Combustion state monitoring of premixed heating appliances with flame ionization current and chemiluminescence

ABSTRACT

The development of a combustion operating point control system has received interests from gas boiler manufacturers in order to ensure optimized performances despite variations of natural gas composition. Fully premixed burners are widely used in these boilers and the equivalence ratio is a key parameter to control. Experiments are carried out in this study for CH₄/air fuel blends diluted by N₂ or CO₂ or enriched by H₂, C₂H₆, or C₃H₈. Two low cost solutions for monitoring the equivalence ratio based on the flame ionization current and the chemiluminescence signal are investigated on a laboratory laminar conical flame. The behavior of the ionization current with changes of gas velocity, fuel composition, and equivalence ratio is shown to be mainly related to the size of the dead space between the flame base and burner rim. In a second stage, changes of the chemiluminescence signal is studied and the use of CH*/OH* intensity ratio as an equivalence ratio indicator is verified. Numerical 1-D premixed flame simulations are performed to support the experimental results on the flame chemiluminescence. Finally, a third equivalence ratio sensing method is proposed, coupling both techniques and the three strategies are compared.

KEYWORDS:

• Combustion control
• Domestic boiler
• Flame ionization current
• Flame chemiluminescence

Acknowledgments

The authors gratefully acknowledge the support of Bosch Thermotechnologie for this program, which is also part of the ZEM-R project supported by FUI (Fonds Unique Interministériel). The authors also wish to thank David Charalampous and Erwann Pannier for their help and advises.

Additional information

Funding

This work was supported by the Fonds Unique Interministériel [ZEM R].