Emre Arabaci

MÜHENDİSLİĞİN GELECEĞİNE ÇOK DİSİPLİNLİ BİR BAKIŞ Günümüz dünyasında mühendislik; yalnızca makineler, yapılar ve sistemler tasarlamak değil, aynı zamanda doğanın kurallarını anlayarak insanlığın en karmaşık sorunlarına sürdürülebilir çözümler üretmek demektir. Modern Approaches in Engineering / Modern Mühendislik Yaklaşımları, sanayiden sağlığa, nanoteknolojiden yapay zekâya kadar mühendisliğin dönüştürücü gücünü gözler önüne seren eşsiz bir bilimsel derlemedir. Türk ve yabancı literatüre katkı sağlayan bu çift dilli eser, araştırmacıları ve endüstri profesyonellerini geleceğin teknolojileriyle buluşturuyor. Kitapta Öne Çıkan Temalar: • Malzeme ve İmalat Teknolojileri: Polimer eklemeli imalatın termodinamiği, plastik dişli aşınma analizleri ve nano düzeyde (CNT/Epoksi) kompozit davranışları. • Enerji ve Kontrol Sistemleri: Asenkron motorlarda model tabanlı hız kontrolü ve deniz dizel motorlarında kompozit uygulamaları. • Sürdürülebilirlik ve Çevre: Hidrojeller ile su arıtımı ve yapay zekânın küresel sürdürülebilir kalkınma hedeflerindeki rolü. • Tıp ve Biyomühendislikte Devrimsel Yaklaşımlar: Termodinamiğin yeni teorileri ve yapay zekâ destekli biyo-robotik sistemlerle pankreas kanseri tanısı ve tedavisi.

The transition toward natural refrigerants is a global imperative under the Kigali Amendment; however, the operational instability of ammonia/carbon dioxide cascade systems due to epistemic uncertainties often hinders their widespread sustainable adoption. This study introduces a novel Uncertainty‐Aware Robust Optimization framework, integrating Gaussian Process Regression with the Grey Wolf Optimizer to enhance the energetic, exergetic, and enviro‐economic performance of industrial refrigeration. Validated against four independent datasets (Mean Relative Deviation 11), the proposed strategy maintains exceptional stability (SI 0.999) are derived to facilitate real‐time industrial implementation on low‐cost controllers, bridging the gap between theoretical optimization and practical sustainability. Concurrently, while this study is bounded by steady‐state performance assumptions and numerical simplifications, it delivers immediate practical application value.

The global transition toward low-global warming potential (GWP) working fluids in Organic Rankine Cycles (ORC) presents complex thermo-economic and environmental dynamics. This study performs a comparative thermo-economic and environmental assessment of a recuperative ORC system utilizing hydrofluoroolefin (HFO) fluids R1233zd(E) and R1234ze(Z) as sustainable alternatives to the conventional R245fa for low-grade geothermal heat recovery (150 ℃). To overcome the computational cost of rigorous thermodynamic simulations near the critical point, a novel data-driven optimization framework is proposed. A comprehensive dataset of 3000 design points was generated using a robust process model incorporating flow-regime-dependent heat transfer correlations. A Bayesian-optimized support vector regression (SVR) surrogate model was developed to replace the physics-based solver, achieving a near-perfect prediction accuracy of R ² = 0.9999 while accelerating the simulation speed by over 10,000 times (from 1.45 s to 0.12 ms). Subsequently, a weighted gray wolf optimizer (GWO) coupled with the SVR model was employed to the thermo-economic performance trajectory. The multi-objective optimization reveals a highly synergistic relationship between efficiency and cost for this specific application; R1233zd(E) is the superior candidate, achieving a maximum exergy efficiency of 40.02%, marginally outperforming the baseline R245fa (39.97%) while operating at a significantly lower evaporator pressure (839 kPa vs. 1381 kPa). Although this necessitates a slightly larger heat transfer area, increasing the specific investment cost (SIC) by 1.6% to 5442 USD/kW, the environmental benefits are decisive. Life cycle assessment (LCA) results indicate a 99.8% reduction in the total equivalent warming impact (TEWI) for R1233zd(E) compared to R245fa (dropping from 2926 to 4.6 tons CO ₂ -eq). These findings demonstrate that AI-driven optimization can effectively leverage the synergistic relationship between thermodynamic perfection and economic viability, validating R1233zd(E) as a technically superior and environmentally imperative successor for next-generation green ORC plants.

The increasing adoption of Fused Deposition Modeling (FDM) for functional applications necessitates a rigorous characterization of diverse filament formulations under mechanical stress. This study addresses the current research gap by systematically evaluating the load-dependent friction and thermal evolution of PETG, PLA+, PLA-Matte, and PLA-Silk. Through dry sliding tests under loads ranging from 5 to 15 N, we integrated real-time temperature monitoring to reveal how visual additives influence functional performance. The findings indicate that aesthetic modifications do more than alter appearance; they fundamentally dictate the tribological response. PLA-Silk demonstrated superior efficiency by maintaining the lowest coefficient of friction (0.54 at 15 N) and minimal heat generation, which is likely attributable to its unique additive formulation. Conversely, PLA-Matte proved susceptible to frictional heating, generating surface temperatures up to 53.9±1.4°C. This heat accumulation, approaching the glass transition region, triggered a rapid transition to severe adhesive wear and subsequently compromised the material’s structural integrity. While PLA+ emerged as the most balanced candidate for general use due to its stable wear rate, PETG showed distinct sensitivity to higher loads. Ultimately, this work identifies surface temperature as a decisive factor in FDM tribology. It concludes that materials designed for aesthetics require specific operational constraints when utilized in functional, sliding-contact applications.

