THE MEASUREMENT OF THE MACH NUMBER AND THE SPEED OF SOUND IN AN ENGINE EXHAUST SYSTEM BY AN ACOUSTICAL METHOD
Abstract
A new acoustical method for the measurement of the Mach number and the speed of sound in small ducts (D (LESSTHEQ) 0.1 m) is developed theoretically and its usefulness tested experimentally on a running Ford V8 351 cu. in. experimental engine. The method is based on the idea, that a tone burst emitted into a flowing medium, propagates at different speeds upstream and downstream. If two microphones are mounted upstream and one downstream, two time lags between signals are observed which can be determined by cross correlation techniques. The computational effort is very small provided the acoustic signal propagates mainly in the plane wave. This is in general the case when kR (LESSTHEQ) 1.0 is satisfied, where k is the wave number and R is the radius of the pipe. Furthermore, the dominance of propagation in the plane wave is enhanced by increasing the number of cycles of the tone burst. The experiment reveals very good agreement between theory and experiment.
Degree
Ph.D.
Subject Area
Mechanical engineering
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