Exhaust manifold in engine is used to transfer the hot exhaust gas from cylinder head to the turbocharger with minimum pressure loss and to support the turbocharger assembly. This puts manifold under intense thermal and mechanical loading and makes the design very complex. While designing the manifold, resonance of the system must be avoided, and thermo-mechanical fatigue life expectations must be met. Different engine applications would call for multiple turbocharger configuration and orientations to be considered in the design layout for system level resonance assessment.
This paper talks about the failure investigation of the manifold which was designed for High mount rear out (HMRO) turbo orientation and then used with high mount front out (HMFO) layout in road miller application resulted into the manifold failures. Root cause identified was mechanical fatigue caused by resonance vibration at machine operating modes in the presence of very high mean stress from thermal expansion of the exhaust manifold. Detailed investigation included metallurgical analysis, vehicle level testing (strain and modal), exhaust manifold thermo-mechanical fatigue analysis, modal impact testing, thermal survey, engine endurance testing.
Design improvements to the manifold included conversion from two-piece design to three-piece design. Design margin improvements in all critical region. Verification of the design and incremental benefits are demonstrated analytically and using testing.