All compressor maps are evaluated with the help of the criteria derived during the requirements analysis. It can be shown that there is no vaned diffuser which increases compressor efficiency in the main driving range while maintaining the baseline surge stability and efficiency at rated engine power. This is a result of the reduced map width when utilizing a vaned diffuser. Results also indicate that there is no impact on the specific work input of the impeller when a vaned diffuser with design parameters of the given range is used. Impeller speed at a given pressure ratio is thus only a function of efficiency difference imposed by the use of vaned diffuser. The goal of a variable compressor geometry is thus defined as maintaining the efficiency benefit in the main driving range while extending the map width to reach the surge and choke mass flow of the vaneless diffuser in order to obtain efficiencies at rated power, peak torque and during engine brake operation which are comparable to the baseline compressor.
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.
In order to improve fuel economy without sacrifices regarding the remaining engine constraints, variable geometries are introduced in order to extend the map width and at the same time make us of the improved compressor efficiency at high pressure ratios of vaned diffusers.
Reference
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
Post time: May-05-2022