In this study, the effect of carbon dioxide diluted (30%～60% in fuel volume) on the combustion characteristics with a tubular flame burner have been systematically investigated, including the flame appearances, the stable flame regions and the axial temperature distributions of the burned gases. For a point of practical view, the exhaust emissions of NO_x and CO at the burner exit have also been examined. The main results obtained are as follow: (1) The tubular flame can be successfully obtained for a wide range in the equivalence ratio and the flow rate of the combustible mixture. However, for a ≥ 0.6, the rich flammability limits are slightly lower than that of a = 0.3. (2) Detailed measurements of the burned gas temperature at the central axis against the various equivalence ratio show that the burned gas temperature is decreased with increasing CO_2 content in the fuel. (3) More detailed measurements on the exhaust emission show that the value of NO_x is reduced approximately to a half value of a = 0.3 with increasing CO_2 content to 60%. Thus, the tubular flame burner has the potential for achieving a stable biogas combustion as well as reducing NO_x emission.
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