On the Applicability of Cold Acoustic Measurements to High-Amplitude Hot Pulsating Flows

The experimental characterization of the acoustic characteristics of engine exhaust devices is usually carried out through measurements in cold conditions, due to the intrinsic difficulties associated with proper temperature control in an acoustic rig. While those measurements may be sufficiently indicative for the cold end of the exhaust (the silencing elements) their significance for the hot end (the aftertreatment system) is more doubtful, as a result of the high temperatures and, eventually, the higher amplitude of pressure waves acting on the system. In this paper, a direct assessment is provided on the significance of acoustic measurements in cold conditions for representing the actual behaviour of an aftertreatment system in a hot pulsating, engine-like flow. Making use of wave decomposition techniques, the measured characterization was convoluted with the hot-flow excitation and the device responses were directly compared. The results indicate that, while it is not possible to fully reproduce the behaviour observed in hot pulsating flow, the tendencies are reproduced, at least qualitatively. In particular, the effect of soot loading is fairly reproduced.