Computational study of ECN Spray A and Spray D combustion at different ambient temperature conditions

Abstract

The combustion process of the Engine Combustion Network (ECN) Spray A and Spray D is studied over a wide range of ambient temperatures from 750 K to 900 K. With nominal diameters of 89.4 μm for the Spray A and 190.3 μm for the Spray D, these n-dodecane sprays are representative for light- and heavy-duty compression ignition engine applications, respectively. Computational Fluid Dynamics calculations are carried out using a Lagrangian parcel Eulerian fluid approach in a Reynolds averaged Navier–Stokes framework. For the Spray D reference condition, two sub-grid flame structure assumptions and the effect of turbulence chemistry interaction (TCI) on autoignition and flame structure at quasi-steady state are assessed in the context of a well-mixed and an Unsteady Flamelet Progress Variable (UFPV) combustion model. After that, UFPV approach is used to evaluate combustion behavior for the different ambient temperature conditions. Reference condition results show that both well-mixed and flamelet assumptions lead to a similar autoignition sequence. In terms of ignition delay time, TCI plays an important role, within the UFPV model, in reproducing the experimental trend observed for the increase in nozzle diameter. In terms of lift-off length, the well-mixed model is observed to predict a longer value compared to the flamelet-based sub-grid assumption. Lastly, the analysis of the autoignition sequence and flame structure at quasi-steady state is also extended over the whole range of ambient temperature conditions.