TURBOCHARGERS For NOx emissions, the benefit of the insulated turbocharger turbine is the increase in temperature, especially during warm-up, for the selective catalytic reduction (SCR) catalyst. In the hybrid vehicle system analysed, the electrically heated catalyst uses energy from the battery that could otherwise have been used to propel the vehicle. Using it to heat the catalyst to control emissions could be seen as a parasitic loss, but the insulated turbocharger turbine reduced the amount of heat required for this. A reduction in fuel consumption could also be achieved during particulate filter regeneration which would therefore require less fuel to raise the temperature of the exhaust. “There will be a further benefit because the NOx aftertreatment can be more effective due to the increase in temperature, so some of the NOx mitigation measures such as late fuel injection and high exhaust gas recirculation rates that usually penalise fuel consumption and increase particulate emissions can be relaxed,” says Burke. The turbocharger is a primary source of heat loss in the exhaust system, as it is cooled to protect the bearings. This means there is a significant heat loss inherent to the turbocharger that needs to be considered at a system level, says Burke. “Is there a chance that we are creating too much cooling to protect the bearings which is compromising the exhaust emissions? There could be some interesting thermal designs to consider here that try to block heat conduction into the bearing housing.” He says the research results on the 48V hybrid system open up the potential for new electrical technologies that could reduce emissions including electrically-assisted
boosting systems, electrically heated catalysts and electric thermal management systems. It also offers the potential for collecting energy via regenerative braking. Burke’s research team is focussed on improving the modelling further such that the thermal insulation effects can be characterised accurately from minimal or no test work using higher order models. “This is essential as hardware decisions will be increasingly made based on simulations in the future. It is essential that we can generate suitable models that truly reflect the behaviour of the technology.”
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8 Dr Richard Burke, head of the research team at the Institute for Advanced Automotive Propulsion Systems at the University of Bath
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