Future Diesel engines must comply with conflicting demands: more stringent emission standards and customer desire for “fun-to-drive” vehicles, i.e. higher torque and power output. Given such objectives, engine development investigates new clean combustion processes, such as low temperature combustion (LTC), highly premixed combustion (HPC) or homogeneous charge compression ignition (HCCI) combustion and the possibility to combine them with current solutions. Lately, IFP has developed a near zero NOx and particulate combustion process, the NADI™ concept, a dual mode engine application switching from a novel lean combustion process at part load to conventional Diesel combustion at full load.
Given the complex nature of these new combustion processes, the concept development relies increasingly on three-dimensional Computational Fluid Dynamics (CFD) tools as they help grasp the basic phenomena at stake and reduce development time and costs. The 3D CFD code used is briefly presented in this paper along with the latest evolutions of the physical submodels for injection, combustion, auto-ignition and liquid film modeling, which have greatly enhanced its use for the simulation of Diesel engines.
The use of the CFD tools for the development of various aspects of the NADI™ concept is presented. Joint optimization of the piston bowl geometry design and fluid motion illustrate the improvements made in terms of mixing and fresh charge usage at full load. A full load study of the sensitivity to wall wetting given the FIS configuration shows the capacity to detect liquid film formation and induced loss of power. Investigations on injection strategies allow to understand and define adequate strategies for very low NOx and soot combustion at part load. Finally the rapid transfer of the concept from passenger car to heavy duty applications is considered and the comparison of first test bench results with simulations is made.