an innovative 3d cfd approach towards virtual development of internal combustion engines pdf
Society is a dynamic being and transportation is a key factor for fulfilling the human needs.
Among different means of transport, vehicles with internal combustion engines represent the
most relevant share in global transportation and namely cars and motorcycles are a self-evident
object in our daily activities. In the future the limitations on the environmental impact, especially
concerning private traffic, will become harder and harder, i.e.
this process towards a real
sustainable mobility will dictate the future development steps in the automotive sector.
Consequently the engine of the future will be light-weight, small, turbocharged, probably with an
unconventional combustion strategy, silent, with extremely low exhaust emissions (also at cold
start), very low fuel consumption and CO2 emission, high specific power, “vigorous” torque at
low engine speed, long-life reliability and, maybe the most difficult target, it has to be still
affordable. In order to meet the expectations of these complex tasks, engine simulation will play
a key role in the future engine-development-process.
During the years engine simulation has continuously gained in reliance but mainly in the last two
decades the rapid increase of computer performance has boosted the utilizability of simulation
programs. At the present time the application of simulation programs towards a reliable “virtual
engine development” represents one of the greatest challenges. An all-embracing tool for a
reliable, detailed and predictive simulation of an internal combustion engine does not exist and
will probably never exist.
But there is another more realistic way represented by a selective
coupling of different simulation tools depending on the different targeted tasks of the engine
development. For the performance of this coupling the 3D-CFD-approach (in particular related
to an analysis of the engine operating cycle) is a decisive component.
The 3D-CFD-simulation represents undeniably the most detailed approach for the investigation
of the engine operating cycle. From its basic concept this approach should allow an unlimited
predictability of engine processes by unrestricted varying of any parameter of both the engine
setting and the operating condition.
Depending on the chosen degree of mesh discretization it is possible to fully record the fluid motion and any chemical and thermodynamic phenomena acting in any part of the 3D-CFD-domain up to a length scale which is not far away from molecular dimensions. But this is the theory, the practice looks quite different.
The computational resources in terms of the required hardware and the related CPU-time are very often prohibitive. In addition the setting of initial and boundary conditions can easily introduce sources of inaccuracy that irremediably compromises the overall quality of the results and drastically reduces the benefits of such resource investments..
Another critical point is represented by few threedimensional engine process models that due to the lack of phenomena understanding at the fundamental physical level, inaccurate mathematical formulations, numerical dependencies on the mesh structure, ambiguous validation processes, etc., are not able to ensure a high level of reliability in reproducing and predicting the requested engine processes.