## 3 Result and Discussion
### Distribution of Temperature  
The spatial and temporal distributions of the temperature resulting from ignition were analysed in the ammonia FPR to assess the influence of the ignition location on thermal propagation. Two representative cases were selected for comparison: Case 19, which exhibited the highest explosion pressure (ignition at Z = 4.9 m near the ceiling) and Case 13, which resulted in the lowest pressure (ignition at Y = 14.9 m near the forward wall). Figures 15 and 16 illustrate the temporal evolution of the temperature at three vertical heights (0.1 m, 2.5 m, and 4.9 m), starting from the instant when the temperature exceeded 300 K. In Case 19, the ceiling-level ignition resulted in rapid and extensive heat accumulation in the upper region during the early stages of combustion. A temperature increase beyond 300 K was detected at 0.152 s at heights of 4.9 m and 2.5 m. This indicates a near-simultaneous upward and mid-level propagation. By 2.0 s, temperatures exceeding 2300 K were observed throughout most of the room, excluding the corners. At the floor level (0.1 m), the temperature began to increase at 1.226 s. However, it diffused rapidly across the space, causing approximately 50% of the room volume to attain temperatures above 2300 K by 2.0 s. Uniform high-temperature zones in the range of 2100-2300 K were formed throughout the space by 2.703 s. The efficient and symmetrical thermal spread was attributed to the minimal structural interference and enhanced buoyancy-driven convection associated with ceiling ignition. Conversely, in Case 13, ignition occurred near the forward wall, resulting in a more confined and delayed heat propagation. At the lowest height (0.1 m), the temperature exceeded 300 K at 0.276 s. However, the flame and heat remained concentrated near the ignition point. Even at 2.0 s, the high-temperature zones continued to be constrained to the vicinity of the FWD wall, covering approximately 10-30% of the room. At 2.5 m, the initial temperature increase occurred at 1.275 s, with high temperatures being present in only 30% of the room by 2.0 s. The upper region (4.9 m) exhibited a further delay, with temperatures exceeding 300 K only at 2.0 s. This indicates sluggish vertical diffusion. This thermal delay is explained by the increased obstruction from the walls and structural elements near the ignition point, which interfered with flame and heat propagation. The time-resolved temperature profiles at all of the monitoring points (Figures 17 and 18) further  
Figure 14: Variation in mass fraction products at monitoring points in Case 13.  
highlight the contrast between the two cases. In Case 19, the temperature at MP9 increased abruptly to approximately 2200 K within 0.8 s and peaked at 2742 K. This indicates a rapid and intense combustion. In Case 13, a comparable temperature level was attained only at 2.1 s at MP10. The peak value was lower at 2627 K and was recorded at MP2. The sequence of temperature increase varied across the monitoring points in each case. This indicates that the ignition location significantly influences the flame propagation paths and rates. These results verify that the ignition location has a substantial impact on the thermal distribution and peak temperatures during combustion. Ignition near the ceiling promotes a rapid and uniform thermal spread owing to buoyancy effects and minimal interference. This, in turn, resulted in higher peak temperatures and faster room-wide propagation. In contrast, ignition near structural boundaries slows heat diffusion and causes localized high-temperature accumulation.  
Therefore, an accurate assessment of the thermal behaviour of explosions based on the ignition position is essential for evaluating fire and explosion hazards in ammonia FPRs. These observations emphasize the need for location-specific fire-protection designs and response strategies.  
Figure 15: Distribution of temperature in Case 19.  
Figure 16: Distribution of temperature in Case 13.  
Figure 17: Variation in temperature at monitoring points in Case 19.