Towards even cleaner diesel engines: Contribution of 3D CFD tools

Abstract

Three-dimensional Computational Fluid Dynamics (CFD) tools have become essential for research on Diesel engines. Indeed they help grasp the basic phenomena at stake, as combustion processes get more and more complex in order to comply with conflicting demands: more stringent emission standards and customer desire for "fun-to-drive" vehicles, i.e. higher torque and power outputs. CFD tools are however only as accurate as their physical submodels. That is why at IFP, injection, combustion and auto-ignition models are constantly evolving in order to keep CFD in pace with test bench innovations and demands. Such a close follow-up of CFD tools enables 3D computations to contribute actively in all IFP research projects on DI Diesel engines. New combustion and low temperature auto-ignition models were developed, enabling an accurate representation of Homogeneous Charge Compression Ignition (HCCI) process. Lately, IFP has developed a near zero NOx and particulate combustion process, the Narrow Angle Direct Injection (NADI™) concept, a dual mode engine application switching from HCCI combustion at part load to conventional Diesel combustion at full load. The new capabilities of CFD tools support the development of the NADI™ concept since they enable the comprehension of the phenomena at stake in both operating modes, provide guidelines to optimize the engine configuration, and help port the concept from an application to another. Simulations, which are now possible for the entire operating range including Exhaust Gas Recirculation (EGR) rates up to 60%, successfully help to design and optimize all generations of DI Diesel engines for passenger cars and heavy duty vehicles. The effects of combustion system parameters such as piston bowl geometry, Fuel Injection System (FIS), in-cylinder fluid motion or EGR rates can be mapped in order to determine the best configuration matching the objectives. Copyright © 2006, Institut français du pétrole.