Experimental Study of Automotive Turbocharger Turbine Performance Maps Extrapolation

Engine downsizing is potentially one of the most effective strategies being explored to improve fuel economy. A main problem of downsizing using a turbocharger is the small range of stable functioning of the turbocharger centrifugal compressor at high boost pressures, and hence the measurement of the performance maps of both compressor and turbine. Automotive manufacturers use mainly numerical simulations for internal combustion engines simulations, hence the need of an accurate extrapolation model to get a complete turbine performance map. These complete maps are then used for internal combustion engines calibration. Automotive manufacturers use commercial softwares to extrapolate the turbine narrow performance maps, both mass flow characteristics and the efficiency curve. These extrapolation and simulation softwares are used in the architecture of designing new engines, integrating an ECU calculator as an observer / estimator (in this case estimating the turbocharger speed), validation (MIL) and verification (HIL) of engine control, and also for engine calibration. So an extrapolation model of the performance maps given by the manufacturer should be reliable and accurate. This paper presents an experimental study on a turbocharger turbine with different techniques to measure the widest turbine performance map. A Renault 1.5L Diesel engine turbocharger was modified and tested at Ecole Centrale de Nantes as a project in an industrial chair between Renault, LMS-Siemens and Ecole Centrale de Nantes. On the test rig, the experimental program dealt with traditional turbine and compressor performance measurements at different turbine inlet temperatures which widened the measuring area. Another technique was also to introduce air at high pressure at the compressor inlet increasing thereby its power consumption and expanding the measuring area. Air is also blown to the compressor exit to fill the cavities created on the blades back that cause the surge limit. In the same logic, the volute casing of the compressor was removed to minimize its power consumption and get new measured points. These extensions of the turbine performance maps (mass flow rate) of 400% for some rotational speeds can be useful for extrapolation models that can be used by automotive manufacturers. As for the turbine efficiency, there are different definitions for the turbine efficiency. There is the turbine total-to-static isentropic efficiency and the turbine efficiency including the mechanical losses. These two elements were also calculated for this turbocharger.