Ammonia as a fuel for internal combustion engines: latest advances and future challenges

Abstract

The use of ammonia as a fuel still poses a series of challenges to be overcome, both in terms of optimization and energy efficiency of the production process, and with regard to its combustion in internal combustion engines. The two main obstacles along this way are undoubtedly the high ignition temperature and the low propagation speed of the flame front due to the slow chemical kinetics of ammonia combustion process. All these issues lead to the need to use this fuel in blended mode with other more “easy burning” fuels. This need is even more felt in cases of non-stationary combustion, such as for alternative internal combustion engines but, on the other hand, it can determine an increase in engine efficiency. In this work, these ammonia technological constraints are exposed and discussed, outlining the most recent technological solutions and those under development, which will allow an increasingly widespread use of this energy carrier as a fuel in internal combustion engines. Finally, the environmental aspects related to the greater potential emission of NOx and the techniques to limit their occurrence are analyzed.

Ammonia as a Fuel for Gas Turbines: Perspectives and Challenges

“…These problems are mainly linked to a low reactivity in relation to other conventional fuels and to high nitrogen emissions (NOx and non-combusted NH 3 ) [6]. The consequences of this low reactivity are a low laminar burning rate (for an NH 3 /air mixture the laminar flame burning rate is about 20% of the respective value of a CH 4 /air mixture [6]), a high ignition, a low volumetric heat release rate and flame instability [7]. Furthermore, the combustion of pure ammonia generates high emissions of nitrogen oxides (NOx) and, due to its chemical-physical characteristics, the quantities of unburned ammonia are relatively high.…”

Numerical Simulation Research on Combustion and Emission Characteristics of Diesel/Ammonia Dual-Fuel Low-Speed Marine Engine

“…The maritime industry, a cornerstone of the global economy, is a significant contributor to annual greenhouse gas emissions [2]. Recent years have witnessed maritime activities contributing between 2% and 3% of total global emissions, primarily consisting of CO 2 emissions [3], with a discernible upward trend. In light of this, the International Maritime Organization (IMO) has issued the "Initial Strategy for Greenhouse Gas Emission Reduction from Ships" [4], outlining crucial emission reduction milestones: implementing specific measures to reduce greenhouse gas emissions from ships by 2023, achieving a minimum of a 40% reduction in emissions by 2030 compared to 2008 levels, and targeting a minimum of a 70% reduction by 2050, ultimately aiming to eliminate ship greenhouse gas emissions by the century's end [5].…”