As electric vehicles (EVs) become increasingly common, managing battery temperature has become a key engineering challenge. During the cooling process, EV batteries release a considerable amount of heat that often goes to waste. This study explores how that residual heat can be converted into electricity using the Organic Rankine Cycle (ORC). A theoretical analysis compares the performance of three working fluids (R123, SES36, and R134a) under the same conditions. The results show that R123 and SES36 reached up to 15% thermal efficiency, while R134a was slightly lower at 14%. The highest turbine outputs were achieved between 20–25°C condenser temperatures and 75–80°C steam generator temperatures. R123 and SES36 produced around 14.7–14.8 kW, while R134a produced 14.4 kW. Interestingly, both peak efficiency and power were observed at the lowest fluid flow rates. What makes this work unique is its focus on applying ORC technology directly to EV battery cooling systems (a concept that has not been widely explored). The findings suggest a new path for improving energy use in EVs and reducing their environmental footprint.

Hybrid electric vehicles aim to both increase fuel efficiency and reduce carbon emissions by combining an internal combustion engine and an electric motor. However, integrating these two power sources most efficiently requires complex engineering and design decisions. The performance and environmental impact of hybrid electric vehicles depend not only on the efficiency of the engines but also on the vehicle's operating conditions and powertrain design. Therefore, understanding how hybrid electric vehicles perform in real-world scenarios and thoroughly examining the factors that affect their performance is critical for future vehicle designs. This study presents a performance and environmental assessment of a series-parallel hybrid electric vehicle (HEV) under quasi-realistic operating conditions. We considered the influence of resistance forces on the demanded traction force. For a real vehicle, performance characteristic curves were derived through calculations utilizing actual performance maps of the internal combustion engine, electric motor, and generator. Furthermore, the impact of power-split mechanism design parameters on vehicle performance was investigated. While keeping the planetary gear unit's gear ratio constant, the angular velocity ratio (ω_R/ω_s) between the ring gear and sun gear was evaluated. Findings indicate that a low ω_R/ω_s value enhances the effective hybridization factor but limits the vehicle's ability to reach desired high velocities. Conversely, a high ω_R/ω_s increases battery power demand to achieve the required vehicle power. From an environmental perspective, a high ω_R/ω_s value proved more advantageous for CO2 equivalent emissions. These findings offer valuable guidance for HEV designers.

In this study, a compact, single-cylinder, spark-ignition, four-stroke engine commonly used in power generators is converted into a six-stroke engine. This conversion employed the free-stroke Kelem model, one of the six-stroke engine approaches described in the literature, which required modifications only to the camshaft. Without modification to the original crankshaft gear, a fixed-ratio epicyclic gear was applied to the camshaft gear to achieve the necessary speed ratio between the crankshaft and camshaft. Following the verification of the engine's original camshaft dimensions, new cam profiles were designed using a two-circular-arc cam profile. The cam lobes and cam gear were manufactured and assembled separately. During the experiments, a resistive load bank with a capacity ranging from 400 to 4000 W was employed to load the power generator and assess the engine's performance parameters. Fuel consumption, oil temperature, and exhaust gas temperature were measured, from which thermal efficiency, specific fuel consumption, and fuel consumption per cycle were calculated. The results showed that oil temperature decreased by 3.1 %, exhaust gas temperature decreased by 15.4 %, and thermal efficiency increased by 15.8 %. However, fuel consumption per cycle in the six-stroke engine increased by 29.9 %, indicating a higher engine load demand to achieve the desired power output. This study uses the original dimensions and characteristics of the test engine as a reference. No further modifications were made apart from the camshaft adjustment. The experimental findings demonstrate that four-stroke engines can be successfully converted into six-stroke engines, achieving improved fuel economy at the expense of reduced power output. The implementation of an epicyclic gear system into the camshaft gear without any modification to the crankshaft gear, along with the experimental validation of the model's usability, distinguishes this study from the existing literature.

This study aims to investigate the effects of valve motion characteristics on the performance of spark-ignition engines. The impact of valve timing, valve lift, and valve duration on the full-load performance characteristics of the engine was analyzed through modeling. For this purpose, the WAVE simulation program, one of the one-dimensional gas dynamics simulation tools, was used. The Taguchi experimental design method was applied for the simulation design of the variables. An analysis of variance (ANOVA) was conducted to examine the relationship between engine performance and valve motion characteristics. A total of 125 simulations were conducted, with 25 solutions for each engine speed. Brake torque, brake thermal efficiency, and volumetric efficiency were chosen as engine performance parameters. Based on the ANOVA, the optimal valve motion characteristics that maximize these three engine performance parameters simultaneously were determined. The results showed that valve overlap and intake valve duration were the most influential parameters affecting engine performance. Moreover, compared to the reference engine's original configuration, increasing valve overlap and reducing intake valve duration improved engine performance. A comparison was made between the optimized values and the original values of the reference engine. While the original configuration of the reference engine performed better at high engine speeds, a significant improvement in engine performance was observed at low and medium engine speeds. Specifically, for low and medium speeds, improvements of 8.1% in brake power and brake torque, 1.5% in brake thermal efficiency, and 6.8% in volumetric efficiency were observed.