Motorcycle Dual Exhaust Muffler Design Improvement to Eliminate Failure Caused by Thermal Stress 2016-01-1080
A single cylinder gasoline engine of a sports bike generates sufficient hot gases to pose great challenge to the designers of exhaust system. The high temperature exhaust gases in muffler creates thermal elongation on the solid parts of exhaust system, which is mounted on the chassis. This arrangement induces thermal stress in exhaust assembly. It is necessary to analyze this thermal stress to ensure the durability of muffler components.
The exhaust design has a diversion at the header pipe to distribute the flow in two branches. This junction and the branches heated up excessively and showed repeated failure. To analyze the thermal stress, the temperature distribution in the muffler components is obtained from Computational Fluid Dynamics (CFD) analysis. The complete motorcycle with detailed exhaust system is modelled in the standard wind tunnel using a commercial CFD software. Conjugate heat transfer (CHT) study is done for normal and adverse operating conditions considering transfer of heat between hot exhaust gases passing through muffler assembly, muffler solid components and external air flowing over motorcycle. The heat generation in the catalytic convertor and the radiation between muffler components are also considered.
Parallelly, complete muffler assembly is modelled in a commercially available FEA code. All the muffler mountings are considered including the bushings and bolted connections. Material properties are defined for each of the muffler components. The temperature distribution obtained from CFD analysis is applied to simulate for thermal expansion, stress and deformation in the exhaust system. Results showed excessive stress on a certain component of the muffler. Design modification is implemented and is validated following similar analysis work flow. Thermal stress is found to have reduced considerably in the modified design as compared to the base design.