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A study on in-cylinder flow field of a 125cc motorcycle engine at low engine speeds
Bambang Wahono,Yanuandri Putrasari,임옥택 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.9
The in-cylinder flow characteristics of a four-stroke, four-valve, pent-roof small engine of motorcycle at engine speeds from 2000 rpm to 4000 rpm were studied using computational fluid dynamics (CFD). The aim of this study was to investigate the in-cylinder flow characteristics of small engines, including tumble, swirl, turbulent kinetic energy (TKE), angular momentum, in-cylinder air mass, turbulent velocity, turbulent length scale, and air flow pattern (in both intake and compression strokes) under motoring conditions. The engine geometry was created using SolidWorks, then was exported and analyzed using CONVERGE, a commercial CFD method. Grid independence analysis was carried out for this small engine and the turbulence model was observed using the renormalized group (RNG) k-ɛ model. The pressure boundary conditions were used to define the fluid pressure at the intake and exhaust of the port. The results showed that the increase in the engine speed caused the swirl flow in the small engine to be irregularly shaped. The swirl flow had a tendency to be stable and almost constant in the beginning of the compression stroke and increased at the end of compression stroke. However, the increase of in engine speed had no significant effect on the increase in tumble ratio, especially during the intake stroke. There was an increase in tumble ratio due to the increase in engine speed at the end of compression stroke, but only a marginal increase. The increase in engine speed had no significant effect on the increase in angular momentum, TKE, or turbulent velocity from the early intake stroke until the middle of the intake stroke. However, the angular momentum increased due to the increase in engine speed from the middle of the intake stroke to the end of compression stroke, and the angular momentum achieved the biggest increase when the engine speed rose from 3000 to 4000 rpm by 10 % at the end of the intake stroke. The increase in engine speed caused an increase of TKE and turbulent velocity from the middle of intake stroke until the end of compression stroke. Moreover, the biggest increase of TKE and turbulent velocity occurred when the engine speed rose from 3000 to 4000 rpm at the middle of intake stroke around 50 % and 25 %, respectively. Turbulent length scales appeared to be insensitive to increasing engine speed, especially in the intake stroke until 490 °CA. From that point, the value of the turbulent length scale increased as engine speed increased. The biggest increase in the turbulent length scales occurred when the intake valve was almost closed (around 20 %) and the engine speed was within two specific ranges (2000 to 3000 rpm and 3000 to 4000 rpm). Regarding the effect of engine speed, there were no significant effects upon the accumulated air mass in the small engine. The increase in engine speed caused an increase of turbulence in the combustion chamber during the late stages of the compression stroke. The increase in turbulence enhanced the mixing of air and fuel and made the mixture more homogeneous. Moreover, the increase in turbulence directly increased the flame propagation speed. Further research is recommended using a new design with several types of intake ports as well as combinations of different intake ports and some type of piston face, so that changes in air flow characteristics in small engines can be analyzed. Finally, this study is expected to help decrease the number of experiments necessary to obtain optimized systems in small engines.
Determinants of Firm Value and Profitability: Evidence from Indonesia
Bambang SUDIYATNO,Elen PUSPITASARI,Titiek SUWARTI,Maulana Muhammad ASYIF 한국유통과학회 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.11
The purpose of this study was to examine the role of profitability as a mediating variable in influencing firm value. This study uses a sample of manufacturing companies listed on the Indonesia Stock Exchange from 2016 to 2018. The data used is panel data, with data analysis using multiple regression. Based on the Sobel test, profitability plays a role in mediating the effect of firm size on firm value. The effect of firm size on firm value is indirect, however, through profitability. Therefore, the market price of the shares of large-scale companies will increase if the resulting profitability is high. The capital structure and managerial ownership directly influence firm value. The results showed that managerial ownership and firm size had a positive effect on profitability, while capital structure had no effect on profitability. Capital structure and managerial ownership have a negative effect on firm value, while firm size and profitability have a positive effect on firm value. The main finding of this study is that profitability acts as an intervening variable in mediating the relationship between firm size and firm value.
Bambang Dwi Argo,Sandra Sandra,Ubaidillah Ubaidillah 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.7
The drying kinetics of cassava chips in a newly developed multipurpose convective-type tray dryer heated by a gas burner (consisting of four drying compartments) was studied. The temperature of the drying air was 50 °C, and drying loads were 8 kg and 12 kg. Drying of cassava chips occurred in both heating and falling periods. It was found that cassava chips dried faster in the drying compartments that were closer to the heat source, that is, the first to the fourth drying compartments, consecutively. Twelve thin layer drying models were placed to the experimental moisture ratio data. The models were compared based on their coefficient of determination (R 2 ), reduced mean square of deviation (χ 2 ), and root means square error (RMSE) between experimental and predicted moisture ratios. From all the mathematical models investigated, the Page and Midilli et al. models satisfactorily described the drying behavior of cassava chips in all drying compartments with drying loads of 8 kg and 12 kg, respectively.
Thin-layer drying of cassava chips in multipurpose convective tray dryer: Energy and exergy analyses
Bambang Dwi Argo,Ubaidillah Ubaidillah 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.1
Energy and exergy data of the drying of thin-layer cassava (Manihot esculenta)chips in a multipurpose convective-type tray dryer at 50 °C were collected to evaluate the technical performance of the drying system. The energy and exergy parameters, i.e. energy utilization, energy utilization ratio, energy efficiency, exergy inflow and outflow, exergy loss, and exergetic efficiency were analyzed. The results indicate that the energy utilization, exergy inflow, exergy outflow, and exergy efficiency increased in the ranges of 9.53-24.66 kJ/s, 5.67-11.34 kJ/s, 2.21-8.04 kJ/s, and 38.90 %-70.86 %, respectively, with increasing drying time. The results also show that the energy utilization ratio, energy efficiency, and exergetic improvement potential tend to decrease in the ranges of 0.49-0.68, 47.48 %-62.62 %, and 0.96-2.33 kJ/s, respectively, with increasing drying time. Additionally, stable exergy losses were observed during the drying process, within the range of 3.30-4.27 kJ/s during drying. Further research and development that could be used to improve the performance of this drying process are also suggested.