ABSTRACT
Wide flow range compressors, both with and without a ported shroud, improve the surge line characteristic by increasing inducer recirculation. These compressors regurgitate hot (>125C) air when operating to the left of peak efficiency. This hot flow is re-ingested by the compressor and the result is reduced efficiency and pressure ratio. The outlet temperature can be increased up to 100C and the pressure ratio reduced by more than 20%. One result is that the turbine power needed to drive the compressor to reach the desired mass flow is increased. Another result is that the intake manifold density is reduced, and additional boost pressure is needed to achieve the desired mass air flow. This is a negative feedback loop which results in the engine performance degradation at low speed/high torque.
Two solutions to this problem are presented, neither of which require a change to the compressor design, and only require a change to the compressor inlet piping. Both result in a more favorable surge line, higher compressor efficiency and much higher boost pressure on the left side of the compressor map. The benefit of both these solutions is quantified by computational fluid dynamics (CFD) analysis and turbocharger test rig testing.
The preferred, simple solution is to divide the inlet pipe into two annular flow paths, both connected to a divided air cleaner, or two separate air cleaners. Flow in the outer flow path can flow either direction depending on the compressor operating point. The second solution has just one air cleaner, but the outer annular flow is cooled by a heat exchanger, then combined back into the core flow. The preferred PureFlow™ has potential for retrofit to existing vehicles.
