## 1 Introduction
This study addresses this deficiency by analysing the effect of the ignition location on explosion characteristics, specifically in ammonia fuel preparation rooms that have been modelled for use on LNG-fuelled bulk carriers. The Flame Acceleration Simulator (FLACS) is a CFD simulation tool that is widely acknowledged for its accuracy in modelling and predicting gas explosion hazards. Its reliability has been validated through analyses of large-scale industrial explosion events across multiple sectors [23; 24; 25; 26; 27]. For example, as illustrated in Figure 1, large-scale explosion experiments using ethane, methane, propane, butane, and pentane gases were conducted in the United Kingdom between 1997 and 2000 as part of the BFETS Phase 3A project. These experiments were performed in full-scale offshore compressor modules (28 m \(\times\) 12 m \(\times\) 8 m) to investigate the influence of various factors, including the equipment congestion, ventilation openings, ignition location, reproducibility, and effects of different water deluge arrangements. [PERSON] et al. [28], [PERSON] et al. [29], and [PERSON] et al. [30; 31] quantitatively evaluated explosion conditions using the FLACS and verified its accuracy through comparisons with experimental data. Furthermore, [PERSON] et al. [32]conducted comparative assessments between FLACS simulations and scaled experimental tests inside a pressurized water reactor (PWR) steam generator casemate under varying hydrogen concentration gradients. This finding reinforces the predictive reliability of the software. This study aims to quantitatively assess the influence of the ignition source location on explosion characteristics in an ammonia fuel preparation room using computational fluid dynamics (CFD) simulations conducted on the FLACS platform. Nineteen scenarios were developed by systematically varying the ignition positions along the X-, Y-, and Z-axes to evaluate the spatial dependencies of the explosion severity and flame propagation behaviour. In contrast to previous studies that primarily examined simplified or open geometries, this study investigated the ignition dynamics in a confined and structurally realistic fuel preparation room. The computational domain was modelled after the layout of an LNG-fuelled vessel FPR, serving as a representative configuration for assessing ammonia-related explosion risks. The key parameters, including the maximum overpressure, pressure rise rate, flammable gas reduction, temperature distribution, and combustion product concentration, were comprehensively evaluated. The findings provide valuable insights into how the ignition location affects the combustion behaviour and explosion severity in complex enclosed environments. These results support the development of safe design strategies and operational guidelines for ammonia-fuelled ships. Furthermore, the outcomes of this study may contribute to international policies and regulatory frameworks, such as those shared by the International Maritime Organization (IMO), by providing scientific data to enhance the overall safety of ammonia-powered marine systems. Figure 1: Explosion experiment and simulation results of BFETS phase 3A [25; 26; 27; 33].