Impact of Using Low Thermal Mass Turbine Housing on Exhaust Temperature with Implication on Aftertreatment Warm-Up Benefit for Emissions Reduction

The present study examines the impact of using low thermal mass (LTM) turbine housing designs on the transient characteristics of the turbine outlet temperature for a light-duty diesel standard certification cycle (FTP75). For a controlled exhaust flow, the turbine outlet temperature will directly determine the impact on an aftertreatment system warm-up from a cold state, typical of engine-off and engine idling conditions. The performance of the aftertreatment system such as a Selective Catalytic Reduction (SCR) system is highly dependent on how quickly it warms up to its desirable temperature to be able to convert the harmful oxides of Nitrogen (NOx) to gaseous Nitrogen. Previous works have focused on mostly insulating the exhaust manifold and turbine housing to conserve the heat going into the aftertreatment system. The use of LTM turbine housing has not been previously considered as a means for addressing this requirement. The current study explores this in detail and shows that the use of LTM turbine housing improves the rise in turbine outlet temperatures quickly. Three turbine housing designs developed by Cummins Turbo Technologies (CTT) were studied with baseline, 20% reduced, and 40% reduced thermal masses. The analysis is performed using a GT-Power engine model, which uses the transient inputs for the simulation from the engine test conducted using the prototype baseline turbine housing. The 40% reduced thermal mass turbine housing is shown to improve the rise in turbine outlet temperature by as much as 21 K in the first 400 s of the Federal Test Procedure (FTP) cycle. This is expected to significantly improve the performance of the aftertreatment system and is verified by an aftertreatment simulation conducted with engine-out results from the present analysis as boundary conditions to the aftertreatment model. The 40% reduced thermal mass case showed a marked reduction in NOx by as much as 15% from the baseline turbine housing case during the first 400 s of the FTP cycle. A detailed look at the turbine housing metal temperatures and the turbocharger heat transfer distributions are provided to explain the fundamental reasons for the improved exhaust temperature for the lower thermal mass housing material.