CFD analysis of the airflow behavior in the intake system of a low-displacement diesel engine

Introduction− The airflow analysis for internal combustion engines (ICE) remains challenging for researchers due to the complexity of the flow interactions inside the cylinder. Different flow characteristics such as turbulence, instability, periodicity, and non-stationary conditions required advanced methods to describe the overall behavior. The present study proposed the implementation of a turbulence model through Computational Fluid Dynamics (CFD) analysis that further simplifies the airflow phenomena for low-displacement engines while describing the parameters that influence the engine efficiency and emissions. Objective− The study aims to analyze the airflow behavior in the intake system of a low-displacement diesel engine with natural aspiration through an experimental model adjusted by CFD analysis. Methodology− The analysis of the airflow behavior in the intake system of the engine was carried out with an experimental model that describes the airflow characteristics. This model is adjusted via CFD analysis in OPENFOAM®, which determines both discharge (DC) and swirl (SC) coefficients to describe the flow interactions in the intake system. Results− The CD values ranged between 0 to 0.5, indicating that this engine can displace 50% of the ideal airflow with a valve diameter of 30.5 mm and a chamber volume of 0.3 L. In contrast, the SC, for a variable reference area, ranged from 0.3 to 0.19, stating that the engine experiences less airflow displacement, specifically 11% of the theoretical capacity as the mass flow increases for each valve lift. Conclusions− In conclusion, the methodology implemented in the study showed that for rotatory regimes of 3000 rpm and 3400 rpm, a concrete vortex is generated with velocity values between 10 and 20 m/s in the peripherical region, which ensures the airflow rotation with vorticity inside the cylinder. At 3400 rpm, the SC value increments are compared to other regimes when the end of the valve lift distance is reached. Thus, it can be verified that under this regime, the optimal vorticity generation is achieved, which contributes to reduce emissions and boost the global efficiency of the engine