سوخت و احتراق

سوخت و احتراق

فرایند کاهش مکانیزم خودکار به منظور مدلسازی احتراق در یک موتور HCCI با سوخت گاز طبیعی و هپتان نرمال

نویسندگان
وحید محمدی
رحیم خوشبختی سرای
امیر کارگر امجد
دانشکده مهندسی مکانیک، دانشگاه صنعتی سهند، تبریز، ایران
چکیده
موتورهای احتراقی HCCI، به دلیل مصرف سوخت و آلایندگی پایین، در سال های اخیر مورد توجه بسیاری از پژوهشگران قرار گرفته اند. همزمان با پژوهش های آزمایشگاهی متعددی که در مورد این موتورها صورت گرفته است، مدلسازی ریاضی نیز همواره به عنوان ابزاری برای پیش بینی رفتار احتراقی، عملکردی و آلایندگی آن ها به کار رفته است. هرچند استفاده از سازوکارهای سینتیک شیمیایی مفصل در مدل های احتراقی به پیش بینی مناسبی از رفتارهای یادشده خواهد انجامید، اما از سوی دیگر این امر به افزایش قابل توجه زمان محاسبات خصوصاً در مدل های احتراقی دقیق تر نیز منجر خواهد شد. در پژوهش حاضر، با هدف رفع این مشکل، فرایند کاهش مکانیزم در شرایط موتور احتراقی HCCIمدنظر قرار گرفت. در این راستا، از یک مدل تک منطقه ای بهینه سازی شده به عنوان ابزار لازم برای شبیه سازی احتراق استفاده شد. براساس مطالعات انجام شده در این پژوهش، روش گراف روابط جهت دار به همراه انتشار خطا (DRGEP)، به دلیل زمان محاسباتی پایین در عین دقت بالا، به عنوان روش مناسب برای فرایند کاهش مکانیزم انتخاب شد.علاوه بر این، به جای رویکرد سنتی کاهش تک مرحله ای، از یک رویکرد نوین مبتنی بر کاهش تدریجی مجهز به کنترل خطا بهره گرفته شد. با این رویکرد، فرایند کاهش مکانیزم به صورت کاملاً خودکار در بازه وسیعی از شرایط کارکردی موتور HCCI بر روی مکانیزم GRI-Mech3.0 برای شبیه سازی احتراق سوخت گاز طبیعی، و مکانیزم گالوویچف برای شبیه سازی احتراق هپتان نرمال اجرا شد. در انتهای این فرایند، اندازه این دو مکانیزم به ترتیب از 53 گونه و 325 واکنش، و 57 گونه و 290 واکنش، به مقادیر 24 گونه و 95 واکنش، و 42 گونه و 146 واکنش کاهش یافت.با این وجود خطای کاهش در همه حالت ها کمتر از 1 درصد باقی ماند.
کلیدواژه‌ها
کاهش مکانیزم
DRGEP
HCCI
گاز طبیعی
هپتان نرمال

عنوان مقاله English

An Automatic Mechanism Reduction Process in Order to Model the Combustion in an HCCI Engine Fueled with Natural Gas and N-heptane

نویسندگان English

Vahid Mohammadi
Rahim Khoshbakhti Saray
Amir Karegar Amjad
Faculty of Mechanical Engineering, Sahand University of Technology, Tabriz, Iran
چکیده English

HCCI combustion engines due to their low fuel consumption and pollution have been studied by many researchers in recent years. Along with several experimental researches performed on these engines, mathematical modeling has also been utilized as a tool for prediction of their combustion, performance and pollution behaviours. Although use of detailed chemical kinetic mechanisms in the combustion models will result in a proper prediction of the above-mentioned behaviours, a significant increase in the computational time particularly for the more accurate combustion models will also occur. In order to overcome this challenge, mechanism reduction process in HCCI combustion engine conditions has been considered in the current study. In this direction, an optimized single-zone combustion model has been used as a necessary tool for simulation of combustion. Based on the studies performed in the current work, the Directed Relation Graph with Error Propagation (DRGEP) method, thanks to its low computational time while having high accuracy, has been selected as a proper method for the mechanism reduction process. Additionaly, instead of the traditional single-stage reduction approach, a novel approach based on gradual reduction with error propagation has been used. Therefore, the mechanism reduction process has been executed fully automatically in a wide interval of operating conditions of HCCI engine on GRI-Mech3.0 mechanism for simulation of combustion of natural gas, and on the Golovichevandrsquo;s mechanism for simulation of combustion of n-heptane. At the end of this process, the sizes of these two mechanisms were reduced from 53 species and 325 reactions, and 57 species and 290 reactions to 24 species and 95 reactions, and 42 species and 146 reactions, respectively. The errors caused by reduction, however, were remained less than 1 percent at all conditions

کلیدواژه‌ها English

Mechanism reduction
DRGEP
HCCI
Natural gas
N-heptane
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