Abstract
The present paper reports a systematic study on different methods of obtaining the chemical length of a turbulent non-premixed CH 4 jet flame. The study is performed based on numerical simulations by the RANS modeling over wide ranges of the fuel jet velocity (25 ∼ 100 m/s), the coflow oxygen concentration (6 ∼ 100 % by volume) and the coflow temperature (300 ∼ 2000 K). To validate the modeling, some calculations are compared with previous measurements of Dally et al. (Proc. Combust. Inst. 29, 1147–1154, 2002) and Kim et al. (Energy Fuels 21, 1459–1467, 2007). Primary results reveal that, among seven different definitions of chemical flame length, the best performance is made by those defined from the yield ratio of CO to CO 2 at y C O / y C O2= 0.02 and the carbon monoxide ratio at R C O = X C O /X C O m a x = 0.01. It is also found that only use of these two definitions exhibit the flame lift-off behavior and to gain the lift-off height properly. Besides, this paper explains the importance of taking the near-zero contour of the CO concentration as the base on which the border of the complete combustion region is defined for chemical flame length.
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