Charge Motion Analysis to Guide Engine Port Development and Enhance Combustion Stability for High Cooled Exhaust Gas Recirculation 2013-01-1313

CAE tools are increasingly important in the automotive design process. In part, CAE tools can be useful in reducing the number of physical prototypes required during a product development effort. CFD tools can assess and predict cylinder charge motion for proposed designs, thereby limiting the need for prototype work. Though detailed combustion simulation results could help guide product development, the time required for such simulations limits their usefulness in the context of a production program. However equally valuable information can be obtained from gas exchange analyses which require less computation time and are run only from Intake Valve opening (IVO) to spark timing. Chemical kinetics is not included in this type of analysis. Using this approach, large numbers of configurations can be evaluated in a short period of time.

Every passing year automotive engineers are challenged to attain higher fuel economy targets. Increasing Cooled Exhaust Gas Recirculation (CEGR) rates is one of the widely used methods to improve fuel economy. To ensure combustion system tolerance for higher CEGR, it is necessary to have high charge motion. Charge motion is governed by port development, interaction of port with chamber, piston geometry, valve design and valve angle etc. Traditionally intake port development is performed using a steady state approach, both numerically and experimentally. Dynamic behavior of in-cylinder flow due to the intake and exhaust valves and piston motion prevents the steady state approach from being an accurate tool. This paper documents our successful use of the gas exchange analysis approach to guide a design. The relationship observed and established between turbulent intensity and combustion characteristics, 10-90 (duration required to burn 10 % to 90 % of trapped fuel) and maximum EGR tolerance, is presented.