Scope and Limitations of Ammonia as Transport Fuel

Abstract

AbstractFuel requirement for the transport sector is a function of population growth. Currently, the automotive industry is powered extensively by fossil fuels. Diesel and gasoline-powered vehicles contribute heavily to environmental pollution by emitting carbon dioxides (CO2) and other pollutant species. Greenhouse gas (GHG) emissions from fossil fuel combustion are significantly increasing since 1900. Fossil fuels depletion depends on discoveries of new petroleum reserves; however, the use of fossil fuels won’t be feasible in the foreseeable future due to GHG emissions and other environmental concerns. To tackle these, several researchers have focused on developing alternative fuels. Although low carbon fuels (energy) are being explored for internal combustion engines (ICEs), nitrogen-based fuels are also beginning to attract researchers worldwide. Ammonia has potential as a low carbon fuel since it has a high-octane number and is carbon-free; therefore, it doesn’t produce soot. Other nitrogen-based fuels are not viable low GHG alternatives for vehicles. Despite higher NOx emissions, ammonia has potential for heavy-duty power generation and the marine sector. This is because, in these applications, the implementation of exhaust gas after-treatment is feasible. Significant challenges that hinder ammonia’s growth in the automotive sector as fuel are (i) narrow flammability limits, (ii) high ignition temperature, and (iii) low flame speed. Also, ammonia’s higher heat of vaporization reduces the temperature when ammonia makes a phase transition from liquid to gas, reducing the in-cylinder temperature. Currently, vehicles are not operated using ammonia as fuel because its production involves extensive use of natural gas, which is not a zero-carbon fuel. Biogas is a sustainable carbon-free feedstock for producing ammonia, which uses a carbon-free path from well-to-tank (WTT). Ammonia can be produced from hydrogen, obtained from electrolysis of water and nitrogen obtained from air. Since, the electricity could be generated from renewable energy sources, ammonia can be considered as E-fuel. This chapter covers production methods, properties, environmental and health aspects, storage and transportation, and the potential of ammonia as a transport fuel in compression-ignition (CI) and spark-ignition (SI) engines. Pure Ammonia operation and dual-fuel modes are extensively discussed for both CI and SI engines. Hydrogen as a combustion improver is also covered towards the end of this chapter. However, for realizing the potential of ammonia as fuel, it is important to determine feasible Ammonia induction and combustion techniques applicable to ICEs, which would enhance engine performance in the entire operating range.KeywordsHigh octane numberNitrogen-based fuelsAmmoniaCarbon-free fuelAlternative fuels