This paper describes an experimental investigation into modifications to reduce catalytic converter radiated shell noise. The two objectives of the paper are to compare the noise radiating characteristics of a traditional heatshielded racetrack shaped clamshell converter to a fully insulated tourniquet wrapped underfloor converter, and compare close-coupled ceramic and metal based preconverters.
Experimental efforts were used to characterize the noise radiating aspects of the various catalytic converter systems. Driving point frequency response measurements were made, at room and at high temperatures, to identify the various modes of the converter. Sound pressure level measurements were made to quantify the radiated noise, while sound intensity measurements were made to calculate the total sound power actually available at the source (the converter). Vibration experiments were also conducted on the surface of the converters.
The results show that the global modes of the converters were found to lie below 800 - 1000 Hz, with minimal temperature variations in the first few modes. In addition, the fully insulated underbody converter and the ceramic preconverter generate 10 dBA and 7 dBA less noise than their counterparts, respectively.