Within a project of a research association
(Forschungsver-einigung Verbrennungskraftmaschinen e.V.) a DI
spark-ignition engine with small engine displacement was designed
at the Institute of Internal Combustion Engines of the Technische
Universitat Braunschweig. The objective of the project is to
investigate the minimum bore diameter which allows the reasonable
use of the advantages of gasoline direct injection.
This article outlines the preliminary studies to identify
suitable geometry variants for lateral and central injector
position concerning effective engine operating data.
Under consideration of current production possibilities and
geometries of available injector and spark plug CAD studies were
carried out. All suitable valve concepts, beginning with a
two-valve (2V) concept and up to a four-valve (4V) concept, were
examined in the CAD studies. The bore diameter was varied in a
range from 56 to 62 mm combined with a variation of the stroke/bore
ratio from 0.9 to 1.2. Further the valve angles, spark plug and
injector position were changed in wide ranges. The selection of the
most suitable variant was based on the criteria of intake valve
seat ring diameter and the spark plug eccentricity.
The effective operating data was calculated by 1D simulations.
Due to the unknown net heat release of the engine the combustion
process was determined by the "turbulent-flame" model
implemented in the simulation software GT-Power. The influence of
the stroke/bore ratio on combustion process was adapted in respect
to published results. The supercharging system also has a
significant influence on effective operating data. The efficiency
of the exhaust turbocharger was modeled by the scavenging pressure
difference of a VTG turbocharger and variable compressor inlet
guide vanes presented in [3]. The engine friction was considered by
an approach developed in [8]. The influence of the stroke/bore
ratio, as can be expected from literature, was added to this
approach. The final assessment of the variants determined by the
CAD studies was carried out by the criteria of charging pressure,
gas exchange losses, residual gas rate and BSFC at design point and
nominal output point.
As a result of the preliminary studies an engine displacement of
200 cm₃ with a bore diameter of 60 mm and a stroke of 71 mm is the
most suitable concept with respect to the boundary conditions.
Whereas the 3V concept is most appropriate for the vertical and the
4V concept for the horizontal mounted injector position. Both
concepts were designed at the institute and will be tested on
engine test bench.