Analysis of Dimensionless Numbers for Convective Heat Transfer Models Used in the Study of Spark Ignition Engines

摘要

Convective heat transfer models derived from equations for turbulent heat transfer in pipes are still used when undertaking thermodynamic calculations with limited data available for engine geometry characteristics. While computational fluid dynamics codes can offer an improved accuracy, they require increased computational power, extensive knowledge of fluid dynamics and numerical modeling. Simple equations derived from turbulent flow in tubes models require empirical correction factors that often need to be adjusted for a specific engine and working conditions. This study proposes an analysis of the dimensionless numbers employed in such convective heat transfer models in order to identify equations that are best suited for premixed charge spark ignition engines. For this purpose, a simple zero-dimensional model was employed to reconstruct the in-cylinder pressure and temperature traces and these values were then used for calculating heat transfer parameters. Ensemble averaged mean fluid velocity was identified as one of the main parameters that influences heat losses to the combustion chamber walls, and therefore, its prediction as accurately as possible is considered to be paramount.