6 Chapter II Literature Study II.1 Ammonia and Its Potential Ammonia (NH3) is a colorless gas with a pungent odor, easily detectable even at low concentrations (1 ppm) (Elbaz et al., 2022). It is a compound of nitrogen and hydrogen with the chemical formula NH3 (Selvan & Maheshwaran, 2018). Ammonia exists in three phases: solid, liquid, and gas, but only the liquid and gaseous phases are suitable for fuel applications due to the risk of sediment formation in the solid phase (Selvan & Maheshwaran, 2018). Its versatility makes it a widely used chemical in various industries, primarily in agriculture as a fertilizer (Aziz et al., 2020). Ammonia's molecular structure, with a trigonal pyramidal shape and a lone electron pair on the nitrogen atom, contributes to its polarity and strong intermolecular hydrogen bonding (Valera-Medina et al., 2018). These properties make ammonia highly miscible with water and influence its behavior as a solvent and its combustion characteristics (Valera-Medina et al., 2018). The high hydrogen content of ammonia (17.6 wt.%) and its ability to be stored as a liquid under moderate conditions make it an attractive energy carrier and a potential carbon-free fuel (Estevez et al., 2023). Ammonia is produced commercially through the Haber-Bosch process, which involves reacting nitrogen and hydrogen at high temperatures and pressures in the presence of a catalyst (Lasocki, 2018; Selvan & Maheshwaran, 2018). However, this process is energy-intensive and relies heavily on fossil fuels, raising environmental concerns (Lasocki, 2018). Efforts are underway to develop "green" ammonia production methods using renewable energy sources to address these concerns (David, 2023; Estevez et al., 2023). 7 Figure II.1 The gravimetric and volumetric densities of hydrogen, ammonia, and other fuels (Elbaz et al., 2022). The use of ammonia as a fuel in internal combustion engines (ICE) and fuel cells present both advantages and challenges. Its carbon-free nature and established infrastructure for production, storage, and transportation are significant advantages (Erdemir & Dincer, 2021). Ammonia has a higher volumetric energy density (10,8 MJ/L at 300 K and 8,6 bar) than liquid hydrogen (7 MJ/L at 300 K and 10 bar) as shown in Figure II.1 above. However, challenges such as low flame speed, narrow flammability limits, and the potential for NOx emissions need to be addressed (Tornatore et al., 2022). Research is ongoing to overcome these challenges through strategies like dual-fuel combustion, ammonia cracking, and advancements in engine design (Lesmana et al., 2019; X. Xu et al., 2022). Ammonia's versatility, potential as a carbon-free energy carrier, and established infrastructure make it a subject of great interest in the pursuit of sustainable energy solutions (Erdemir & Dincer, 2021). While challenges remain, ongoing research and development efforts are paving the way for ammonia to play a significant role in the future energy landscape. 8 II.2 The History of Ammonia as a Fuel The utilization of ammonia as a fuel has a history dating back to the early 19th century (Valera-Medina et al., 2018).