Engineering Material Selection for Automotive Exhaust Systems Using CES Software

Abstract

This report reviews the automotive exhaust system with respect to its in-service conditions and selection of suitable materials for exhaust manifold, downpipe silencer/ muffler box and tail pipe which comprises the exhaust system. The functions of each component were discussed, highlighting how they function as part of the exhaust and Cambridge Engineering Software (CES) software was employed in the material selection process. Mass, cost, high temperature (>800 o C for exhaust manifold and >400 o C for downpipe silencer/ muffler box and tail pipe) and high corrosion resistance were used as basic criteria for the material selection. Variety of materials including Nickel-based superalloys, stainless steel, Nickel-chromium alloys were obtained in the material selection route for exhaust manifold. Similarly, low alloy steels, stainless steel, grey cast iron, Nickel-based superalloys, Nickel-chromium alloys were obtained in the material selection for downpipe silencer/ muffler box and tail pipe. Nickel-based superalloys and Nickel-chromium alloys possess suitable properties for this application, but were not considered due to their high densities and high cost. Low allow steels were not selected because they tends to exhibits poor corrosion resistance when exposed to salt on the road surface and condensate from the exhaust system. Grey cast iron has low tensile strength and elongation and therefore not exhibit enough toughness required to withstand the severe working conditions. However, stainless steel (Ferritic stainless steel and Austenitic stainless steel) was considered as a better choice of material for automotive exhaust systems due to its considerable price and density, acceptable strength at elevated temperatures and excellent corrosion resistant it possesses as a result of the protective film of chromium oxide which forms on the surface of the metal.