Emir Yilmaz

Abstract Aquifer thermal energy storage is a versatile method for regulating building temperatures, utilizing groundwater as a medium for both summer cooling and winter heating. Water has high thermal conductivity and specific heat but is corrosive, creating a mineral build-up that causes scaling. Additionally, its high freezing point presents operational challenges. Vegetable oils emerge as a promising alternative, owing to their lower freezing points. In light of environmental concerns, researchers are exploring vegetable oils as substitutes for petroleum-derived mineral oils. This paper is intended as an initial study using vegetable oils, i.e. coconut and sunflower oil, as the heat-transfer medium in aquifer thermal energy storage. The experiments assess the heat-transfer coefficient of coconut, sunflower, mineral, and synthetic oils when exposed to the same heat source. The study also evaluates the impact of introducing micro-carbon (graphite and charcoal) to the oils. Results indicate that sunflower oil has the highest heat-transfer coefficient of 374.4 W/m2 K among the oils, making it suitable for aquifer thermal energy storage applications. Furthermore, augmenting sunflower oil with charcoal powder enhances its performance by increasing the heat-transfer coefficient to 474.9 W/m2 K, or a 27% increase. In contrast, coconut oil proves unsuitable for aquifer thermal energy storage deployment because of its low heat-transfer coefficient of 293.7 W/m2 K. The heat-transfer coefficient of synthetic oil increases with graphite powder but decreases with charcoal powder introduction.

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.

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 NOX 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.