Predicting the Influences of Intake Port Geometry on the Tumble Generation and Turbulence Characteristics by Zero-Dimensional Spark Ignition Engine Model

摘要

The flame propagation characteristic is one of the greatest factor that determines the performance of spark ignition (SI) engines. The in-cylinder flow dynamics is very significant in terms of flame propagation because of its direct influence on the flame shape, turbulent flame speed, and the ignition quality. A number of different techniques are available to optimize the in-cylinder flow and maximize the utilization of turbulence for faster combustion, and tumble enhancement by intake port geometry is one of them. It requires excessive computational expenses to evaluate multiple designs under wide range of operating conditions by 3D-CFD, therefore, a low-dimensional model would be more competitive in such design optimization process. This work suggests a new modification approach for typical 0D turbulence model to take account for the tumble generation during the intake process as well as the turbulence characteristics associated with it. The angular momentum of cylinder gas is used to represent tumble motion on zero-dimension. In order to estimate the degree of tumble generation, the intake mass flow is directionally subdivided and simple physics-based assumptions, supported by a minimal steady-state CFD simulation, are applied to each division. The 0D k- ε turbulence model has been modified to consider the rotational energy equivalent to the calculated angular momentum, and the temporal evolution of the angular momentum and turbulent kinetic energy (TKE) over the engine cycle is attainable using this modified model. The results with varying port geometry, engine speed, and load are compared to the results of 3D-CFD as a verification of model’s predictability.