Combustion Acoustics

Acoustic Phenomena of Heating Systems

The evaluation of noise emissions of heating systems has taken on an important role in recent years because of two main reasons: in modern buildings the installation room is often near to the living area so that the demand for quiet systems grows and a reduction of emissions is often achieved by increasing flow velocities and turbulence degrees of the combustion air, which causes higher noise emissions. At OWI, acoustic investigations are carried out measures for the reduction of noise emissions are audited. This applies to devices which are already available at the market as well as to new systems in their development phase. For this purpose, a broad range of acoustic analysis methods are at hand. This includes

  • the measurement of the sound power which is emitted into the environment of the device. For the performance of these measurements, OWI has a sound-isolated acoustic laboratory which has been optimised for the application of the sound intensity method according to ISO 9614-1 and allows measurements up to the accuracy class 1. In comparison to simple pressure measurement the sound intensity method allows measurements with low standard deviation even for applications which cannot be installed in specifically equipped laboratories due to their dimensions.
  • the measurement of noise emissions into the exhaust gas stack as a huge part of the combustion noises is emitted into the exhaust gas system. Disturbing noises can thus be transmitted into parts of a building that are distant from the installation room. OWI owns heat-resistant microphones which enable measurements of the sound power inside the exhaust gas stack in the hot off-gas stream.
  • the analysis of self-excited combustion oscillations. This phenomenon occurs, when the acoustic transfer functions of the burner, the flame and the boiler in discreet frequencies supports an increase of stochastic pressure fluctuations during the combustion. In case that these pressure fluctuations become too strong, even the stability of the combustion can be affected additional to high noise emissions. Investigations relating to this complex topic are carried out at OWI. Furthermore, problems with commercial devices are analysed and solved. In addition to the pressure in the systems, the light emission fluctuations of the flame and the velocities of the fluids in the device are measured. High-frequency multi-channel analysis software for the frequency and phase analysis of these signals is at hand at OWI.