Direct Numerical Simulation of Fundamental Processes in Engines

Abstract

With the advent of high-performance computers and advanced numerical algorithms, direct numerical simulation (DNS) has emerged as a computational research tool, in concert with experimentation and theory, to provide fundamental insight into the physics of turbulent combustion and statistical information required to develop and validate predictive models used for engine design and optimization.  To illustrate the utility of this approach results from DNS are presented to understand the effects of temperature stratification on characteristics of combustion in a homogeneous charge compression ignition (HCCI) environment, and implications for modeling are discussed.  HCCI engines are being considered as an attractive alternative to diesel and spark-ignited engines.  By exploiting a lean-intake charge that is well-mixed prior to combustion HCCI engines may provide efficiency gains over spark-ignited engines, while generating lower emissions compared with diesel engines.  However, a major challenge posed by HCCI is to control the heat release rate to prevent damaging engine knock.  One possible strategy is to tailor spatial variations in mixture composition or temperature to produce a desired heat release rate.  As revealed for the first time by DNS, these spatial variations contribute to a range of combustion modes distinct from homogeneous autoignition.