Ammonia as Green Fuel in Internal Combustion Engines: State-of-the-Art and Future Perspectives

Abstract

Ammonia (NH3) is among the largest-volume chemicals produced and distributed in the world and is mainly known for its use as a fertilizer in the agricultural sector. In recent years, it has sparked interest in the possibility of working as a high-quality energy carrier and as a carbon-free fuel in internal combustion engines (ICEs). This review aimed to provide an overview of the research on the use of green ammonia as an alternative fuel for ICEs with a look to the future on possible applications and practical solutions to related problems. First of all, the ammonia production process is discussed. Present ammonia production is not a “green” process; the synthesis occurs starting from gaseous hydrogen currently produced from hydrocarbons. Some ways to produce green ammonia are reviewed and discussed. Then, the chemical and physical properties of ammonia as a fuel are described and explained in order to identify the main pros and cons of its use in combustion systems. Then, the most viable solutions for fueling internal combustion engines with ammonia are discussed. When using pure ammonia, high boost pressure and compression ratio are required to compensate for the low ammonia flame speed. In spark-ignition engines, adding hydrogen to ammonia helps in speeding up the flame front propagation and stabilizing the combustion. In compression-ignition engines, ammonia can be successfully used in dual-fuel mode with diesel. On the contrary, an increase in NOx and the unburned NH3 at the exhaust require the installation of apposite aftertreatment systems. Therefore, the use of ammonia seems to be more practicable for marine or stationary engine application where space constraints are not a problem. In conclusion, this review points out that ammonia has excellent potential to play a significant role as a sustainable fuel for the future in both retrofitted and new engines. However, significant further research and development activities are required before being able to consider large-scale industrial production of green ammonia. Moreover, uncertainties remain about ammonia safe and effective use and some technical issues need to be addressed to overcome poor combustion properties for utilization as a direct substitute for standard fuels.

Enroute to the Carbon-Neutrality Goals via the Targeted Development of Ammonia as a Potential Nitrogen-Based Energy Carrier

“…Ammonia is a carbon-free compound that only produces water, nitrogen and a small amount of nitrogen oxides when burned, since it can be easily adopted as a clean energy source to replace fossil fuels as its energy density is higher than that of gasoline, methanol, and other fuels. , With the easier ways of handling and shipping, it can replace the fuel oil-based systems in decarbonizing the existing uses to a medium of transport fuel (such as hydrogen or ammonia-hydrogen mixture) to release energy in a fuel cell by chemical reaction with oxygen or release energy in direct combustion engine, containing the only byproducts of water and nitrogen. The synthesis, storage, transportation, and transformation of NH 3 in a cyclic manner shown in Figure illustrated that it could be integrated well in the hydrogen energy regime.…”

“…Compression ignition is the ideal approach when running ammonia in a dual-fuel engine with a lower autoignition temperature such as diesel, dimethyl ether, or biodiesel. Due to the high fuel nitrogen content in ammonia and the influence of clearance volume, relatively high levels of unburned ammonia and NO X are prevalent in the exhaust gas of ammonia-doped dual-fuel engines. , Therefore, a selective catalytic reduction (SCR) post-treatment system is very necessary. The application of ammonia in gas turbines is also the most widely studied factor, including pure combustion of ammonia, mixed combustion of ammonia and hydrogen, and mixed combustion of ammonia and methane.…”

Addressing the Training Gap for Ammonia-Fuelled Propulsion Systems: A Literature Review and Proposal for a New Job Training Program

“…Ammonia-fueled propulsion systems are gaining interest as a potential carbon-free fuel for transportation and energy production (Kobayashi et al, 2019;Ma et al, 2023;Machaj et al, 2022;Tornatore et al, 2022;Valera-Medina et al, 2021;Xu et al, 2022). Ammonia is a molecule that can be synthesized from renewable energy sources and has a high energy density, making it a promising alternative to fossil fuels (Valera-Medina et al, 2021).…”

“…The transportation and onboard utilization of ammonia also pose risks of exposure (Wang et al, 2023). Nonetheless, the advantages of green ammonia, including its carbon-free nature, relatively highvolume energy density, and ease of storage and transportation, continue to garner favorable attention (Tornatore et al, 2022).…”

Laboratory Tests of Electrical Parameters of the Start-Up Process of Single-Cylinder Diesel Engines

“…Despite huge progress in the field of individual electromobility [86][87][88][89][90] and in the field of public transport [91,92], they still encounter many barriers [93,94], and space for piston engines is still huge. The opening of new research directions in the field of alternative fuels used for transport modes, such as hydrogen [95][96][97][98] or ammonia [99][100][101], for powering internal combustion piston engines in various means of transport pose new challenges for internal combustion engines. Also, in non-road applications, there is an important share of single-cylinder combustion engines [102].…”