EGR and Swirl Distribution Analysis Using Coupled 1D-3D CFD Simulation for a Turbocharged Heavy Duty Diesel Engine 2011-01-2222

A new diesel engine, called the 6.7L Power Stroke® V-8 Turbo Diesel and code named "Scorpion" was designed and developed by Ford Motor Company for the full-size pickup truck and light commercial vehicle markets. A high pressure Exhaust Gas Recirculation (EGR) layout in combination with a Variable Geometry Turbine (VGT) is used to deliver cooled EGR for in-cylinder NOx reduction. The cylinder-to-cylinder variation of EGR and swirl ratio is tightly controlled by the careful design of the EGR mixer and intake system flow path to reduce variability of cylinder-out PM and NOx emissions. 3D-CFD studies were used to quickly screen several EGR mixer designs based on mixing efficiency and pressure drop considerations. To optimize the intake system, 1D-3D co-simulation methodology with AVL-FIRE and AVL-BOOST has been used to assess the cylinder-to-cylinder EGR distribution and dynamic swirl. The details of 1D-3D coupling, the computational performance and its integration into the overall intake design process are presented. Several mixer and intake system designs have been analyzed at rated power for the dynamometer certification engine. Trends for EGR mixing, intake pressure losses, cylinder-to-cylinder mass flow variation are presented. EGR mixing and pressure drop values show good correlation to engine measurements. The bank-to-bank and cylinder-to-cylinder EGR distribution was measured at several points on the engine map using the intake CO2 measurement technique. The dynamic swirl estimation trends derived from simulation showed weak correlation with flow bench data. A possible reason may be the absence of a straight section within the intake port for locating 1D-3D boundaries leading to exchange of distorted velocity profile between the solvers. A brief discussion of proposed improvements to the methodology is presented. The simulation approach has been demonstrated on a production engine intake system design program for the first time with AVL FIRE and AVL BOOST. The benefit of this approach to minimize prototype hardware costs, evaluate large number of concepts and early identification of potential issues leading to faster product development.