CFD Study of Low Soot Spray Combustionin a Heavy-Duty Diesel Engine 2018-01-0186
This CFD study focuses on the influence of the nozzle diameter on the mixing process and the soot formation and oxidation process in a heavy-duty diesel engine. The CFD simulation is based on the Reynolds Averaged Navier-Stokes approach. The engine set-up is similar to an experimental case that showed rather low soot emission. The aim of the paper is to improve the understanding of the physics of the mixing process in a real engine environment with the attention to scrutinize its effect of fuel injection on combustion and soot emission. Two non-reacting cases with different injector nozzle diameters but constant injection pressure and their corresponding reacting cases are simulated with dynamic mesh motion and fuel spray modeling. The influence of injections on the mixing, combustion and emissions is analyzed and the simulation results are compared with the measurement data. The differences in the mixing process between a constant volume vessel and a dynamic combustion chamber with piston motion are evidenced. The results show that a smaller nozzle diameter leads to a lower equivalence ratio and a higher gas temperature along the centre of the spray axis. The piston expansion causes the break-down of a recirculation zone around the spray which can affect the air entrainment. The CFD study captures the trend of the measurement data concerning the equivalence ratio around lift-off and the results explain the formation and oxidation process of soot.