Ammonia (NH₃) is a promising hydrogen carrier and an attractive carbon-free energy vector owing to its high volumetric energy density, ease of liquefaction under moderate pressure, and well-established production, storage, and transportation infrastructure. These advantages make ammonia particularly suitable for the deployment of decentralized energy systems, allowing hydrogen to be transported and stored efficiently without requiring major investments in dedicated hydrogen distribution networks or reinforcement of electrical grid infrastructures. Although ammonia is toxic and corrosive, its industrial handling is mature and supported by decades of experience in the fertilizer and chemical sectors, providing a strong basis for its safe large-scale deployment. Beyond its role as a hydrogen carrier, ammonia is increasingly considered as a direct low-carbon fuel for internal combustion engines, gas turbines, industrial burners, and combined heat and power systems. Nevertheless, its practical utilization remains challenging because of its low laminar flame speed, high ignition energy, narrow flammability limits, and slow chemical kinetics, which can lead to poor combustion stability and reduced efficiency. In addition, ammonia combustion is associated with significant emissions of nitrogen oxides (NOₓ), nitrous oxide (N₂O), and unburned ammonia (NH₃ slip), all of which must be carefully controlled to ensure environmental sustainability. To overcome these limitations, several combustion enhancement strategies are being investigated, including partial ammonia cracking to generate hydrogen-rich mixtures, fuel hybridization with hydrogen or conventional fuels, advanced injection and mixing techniques, optimized combustion chamber designs, and after-treatment technologies. These approaches aim to improve flame stabilization, increase combustion efficiency, reduce pollutant emissions, and enable ammonia to become a key carbon-free fuel for future sustainable energy and transportation systems.