Afif Ahmed

Numerical investigations on methods to control the rate of heat release of HCCI combustion using reduced mechanism of n-heptane with a multidimensional CFD code

In this study a semi-reduced reaction scheme developed previously was used to derive a 26 step reduced mechanism, using the sensitivity approach and the steady state approximation (QSS) with Chemkin code. This 26 step model has been implemented in a CFD combustion code (Star-CD/Kinetics) to study combustion process in homogeneous charge compression ignition (HCCI) engines. The first results obtained have confirmed the very rapid combustion phase and fast heat release with completely homogeneous mixtures, for a wide range of operating conditions. This numerical approach has been used first to study the effects of natural thermal stratification when the mixture is initially homogeneous. In a second step, the different possible methods to control the heat release rate have been studied. The stratification with several homogeneous regions of different composition is shown to be very efficient; the limits of this process are discussed.

Turbulence Modelling in the Automotive Industry

ABSTRACT Flow and combustion modelling has been extensively used for more than two decades in design in the automotive industry with promising success in reducing the development period. This paper is an overview of the state of art of CFD simulations used in automotive engineering. Some of the automotive applications, such as pressure loss in pipes, cooling system flow repartition do not require specific turbulence modelling and are fully operational in the industry. In other applications, such as external vehicle aerodynamics and drag coefficient simulations, despite the tangible accomplishment of CFD modelling associated with improved experiment data, the precision of simulations is still behind the requirements of todays developments. In the challenging case of in-cylinder combustion simulation where compressible, transient, 2-phase turbulent flow with heat and mass transfer occurs in moving wall geometry, progress has been mainly accomplished in the description of complex variable geometry and mesh generation treatment rather than the physical aspects of turbulence in swirling flows in the cylinders. Nevertheless, substantial advances have been made in CFD model development through validation by visualisation and other experimental techniques. Examples of different application fields in the automotive industry are provided

Developments of a new air-guided direct injection SI combustion chamber

The simultaneous use of experimental and computational techniques allows us to achieve both a good understanding of the physical phenomena as well as quicker, safer and cheaper engine developments.