A Feasible CFD Methodology for Gasoline Intake Flow Optimization in a HEV Application - Part 2: Prediction and Optimization 2010-01-2238

Today's engine and combustion process development is closely related to the intake port layout. Combustion, performance and emissions are coupled to the intensity of turbulence, the quality of mixture formation and the distribution of residual gas, all of which depend on the in-cylinder charge motion, which is mainly determined by the intake port and cylinder head design. Additionally, an increasing level of volumetric efficiency is demanded for a high power output.

Most optimization efforts on typical homogeneous charge spark ignition (HCSI) engines have been at low loads because that is all that is required for a vehicle to make it through the FTP cycle. However, due to pumping losses, this is where such engines are least efficient, so it would be good to find strategies to allow the engine to operate at higher loads. The HEV strategy becomes relevant because the electric motor allows downsizing the IC engine and the engine can also be used to charge the batteries when it is otherwise in a low load condition when not under electric power. This means it will tend to run at higher load than an engine in a similar vehicle with a conventional drivetrain.

It is known that the experimental characterization of the near top dead center flow field in engines is not practical and cost effective in an engine development environment. Instead, CFD is more convenient, more economical, and more versatile to study the in-cylinder flow physics if its accuracy is validated with experimental results. Part 1 of this two-part paper presents a CFD based computational methodology. It includes software selection and a systematically validation study of verifying the accuracy of the CFD tool.

For the results reported in Part 2 of this two-part paper, the methodology developed in Part 1 was applied to new intake port development for HEV application. A transient study was performed on a straight-shape intake port model by adding an upper vane. The resulting tumble ratio in the modified intake port has a much larger peak value, about twice the original peak. This indicates that airflow is well organized and the momentum provided by intake port is also well preserved in modified design. In the modified design, the well-preserved tumble breaks up through the end of compression, which will transfer the energy stored as tumble into kinetic turbulence energy. It is found the turbulent kinetic energy in the modified case is twice that of the original version when tumble breaks up, which will greatly improve the combustion quality and increase tolerance to EGR. The developed CFD based methodology was proven with the successfully application in the HEV gasoline intake port configuration design.