OCR Text |
Show 4 3.2.Factor to subject the heat distribution by combustion Evaluated the enthalpy distribution by combustion, a flame length is often used as the reference. A flame length was defined in this paper as the distance from 02/N2 burner nozzle to the point at a certain value of 1- 77. Figure 3 presents the relationship between the flame length and the velocity of oxidized gas jet at 02/N2 burner nozzle exit. Here, flame length was determined by the interpolation of the experimental values on each graph, from Figure 2a to Figure 2g. Both flame length at 1- 77 =10% and 30% were plotted on Figure 3. As shown in Table 1, regardless of different conditions, conducted in several CO concentrations in fuel gas, several oxygen concentrations in oxidized gas and several diameters of 02/N2 burner nozzle, it was found that flame length at each 1- 77 was mainly determined by the velocity of oxidized gas jet at the nozzle exit. This suggests that the mechanism of the combustion depends on the flow characteristics in the test equipment more than the chemical kinetics. In order to make the relation between the flame length and the flow characteristics clear, Figure 4 presents the relationship between flame length and k/ s , where k is the turbulent kinetic energy and e is the dissipation rate of k, using the same data as Figure 3. Here, k/ £ is determined by the calculation mentioned in the equation (2) and equation (3), and is averaged over the volume of the test rig in Figure 1 from oxidized nozzle exit to 400 millimeter downstream corresponding to the flame length of 1- 77 =0 on Figure 2a. It is the largest combustion rate among test conditions in Table 1. It was found in Figure 4 that flame length was determined by the k/ € value in the combustion space. k/ s represents the time scale of the turbulent eddies following the eddy-dissipation model of Spalding[3]. Considering the value 'k/ E ' means the degree of turbulence, Figure 4 describes that the flame length is determined by the degree of turbulence. Desired to get the short flame in combustion, the process design and the operations to obtain strong turbulence in a furnace are required, such as the nozzle design acquired the large velocity in Figure 3. It seems to be reasonable to conclude, from what has been said above, that the mechanism of the combustion using high temperature fuel gas is followed by turbulent diffusion, and that the flame length can be determined by k/ e as the degree of turbulence. 4.Summary The mechanism of combustion using high temperature CO and N2 mixed gas has been studied to determine the enthalpy distribution by means of the experiment and the numerical simulations. The experimental results showed that the flame length as the reference of the enthalpy distribution was determined by the velocity of oxidized gas jet at the nozzle exit, regardless of different conditions, conducted in several C O concentrations in fuel gas, several oxygen concentrations in oxidized gas and several diameters of 02/N2 burner nozzle. Also numerical simulations incorporating an eddy-dissipation combustion model are in close agreement with |