Recently, ammonia (NH₃), which has a higher energy density than hydrogen, has gained attention for zero-carbon emission goals in the transportation sector. However, in a conventional internal combustion engine (ICE), NH₃ combustion mechanism is still under investigation. In this paper, to further expand the knowledge on the adoption of NH₃ in ICEs, authors conducted NH₃/gasoline co-combustion experiments in a modified, 17.7:1 compression ratio, naturally aspirated spark-assisted CI engine with sub-chamber. The sub-chamber was chosen in order to enhance the combustion speed of NH₃. In addition, the sub-chamber was equipped with glow and spark plugs to overcome the high auto-ignition temperature of NH₃. Engine performance and NO_X emissions were studied under three different intake air temperatures. During the experiments, NH₃ content was increased gradually where the engine was run under lean conditions. Although higher NH₃ content was achieved compared to our previous work, increasing the intake air temperature resulted in decreased charging efficiency. In addition, corrosion was found on the piston ring after 120 h of operation, negatively affecting the engine performance. Furthermore, NH₃/gasoline co-combustion duration was shortened drastically with the influence of the sub-chamber, where the longest combustion duration under the present conditions was found to be 17°CA.

Road vehicles, particularly cars, are one of the primary sources of CO₂ emissions in the transport sector. Shifting to unconventional energy sources such as solar and wind power may reduce their carbon footprints considerably. Consequently, using ammonia as a fuel due to its potential benefits, such as its high energy density, being a carbon-free fuel, and its versatility during storage and transportation, has now grabbed the attention of researchers. However, its slow combustion speed, larger combustion chamber requirements, ignition difficulties, and limited combustion stability are still major challenges. Therefore, authors tried to analyze the combustion pressure of ammonia in a constant-volume combustion chamber across different equivalence ratios by adopting a machine learning approach. While conducting the analysis, the experimental values were assessed and subsequently utilized to predict the induced combustion pressure in a constant-volume combustion chamber across various equivalence ratios. In this research, a two-step prediction process was employed. In the initial step, the Random Forest algorithm was applied to assess the combustion pressure. Subsequently, in the second step, artificial neural network machine learning algorithms were employed to pinpoint the most effective algorithm with a lower root-mean-square error and R². Finally, Linear Regression illustrated the lowest error in both steps with a value of 1.0, followed by Random Forest.

The push for decarbonization of internal combustion engines (ICEs) has spurred interest in alternative fuels, such as hydrogen and ammonia. To optimize combustion efficiency and reduce emissions, a closer look at the intake system and in-cylinder flows is crucial, especially when a hard-to-burn fuel, such as ammonia is utilized. In port fuel injection ICEs, airflow within cylinders profoundly affects combustion and emissions by influencing the air–fuel mixing phenomenon. Adjusting intake port openings is an important factor in controlling the in-cylinder airflow. In previous experiments with a transparent cylinder, tangential and helical ports demonstrated that varying the helical port’s opening significantly impacts flow velocities, swirl ratios, and swirl center positions (SCPs). In this study, we used a particle image velocimetry technique to investigate how the tangential port’s opening affects intake and in-cylinder flows. Flow velocities were assessed at different planes near the cylinder head, evaluating streamline maps, turbulent kinetic energy (TKE), and SCPs. Under the given experimental conditions, swirl flows were successfully generated early in the compression stroke when the tangential port opening exceeded 25%. Our findings emphasize the importance of minimizing TKE and SCP variation for successful swirl flow generation in engine cylinders equipped with both tangential and helical ports.

The greenhouse effect issue is becoming more serious, and renewable energy is playing an increasingly important role. Among all alternative fuels, ammonia has been attracting attention as a carbon-free energy carrier for hydrogen, because of its large energy density per volume and easy storage and transportation. On the other hand, ammonia has a low combustion speed, which is an important issue for the use of ammonia as a vehicle fuel. To increase the mean flame speed of ammonia, the present study used the burned gas ejected from the sub-chamber for the compression of the mixture in the main chamber and the promotion of its HCCI combustion. Thus, the constant volume combustor with sub-chamber was used to realize the above combustion and to study the combustion characteristics of ammonia and oxygen mixture. In the experiments, initial pressure and initial temperature were unchanged and only the equivalence ratio was changed. The combustion pressure data were recorded and analyzed. As the result, the maximum combustion pressure (2.5 MPa) was obtained when the equivalence ratio was 0.4. The combustion speed was the fastest when the equivalence ratio was 0.6, and the mean flame speed was about 57.5 m/s.