ABSTRACT
Current practice is to control combustion in open loop without feedback of information to the system. This does not allow optimization of the process and may also pose serious problems for future developments. It is therefore thought that new combustion technologies should integrate feedback con trol. Automotive engines already exploit closed-loop concepts [1] and this allows a fine tuning of operating conditions. This adjustment of operation with sensors probing the exhaust gases is investigated in many current applications including biomass combustion [2] and gas turbines [3]. In this last area, a notable decrease of NO* emissions has been reached by adopt ing a premixed mode of operation in which the flame temperature is reduced and the level of NOx is diminished significantly. However, premixed com bustion requires a precise determination of the equivalence ratio which could be deduced from measurements on the flame and in the flue gases. Moreover, the premixed mode of combustion, which is now favored in gas turbine applications, leads to large amplitude instabilities, which may have serious consequences. As a result, efforts are being made to develop active control solutions to this problem and this in turn will require sensors for process monitoring and feedback input.
