Comparison of Eulerian and Lagrangian 1D Models of Diesel Fuel Injection and Combustion 2017-24-0006
Diesel engines are being more commonly used for light automotive applications, due to their higher efficiency, despite the difficulty of depollution and extra associated costs. They require more accessories to function properly, such as turbocharging and post-treatment systems. The most important pollutants emitted from diesel engines are NOx and particles (in conventional engines), being difficult to reduce and control because reducing one increases the other. Low temperature combustion (LTC) diesel engines are able to reduce both pollutants, but increase emissions of CO and HC. Besides HCCI and EGR systems, one method that could achieve LTC conditions is by using multiple injections (pilot/main, split injection, etc.). However, understanding multiple diesel injection is no easy task, so far done by trial and error and complex 3D CFD models, or too simplified by 0D models.
Therefore, a numerical 1D model is to be adapted to simulate multiple injection situations in a diesel engine. In this paper, existing models are compared to determine the necessary conditions to adapt the model to handle multiple diesel injections. The base model used is that of Ma et al, which is based on the eulerian model of Musculus and Kattke for inert diesel jets. One limitation found on this model was the simplification of the radial distribution of fuel/air mixture, which alters the values obtained from it.
This model is compared with a lagrangian model (Hiroyasu, Poetsch), which has an inherent 2D treatment of the diesel jet. A pseudo 2D radial distribution is calculated from the 1D model to create a 2D image of the jet, to be able to compare it to the 2D image obtained from the lagrangian model. Important differences are noted from both models, especially in the thermal dilatation due to the burning of fuel. Since the eulerian model has a fixed spreading angle for the jet, the thermal dilatation is only axial (such as described in Desantes et al.); while in the lagrangian model, since the penetration is fixed, the dilatation is only radial. This difference modifies the fuel/air mixture within the jet, resulting in different heat release traces for both models.
To reconcile this difference, a thermal dilatation model is introduced to consider both radial and axial dilatations, to approach a more appropriate fuel/air mixture that properly models the diesel combustion. This lays a first step to arrive to a properly adapted 1D model for multiple diesel injection.