Yilmaz Emir

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.

The overreliance on fossil fuels to generate energy is not sustainable because of their carbon emissions that are harming our environment. To substitute the fossil fuels with a more sustainable options, alternative fuels, such as carbon-free ammonia has been gaining worldwide attention. To allow the application of ammonia in internal combustion engines, its performance as an engine fuel need to be investigated. Ammonia as fuel has some shortcomings that can be outlined as slow combustion rate and corrosion due to the generation of hydrogen which makes it difficult to utilize in conventional internal combustion engines. In this study, an engine equipped with sub-chamber feature was used to overcome slow combustion rate of lean-burn condition of iso-octane/air mixture. Iso-octane was chosen as the fuel specifically since in lean-burn conditions, where the excess air ratio is near 1.8, its laminar burning velocity is similar to that of ammonia. The study was conducted using a single cylinder modified diesel engine which features spark plug and glow plug in a sub-chamber. The investigations varied the engine speeds (1000 and 1500 RPMs), glow plug voltages (6 V and 10 V), excess air ratios (1.4 to 1.8), and ignition timings (362 °CA to 365 °CA). The results suggested improved engine performances with a lower excess air ratio and higher glow plug voltage due to more complete and stable combustion. By increasing the engine speed, the lean burn limit was extended as seen from the improved engine performances. Because of the subchamber feature, advancing the ignition timing, with respect to the after top dead centre, resulted in lower engine performances. Larger excess air ratio was found to increase the sensitivity of the engine performances with the ignition timing. The brake mean effective pressure for all conditions has a coefficient of variation of less than 5%, indicating stable combustion. The results suggested that the current setup can be used to investigate ammonia blended fuel and direct ammonia combustion in future works.

To improve the cooling system of internal combustion engines, the utilization of the nucleate boiling heat transfer is desired. Our previous study revealed the relationship between the water nucleate boiling heat flux and dimensionless numbers. By using 50% ethylene glycol aqueous solution (EG50%) as coolant, the nucleate boiling heat flux was measured on the corroded heating surface and compared with the experimental data of water as coolant. Subsequently, dimensional analyses were done to investigate the necessary dimensionless numbers affecting the forced flow nucleate boiling. Two new models are proposed for water and EG50% as coolants, and predicted heat flux results were found to be in an average error of 9.7% and 10.1%, respectively.

Injection characteristics play an important role in the emission and overall thermal efficiency of an engine. Several methods have been proposed for analyzing different fuel injection characteristics. This study focused on the interferometric laser imaging for droplet sizing (ILIDS) technique to investigate the effects of droplet size and velocity under different conditions of water-glycerin mixtures. These effects were evaluated using intermittent spray flows in both ambient and pressurized constant volume spray chamber conditions. The initial results were compared to those reported by previous studies and used to determine the Sauter mean diameter (SMD), arithmetic mean diameter (AMD), droplet velocity, and probability density function of the spray droplet size. SMD and AMD tended to decrease as the plate temperature, injection pressure, and viscosity were increased at specific observation areas. The average velocity of the droplet increased with higher plate temperature and injection pressure at specific observation areas. The distribution of the smaller droplet increased with higher plate temperature and injection pressure. For the water-glycerin mixture, as the glycerin ratio increased, more viscous droplets were created. This was followed in higher nozzle shear force at the outlet of the fuel injector, which decreased the particle size and generated more atomized fuel sprays. This result can enable the reduction in hydrocarbon and carbon monoxide emissions from internal combustion engines.

