Sürdürülebilir Kalkınma Amaçları

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• MakaleAçık Erişim2025/r/gumushane/14327
  A strategy for the one-pot direct production of 5-hydroxymethylfurfural (HMF) from sucrose using organic weak acid in situ as a catalyst

  Gül, Abdulkadir; Tanyıldızı, Muhammet Şaban

  5-Hydroxymethylfurfural (HMF), which can be produced in high yields by acid-catalyzed dehydration of carbohydrates, is used as a feedstock in biofuel and biopolymer production. However, these acidic catalysts are usually added externally, which increases HMF production costs. Furthermore, other important parameters for high yields of HMF production are raw material selection, reaction medium, and separation-purification processes. The aim of this study is to produce HMF in one-pot without the addition of any exogenous catalyst by evaluating the fructose remaining in the production medium in which the glucose from sucrose hydrolysis is microbially fermented into gluconic acid (GA). HMF production from fructose in a biphasic system consisting of a fermentation liquid containing GA and fructose and 2-Methyltetrahydrofuran (2-MeTHF) was optimized using Central Composite Design (CCD). The variables examined included reaction time, reaction temperature, solvent type, salt type, and organic/aqueous phase ratio. In the study, by chelating GA and calcium ions, the low degree of ionization of GA was increased, and HMF was produced in high yields without the addition of a catalyst. Under optimum conditions, using 2-MeTHF/ fermentation liquid (6:1) and 7.56 wt% CaCl2, the yield of HMF produced in pressurized (hydrothermal) vessels at about 147 °C for 158 min reached 77.6 % of the theoretical yield. The amount of GA in the production medium was 92.64 % preserved from degradation. GA and HMF in different phases of the biphasic system were purified from the production medium in high yields. Furthermore, 2-MeTHF, which constitutes the organic phase of the biphasic system, was recovered at approximately 95 % by vacuum evaporation. As a result, HMF production from sucrose, which is a more economical and abundant raw material compared to glucose and fructose, was realized in one-pot without the addition of any catalyst.

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• MakaleYalnız künye2019/r/gumushane/12544
  Theoretical investigation on combustion characteristics of ethanol-fueled dual-plug SI engine

  Altın, İsmail; Bilgin, Atilla; Sezer, İsmet

  In this study, effects of equivalence ratio, spark timing and spark plug number and locations on combustion characteristics were theoretically investigated using an ethanol-fueled dual-plug SI engine. Two-zone quasi-dimensional model was used throughout analyses. Three spark plug configurations (diagonally, centrally and side located), three equivalence ratios (0.8, 0.9, and 1.0), and three spark timings (−30, −25, and −20 CA @ BTDC) were considered to analyze variation of total burn duration, mass fraction burned, cylinder pressure, and temperatures (exhaust and maximum burned gas). Variation of mass fraction burned and cylinder pressure were also investigated at lean mixture ratio and 2800 rpm (MBT engine speed). Lastly, the effect of engine speed on total burn duration, maximum cylinder pressure and aforementioned temperatures were investigated in the range of 1000–6000 rpm. The findings show that dual-plug configuration yields approximate combustion characteristics by comparison with centrally located single plug configuration in ethanol-fueled SI engine.

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• MakaleYalnız künye2013/r/gumushane/15389
  Effects of charge properties on exergy balance in spark ignition engines

  Sezer, Ismet; Bilgin, Atilla

  This study investigates the effects of the air-fuel mixture (charge) properties on the exergy balance in spark ignition engines. A thermodynamic cycle model including compression, combustion and expansion processes is used. The principles of the second law are applied to the cycle model to perform an exergy analysis. Variation of the exergetic variables during the investigated portion of the cycle are examined as a function of the charge properties, i.e., fuel-air equivalence ratio, residual gas fraction and initial charge temperature. The results show that increasing fuel-air equivalence ratio causes an increase in irreversibilities and also exergy losses with heat transfer and exhaust gases, but enriching the air-fuel mixture beyond the stoichiometric ratio makes no significant contribution to the exergy transfer with work transfer. A slightly lean mixture also gives the best first and second law efficiencies. It is observed that there is a linear relation between the residual gas fraction and the exergetic variables. An increase in the residual gas fraction decreases the irreversibilities and exergy losses aside from the exergy transfer with work transfer. However, increasing the residual gas fraction positively affects the first and second law efficiencies because of the diluting of the charge. Increase of initial charge temperature creates a reduction in the irreversibilities and the exergy losses and, it also results in a lower exergy output by work transfer. Further, increase of initial charge temperature negatively influences the first and second law efficiencies.

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