Evaluation of EC-CCM for numerical simulation of diesel-ignited ammonia combustion

Abstract

The maritime sector needs to reduce greenhouse gas emissions and improve the sustain
ability of energy systems. Ammonia has attracted increasing attention as a potential
carbon-free marine fuel. However, ammonia has low reactivity, a high ignition energy
requirement, and a low flame propagation speed, which make stable combustion difficult.
Diesel-ignited ammonia combustion is therefore a promising method for improving
ammonia combustion performance.
This work is based on previous experimental studies conducted in a constant-volume
combustion chamber under high-pressure and high-temperature conditions, as well
as on a lab-scale, water-cooled two-stroke engine at Dalian University of Technology.
In the engine experiments, liquid ammonia and diesel were directly injected into the
cylinder through two opposing injectors. This provided relevant conditions for studying
diesel–ammonia dual-fuel combustion.
In this thesis, numerical simulations were carried out using OpenFOAM. The aim was to
investigate how injection angle and injector position affect flame development, ignition,
combustion intensity, and pollutant formation. Three different injection configurations
were compared under similar operating conditions.
The results show that the injection strategy has a significant influence on the combustion
process. Case 1 showed the most stable late-stage combustion. Case 2 produced the
highest heat release rate and the strongest localized combustion intensity. Case 3 showed
earlier ignition but weaker stability during the later combustion stage. Differences in
the distributions of NO and N2O also indicate that the interaction between the diesel
and ammonia jets affects the formation of nitrogen-containing pollutants.
To reduce computational cost, Chemistry Coordinate Mapping (CCM) and Error
Controlled Chemistry Coordinate Mapping (EC-CCM) were used. Both methods
reduced the computational time. EC-CCM provided the best balance between accuracy
and efficiency. Compared with the standard chemistry solver, EC-CCM achieved an
acceleration of approximately 3.67×, while maintaining good agreement in pressure,
temperature, and OH results.
This study provides numerical insight into diesel–ammonia dual-fuel combustion under
high-pressure conditions and shows that EC-CCM is a promising method for accelerating
detailed CFD simulations of combustion.

Popular Abstract

Ships usually use diesel or other fossil fuels. These fuels are easy to burn and can produce strong power. However, they also produce carbon dioxide and other harmful emissions. Carbon dioxide is one of the main gases that cause global warming and sea level rise. Therefore, future marine engines need cleaner fuels to reduce their impact on the environment.
Ammonia is one possible clean fuel. It does not contain carbon, so it does not directly produce carbon dioxide when it burns. However, ammonia is difficult to use in engines. It is hard to ignite, burns slowly, and its flame is not very stable. Because of this, ammonia usually needs another fuel to help it burn. In this thesis, diesel is used as the ignition fuel. Diesel burns first and creates a hot region. Then ammonia can burn in this hot region.
This thesis studies diesel--ammonia combustion for future marine engines. The main aim is to understand how the positions and angles of the diesel and ammonia injectors affect the combustion process. In simple words, this study looks at how diesel and ammonia meet inside the combustion chamber, and how this changes the flame, heat release, and pollutant emissions.
This study uses computer simulations in OpenFOAM. The simulation conditions are based on high-pressure and high-temperature engine-like conditions. Three different injection arrangements are compared. In addition, a chemistry acceleration method called EC--CCM is tested. This is because the standard simulation method takes a long time. The aim is to see whether EC--CCM can make the simulation faster while still keeping the main results reliable.
Three injection strategies/cases are studied. The results show that the injection arrangement has a strong effect on diesel--ammonia combustion. In Case 1, the ammonia jet partly bypasses the main hot region created by the diesel. Therefore, the ammonia reaction is not strong; the ammonia remains largely unburned.
In Case 2, ammonia interacts more strongly with the hot products from diesel combustion. This gives the highest heat release rate and strong local combustion. However, the ammonia jet also tends to dilute and quench the hot region, so the reaction becomes weaker in the later stage.
In Case 3, diesel and ammonia meet more directly in an opposing-jet arrangement. This helps ammonia react more strongly. However, it also makes the combustion more intense and increases pollutant formation.
For emissions, NO is mainly formed in high-temperature combustion regions. Therefore, stronger ammonia combustion may produce more NO. N2O and unburned NH3 are more related to incomplete ammonia combustion and lower-temperature regions. This means that lower NO emissions do not always mean better ammonia combustion.
The results show that ammonia needs good contact with the hot region created by the diesel to burn well. If this contact is weak, ammonia burns poorly. If the interaction is too strong, the combustion process and emissions may become harder to control.
Finally, EC--CCM makes the simulation about 3.67 times faster than the standard chemistry solver. At the same time, the main pressure, temperature, and OH results are still close to the standard method.
Overall, this thesis shows that ammonia can be a useful fuel for future marine engines, but its combustion must be carefully controlled. A good injection design needs to balance stable combustion, good ammonia use, and low pollutant emissions.

• author: Liu, Yulong
• supervisor: Xue-Song Bai
• organization: Department of Energy Sciences
• course: MVKM05 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: OpenFOAM, diesel–ammonia combustion, marine engine, EC-CCM, pollutant emissions
• publication/series: Student paper
• report number: ISRN: LUTMDN/TMHP-26/5693-SE
• ISSN: 0282-1990
• language: English
• id: 9236272
• date added to LUP: 2026-06-16 11:23:45
• date last changed: 2026-06-16 11:23:45