CHARACTERISATION OF BURNER NOISE AND COMBUSTION CHAMBER TRANSFER FUNCTION IN A DOMESTIC HEATING BOILER

摘要

The combustion noise of a domestic heating boiler has been investigated so that a Virtual Acoustic Prototype of a boiler system may be developed. In order to construct a Virtual Acoustic Prototype it is necessary to separate the system into active source components and passive structural components. In particular, the source strength of the burner combustion noise, independent of the combustion chamber geometry, and the passive Acoustic Conductivity Function of the combustion chamber have been investigated. In characterising the burner it was necessary to determine the minimum set of components which could be considered an invariant source, independent of the surrounding structure. This was achieved by measuring the sound of a plate burner, typical of those used in a UK domestic heating boiler, fitted within a number of idealised combustion chambers consisting of rectangular section tubes of varying length. It was found that the completely unenclosed burner could not be considered an invariant source and that some part of the surrounding enclosure must also be included in order to obtain invariance over a number of idealised combustion chamber lengths. Transfer functions of the transmission path from the flame-front to the far-field reception point were determined for the idealised combustion chambers using reciprocal measurement techniques and these were used to determine the limits of invariance of the burner source strength. Practical problems encountered when measuring source strengths and transfer functions of components which operate at elevated temperatures are discussed.