A 3D-CFD numerical framework for the simulation of both light- and heavy-duty Diesel injectors

Abstract

In spite of the effort of the engine manufacturers to improve exhaust aftertreatment efficiency, thus reducing tailpipe pollutants, the unaffordable tightening of the laws dealing with emissions puts a strain on the use of Diesel engines for passenger cars in the next decades. However, for trucks and marine applications, such technology may remain the predominant solution all over the world. For this reason, development of heavy-duty Diesel engines goes on and Computational Fluid Dynamics (CFD) can play a crucial role in supporting designers. Among the different goals of the numerical analyses on Diesel engines, 3D-CFD Lagrangian simulations can be adopted to optimize fuel injection, which is a crucial aspects as able to affect both combustion efficiency and emissions. For this purpose, a robust numerical framework is needed. The present work aims at proving that models suitable for the simulation of light-duty Diesel injectors can be proficiently extended for heavy-duty ones. In particular, attention is here focused on droplet break-up. An alternative secondary break-up model is proposed. It is purposely calibrated on the well-known Spray A injector provided by the Engine Combustion Network (ECN), which can be assumed as representative of injectors for light-duty applications. 3D-CFD simulations are validated against experimental data in terms of both liquid and vapour penetrations and imaging. Then, the numerical set-up adopted for the Spray A is employed without any further adhoc tuning to investigate Spray C and Spray D which can be considered, instead, representative of heavy-duty nozzles. The proposed model proves to be effective for the prediction of the break-up rate. All the injectors are tested via vessel simulations characterized by the same ambient pressure and temperature, equal to 6 MPa and 900 K respectively. Even the adopted fuel is common, namely n-Dodecane, whose injection pressure and temperature are fixed to 150 MPa and 363 K, respectively.