In order to get better results in the Formula SAE of Japan, it is necessary to develop a small displacement engine with an ideal fuel consumption rate. Therefore, the authors started to improve an existing engine by combining with glow plug heated sub-chamber and lean burn. Lean burn conditions are usually adopted in gasoline engines, having the advantages of high specific heat ratio, low pump loss, and low cooling loss due to requiring a decreased combustion temperature. The combination of these elements can be expected to vastly improve thermal efficiency and fuel consumption. Unfortunately, however, when the mixture becomes lean, the ignition delay increases, and the flame propagation speed reduces. This leads to an increase in combustion fluctuation. The authors intend to solve this problem by installing a glow plug in a newly designed sub-chamber. This type of device would usually be used to heat the sub-chamber of a diesel engine to solve the cold start problem. Experiments were conducted on a modified single-cylinder four-stroke CI engine (YANMAR TF120V) to operate as an SI engine with a higher compression ratio than conventional SI engines- 15.1:1. The engine is operated at a constant speed of 1000 and 1500 rpm, and temperature variation is created by varying excess air ratio and the glow plug's voltage. The coefficient of variation of BMEP was calculated to ensure the engine's cycle-by-cycle variation. According to the experimental results of glow plug voltage, when the excess air ratio is between 1.2 and 2.0, stable combustion can be achieved at excess air ratios up to 1.96 - this value is shown as the maximum lean burn limit in this study. Also, when compared to a system with the same conditions except without the glow plug, the brake thermal efficiency has been improved by up to 5.0 points, the brake specific fuel consumption rate also has been reduced by up to 17.4%. In the follow-up experiments on the ignition timing, it can be found that in case of ignition in the sub-chamber, MBT is after top dead center and the variation of ignition time has a limited effect on brake thermal efficiency or brake specific fuel consumption at a fixed glow plug voltage.

For improving the thermal efficiency and the reduction of hazardous gas emission from IC engines, it is crucial to model the heat transfer phenomenon starting from the intake system and predict the intake air's mass and temperature as precise as possible. Previously, an empirical equation was constructed using an experimental setup of an intake port model of an ICE, in order to be implemented into an engine control unit and numerical simulation software for heat transfer calculations. The empirical equation was based on the conventional Colburn analogy with the addition of Graetz and Strouhal numbers. Introduced dimensionless numbers were used to characterize the entrance region, and intermittent flow effects, respectively. In this study, further improvement of the model was done by characterizing the effect of backflow gas on intake air temperature by the introduction of the Euler number. 1-D engine simulations were done to analyze the valve-overlap and displacement backflow gas phases' effect on the intake air temperature. Additionally, engine test-bench experiments were conducted to validate the in-house built model and its applicability into engine control unit algorithm. The outlet temperature of the intake manifold was measured and results were compared to the various correlations. The in-house built equation showed the best accuracy when compared with the conventional approach, Colburn analogy. Maximum and average errors between the measured and estimated outlet temperatures were found to be 2.7% and 0.8%, respectively. The coefficient of variation for the in-house built equation was found to be 6.2%, which is considered to be a strong correlation. The average calculation time for the model is found to be 32 microseconds which satisfies the requirement for the current engine control unit technology.

To improve the thermal efficiency of ICEs, effective control of in-cylinder temperature is important. Utilization of nucleate boiling phenomenon to model the heat transfer is one of the measures that can be used for this purpose. Surface heat flux and bubble departure frequency measurements were done under the different wall superheat, coolant flow-rate, and temperature conditions. Subsequently, dimensional analyses were done to investigate the necessary dimensionless numbers acting on the heat flux model. The addition of power and exponential function of Jakob number was found to be effective, resulting in an average and minimum errors of 11.2% and 6.5%, respectively.

An optimum diesel engine helps to solve the increasing energy demand, the depletion of fossil fuels, and the environmental problems from the utilization of combustion engines. To optimise the operation of a direct injection diesel engine, the effects of various boost pressures under different rotations and main injection timings were studied experimentally and numerically. The boost pressure was set between 0 kPa to 60 kPa with increment of 20 kPa using a supercharger. The engine rotation was set between 800 RPM to 2000 RPM with an increment of 400 RPM. The main injection timing was varied with 2° increment from 1° BTDC to 3° ATDC. The results indicated the increase of in-cylinder pressure and heat release rate with increased boost pressure. Higher engine rotation led to the decrease of the maximum heat release rate, maximum in-cylinder pressure, and the difference between the magnitude of the first and second onsets of the in-cylinder pressure raise. It also shifted the timing for the peak of the heat release rate to occur further away from TDC. The change of the main injection timing from 1° BTDC to 3° ATDC decreased the maximum in-cylinder pressure and moved the location of the maximum in-cylinder pressure away from TDC. The delay of the main injection timing brought larger in-cylinder pressure raise for the first onset but lower cumulative heat release rate. The difference between experimental and numerical measurements of the in-cylinder pressure was found to be less than 4%. The results of the study suggested that boost pressure of 60 kPa and main injection timing of the 1° BTDC provide higher in-cylinder pressure and cumulative heat release rate and consequently better engine performance.

