Exhaust Gas Recirculation (EGR) is an effective post combustion measure to reduce the formation of NOx. High EGR rates lead to poor turbine aerodynamic performance, limiting its energy extraction capability. A double entry turbine is often used to split the engine exhaust, but given that EGR is taken from one of the entries, it leads to an unwanted imbalance of mass flow at the turbine rotor.
This new innovative approach solves this problem by introducing an asymmetry in the turbine volute configuration that responds to the EGR rate. In this way it is possible to balance the flow around turbine wheel and hence enhance the energy extraction capability. In existing double entry turbines, the entries are symmetric each feeding 180° of the turbine. In our new approach, the small scroll feeds 160° and the large scroll 200°. This has the compounding effect of keeping one bank of cylinders unaffected by the EGR extraction, while rebalancing the turbine flow that leads to better turbine performance.
A prototype has undergone extensive laboratory testing at Imperial College cold flow test facility. The experimental results shows that ADT is able to meet 10% EGR rate in vaneless configuration at 75% peak efficiency. When nozzles were present on both entries the average turbine efficiency increased by 13 percentage point than the conventional nozzleless configuration. A Brake Specific Fuel Consumption (BSFC) improvements of between 2% and 3% can be anticipated.
It is considered that this technology will be best suited to applications using heavy-duty engines utilising EGR.
Imperial internal funding and Malaysian Government funding has supported the research in computational fluid dynamic (CFD) modelling and aerodynamic testing to date.
The concept is patented by Imperial Innovation (published WO2014140598). The team at Imperial are now seeking investment and/or industrial partners to assist in development of the new turbocharger through transient dynamometer and in vehicle testing.
Leading the team at Imperial is Prof Ricardo Martinez-Botas , one of the world’s foremost authorities on fluid dynamics in turbochargers.
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