3D-1D Analyses of the Turbulent Flow Field, Burning Speed and Knock Occurrence in a Turbocharged SI Engine 2007-24-0029

CFD techniques are more and more utilized in the development of new solutions for performance improvement of internal combustion engines.

Three dimensional models, in general, are able to provide detailed and sound information on engine phenomena, but often they are time consuming and hard to be implemented. On the other hand, one-dimensional models can reproduce the entire engine cycle with acceptable computational times; however they need semi-empirical correlations in order to model the flow field details and the burning speed within each cylinder.

In this paper, an example of hierarchical structure of 3-D and 1-D models has been proposed. The main performances of a small turbocharged spark-ignition engine have been calculated. Variable-speed and full load operating points have been analyzed. The 3-D model provided the details of the in-cylinder flow field and turbulent indices. These results have been utilized as reference data in tuning a quasi-dimensional turbulent combustion model, included within a 1-D model of a “downsized” turbocharged spark-ignition (SI) engine. Combustion modeling utilizes a deeply validated approach based on a fractal schematization of the flame front surface. Knock occurrence has been predicted by the solution of a kinetic-scheme inside the “end-gas” unburned zone. Once tuned, the one-dimensional code has been finally applied to find the knock-limited spark-advance at wide-open-throttle conditions, for different engine speeds. Numerical results have been compared to the experimentally determined values and a good agreement has been found.

This work demonstrates as matching models of different hierarchical levels could be a useful tool in the industrial development of high efficiency engines.