The Evolution of Flow Structures and Turbulence in a Fired HSDI Diesel Engine

In-cylinder fluid velocity is measured in an optically accessible, fired HSDI engine at idle. The velocity field is also calculated, including the full induction stroke, using multi-dimensional fluid dynamics and combustion simulation models. A detailed comparison between the measured and calculated velocities is performed to validate the computed results and to gain a physical understanding of the flow evolution. Motored measurements are also presented, to clarify the effects of the fuel injection process and combustion on the velocity field evolution.

The calculated mean in-cylinder angular momentum (swirl ratio) and mean flow structures prior to injection agree well with the measurements. Modification of the mean flow by fuel injection and combustion is also well captured. Substantial changes in the tangential velocity near the spray path are observed during the fuel injection event and, after combustion, a radial profile of the mean tangential velocity that favors turbulence production is developed within the bowl. RMS fluctuations show significant deviations between measurements and predictions over technologically important portions of the cycle. Significant increases in measured fluctuations-in the tangential component near the fuel spray path at start of injection (SOI), and in both the radial and tangential components within the bowl after combustion-are absent from the model predictions. Measured fluctuations are anisotropic, and suggest turbulence production enhancing the tangential fluctuations near SOI, and enhancing the radial fluctuations after combustion.