In 2015, a novel control concept for the partial admission of a turbocharger turbine
named MEDUSA (Multiple Exhaust Duct with Source Adjustment) was presented at
the Stuttgart International Symposium. The basic idea of this control concept is to divide
the turbine inlet into several sectors along the circumference and to control the
admission of the different sectors individually. This partial admission approach works
similar to a Variable Nozzle Turbine (VNT) control system and allows to increase the
turbine inlet pressure at low engine mass flows by closing turbine inlet segments and
thus restricting the effective flow area. As a consequence higher turbocharger power
output at low engine load conditions can be achieved. Contrary to a VNTturbocharger,
however, the presented control system can also be used at elevated exhaust
gas temperatures as featured by spark-ignition engines, because the admission
valves can be placed at the turbine periphery and cooled accordingly.
To date, only data obtained from the turbocharger test rig at the Institute of Thermal
Turbomachinery and Machinery Laboratory (ITSM) at the University of Stuttgart
have been published, showing that the MEDUSA-concept does indeed yield a higher
turbine pressure ratio and thus better turbocharger power output at low mass flows
compared to a standard Waste-Gate turbocharger. An assessment of combined engine
and turbocharger performance has not been available so far.
In the present publication, results of the first measurements of combined engine and
turbocharger performance obtained from tests at the Institute of Internal Combustion
Engines (IFKM) at Karlsruher Institute of Technology (KIT) will be reported. For the
tests, an Audi 2,0l R4 TFSI engine has been used. Reference measurements have been
done using the standard Waste-Gate turbocharger (BorgWarner KKK03). Thereafter,
the test configuration has been adapted to accommodate a MEDUSA-control system
designed to fit the original turbocharger turbine.
Some compromises with regard to the layout of this prototype setup due to constraints
of the existing equipment, such as noticeably increased volumes between compressor
and engine inlet as well as between engine outlet and turbine had to be made. Nevertheless,
the MEDUSA control system shows performance improvements at low engine
load and mass flow conditions as expected from layout specifications and the
previous turbocharger test rig experiments.