Predicting the Combustion Behavior in a Small-Bore Diesel Engine

Accurate modeling of the characteristics of diesel-engine combustion leads to more efficient design. Accurate modeling in turn depends on correctly capturing spray dynamics, turbulence, and fuel chemistry. This work presents a computational fluid dynamics (CFD) investigation of a well characterized small-bore direct injection diesel engine at Sandia National Laboratories’ Combustion Research Facility. The engine has been studied for two piston-bowls geometries and various injection timings. Simulation of these conditions test the predictive capabilities of our approach to diesel engine modeling using Ansys Forte. An experimental database covering a wide range of operating conditions is provided by the Engine Combustion Network for this engine, which is used to validate our modeling approach. Automatic and solution-adaptive meshing is used, and the recommended settings are discussed. The analyses capture the turbulent effects on the flow field with both the conventional and the stepped-lip piston bowls. The flow mixing sensitivity to the bowl features is consistent with the data for the two configurations in this swirl-supported diesel combustion. The fuel injected is made of n-hexadecane and heptamethylnonane, and the workflow involved in deriving an accurate chemistry mechanism from the well validated Ansys Model Fuel Library is reported. The same set of spray breakup and atomization model constant values is used in all simulation cases. The good agreement with the experiments provides confidence in the reliability of the simulation approach in the development of the next generation of light-duty engines.