Citation: Agocs, A.; Rappo, M.; Obrecht, N.; Schneidhofer, C.; Frauscher, M.; Besser, C. The Impact of Ammonia Fuel on Marine Engine Lubrication: An Artificial Lubricant Ageing Approach. Lubricants 2023, 11, 165. https://doi.org/10.3390/ lubricants11040165 Received: 8 March 2023 Revised: 3 April 2023 Accepted: 5 April 2023 Published: 6 April 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). lubricants Article The Impact of Ammonia Fuel on Marine Engine Lubrication: An Artificial Lubricant Ageing Approach Adam Agocs 1, *, Maria Rappo 2 , Nicolas Obrecht 2 , Christoph Schneidhofer 1 , Marcella Frauscher 1 and Charlotte Besser 1 1 AC2T Research GmbH, 2700 Wiener Neustadt, Austria 2 TotalEnergies, 64018 Courbevoie, France * Correspondence: adam.agocs@ac2t.at Abstract: Ammonia is a prospective zero-carbon-emission fuel for use in large marine diesel engines. Current research focuses on several technical aspects, such as injection strategies or exhaust gas aftertreatment options, but investigations regarding the impact of ammonia on engine oil degradation are largely absent from the literature. This study provides a methodology with which to evaluate this phenomenon via artificial oil alteration. By using an admixture of various contaminations to air, such as ammonia and its partial combustion product nitrogen dioxide, their respective impacts on chemical oil degradation were assessed. Subsequently, the lubricating performance of altered oils was investigated, with a focus on corrosion properties, deposit formation, and load-bearing capability. Although the application of a stoichiometric ammonia–air mixture resulted in less pronounced thermo-oxidative degradation compared to alteration with neat air, static and dynamic deposit formation as well as corrosion properties and load-bearing capability were severely impacted by the presence of ammonia. On the contrary, nitrogen dioxide contamination resulted in higher oxidation and acidification of the oil, but altered samples performed considerably better than ammonia-altered aliquots in terms of coking tendencies, corrosivity, and load bearing. Keywords: ammonia; engine oil degradation; internal combustion engine; combustion; corrosion; deposit formation; extreme pressure; oil ageing 1. Introduction In April 2018, the International Maritime Organization (IMO) adopted its strategy to reduce carbon emissions by 40% by 2030 and by 70% by 2050 for individual vessels, and to reduce all greenhouse gas (GHG) emissions by 50% across the shipping industry by 2050 [1]. The use of zero-carbon fuels on a tank-to-wake basis is being strongly considered to achieve these goals. From that perspective, ammonia has emerged as one of the zero- or near-zero-emission fuels of the future in line with global decarbonization objectives. [2–4] It offers great potential to power large oceangoing ships, as ammonia is composed of three hydrogen atoms connected to one nitrogen atom (NH 3 ) and hence is carbon-free. Accordingly, it represents one of the few chemical compounds whose combustion produces zero carbon emissions when used as a fuel in an internal combustion engine. [4] Ammonia possesses characteristics which make it one of the most promising solutions to the question of powering large vessels: its worldwide commercial availability [5], mainly driven by the fertilizer industry [2]; the possibility to produce it in a green way [6–8]; its acceptable energy density, which is slightly lower than that of methanol and higher than that of hydrogen; [3,9] and the relative ease of managing it [5]. Equation (1) shows the combustion process of ammonia and the corresponding reac- tion enthalpy (ΔH 0 ) for standard state reactants and products. Lubricants 2023, 11, 165. https://doi.org/10.3390/lubricants11040165 https://www.mdpi.com/journal/lubricants