## 4 Conclusions  
This study quantitatively analyses the influence of the ignition location on explosion characteristics within an ammonia FPR onboard ammonia-fuelled vessels using FLACS-based computational fluid dynamics (CFD) simulations. To reflect the three-dimensional spatial characteristics of the preparation room, 19 ignition scenarios were designed systematically based on the distribution of the ignition locations along the X-, Y-, and Z-axes. The analysis focused on key explosion metrics, including the peak explosion pressure, rate of pressure increase, flammable gas reduction rate, initial detection times of combustion indicators, and spatiotemporal distribution of temperature and combustion products. The main observations of this study are as follows. The ignition location was identified as a critical factor that influences the explosion intensity and combustion spread behaviour. The lowest peak pressure (3.24 bar) occurred in Case 13 (Y = 14.9 m, forward wall), whereas the highest pressure (4.27 bar) was recorded in Case 19 (Z = 4.9 m, near the ceiling). The rate of pressure increase ranged from 1.11 bar/s to 2.20 bar/s, with symmetric and rapid flame propagation being observed in the central and upper ignition scenarios (e.g., Case 4, Case 8, Case 19). In contrast, ignition near the structural boundaries resulted in attenuated explosion reactivity owing to wave reflection and asymmetric combustion;  
The flammable gas reduction rate also varied significantly with the ignition position. The fastest depletion occurred in Case 7 (centre-bottom ignition) at 456.64 m\({}^{3}\)/s, whereas the slowest was recorded in Case 13 at 313.89 m\({}^{3}\)/s. These results indicate a strong correlation between the gas depletion rate and the rate of pressure increase. Thus, these results reaffirm the importance of fuel consumption dynamics in determining the severity of explosions;  
The initial detection times of combustion products and changes in temperature were shortest in the central and upper ignition scenarios (averaging between 0.36 s and 0.91 s). Conversely, the forward-wall ignition (Case 13) resulted in significantly delayed detection (exceeding 2.03 s). These results indicate that the ignition location directly affects the early detection performance and should be considered in the design of fire alarm and suppression systems;  
Figure 18: Variation in temperature at monitoring points in case 13. Case 19 exhibited the most extreme explosion behaviour in terms of the pressure, temperature, and product spread. Combustion products were first detected at 0.176 s at a height of 4.9 m. By 2.0 s, the room was fully saturated, with temperatures exceeding 2742 K and mass fractions above 0.34 kg/kg. In contrast, Case 13 exhibited limited propagation, affecting less than 30% of the space and reaching a lower peak temperature of 2627 K.  
These results verify that the ignition location is a dominant factor in explosion dynamics, influencing the peak pressures, reaction rates, detection times, and distribution profiles of heat and combustion products. This paper presents a customized explosion risk assessment framework for ammonia fuel preparation systems. It provides essential insights into ignition source control, optimal sensor placement, and spatially differentiated safety design strategies. In particular, ignition near the floor centre was identified as the most critical scenario owing to its steep pressure rise rate and rapid gas consumption. To minimize the risk under such worst-case conditions, it is recommended to restrict ignition sources in this zone and implement passive safety systems, such as flame arresters or explosion vent panels, to suppress early-stage pressure escalation. These preventive measures can enhance the structural resilience and safety of ammonia FPRs. Future research should incorporate multivariable scenarios that involve actual ammonia leakage, gas dispersion behaviour, and ventilation conditions to enhance the predictive accuracy of the explosion risk model.