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Show A large pressure drop across a burner is a feature that compromises energy efficiency as well as increases capital cost. The advantage of the open tube L S B design is that its throat diameter is larger than burners of comparable capacity and is free of obstructions such as a bluff body. The air-jet L S B is essentially an open tube with no physical or fluid mechanical flow barriers. The version with a guide-vane is designed to be low drag. Therefore, the pressure drop across a L S B is very low and can be operated by a small low cost blower that utilizes little parasitic energy. Another attribute of the LSB is its flame stability. Despite the freely propagating flame, it is very stable in different enclosures and flue constrictions. In a recent study [11], w e found that the flame is relatively free of the back-pressure effects that affect other lean premixed burners. Without a T R Z , the L S B flame does not have a distinctive acoustic signature and therefore operates much quieter than other burners. Because of the propagating nature of all premixed gaseous flames, the L S B can be engineered to accept different gaseous fuel. W e have operated the laboratory L S B with pure methane, natural gas, propane, and ethylene. APPARATUS AND DIAGNOSTICS Schematics of three LSBs and their respective test configurations are shown in Figures 1-3. Only the air-jet version of the L S B has been used for this study. The L B N L water heater simulator (Figure 1) has a 5 c m L S B (5.26 c m ID exact) that sits atop a pipe cross (Figure la). The interior of the cross is filled with glass beads to break down large flowfield disturbances. T w o perforated screens help to promote flow uniformity, as well as generating moderate turbulence (6-8%) in the flow. The other dimensions of the burner include the swirl injector radius Rg = 1.6 m m , and exit tube length of £ = 70 m m . The rim of the exit tube is tapered to 45° to guide the flow's divergence. The water heater simulator uses a commercial heat exchanger from a Telstar 50,000 Btu/hr spa heater (Figure lb). It is rectangular in shape (15 c m deep, 22 c m wide, 24 c m tall), with a fin-and- tube heat exchanger 4 c m below the top. Emission samples were taken 50 cm downstream of the heat exchanger in a 10 c m (diameter) exhaust flue. In conjunction with the 5 c m LSB, the L B N L water heater simulator has a chamber area / burner area ratio A c / Ab = 15. More details of this configuration can be found in [12]. Figure 2a shows the schematics of a 5 cm LSB used in the UCICL burner evaluation facility. Natural gas is entrained through a venturi upstream of the swirler section and is mixed with the reactant air. Downstream of the screens, the dimension of the burner is identical to one described above. The burner fires vertically into an octagonal shaped enclosure that measures 60 c m across and 175 c m in height. The enclosure is fitted with eight high temperature windows (25 c m by 30 c m ) at the lower third of the enclosure, and eight water cooled panels (25 c m by 60 cm) above the windows (Figure 2b). Emissions are sampled 150 c m above the enclosure floor. The area ratio of the enclosure to burner A c / Ab is an order of magnitude larger than the L B N L water heater simulator. 5 |