**1. Introduction**

258 Computational Simulations and Applications

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(2004). Hydrodynamics of gas-solid flow around immersed tubes in bubbling fluidized beds. *Powder Technology*, Vol.145, No.2, (July 2004), pp. 88-105, ISSN 0032The design of modern internal combustion (IC) engines requires the understanding and quantification of many physical phenomena, including their impact on engine performance and emissions. In fact, the investigation of thermo-fluid-dynamic processes, combustion, performance and emissions is essential to fulfil the emission regulations, that are becoming more and more severe. Although the experimental analysis of such processes is mandatory to obtain fully quantitative results, the application of numerical simulation techniques is continuously increasing in popularity amongst the research community. This is due, on one hand, to the increased accuracy of specific sub-models, which are dedicated to several physical aspects in IC engines, and, on the other hand, to the availability of computational resources of increasing power. Nowadays, simulation tools can range from zerodimensional analysis tools of the combustion process in the engine chamber, to complete three-dimensional simulation models of turbulent flows and combustion.

This chapter is intended as an overview of the state-of-the-art of 1-D computational fluiddynamics (CFD) and thermo-dynamic tools applied to IC engines, with specific reference to compressed natural gas (CNG) fuelling. Moreover, the specific modelling approaches of the authors are presented, within the 0-D and 1-D frameworks.
