Fuel Injector Nozzle Hole Geometry Impact on Spray Morphology and Emission Performance in a Heavy Duty DI Diesel Engine – CFD compared to engine test bed data

In the context of reducing pollutant emissions from heavy-duty engines, CFD simulations offer significant advantages in prototyping and testing new components and engine designs. In Diesel engines, combustion quality and the complete burning of fuel are essential to avoid pyrolysis of diesel droplets, which generates soot precursors, one of the main Diesel cycle pollutants. The injector plays a crucial role in pollutant control, as its ability to atomize and distribute fuel within the cylinder directly impacts combustion. Using AVL Fire M, a CFD injector model, based on the production design, was developed to study its behavior and performance under different injection and load conditions. The simulation considers a multiphase domain (gas, vapor, liquid), allowing detailed tracking of fuel evolution both inside injector components and in interaction with the gaseous spray environment. However, coupling a full injector model with a complete combustion chamber and piston is extremely complex and computationally expensive. Therefore, injector-only simulations were used to generate interface data for combustion simulations. In the latter, the Eulerian multiphase domain was a single-phase gas/vapor domain, into which liquid particles (Lagrangian domain) were injected, following data from the injector-only case. The aim of this work is to analyze how changes in nozzle geometry affect engine performance in terms of pollutant particle emissions. To achieve this, spray and combustion models were calibrated using experimental test-bench data, enabling the creation of a CFD model capable of reproducing real conditions and supporting detailed investigations into in-cylinder spray and combustion dynamics. Results highlighted that one of the main factors influencing performance differences between injector geometries is the interaction of injected liquid particles with the environment, particularly with piston walls. These interactions determine the fraction of fuel actively participating in combustion and the fraction undergoing pyrolysis upon wall impingement, leading to the formation of soot precursors. The study was further complicated by the low air–fuel ratio conditions of the simulations. Such conditions challenge pollutant prediction models, often making results unreliable at exhaust valve opening. To address this, ad hoc post-processing and interpretation criteria were developed, ensuring more robust analysis under these demanding operating conditions.