Research and development services provided to improve existing exhaust system performance
Sinclair Knight Merz undertook a research project to investigate the feasibility of using multiple Helmholtz resonators to reduce the external noise emissions from a 4000 HP diesel engine. To meet environmental regulations, an improvement was required in the low frequency performance of the existing muffler. The project involved theoretical analysis followed by design and testing of prototypes in a test rig and also on a locomotive.
The resonator performance envelope was complicated due to the wide range of operating temperatures and exhaust gas velocities that accompany changes in engine speed. Another design constraint was the extremely tight space envelope for the resonators.
Test rigs designed and prototypes trialed and refined
The test rig incorporated a high powered loud speaker to trial prototypes when removed from the locomotive. Prototype resonators were designed with variable volumes to allow for tuning of the devices. Water cooled pressure transducers were used to measure acoustic pressures inside the turbocharger casing while the acoustic response was simultaneously measured at the muffler discharge.
The project showed that the acoustic properties of the existing muffler could be improved significantly in specific frequency bands. However, the modal characteristics of the muffler dominated the acoustic response and a satisfactory solution could not be found that achieved compliance at all engine operating speeds . This project demonstrated the ability of Sinclair Knight Merz to work closely with manufacturers to solve their vibro-acoustic and dynamics problems in a commercial framework.