ディーゼル機関のモデルベースト燃焼制御器では，冷却損失を考慮した圧縮ポリトロープ指数の予測にこれまで実験式を用いてきた．著者らは，実験数を軽減するため，新たに物理モデルを開発し，制御器に実装した．実機にて過渡運転性能を評価したところ，実験値と比較して，モデルの予測誤差は0．３１％と評価された．

Diesel engines need to optimize the fuel injection timing and quantity of each cycle in the transient operation to increase the thermal efficiency and reduce the exhaust gas emissions through the precise combustion control. The heat transfer from the working gas in the combustion chamber to the chamber wall is a crucial factor to predict the gas temperature in the combustion chamber to optimize the timing and quantity of fuel injection. Therefore, the authors developed both the heat loss and the polytropic index prediction models with the low calculation load and high accuracy. In addition, for the calculation of the heat loss and the polytropic index, the wall heat transfer model was also developed, which was derived from the continuity equation and the energy equation. The present study used a single cylinder diesel engine under the condition of engine speed of 1200 and 1500 rpm, and measured the local wall temperature and the local heat flux of the combustion chamber. The measured data were compared with the prediction results of the heat loss and the polytropic index and evaluated the prediction accuracy of those models. The average relative errors for the heat loss and the polytropic index prediction models were evaluated to be 6.6% and 0.3%, respectively.

© 2019, KSAE. Improving thermal efficiency of internal combustion engines has been a priority in the automotive industry. It is necessary to model the heat transfer phenomenon at the intake system and precisely predict intake air’s mass flow rate into the engine cylinder. In the previous studies, the heat transfer at the intake system was modeled as quasi-steady state phenomenon, based on Colburn analogy. Authors developed two empirical equations with the introduction of Graetz and Strouhal numbers. In the present study, further improvements were done by the addition of pressure ratio between the intake manifold and atmospheric pressure, along with Reynolds number in order to characterize the backflow gas effect on intake air temperature. Compared with the experimental results, maximum and average errors of intake air temperature estimations inside the manifold found to be 2.9 % and 0.9 %, respectively.

ディーゼル機関の過渡運転性能向上には，モデルベースト制御によるサイクル毎の燃料噴射量と時期の予測が有効である．本研究では，燃焼室の局所壁温度履歴および局所壁面熱流束履歴を測定し，著者らが構築したオンボード用筒内壁温度推定モデルおよび壁面熱伝達モデルの予測精度を評価したので報告する．

A new equation, which was dependent on physical principles, was developed for the study of heat transfer in CI engines which needs turbulence of gas flows to calculate heat flux. Proposed approach was implemented into a 1-D engine simulation, which was used to determine heat flux between in-cylinder gas and wall. Results from the suggested equation were compared to the previous conventional equations; Morel and Hohenberg, and to the engine experiments. The proposed equation showed better accuracy when compared with the conventional equations due to detailed representation of in-cylinder gas flow by dividing the combustion chamber into 6 different regions.

© 2018 SAE International. All Rights Reserved. An empirical equation was developed for modeling the heat transfer phenomena taking place in an intake manifold which included the backflow gas effect. In literature, heat transfer phenomenon at intake system is modeled based on steady flow assumptions by Colburn analogy. Previously, authors developed an equation with the introduction of Graetz and Strouhal numbers, using a port model experimental setup. In this study, to further improve the empirical equation, real engine experiments were conducted where pressure ratio between the intake manifold and engine cylinder were added along with Reynolds number to characterize the backflow gas effect on intake air temperature. Compared to the experimental data, maximum and average errors of intake air temperature estimated from the new empirical equation were found to be 2.9% and 0.9%, respectively. Furthermore, Colburn analogy and suggested empirical equation were consecutively implemented to 1-D engine simulation software on gasoline and diesel engine setups. Naturally aspirated gasoline engine simulations revealed the importance of the backflow gas effect in line with the real engine experiments. Maximum and average temperature differences between the Colburn analogy and suggested equation showed 36.0 K and 28.7 K, respectively. In turbocharged diesel engine simulations, intake air temperature's effect on auto ignition timing was analyzed. At engine speed of 2250 rpm, in-cylinder air temperature difference at IVC was found to be 5.8 K. This difference corresponded to an advanced auto-ignition timing by 1.15 deg. CA, which could be interpreted an estimated reduction of CO2 gas by 0.28%.

