# Polyisocyanurate Foam Pyrolysis and Flame Spread Modeling
## 3 Results and Discussion
### Full-Scale Experimental Results and Modeling  
The temporal HRR profiles measured in the vertical corner flame spread setup are shown in Figure 7. Two HRR profiles are presented: the average of the two experiments on the Tuff-R insulation panels without facers and the results of a single experiment on the panels with facers. The error bars were calculated by assuming 10% uncertainties in the oxygen-consumption-based heat release measurements [32; 43]. In both cases, the insulation panels ignited within 5-15 s after the burner was turned on. The ignition was followed by a formation of a single fire vortex that rolled from the bottom to the top of the corner. This vortex formation was attributed to a quick release of some of the blowing agent from the pyrolyzing foam. For both types of panels, the total HRR (including 30 kW from the burner) initially increased above 70 kW, which corresponded to the time when the flame tips extended above the top of the panels. After these peaks, the flames gradually subsided. After about 200 s, the HRR curves nearly flattened at around 35 kW, just 5 kW above the HRR of the burner. The presence of a foil facer on the front panel surfaces delayed and slightly increased the peak HRR. The aluminum foil appeared to trap and accumulate the gaseous pyrolysis products and blowing agent in localized bubbles formed on the panel surfaces. These bubbles eventually burst, nearly simultaneously, which produced a higher HRR maximum. A visual inspection of both types of panels after the tests reveal  
Figure 7: Heat release rates measured in the vertical corner flame spread experiments on the Tuff-R insulation panels with and without facers. flame spread and limited upward spread. Significant portions of the panels away from the burner remained effectively intact. The results of the flame heat flux (\(\dot{q^{\prime\prime}}\)) measurements collected in the experiments on the insulation panels with and without facers are shown in Figure 8 together with the data obtained on PMMA in the same experimental setup, at the same burner setting, and the same panel locations [32]. All heat flux data are presented as a function of HRR. The insulation panel data exhibit a considerably larger scatter but, overall, follow the same trends as the data obtained for PMMA, which justifies their use in the semi-empirical modeling of the panel experiments. The only systematic discrepancy was observed for the (0.10, 0.10) gauge location. This discrepancy was attributed to abstraction of the gauge surface by expanding foam. This expansion was most notable for the bottom portions of the panels located near the corner. Figure 8: Flame heat flux dependencies on heat release rate measured with water-cooled heat flux gauges in the vertical corner flame spread experiments on the Tuff-R insulation panels and on PMMA [32]. The results of the modeling of the vertical corner flame spread experiments are compared with the experimental data in Figure 9. Only the experiments on the Tuff-R insulation panels without facers were modelled. The figure shows fully converged simulated HRR profiles using the pyrolysis models without and with the blowing agent component. The model that does not take into account the blowing agent systematically underestimates the experimental HRR. The model, including the blowing agent, provides an accurate prediction of the experiment, within 5% of the experimental data, on average. It is important to point out that the same approach used in the current study to model the corner flame spread was also used in a previous study [32] to model flame spread on PMMA and the resulting predictions were not nearly as good as those obtained in the current work, despite the fact that PMMA is generally considered to be a much simpler material. This apparent inconsistency can be explained by two factors. First, the assumption that the flame heat flux is purely radiative is more accurate in the case of the PIR foam because its gaseous pyrolysates are likely to be better precursors for soot, which is the main radiating species.