バイオマスガス燃料使用の噴流拡散火炎に対するコンサーブド?スカラ?アプローチモデルの適用性に関する一検討

摘要

The conserved scalar approach is widely used for a reaction model in the numerical simulation of turbulent diffusion flames. This model is based on the assumption that all the effective diffusion coefficients of scalar quantities, such as chemical species concentrations and heat, are the same. When turbulent diffusion coefficient is much larger than molecular one, this assumption is applicable. However the assumption would cause serious error if molecular diffusion cannot be neglected and differential diffusion takes place among various species. Then, in the present study, experimental examination was carried out on the diffusion rate of chemical species in turbulent diffusion flames, using two kind of coaxial jet flames which are different from each other in turbulence condition. The mixture of CO and H_2, which have much different diffusivities, was used as fuel. The results of the study can be summarized as follows: (1) The assumption that all the effective diffusion coefficients of scalar quantities are the same can be effectively applied to triple jet diffusion flames, where the combustion field is surrounded by strong turbulence. However, this assumption is difficult to apply to flames with weak turbulence, such as coaxial jet diffusion flames. (2) The findings in above should be considered for the modeling of jet diffusion flames used for biomass-gas fuel and syngas.