i.e. Single and Double J-electrode), three different orientations for the first one (Uni-, Cross- and Counterflow with respect to the tumble motion) and two for the second one (Uni- and Crossflow with respect to the tumble motion). In the second part was developed a 3-D CFD model on the software Converge CFD (v3.0), which reproduced the in-cylinder thermofluidodynamic phenomena of the engine, the data obtained in the experimental part and the previous analysis were used to validate the simulation model. The Reynolds Averaged Navier-Stokes (RANS) together with the RNG k-ε turbulence model was used to account for the variation of the flow field. To simulate appropriately the combustion phase a detailed chemical kinetics solver (SAGE) was used. The 3-D CFD model allowed us to analyse the variations of the flow field and the mixture composition during the kernel formation to understand the influence of these and different spark plugs on CCV.