مدل سازی عددی اغتشاش در جریان احتراقی اسپری دیزل با استفاده از روش شبیه سازی گردابه های بزرگ

نوع مقاله : مقاله پژوهشی

نویسندگان

دانشکده مهندسی مکانیک، دانشگاه تربیت مدرس، تهران، ایران

چکیده

در موتورهای دیزل پاشش مستقیم امروزی، فرآیندهای اسپری و احتراق آن، از طریق اختلاط کنترل می‌شوند. در روش شبیه سازی گردابه‌های بزرگ به دلیل اینکه مقیاس‌های بزرگ جریان به طور مستقیم حل می‌شوند و مقیا سهای کوچک مدل می‌شوند، بنابراین اختلاط هوا و بخار سوخت به روش شبیه سازی گردابه‌های بزرگ بهتر پیش بینی می‌شود و در نتیجه قابلیت پیش بینی مشخصات جریان واکنشی افزایش می یابد. در این پژوهش اغتشاش در جریان احتراقی اسپری دیزل با استفاده از روش شبیه سازی گردابه‌های بزرگ و مدل احتراقی راکتور اختلاط جزئی بر روی کد EPISO-SPRAY مورد مطالعه قرار می‌گیرد. با توسعه‌ی این کد، روش شبیه سازی گردابه‌های بزرگ بر روی حلگر جریان دوفازی مربوط به این کد اعمال می‌شود که درآن از دیدگاه اولری - لاگرانژی، دینامیک جریان بررسی می‌شود و در نهایت با روش رنس مقایسه می‌گردد. در این پژوهش، به منظور شبیه سازی اغتشاش در جریان احتراقی اسپری دیزل از مدل‌های زیرشبکه‌ی اسماگورینسکی و اسماگورینسکی دینامیکی و مدل احتراقی راکتور اختلاط جزئی استفاده شده است و نشان داده شده که استفاده از شبکه‌ی نسبتاً ریز نتایج قابل قبولی به دست می‌دهد. نتایج به دست آمده از طول نفوذ اسپری غیرواکنشی در محیط گازی و همچنین پروفیل سرعت فاز گاز در مرحله‌ی مکش جریان هوا به درون سیلندر در موتور دیزل به منظور اعتبارسنجی عملکرد کد حاضر در جریان تک فازی و دوفازی با داده‌های تجربی مقایسه گردیده است که نسبت به داده‌های تجربی دارای تطابق نسبتاً خوبی می‌باشد، به طوری که با مقایسه‌ی نتایج با داده‌های تجربی می توان نتیجه گرفت که نتایج شبیه سازی گردابه‌های بزرگ با شبکه‌ی ریز در جریان مغشوش غیر واکنشی از نتایج رنس بهتر است. نتایج احتراق اسپری دیزل با دو روش شبیه سازی گردابه‌های بزرگ و رنس نیز با استفاده از سینتیک تک مرحله ای با نتایج تجربی گروه آزمایشگاهی سندیا مقایسه گردیده است. مشخصات کلی جریان واکنشی مغشوش اعم از طول نفوذ اسپری سوخت و بخار آن با استفاده از هر دو روش اغتشاشی به‌خوبی پیش بینی می‌شود. با مقایسه‌ی شکل شعله با استفاده از دو روش اغتشاشی تفاوت‌های اندکی می‌توان مشاهده نمود، ولی مقدار کمینه و بیشین هی دما در هر دو یکسان است.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Numerical Study of Turbulence in Diesel Spray Combustion Using Large Eddy Simulation

نویسندگان [English]

  • M.R. Keshtkar
  • H. Khaleghi
  • S. Yazdanparast
  • M. Khoramdel
Department of Mechanical Engineering, Tarbiat Modares University, Tehran, Iran
چکیده [English]

Under modern direct injection diesel engine conditions, the spray and combustion processes are known to be controlled by mixing. In large eddy simulation method, large eddies are solved directly and small scales are modeled, so it can potentially improve the predictive capability by better capturing the large-scale mixing of ambient air with the fuel vapor. In this paper, turbulent spray combustion is studied using the large eddy simulation method together with partially stirred reactor model using EPISO- SPRAY code. To develop this code, large eddy simulation method is applied in an Eulerian – Lagranian approach in which conservation equations of both phases are solved and then results of large eddy simulation are compared with those of Reynolds averaged of Navier-Stocks. Simulation of spray combustion using different sub-grid scale models of large eddy simulation method (Simple Smagorinesky and dynamic Smagorinesky) with partially stirred reactor combustion model are presented here. It is shown that with a fine mesh, results are in good agreement with experimental data. Results of non-reacting spray penetration length in gas environment and velocity profile during the intake stage are compared with related experimental data in order to validate the EPISO-SPRAY code performance. It is proved in this study that large eddy simulation results with relative fine mesh are much better than the Reynolds-averaged Navier–Stokes equations results. Results of reacting liquid spray using simple step kinetic and fuel vapor penetration length are compared with experimental data. It is shown that overall characteristics of diesel spray combustion such as liquid spray penetration and fuel vapor penetration are both in good agreement with experimental data using Reynolds-averaged Navier– Stokes equations or large eddy simulation models. Although small differences in the flame shape are seen with the two methods, maximum and minimum temperatures are predicted to be the same in both models.

کلیدواژه‌ها [English]

  • Turbulence
  • Diesel Spray combustion
  • