Tomorrow’s engine simulation today
Alex Read, Gerald Schmidt and Erwan Gautier, CD-adapco

CD-adapco’s position as a full-spectrum CAE solutions provider is built on a history of technology leadership: performing tomorrow’s calculations today. STAR-CD was the first general purpose CFD code to handle unstructured meshes; it was the first to perform moving mesh calculations for complex industrial applications; it was the first to handle rotating nd reciprocating machinery; and more recently, CD-adapco was the first of the mature CFD providers to deliver an arbitrary polyhedral mesh solution and to embed this into CAD and PLM systems.

This technology-leading position requires continuous innovation so that we are able to provide timely solutions for our customers. One such recent activity has been to run a complete V6 engine, shown in Figure 1, with intake and exhaust systems, moving pistons and valves and combustion.

Although such calculations can be considered embryonic today, as computer speeds continue to increase such calculations will become more common. Engineers will benefit from detailed insight that simply is not possible with current methods, and attain levels of accuracy that cannot be achieved with coupled 3D-1D simulations.There are a number of examples where current idealized methods are inadequate, including high-speed transient events, such as cylinder de-activation and re-activation and changes in variable geometry intake systems that may result in single cycle changes in air-fuel ratio and hydrocarbon breakthrough. In this calculation, the uniformity of charge mass from cylinder to cylinder was investigated, though follow-up studies for EGR distribution and other phenomenon are readily attainable.

However, even with the advanced capabilities of es-ice, such complex calculations - with thirty independent moving parts, combustion and multiple, simultaneous solution domains, are challenging to set-up and run. But, with the methodologies developed here going into es-ice and STAR-CD, CD-adapco is committed to delivering engineering solutions to even the most complex problems. There are enhancements to the specification of boundary conditions, initial flow field values, an idealized combustion model, and advanced post-processing.

The geometry is an engine in production, supplied by a major OEM. From the starting IGES data, pro-STAR’s surface meshing module was used to generate the surface mesh. The volume mesh was then created in three parts. The inlet and exhaust systems were generated in pro-STAR’s automatic meshing module. The mesh and movement of the pistons and valves was then dealt with in es-ice. This method has the significant advantage that es-ice will automatically deal with the set-up of the complex movement of the valves and pistons. Once this has been achieved for one cylinder, a simple “copy and paste” operation can be used to generate the multi-cylinder configuration. The final mesh contained 3.1 million cells, when all cylinders were at bottom dead centre.

During this first calculation, the effects of combustion were modeled with enthalpy sources, where the heat release was dependant on the mass of fluid in the cylinder. In future calculations this will be enhanced to use the ECFM-3Z combustion model. Figure 3 shows the temperature contours in the near-cylinder region, shortly after ignition has occurred in Cylinder 5.

One of the objectives of this analysis was to evaluate the charge mass in each cylinder, i.e. is there an even distribution of air going to each cylinder? An uneven distribution of air will affect the stoichiometry, combustion and ultimately engine performance. By performing such an analysis, a detailed understanding of the intake manifold system and its performance throughout the engine cycle can be obtained. Figure 4 shows the mass of air in each cylinder as a function of crank angle for one complete cycle. The charge mass distribution is near optimal, although Cylinders 4 and 5 get more air than the others.

Dr Richard Johns, CD-adapco’s Director for the Automotive Sector, appreciates the importance of the engine community to CD-adapco and investigations such as these:

“CD-adapco has a long track record of developing solutions “ahead of the curve” and the challenge for us now is to refine and package this technology so that it is available for routinely solving the most difficult of engine related flow and combustion problems. This is one of the most exciting developments to emerge for the engine CFD community for many years”

At CD-adapco we pride ourselves on delivering fullspectrum CAE solutions. Our history tells us that by taking a lead in technology, as driven by our partners needs, we can become your CAE partner for success.