| OCR Text |
Show - 3 - on this band width limitation has been given. To explore the mechanisms of combustion noise emission to a further extent, the spectra of the sound emitted from turbulent flames should be examined in detail varying paralneters systematically. MEASUREMENT AND ANALYSIS OF COMBUSTION NOISE[9,lO] In order to examlne the characteristics of combustion sound, it is necessary to make time-resolved investigation of the sound pressure. Measurements of the sound pressure were made on a methane-air turbulent premixed flame stabilized on a burner shown in Fig. 1. A burner with circular cross-section of 22 mm diameter was employed to stabilize the turbulent flames. A mesh screen flame holder was incorporated around the burner mouth to anchor flames at higher flow velocities. A 2 mm-holes-pe rforat.ed brass plate was employed to ensure fully developed turbulent flows a t the burner mouth. The n1ethane and air were metered separately by means of orifices and fed in to a mixing piping of 2 m long. The maximum mixture flow velocity was 9 m/s. The sound emitted from a turbulent flame was measured with an electric condenser microphone located 120 mm from the cen ter of the burner and 50 mm above the burner mouth. The sensitivity of the microphone was calibrated by a B &, K Type 113 microphone, 1.26 m VIP a and the signal was amplified, sampled with a 12 bit A-D converter, and analyzed by a computer. 1024 data were sampled at a rate of 25 kwords/s. The total sampling period was 41 ms. A 10 kHz low pass filter of - 18 dB loct . was used as an anti alias filter. The frequency range to analyze was from 0 Hz to 12.5 kHz. The frequency components of the signal were examined by a fast Fourier transformation system with hamming window function(Eq.(I)), f (t), i.e., w (1) where T is the total sampling period and t is the time. |
