Abstract    One of the important problems in reducing pollutant emission from diesel engines is trade-off between soot and NOx. Split injection is one of the most powerful tools that decrease soot and NOx emissions simultaneously. At the present work, the effect of split injection on the combustion process and emissions of a direct-injection diesel engine under full-load conditions is investigated by the commercial CFD code AVL-FIRE. The study of injection timing and split injection parameters, including the delay dwell and the fuel quantity injected between injection pulses is carried out. Three different split injection schemes, in which 10-20-25 % of total fuel is injected in the second pulse, have been considered. The results show that 25 % of total fuel injected in the second pulse, reduces the total soot and NOx emissions effectively in DI diesel engines. In addition, the optimum delay dwell between the pulses is about 25°CA. The predicted values of combustion process, emission and delay dwell by this CFD model show a good agreement with the corresponding data of multi-zone phenomenological combustion model in the literature.

Keywords    Split injection, Combustion, Emission, NOx, Soot

چکیده    يکي از مهم ترين مسائل در کاهش آلاينده هاي موتورهاي ديزلي، تقابل آلاينده هاي اکسيد نيتروژن و دوده است. تزريق چند گانه يکي از قوي ترين ابزارها براي کاهش همزمان اين دو آلاينده است. در اين تحقيق با نرم افزار تجاري ديناميک سيالات محاسباتي فاير، تأثير تزريق چندگانه بر فرآيند احتراق و آلايندگي موتور ديزلي تزريق مستقيم تحت بار کامل بررسي شده است. زمان تزريق و پارامترهاي تزريق چندگانه که شامل زمان تأخير و مقدار سوخت تزريق شده در خلال پالس هاي تزريق، مطالعه شده است. سه الگوي متفاوت تزريق که به ترتيب 10، 20 و 25 درصد کل سوخت در پالس دوم تزريق مي باشد در نظر گرفته شده است. نتايج نشان مي دهند که 25 درصد کل سوخت تزريق شده در پالس دوم آلاينده هاي اکسيد نيتروژن و دوده به طور چشمگير و همزمان در موتور ديزلي تزريق مستقيم کاهش مي يابد. به علاوه، زمان تأخير بهينه در خلال پالس هاي تزريق 25 درجه ميل لنگ است. نتايج پيشگويي شدة احتراق، آلايندگي و تأخير پالس هاي تزريق با مدل ديناميک سيالات محاسباتي استفاده شده، توافق خوبي را با نتايج حاصل از مدل هاي شبه چند بعدي موجود در ادبيات فن نشان مي دهد.

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