A comparison between frequency- and amplitude-modulated adaptive control of a non-premixed flame

Acoustic forcing of a laminar non-premixed flame issuing from a Wolfhard-Parker slot burner affects soot production in the flame and thus its luminosity. This research details how the relationship between acoustic forcing and the luminous response can be used to implement full closed-loop adaptive feedback that actively controls the flame luminosity. Results show that in an open-loop configuration both the frequency and amplitude of an acoustic square wave produce large overall changes in flame luminosity and that both methods may be useful in implementation of a closed-loop controller. A one-step-ahead adaptive control law with least-mean-square recursive parameter identification was used to compare the control performance using frequency- and amplitude-modulation schemes. For the frequency-modulation case, the adaptive controller changes the frequency of the acoustic wave, and for the amplitude-modulation the amplitude is changed at every control period to try to attain the desired luminous output from the flame. Several test cases were run, including fixed-point, linear, square wave (multiple step), and fixed-point with disturbance, in an effort to determine which control implementation best met the control objectives. The results from the tests indicate that the frequency-modulated control input was able to operate large difference in control frequencies and also tracked the desired output more closely. The relatively large difference in performance found from these trials demonstrates the importance of selecting the proper actuation for a particular system and the potential benefits in relating the actuation mechanism to the combustion process.

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