## 3 Results and Discussion
### Effects of Exhaust Flow Rate and Hood Height on CO and Soot Yields  
In addition to the external heat flux, which was examined as a factor affecting CO and soot yields in a cone calorimeter, the exhaust flow rate and hood height can also be considered as factors that influence the formation and emission of CO and soot. More specifically, changes in the exhaust flow rate and hood height have the potential to affect CO and soot yields owing to the following factors: air entrainment in post-flame and plume regions, mixing rate of combustible gas and air, flame stretching by the suction flow of the hood, and direct quenching phenomena when a flame or high-temperature plume crashes on the surface of the upper part of the hood. The exhaust flow rate proposed in ISO 5660-1 is 24 L/s, while the hood height that corresponds to the vertical distance from the specimen surface to the bottom of the hood is 0.25 m. Considering that the exhaust flow rate is based on volume rather than on mass, however, it is difficult to maintain a constant volume flow rate inside the exhaust duct, where there is a significant temperature change in exhaust gas. That is, the exhaust flow rate and hood height can vary significantly in the experiment process and setup of a cone calorimeter according to the individual researchers. Therefore, examining the effects of changes in the exhaust flow rate and hood height on CO and soot yields will provide an opportunity to inspect quantitative errors on the dependence of researchers. By inspecting the exhaust flow rate and hood height as variables within a wide range rather than as fixed values, the relevance of reference values proposed in ISO 5660-1 can also be assessed. Figures 10 and 11 show MLR and HRR when the exhaust flow rate and hood height (h) change according to auto and spark ignitions under the fixed external heat flux condition of 50 kW/m\({}^{2}\). The exhaust flow rate was varied up to 86 L/s, including the reference condition of 24 L/s. Hood heights of 0.25 and 0.55 m were considered; however, for 0.55 m, the exhaust flow rate of 72 L/s at which overflow of exhaust gas does not occur was examined limitedly. As shown in Figure 10a, changes in exhaust flow rate under the conditions of h = 0.25 m and auto-ignition did not affect MLR significantly. The mean HRR of the section between 100 and 400 s was around 5.3 kW under all flow rate conditions that were quantitatively considered. The mean HRR was still around 5.1 kW when the hood height was increased to 0.55 m, thus proving that the effects of changes in hood height on MLR was negligible. The same trend was also observed under the spark ignition shown in Figure 10b. The results of HRR shown in Figure 11a,b indicate that HRR did not vary substantially according to the exhaust flow rate and hood height, thus resembling the results of MLR. Figure 9: CO, CO\({}_{2}\), and soot yields as a function of external heat flux. Figure 12 illustrates CO, CO\({}_{2}\), and soot yields according to the exhaust flow rate for the two hood heights that were considered. As shown in Figure 12a, CO and CO\({}_{2}\) yields were constant at 0.0070 and 2.2030 g/g, respectively, regardless of the exhaust flow rate and hood height. Similar to the results of CO and CO\({}_{2}\) yields being constant with respect to the external heat flux in Figure 9a, the changes in the exhaust flow rate and hood height did not influence the CO and CO\({}_{2}\) yields. In Figure 12b, which shows the results of soot yield, the value remained constant at 0.0184 g/g regardless of changes in the exhaust flow rate and hood height, which is similar to the results of the CO yield. The hypothesis that changes in the exhaust flow rate and hood height will cause velocity and temperature fields in post-flame and plume regions to change as well, thus affecting CO and soot yields, was not supported. Although it was not presented in this study, the vertical (axial) velocity was measured on the specimen and at the cone heater outlet and bottom part of the exhaust hood.