Study notes of turbochargers

In the world, the main goal is the improvement of fuel economy without sacrifices regarding any other performance criteria. In a first step, a vaned diffuser parameter study shows that efficiency improvements in the relevant operating areas are possible at the cost of reduced map width. Concluding from the results three variable geometries with varying complexity based on vaned diffusers are designed. Results from the hot gas test stand and engine test rig show that all systems are capable of increasing compressor efficiency and thus improving fuel economy in the main driving range of heavy-duty engines.

Additional challenges are represented by the need for high durability, low noise emissions and good transient performance of the engine. Therefore, the design of the compressor system is always a compromise between high efficiency, a broad map width, low weight of the impeller and high durability leading to compressor stages with significant aerodynamic losses in the main driving range of long-haul vehicles and thus a decrease in fuel economy. Solving this fundamental problem of compressor design by introducing a variable geometry can lead to reduced total costs of ownership which is the foremost selling point regarding heavy duty engines. Apart from recirculation valves applied in passenger car turbochargers, compressors with variable geometry have not found their way into series production although profound research has been conducted on this field.

Three variable compressors have been developed with the goal of improving fuel economy of heavy-duty engines in the main driving range without deteriorations regarding rated power, peak torque, surge stability and durability. In a first step, requirements of the engine with respect to the compressor stage have been derived and the most relevant compressor operating points are identified. The main driving range of long-haul trucks corresponds to operating points at high pressure ratios and low mass flows. Aerodynamic losses due to very tangential flow angles in the vaneless diffuser play a dominant role in this operating range.

Reference

BENDER, Werner ; ENGELS, Berthold: VTG Turbocharger for Heavy Duty Commercial Diesel Applications with High Braking Performance. 8. Aufladetechnische Konferenz. Dresden, 2002

BOEMER, A ; GOETTSCHE-GOETZE, H.-C. ; KIPKE, P ; KLEUSER, R ; NORK, B: Zweistufige Aufladungskonzepte fuer einen 7,8-Liter Tier4-final Hochleistungs-Dieselmotor.16. Aufladetechnische Konferenz. Dresden, 2011