The Effect of a Flame Holder Shape Modification Toward the Diffusion Flame Stability Zone Shift

The flame stability limit, which was involving the critical flow condition, lift off and blow out, could be affected by the burner geometry in the combustion system installation. Consequently a flame holder should be put in, to hold the flame as big as possible on a stable condition. The flame holder itself, is a device to hold the flame, whereas the flame holder could disturb the air and fuel flow. The fluid flow will be disturbed if the forces work on the fluid flow will be interrupting their stability. The fluid flow blockage by the flame holder will generate vortex and this vortex will end up with a turbulence condition. This turbulence condition will shift the critical stability limit and will produce a perfect combustion. In this research a concentric jet flow burner was implemented and the fluid flow speed and air speed was variated. To achive a perfect result, it is necessary to visualize the flow pattern using a schlieren photograph system. A thermocouple was introduce to measure the flame temperature and to know the temperature distribution. It is recocnized that a flame holder could be able to increase the flame stability zone. The hollow shaft flame holder was the one who could increase the stability zone significantly, because this kind of flame holder could hold the flame excellently and no lift off take place. The flame temperature distribution increase. The temperature increase has the smallest range compare with the combustion using the other kind of flame holders. Key word: Flame holder Stability limit Concentric jet flow burner Flow speed and air speed INTRODUCTION is functioned as an obstacle or a flow obstruction. The flame limit stability was the operation limit of a fluid was disturbe their stability. Flows colliding a flame combustion system. There were two kind of critical holder will produce a small circulating flow and up with a condition related to the flame stability, which is the flame turbulence flow. lift off and the flame blow out. The critical flame limit To find out about the different flame patern, it is stability depends on the burner geometry condition. recomended to look the fuel and air flow patern Wijayanti [1] studied the reactan flow mixing, it was implementing the schlieren photograph visualization found that a little increase of the fuel and air flow would system. release the flame from the burner port. Since this condition The research was conducted to find out how the continued the combustion condition would go on a verry shift of the diffusion flame stability zone moved because unstable phase. a flame holders attached and to find out how far these On the test section a flame holder should be applied, three kind of flame holders will influence the air and fuel because the critical condition of the stability is caused by mixing stabilizer. Furthermore, it is necessary, to know the the burner geometry. There were some flame holder flow patern visualitation caused by the flame holder models to hold the fire flame as big as possible and on a attached. stable condition. Takahashi F. [2] conduct a research on a double A Flame Holder is an instrument designed to hold concentric jet flow. In this research the flame diffusion the fire flame not easy to leave the burner port. The flame turbulence was observed to know the flame turbulence holder shape was designed into some models. The flame structure. In more detail the research is trying to find out holder shape used on this research is a ring shape, a cone the influence of the swirl attached toward the flame shape and a holow shaft shape. Actually, the flame holder structure. A fluid flow would be disturbe if forces works on the World Appl. Sci. J., 8 (3): 339-344, 2010 340 Rohmat T.A. [3] observe the diffusion flame stability on a hollow shaft attach inside a combustion chamber. This research was carried out inside an experimental kit which is connected to a wind tunnel with a low speed air flow. A porous plate burner was attached on the inlet experimental kit. The fuel used in this experiment is a 98% methane. From this experiment, it is found that there was a connection between the visual flame diffusion shape and the flame diffusion stability. Another research on a double concentric jet flow Fig. 1: Flame Difussion Lift burner was extended by Wijayanti, W. [4]. Wijayanti was trying to examine the diffusion flame visualization and the shifting of the flame stabilization zone. The result of this research was a Figure of a flame visualization, which was influence by the fuel flow speed, primer air, secondary air and the concentric annulus tube. The Flame Diffusion Reactant Flow Structure: Several researches reporting that dynamic vortex always occur on the non-premixed flame flow structure, with an intention to stabilize the combustion process [5]. According to Marios [6], the reactant flow were Fig. 2: Recirculation zone of a disc flame holder dominated by the large scale vortex structure, because the reactant flow destabilization is passing through an Flame Holder: Flame holder is a device designed to hold amplification stabilization. The instability was influenced the fire flame. The flame holder designed in this research by the combustion temperature fluctuation and by the has three kind of shapes. Fluid flow would be disturbed if speed fluctuation. Takahashi, [2] from his research, said the force working on the fluid is disturbing their stability. that the flame flow structure was strongly affecting the A flow which is disturbe by a flame holder will generate flow stability. The flow stabilizer were the vortices, which vortex, which ended with turbulence. will dominate the combustion process. By adding a flame holder on this research, it is There were two kinds of flow reactant mixing, which expected that the flow will be disturbe and the combustion will be observed on this research. The first one was the process would be better and the fire flame would be much unburned gas and the burned gas. Daily, [7] examine the stable. Consequently the flame stabilization zone will be flow structure of these two conditions. Which means that increase too. the combustion process did not induced the reactant flow Furthermore, on a fuel speed of over 40 cm/sec, the mixing. combustion stabilization would occur, so that the fire Physically, the flame lift mechanisme could be seen flame will be occur continuously. Some of the flame holder when the flame starts to leave the burner port. The flow model could be attached on the nozzle tip ends. transition goes to turbulence would be seen affecting the The recirculation zone and the fire flame flow pattern flame lift. For a good orifice, probably the flame woud with a disc flame holder could be seen on the Figure flickering before the lift occure. The lift phenomenon below. could be clarified by looking at the diffusion process, Daily [7] mentioned, that the air and fuel mixing the flow distribution, the speed distribution or the would strongly influenced the combustion stabilization. temperature. Every theory about the lift phenomenon were At an instabil condition, the occurance of the Kelvinclarifying each other. Helmhotz vortex will be verry important as a fluid steerer The blow out phenomenon could be interprated with equipment on the mixing process. Flow mixing occur on the premix flame concept. Blow out would take place at a the boundary layer zone, as a result of the temperature certain flow speed where the turbulence flame speed is gradient involve at that area. This occasion was higher then the local speed on the maximum flame speed demonstrated on a flow pattern visualization and was position. supported by some researcher opinian, such as