Combining Early Intake Valve Closure and Exhaust Throttling to Achieve Rapid Exhaust After-treatment Warm up in Diesel Engine Systems

Öz

Nowadays, the thermal management of exhaust after-treatment (EAT) units is a paramount concern for diesel automotive vehicles to meet the stringent emission regulations. In general, EAT temperatures above 250oC are favorable for effective emission conversion efficiency. At low-loaded operations, it is difficult to achieve that since exhaust temperature remains much below 250oC. Therefore, this numerical work aims to elevate exhaust temperature at a light-loaded diesel engine model through adopting two different engine- base techniques, namely early intake valve closure (EIVC) and exhaust throttling (ET). Both individual and combined modes of EIVC and ET are examined for high exhaust temperatures in the system. ET enhances exhaust temperature over 250oC with high exhaust flow rate, which is desirable for rapid EAT warm up. However, it causes up to % 15 fuel penalty, which highly impairs its practicality. Unlike ET, EIVC is thermally efficient and can raise exhaust temperature above 250oC. Yet, it has the disadvantage of significantly lowered exhaust flow rates, which is inconsistent with fast EAT warm up. Simultaneous application of ET and EIVC, as EIVC+ET, can still keep exhaust temperature above 250oC with reduced fuel penalty (down to % 8.8). It also has the benefit of increased exhaust flow rates compared to EIVC mode, which substantially heightens heat transfer rates to the EAT unit (up to % 101). Thus, it can sustain accelerated EAT warm up in the system. EIVC+ET method is also seen to be effective to improve EAT stay-warm performance (delaying EAT cool off) as it enables high exhaust temperature and high exhaust rates, which is not possible with other methods examined in the analysis.

Anahtar Kelimeler

• Diesel Engines
• Early Intake Valce Closure
• Exhaust Throttling
• Exhaust Temperature
• After-treatment Thermal Management

Dizel Motor Sistemlerinde Hızlı Egzoz Son-işlem Isınması Sağlamak için Erken Emme Valfi Kapatma ve Egzoz Kısma İşleminin Birleştirilmesi

Öz

Günümüzde, egzoz son işlem (ESİ) ünitelerinin ısıl yönetimi, dizel otomotiv araçlarının sıkı emisyon düzenlemelerini karşılaması açısından büyük önem taşımaktadır. Genel olarak, etkili emisyon dönüşüm verimliliği için 250oC’nin üzerindeki ESİ sıcaklıkları uygun olmaktadır. Düşük yüklü operasyonlarda egzoz sıcaklığı 250oC’nin çok altında kaldığı için bunu başarmak güçleşmektedir. Bu nedenle, bu sayısal çalışma, erken emme valfi kapatma (EEVK) ve egzoz kısılması (EK) olmak üzere iki farklı motora bağlı tekniği kullanarak düşük yüklü bir dizel motor modelinde egzoz sıcaklığını yükseltmeyi amaçlamaktadır. Sistemde yüksek egzoz sıcaklığı elde etmek için EEVK ve EK’nin hem tekil hem de birleşik modları incelenmiştir. EK, hızlı ESİ ısınması için ihtiyaç duyulan yüksek egzoz akış hızıyla egzoz sıcaklığını 250oC’nin üzerine çıkarmaktadır. Ancak bu metot % 15’e varan yakıt tüketimi artışına neden olmakta ve bu da pratikte uygulanabilmesini oldukça zorlaştırmaktadır. EK’den farklı olarak, EEVK termal verimliliği iyileştirmekte ve egzoz sıcaklığını 250oC’nin üzerine çıkarabilmektedir. Ancak ESİ ünitesinin hızlı ısınmasını aksatan, ciddi ölçüde düşürülmüş egzoz akışı hızı gibi bir dezavantajı bulunmaktadır. EK ve EEVK’nin EK+EEVK olarak eş zamanlı uygulanması, azaltılmış yakıt tüketimi artışı (% 8.8’e kadar) ile egzoz sıcaklığını hala 250oC’nin üzerinde tutabilmektedir. Ayrıca, EEVK moduna kıyasla daha yüksek egzoz akış hızı avantajına da sahiptir ki, bu da ESİ ünitesine olan ısı transfer oranlarını önemli ölçüde (% 101’e kadar) arttırmaktadır. Bu nedenle, ESİ ünitesinin motor sisteminde çok daha hızlı ısınmasına sağlayabilmektedir. EEVK+EK yönteminin, analizde incelenen diğer yöntemlerle mümkün olmayan, yüksek egzoz sıcaklığına ve yüksek egzoz akış hızlarına olanak verdiği için ESİ ünitesi sıcak kalma performansını (ESİ ünitesi soğumasının geciktirilmesi) iyileştirmede de etkili olduğu görülmüştür.

Anahtar Kelimeler

• Dizel Motorlar
• Erken Emme Valfi Kapanması
• Egzoz Kısılması
• Egzoz Sıcaklığı
• Son-işlem Isıl İdaresi

Kaynakça

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