Double Concentric Burner Research Articles

Effect of N2 Replacement by CO2 in Coaxial-Flow on the Combustion and Emission of a Diffusion Flame

In this study, a double concentric burner burning methane with an annular coaxially-flowing oxidizer was adopted to operate the diffusion flame in lifted flame regime. The effects of coaxial-flow velocity, coaxial-flow composition variation through total and partial replacement of N2, and coaxial-flow oxygen enrichment were experimentally investigated in terms of the resultant changes in the flame stability, and thermal and emission characteristics. Consistent with the triple flame theory, the current stability tests show a linear increase in flame lift height with increasing coaxial-flow velocity and the blowout of lifted flames occurred at constant flame tip height. Replacement of N2 by CO2 in the coaxial-flow deteriorated the flame stability by significantly reducing the threshold coaxial-flow velocity. Due to combustion enhancement that is caused by oxygen enrichment, the threshold coaxial-flow velocity increased and this increase is more significant for the N2-diluted flame than CO2-diluted. Two of the most important NOx formation mechanisms, Zeldovich and Fenimore, were analyzed under the relatively low temperature flame conditions, generally below 1300 °C in this study. Results show that NOx is principally produced via the Fenimore mechanism for both N2- and CO2-diluted flames. NOx productions can be significantly affected by coaxial-flow composition and coaxial-flow velocity. An increase in the velocity of N2-diluted coaxial-flow increases NOx emissions, while a reverse trend occurred, as N2 in the coaxial-flow was replaced or partially replaced by CO2, which is ascribed to the strong combustion-resisting behavior of CO2. For all cases, CO emissions vary in the opposite direction of NOx emissions. Due to the strong thermal and chemical effects of CO2 on combustion in comparison to N2, total or partial replacement of N2 by CO2 results in a steep increase in CO emissions.

Characteristics of Premixed Flames in a Double Concentric Burner

Various flame types are observed in a double concentric burner by varying equivalence ratio and flow rates in each tube. Observed flame types include bunsen-type flame, ring-shaped flame, outer lifted flame, inner lifted flame, and oscillatory lifted flame, The doman of existence of various flames is mapped with equivalence ratio and annular jet velocity. Each flame is investigated through direct photography and OH PLIF. As central air velocity increase, the blowout region is diminished and lifted oscillating flames are observed. Inner lifted flames are observed from bunsen flames or rich shaped flames by increasing central air velocity. For inner lifted flames, annular jet velocity, at flame liftoff decreases with increasing central air jet velocity. Axial velocity profile and temperature fie이 using LDV and CRS, respectively, for a typical inner lifted flame are also measured through which the role of tribrachial flame for stabilization in emphasized.

Mixing and recirculation characteristics of a double concentric burner with bluff-body

The concentric bluff-body jet burner is widely used in industrial combustion systems. This kind of burner often generates a considerably complex recirculation zone behind the bluff body. As a result, the fuel often remains in the recirculation zone, achieving stability of flame. This study investigates, by means of experiments, the variations of the aerodynamics as the fluid is injected into a combustion chamber through a double concentric burner with a bluff-body. The observation and measurement of the aerodynamics in our experiment are conducted under a cold flow. The controlled parameters in our experiment are: variations in the blockage ratio of the center bluff body, the cone angle of the bluff body, and the velocity ratio (U s/Up) of the secondary jet and primary jet; the injection of helium bubbles into the primary and secondary jets to observe the recirculation zone behind the bluff body; using Tufts for observing the characteristics of corner recirculation zone in a combustion chamber, measuring the average velocity of each point within the aerodynamics by the 5-hole pitot tube; measuring the distribution of static pressure of the combustion chamber walls with a static pressure tap.