DİZEL MOTOR YANMA ODASINDA ISI TAŞINIM KATSAYISI VE ISI AKISININ FARKLI MODELLERLE KARŞILAŞTIRMALI ANALİZİ

Abstract

İçten yanmalı motorlarda yanma odasında gerçekleşen ısı transferi, motor performansı, soğutma ve yağlama sistemleri açısından kritik öneme sahiptir. Silindir içi karmaşık akış ve ısı transferi süreçlerinin pratik ve kabul edilebilir doğrulukta modellenmesine olanak sağlayan çeşitli ampirik bağıntılar, motor yanma analizlerinde yaygın şekilde tercih edilmektedir. Bu çalışmada, common-rail sistemine sahip bir dizel motorda yanma gazları ile yanma odası duvarları arasındaki ısı transferi, deneysel veriler ve ampirik modeller kullanılarak incelenmiştir. Analizler, 1600–2000 dev/dak aralığında ve sabit yük altında gerçekleştirilmiştir. Isı taşınım katsayısının (ITK) belirlenmesinde Woschni, Hohenberg ve Eichelberg modelleri kullanılmıştır. Sonuçlar, Eichelberg modelinin diğer modellere kıyasla daha düşük ve daha geç ITK değerleri öngördüğünü ve pik değerlerin 1588,4–1639,7 W/m²K aralığında değiştiğini göstermiştir. Hohenberg ve Woschni modelleri ise birbirine yakın sonuçlar üretmiş olup ITK değerleri 2121,2–2607,2 W/m²K aralığında belirlenmiştir. Isı akısı sonuçları ise birbirine yakın sonuçlar göstermiş; Eichelberg, Hohenberg ve Woschni modelleri için sırasıyla 2,3–2,51 MW/m², 2,38–2,81 MW/m² ve 2,73–2,83 MW/m² aralıklarında değerler elde edilmiştir. Motor devrinin artmasıyla birlikte silindir içi basınç ve sıcaklık artmış, buna bağlı olarak ısı transferi şiddetlenmiştir. En yüksek ısı transferinin meydana geldiği krank açıları modellere göre değişmekte olup üst ölü noktadan sonra 20-25o krank açısı aralığında oluşmuştur.

Keywords

• Isı geçişi
• ısı taşınım katsayısı
• motor devir sayısı
• ampirik ısı taşınım katsayısı modelleri

COMPARATIVE ANALYSIS OF HEAT TRANSFER COEFFICIENT AND HEAT FLUX IN COMBUTION CHAMBER OF DIESEL ENGINE USING DIFFERENT MODELS

Abstract

Heat transfer occurring in the combustion chamber of internal combustion engines is of critical importance for engine performance, as well as cooling and lubrication systems. Various empirical correlations that allow the complex in-cylinder flow and heat transfer processes to be modeled with practical and acceptable accuracy are widely preferred in engine combustion analyses. In this study, the heat transfer between the combustion gases and the combustion chamber walls in a diesel engine equipped with a common-rail system was investigated using experimental data and empirical models. The analyses were carried out within the engine speed range of 1600–2000 rpm under constant load conditions. The Woschni, Hohenberg, and Eichelberg models were used to determine the heat transfer coefficient (HTC). The results showed that the Eichelberg model predicts lower and later HTC values compared to the other models, with peak values ranging between 1588,4 and 1639,7 W/m²K. The Hohenberg and Woschni models produced similar results, with HTC values in the range of 2121.2–2607.2 W/m²K. Heat flux results exhibited a similar trend; values were obtained in the ranges of 2,3–2,51 MW/m², 2,38–2,81 MW/m², and 2,73–2,83 MW/m² for the Eichelberg, Hohenberg, and Woschni models, respectively. As the engine speed increased, in-cylinder pressure and temperature also increased, leading to intensified heat transfer. The crank angles at which the maximum heat transfer occurred varied depending on the model, and were found to be in the range of 20–25° crank angle after top dead center.

Keywords

• Heat transfer
• heat transfer coefficient
• engine speed
• empirical heat transfer coefficient models

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