IJE TRANSACTIONS B: Applications Vol. 28, No. 2 (February 2015) 251-260   

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S. Kharazmi, A. H. Benisi and A. Mozafari
( Received: July 06, 2014 – Accepted: November 13, 2014 )

Abstract    Turbocharged CNG engines produce high NOx emission due to the fuel type and high combustion temperature. In this research, the effects of lean-burn and waste gate opening pressure threshold on NOx emission are studied theoretically and experimentally at WOT condition as well as 13-mode ECE-R49 test cycle. A code is developed in MATLAB environment for predicting engine NOx and the results are validated with the research experiments. Simulations show that NOx increases by increase of excess air ratio and reaches at most to 2486ppm at excess air ratio of 1.1 and then decreases. It is also experimentally found that changing waste gate opening pressure threshold from 165mmHg to 200 and 265mmHg decreases total bsNOx at a rate of 6% and 12% respectively. Increase of the threshold to 323mmHg increases total bsNOx. Therefore, to minimize the cycle bsNOx, the threshold of 265mmHg is the optimum threshold for the engine between the four pressure thresholds experimented.


Keywords    Turbocharged CNG SI engine, NOx emission, ECE-R49 test cycle, lean-burn, waste gated turbocharger


چکیده    در این پژوهش، اثرات نسبت هوای اضافی و فشار آستانه بازشدگی دریچه هدرروی توربوشارژر بر آلایندگی NOx و عملکرد یک موتور گازسوز توربوچارجری بصورت تجربی در سیکل آزمون 13 نقطه ای ECE-R49 ارزیابی می­شوند. یک کد رایانه ای در محیط نرم افزار MATLAB ایجاد می­شود تا NOx و عملکرد موتور را پیش­بینی کند و نتایج آن با نتایج تجربی همین پژوهش ارزیابی می شوند. اثر نسبت هوای اضافی موتور بر آلایندگی NOx، توان و مصرف مخصوص سوخت اندیکاتوری بصورت مطالعه پارامتری بوسیله کد رایانه ای این پژوهش ارزیابی می شود. آلایندگی NOx بارکامل در نسبت هوای اضافی 1/1 بیشینه است. مطالعه پارامتری نشان می دهد که افزایش نسبت هوای اضافی بمیزان %20، توان اندیکاتوری بیشینه را %9 کاهش و حداقل مصرف مخصوص سوخت اندیکاتوری را %7 بهبود می دهد. نتایج آزمایشها نشان می دهند با افزایش فشار آستانه باز شدن دریچه هدررو، توان ترمزی موتور بخصوص در دور و بار زیاد، افزایش می یابد. بصورت آزمایشگاهی دریافته می شود آلایندگی NOx مخصوص ترمزی کل با تغییر فشار آستانه بازشدگی دریچه هدررو از mmHg165 به 200 و mmHg265، به ترتیب6 و %12 کاهش می­یابند. افزایش این آستانه فشار به mmHg323، NOx مخصوص ترمزی کل را افزایش می دهد. در نتیجه بمنظور کمینه کردن NOx مخصوص ترمزی کل، فشار آستانه mmHg265، آستانه بهینه این موتور بین چهار حالت مورد آزمون می باشد.



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