Reducing emissions from light duty vehicles is critical to meet current and future air quality targets. With more focus on real world emissions from light-duty vehicles, the interactions between engine and exhaust gas aftertreatment are critical. For modern engines, most emissions are generated during the warm-up phase following a cold start. For Diesel engines this is exaggerated due to colder exhaust temperatures and larger aftertreatment systems. The De-NOx aftertreatment can be particularly problematic. Engine manufacturers are required to take measures to address these temperature issues which often result in higher fuel consumption (retarding combustion, increasing engine load or reducing the Diesel air-fuel ratio).In this paper we consider an inner-insulated turbocharger as an alternative, passive technology which aims to reduce the exhaust heat losses between the engine and the aftertreatment. Firstly, the concept and design of the inner-insulated turbocharger is presented. A transient 3D CFD/FEM (Computation Fluid Dynamics/ Finite Element Modelling) simulation is conducted and predicts that external heat losses will be reduced by 70% compared to a standard turbocharger, i.e. non-insulated turbocharger. A 1D modelling methodology is then presented for capturing the behaviour of the inner-insulated turbocharger. This is important as conventional models based on isentropic efficiency maps cannot accurately predict turbine outlet temperature. The alternative model is essential to demonstrate benefits in system-level simulations. Experimental results are presented from a transient air-path testing facility to validate the 1D model and demonstrate the characteristics of the inner-insulated turbocharger. Finally, the validated 1D model is used within a powertrain optimization simulation to demonstrate an improvement in fuel consumption for iso-NOx emissions over a low load city cycle of up to 3%.The work was conducted under the THOMSON project which has received funding from the European Union's Horizon 2020 Program for research, technological development and demonstration under Agreement no. 724037. The project aims to increase the market penetration of 48V hybrid vehicles.

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For turbocharged diesel engine systems, emission reduction is the most significant challenge that manufacturers should overcome. In response to the emission reduction challenge most turbocharged diesel engine systems have adopted complex exhaust aftertreatment systems. Due to the current stringent emission regulation, exhaust aftertreatment system nowadays needs to discover new methods to increase its efficiency of pollution conversion. Increasing the inlet temperature of aftertreatment systems can help reduce the light-off time. Whilst most methods to do this involve increases in fuel consumption (retarded injection, engine throttling), insulating the turbocharger turbine to reduce heat loss does not have this drawback. This paper presents a simulation and experimental study the performance of a turbocharger with inner insulated turbine housing, compared with the standard turbocharger (same turbine wheel without inner insulation). Both turbochargers were tested on an engine gas stand test rig with a 2.2L prototype engine acting as an exhaust gas generator. In a steady state condition, the insulated turbocharger can achieve 5 to 14K higher turbine outlet temperature depending on the engine speed and load conditions. Three types of transient tests were implemented to investigate turbocharger turbine heat transfer performance. The test plan was designed to the engine warm up, step load transient, WLTC cycle and simplified RDE cycle. In the engine warm up test result, the temperature drops between the turbine inlet and outlet was reduced by 4K with the insulated turbine housing. In the results of step load transient test, the turbine with insulated turbine housing was observed to get only 4K temperature benefit but with 2kRPM higher turbocharger speed under the same turbocharger inlet and outlet boundary conditions. In the WLTC cycle test result, turbocharger average speed was increased by 0.8kRPM due to the increased enthalpy of the turbine with insulation, the turbine outlet temperature has an average 1.7K improvement. The experimental results were used to parameterise a simple, 1D, lumped capacitance model which could predict similar aerodynamic behaviour of the two turbines (turbine housing insulated and non-insulated). However, current model has less accuracy in highly transient process as the heat transfer coefficients are unchangeable in each process. The turbine outlet temperature got at most 10K error for the turbine with non-insulated housing and 13K error for the insulated one. The model was shown to over-estimate the benefits of the inner insulation for 1K in turbine outlet temperature.

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