Fricke, F., Bhardwaj, O., Holderbaum, B., Scofield, T. et al., "Investigation of Insulated Exhaust Manifolds and Turbine Housings in Modern Diesel Engines for Emissions and Fuel Consumption Reduction," SAE Technical Paper 2016-01-1003, 2016, doi:10.4271/2016-01-1003.
Improvements in the efficiency of internal combustion engines has led to a reduction in exhaust gas temperatures. The simultaneous tightening of exhaust emission limits requires ever more complex emission control methods, including aftertreatment whose efficiency is crucially dependent upon the exhaust gas temperature.Double-walled (also called air-gap) exhaust manifold and turbine housing modules made from sheet metal have been used in gasoline engines since 2009. They offer the potential in modern Diesel engines to reduce both the emissions of pollutants and fuel consumption. They also offer advantages in terms of component weight and surface temperatures in comparison to cast iron components. A detailed analysis was conducted to investigate the potential advantages of insulated exhaust systems for modern diesel engines equipped with DOC and SCR coated DPF (SDPF).The results suggest that the application of air-gap insulated exhaust systems could lead to a reduction of HC, CO, and NOx emissions at the tailpipe in the range of 20 to 50%, depending on the engine design, vehicle inertia class, and driving cycle, when compared to a baseline exhaust system fitted with a conventional cast iron exhaust manifold and turbine housing.With the application of optimized EGR strategies, an increase in the engine out NOx levels could be allowed by taking advantage of the higher NOx conversion rate in the SDPF. As a consequence, an overall fuel savings potential of up to 2% was observed in WLTP and FTP-75 test cycles. In addition, depending on the application, component weight savings of up to 50% and a reduction of the maximum component surface temperature of up to 300 K are possible.