ディーゼル機関の過渡性能向上にはオンボード・モデルベースト制御による着火時期の予測が重要である．著者らは，筒内ガス温度をサイクルごとに予測するため，低計算負荷の圧縮ポリトロープ指数予測モデルを開発した．過渡運転条件に適用し，１Ｄ数値計算と比較した結果，構築したモデルの有用性が認められたので報告する．

<p> The present study conducted the derivation of the empirical equation in terms of the heat transfer phenomena at the intake manifold of internal combustion engines and the implementation of its equation to 1-D engine simulation. The derived equation allows to calculate the Nusselt number at the intake system, which causes to predict the mass flow rate of intake air into the cylinder accurately, ultimately improving the fuel consumption by controlling the auto-ignition timing. The empirical equation was developed based on the Colburn equation, taking into consideration of the effects of the thermal boundary layer development and the intermittent air flow induced by the opening and closing of intake valves. Compared with the experimental data, the average errors of the Colburn equation and the empirical equation were estimated to be 91.1% and 2.7%, which gives to improve the prediction accuracy of the Nusselt number by deriving the empirical equation. The equation was then implemented in 1-D engine simulation and compared to the results of the Colburn equation, revealing the maximum and average intake air temperature differences of 11.4 K and 2.7 K, respectively.</p>

Overall efficiency of internal combustion engines are heavily depended on intake air temperature which is directly related to the heat transfer inside an intake system. Previously, authors developed an equation by using port model setup to calculate Nusselt number with introduction of Graetz and Strouhal numbers. This study modified the port model equation to improve its accuracy in a real engine experimental setup. Predicted intake air temperature was compared to the measured data with a maximum error of 5.6%. Additionally, 100 K of temperature difference was found between the boost pressure values of 944hPa and 678hPa from 1-D engine simulation results.

In the past two decades, internal combustion engines have been required to improve their thermal efficiency in order to limit hazardous gas emissions. For further improvement of the thermal efficiency, it is required to predict the mass of intake air into cylinders in order to control the auto-ignition timing for CI engines. For an accurate prediction of intake air mass, it is necessary to model the heat transfer phenomena at the intake manifold. From this intention, an empirical equation was developed based on Colburn equation. Two new arguments were presented in the derived formula. The first argument was the addition of Graetz number, where it characterized the entrance region thermal boundary layer development and its effect on the heat transfer inside the intake manifold. As the second argument, Strouhal number was included in order to represent intake valve effect on heat transfer. This study compared experimental data with the present empirical equation, and average error was estimated to be 3.1%, which was significantly improved in comparison with the Colburn equation. Furthermore, derived empirical heat transfer equation was implemented to the intake manifold model of a diesel engine in 1-D engine simulation. The study confirmed the influence of the heat transfer phenomena, and its importance to intake air. At IVC, temperature difference between Colburn equation and derived equation was calculated to be 3.8 K. This corresponded to an advanced auto-ignition timing by 0.78 deg. CA, which gives an estimated improvement of 0.22% when evaluating both the thermal efficiency and CO2 emission.

本論文は，実機エンジンの吸気管にて温度測定を行い，吸気システムでの伝熱現象を検討した．その際，流れの非定常性および温度境界層の発達を考慮し，Nu数をRe数，Gz数，St数で表した実験式を導出した．また，熱力学モデルに基づきシリンダに吸入される空気温度を推定したところ，5.6%の誤差で推定可能であることがわかった．