Detection of Obstructions in Automotive Manifolds by Aeroacoustic Means*

An aeroacoustic method has been developed to detect obstructions in automotive manifolds. The method has been tested extensively in the laboratory and on production lines of exhaust manifolds and has shown superior performance compared to other methods currently used in industry. It provides the most reliable diagnosis of small-size obstructions. Moreover, the method is very simple, provides fast results, is easy to implement into production lines, has low maintenance cost, and is insensitive to acceptable manufacturing tolerances, such as the inner surface roughness of the manifold. The developed method is based on the phenomenon of sound generation when the flow passes over obstructions or protrusions from the inner surface of a flow duct. A microphone is used to measure the noise level generated by air flow through the manifold. This noise level is compared with the averaged baseline value of unobstructed manifolds. An obstruction is detected if the noise level exceeds the baseline by a critical amount. Reliable detection is achieved only when the noise level is measured over a specific range of frequencies.