## 4 Validation Results
### Comparison Model/Experiments  
Fire scenarios 1 to 10 have been simulated using the two-zone model. For all simulations, the time step was 50 \(\upmu\)s. A run for the simulation of 1 h of fire takes less than 2 CPU minutes on a PC with Intel(r) Core i7-4770 (3.40 GHz) and 16 GB RAM. Figures 9-18 show the individual and total HRR time histories and the comparison between numerical and experimental results for the ten tests, including the time evolution of the smoke layer interface height. The model captures well the experimental trends for all fire conditions, regardless of the confinement level of the enclosure. Figure 9: \(Cont.\)  
Figure 10: Test 2: (**a**) individual and total HRRs, (**b**) average gas temperature, (**c**) average wall temperatures, (**d**) volume fractions of O\({}_{2}\) and CO\({}_{2}\) in the exhausted gases, and (**e**) smoke layer interface height. Figure 9: Test 1: (**a**) individual and total HRRs, (**b**) average gas temperature, (**c**) average wall temperatures, (**d**) volume fractions of O\({}_{2}\) and CO\({}_{2}\) in the exhausted gases, and (**e**) smoke layer interface height. Figure 11: Test 3: (**a**) individual and total HRRs, (**b**) average gas temperature, (**c**) average wall temperatures, (**d**) volume fractions of O\({}_{2}\) and CO\({}_{2}\) in the exhausted gases, and (**e**) smoke layer interface height. Figure 12: Cont. Figure 12: Test 4: (**a**) individual and total HRRs, (**b**) average gas temperature, (**c**) average wall temperatures, (**d**) volume fractions of O\({}_{2}\) and CO\({}_{2}\) in the exhausted gases, and (**e**) smoke layer interface height. Figure 13: Cont. The predicted and experimental average gas temperatures versus time are similar in shape. The maximum level reached by the gas temperature and the time required to reach the peak are typically predicted within 12.5 and 20% of the experimental measurements, respectively. For test 9, the model underestimates the maximum value of the gas temperature. This can be attributed to not knowing the exact composition and combustion properties of the PUF we used (here, assimilated to GM23 foam). The maximum deviation in time to peak gas temperature is observed for test 4, with 20%, but this must be qualified due to the quasi-steady behavior of fire (Figure 12b). The overall comparison is more favorable to the model. Figure 15: Test 7: (**a**) individual and total HRRs, (**b**) average gas temperature, (**c**) average wall temperatures, (**d**) volume fractions of O\({}_{2}\) and CO\({}_{2}\) in the exhausted gases, and (**e**) smoke layer interface height. Figure 16: Test 8: (**a**) individual and total HRRs, (**b**) average gas temperature, (**c**) average wall temperatures, (**d**) volume fractions of O\({}_{2}\) and CO\({}_{2}\) in the exhausted gases, and (**e**) smoke layer interface height. Figure 17: Cont. Figure 10:0 Test 9: (**a**) individual and total HRRs, (**b**) average gas temperature, (**c**) average wall temperatures, (**d**) volume fractions of O\({}_{2}\) and CO\({}_{2}\) in the exhausted gases, and (**e**) smoke layer interface height. Figure 10:1 _Cont._  
By comparing the predicted and measured wall temperatures, it is clear that the ceiling jet effect acts differently depending on the size of the fire. For relatively small fires, those that do not involve heptane, the model tends to overestimate the ceiling temperature, making it conservative. In contrast, when heptane is burning, the rate of convective heat release, and thus the ceiling temperature, is underestimated. This is particularly visible in the c-diagrams of Figures 11 and 16 for tests 3 and 8. The sidewall temperature is generally well reproduced by the model. The largest difference between the model and the experiment is observed for test 5, once the PMMA begins to burn. The strength of the ceiling jet is then not sufficient to allow the hot gases to flow back down the walls. Combustion dynamics is well reproduced by the model (diagram d in Figures 9-18), which validates the concept of surrogate fuel molecule (SFM).