Ağır İş Dizel Motoru Silindiri İçerisindeki Soğuk Hava Akışının Sayısal İncelenmesi

Bu çalışmada, lokomotiflerde kullanılan ağır iş dizel motorunun silindiri içerisindeki soğuk hava akışı ve oluşan girdaplar Hesaplamalı Akışkanlar Dinamiği (HAD) yöntemi ile hareketli çözüm ağı kullanılarak modellenmiştir. Ele alınan motor silindirinde emme ve egzoz portları, valfleri ve ön yanma odalı tip yanma odası vardır. Krank açısına göre değişen piston ve emme-egzoz supapları için hareketli çözüm ağı kullanılmıştır, soğuk hava akışı RNG k-ε türbülans modeli kullanılarak modellenmiş ve emme ve sıkıştırma işlemlerinde yanma odası içerisindeki hız, türbülans kinetik enerjisi (TKE) ve girdap oranları incelenmiştir. HAD analizleri mevcut motorun modernize edilerek farklı yanma odası tasarımları ile sıkıştırma işlemi sonunda daha yüksek TKE’sine ulaşabileceğini göstermektedir. Sıkıştırma işlemi sonunda girdap oranının yeterince artmadığı ve ön yanma odası içerisinde, ana yanma odasına göre daha yüksek hızlara ulaşıldığı görülmüştür. Bu çalışma neticesinde TKE ve girdap oranı üzerinden yapılan değerlendirmeler ile motor performansı açısından mevcut ağır iş dizel motoru yanma odasının iyileştirilmesi gerekliliği ortaya çıkarılmıştır. Mevcut ağır iş tipi dizel motorunda silindir içerisindeki NOx emisyonlarında kötüleşme olmayacak şekilde girdap oranını belli ölçüde arttırmak veya farklı girdap oranı oluşturabilecek yanma odası tiplerini denemek uygulanabilecek tasarımsal önlemler arasındadır. Ayrıca TKE artırımı ile hava yakıt karışımını arttırmak için yanma sonu gazlarının tahliyesi için gerekli olan supap bindirme süresini azaltmak da uygulanabilecek bir önlemdir.

Numerical Investigation of Cold Air Flow Inside the Cylinder of a Heavy Duty Diesel Engine

In this study, cold air flow and related swirls occurring in the cylinder of a heavy-duty diesel engine in locomotives was investigated by means of Computational Fluid Dynamics (CFD) using a moving mesh. The engine cylinder of interest has intake and exhaust ports, valves and combustion chamber with pre-combustion chamber. A moving mesh was used for the crankshaft-dependent motion of the piston and intake exhaust valves, and the cold air flow was modeled using the RNG k-ε turbulence model and the velocities, turbulence, kinetic energy (TKE) and swirl ratios (SR) in the combustion chamber during intake and compression processes were investigated. At the end of the compression process, the swirl ratio did not increase sufficiently and higher velocities were achieved in the pre-combustion chamber than in the main combustion chamber. As a result of this study, evaluations based on TKE and swirl ratio have revealed the necessity of improving the current heavy-duty diesel engine combustion chamber for better engine performance. In the current heavy-duty diesel engine, it is possible to increase the swirl rate without any deterioration in the NOx emissions in the cylinder or to try new types of combustion chambers that can create different swirl ratio.

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