Concepts of ammonia/hydrogen engines for marine application

The objectives of this project were to study two alternative novel concepts of ammonia/hydrogen engines for maritime application, addressing both technical/scientific aspects, and social/economic/regulatory aspects, and develop guidelines for designing ammonia/hydrogen marine engines. By combining complementary competence in the field from four universities in Nordic countries (Lund Univ, Sweden, World Maritime Univ, Sweden, Aalto Univ, Finland, and NTNU, Norway) and having support from world-leading marine engine companies based in Nordic region (Wärtsilä and MAN), as well as ship owners Stolt Tankers and ForSea to build a Nordic network in ammonia/hydrogen marine engine R&D, the project output results from sharing chemical kinetics modeling, computational fluid dynamics simulations, laboratory engine experiments, and social/economic/regulatory assessment. The findings address conditions for optimal reduction of emissions such as N2O, operational conditions for high fuel efficiency, and challenges associated with the use of these fuels. Indicative examples encompass safety concerns, regulatory aspects, restricted availability, and an uncertain regulatory framework as different alternative fuels with GHG emission reduction potential have been proposed and considered for marine application. Regarding emission control, a trade-off between NO and N2O emissions in RCCI engines exists, i.e., decreasing N2O emissions would lead to increasing NO emissions. A small fraction of hydrogen blending with ammonia is helpful. The formation process of N2O is strongly influenced by the physical processes of mixture formation and flame behavior, rather than purely governed by chemical kinetics. The location of the injector and jet direction are essential for the fuel-air mixing processing. Smaller injection angles might avoid high fuel concentrations at one side of the piston which is advantageous for complete combustion. It is evident, however, that shipping industry coalitions can also play a critical role in scaling up the uptake of renewable fuels and accelerating the energy transition of the sector. Green corridors can pave the way for the development of ecosystems with targeted regulatory measures, financial incentives, and safety regulations.

It was expected that the TRL4-5 level of this project will allow various stakeholders to collaborate on a pre-competitive / predevelopment level and the knowledge generated can be used rapidly by industrial stakeholders for further product development (to a higher TRL). It was evident, however, that challenges related to emission control and injection strategies resulted in a lower TRL focus. The detailed simulations conducted of combustion in internal combustion engines did however reveal the potential for varying combustion modes. Furthermore, such novel combustion modes have not before been investigated for new and non-carbon containing fuels with different mixing and burning properties, which is one of the novel outcomes of this work. The more fundamental understanding of both fuel mixtures and their behavior in combustion engines is shown to impact the readiness for the marine sector to move towards low-carbon freights

The “CAHEMA” project aims at increasing fundamental and practical knowledge in ammonia/hydrogen engines for marine application. On the one hand, developments of chemical kinetic mechanism (NTNU) and CFD modelling tools (Lund) will provide a strong base for analysis of ammonia/hydrogen combustion. On the other hand, engine experiments (Aalto) will be carried out, in research laboratories, to verify two different novel engine concepts firing with ammonia/hydrogen fuels. Furthermore, the project will assess economical, regulatory and environmental aspects of ammonia/hydrogen marine engines. The two novel combustion concepts under investigation are referred to as reactivity-controlled compression ignition, RCCI); (b) direct-injection dual fuel stratification (referred to as DDFS). NTNU will be the principal investigator (PI) of WP1, in which detailed chemical kinetic mechanisms for ammonia (NH3), hydrogen (H2) and n-heptane (C7H16) mixture will be developed. At DTU there is a well-established laminar flow reactor (LFR) experimental rig that will be used to measure the species profiles under pressure upto 100 atm, or at atmospheric pressure but high temperatures. These data will be used to validate the chemical kinetic model. In subtask 2 of WP2, LU will apply the CFD model and NTNU will use the stochastic reactor model (SRM) to study two different engine concepts (RCCI and DDFS). WP3 will have AU as the PI will use research engines to evaluate the two combustion concepts RCCI and DDFS. WP4 with WMU as PI, will assess the environmental and socio-economic impacts of the two engine concepts for NH3/H2 marine engines.