In an effort to reduce fuel consumption, more and more vehicles are now being powered by turbocharged engines. Both manufacturers and OEMs are stepping up efforts to optimize turbocharger systems and, anticipating this trend, IAV began to work on turbocharger test stands more than ten years ago. IAV was confident that full-range, whole-system testing would be critical in optimizing the more complex boosting configurations that would eventually come into use. To this day, IAV believes that independently produced testing data is of great value to OEMs working toward optimized boost systems.
In October 2009, IAV commissioned a new, enhanced turbocharger test bench at the IAV Technical Center in Berlin. After 12 months of construction, IAV experts are now able to execute detailed performance measurements on such key engine components.
"Test benches allow us to measure turbochargers independent of the engine,” explains Marc Sens, head of the Thermodynamics and Turbocharging department. "We are thus able to minimize any disturbing influences, including those caused by the engine, such as oscillations, vibrations or irregular gas flows."
The test bench consists of both a compressor and a combustion chamber running on compressed natural gas. It can generate an air-mass flow rate of up to 2,640 lbs/hr, with pressures up to five bar and temperatures up to 2010° F. The facility is capable of replicating any condition encountered with a turbocharged engine application up to 400 bhp, which covers most passenger cars and light/medium trucks. Although most testing is conducted with a single turbocharger, systems with two turbochargers can be investigated as well, either as a complete assembly or with the subassemblies measured individually.
Sensing temperatures and pressures at points where the flow of hot gas enters and leaves the turbine, and where air enters and leaves the compressor, the test bench records mass flow rates along with the temperatures of cooling medium and lubricant. The testing includes monitoring the air or combustion gas in the crankcase; "blow-by" may penetrate the running gear by leaking through the seals between the compressor and turbine.
Turbochargers Still in Need of Much Research
IAV was motivated to develop the new facility due to the need to achieve a better understanding of turbochargers. Heat-flow behavior and mechanical components are still in need of much research: for example, plain bearings might be replaced with roller or air-cushion bear ings to reduce friction and improve efficiency. A good turbocharger currently achieves efficiencies of 78 % (compressor) and 65 % (turbine plus mechanical components). The overall efficiency is the product of these two values.
Since more and more manufacturers are planning to use turbocharged engines, it is vital that any advancement be fully investi gated for its benefit and application.
Turbochargers allow for higher power densities, enabling manufacturers to use smaller engines for improved fuel economy ("downsizing and boosting"). If a high level of torque is made available at low engine speeds, the powertrain's transmission ratios can be altered to benefit running the engine at lower engine speeds ("downspeeding"), thereby reducing overall fuel consumption and CO2 emissions.
Most of today's diesel engines are turbocharged; still, system complexity and sophistication continue to increase as the dieselengine segment seeks out performancerelated improvements. IAV ex perts foresee that gasoline turbocharging systems will follow suit. Those working in the automotive industry need to fully understand all of the influencing parameters necessary to capitalize on the many potential improvements to turbochargers. New fuels and combustion processes offer further possibilities for turbocharging: natural gas and ethanol both have antiknock properties superior to gasoline, and open the door to increased boost pressure and engine performance.
New Guidelines on Turbocharger
Measurement Methodology The new test bench enables IAV to provide OEMs and turbocharger manufacturers with the development assistance crucial to building a better understanding of the system and its details: the improvement of individual components and precisionmap measurements. IAV’s turbocharger mapping research project has developed measurement methodology guidelines recognized by OEMs and component suppliers throughout the industry. "We now have the ability to compare turbochargers on the basis of standardized measurements," comments Marc Sens.
In the future, it will be possible to do this automatically with the new test bench’s unmanned operation feature. Depending on the number of measurement points involved, conventional measurement methods may take four to six hours to fully map a turbocharger, but, using new approaches, IAV sees the potential to reduce test-operation time significantly.
The IAV facility is also capable of measuring other powertrain components requiring development in which hot gas may play a part. There is space available to set up and test even entire exhaust systems under realistic vehicle conditions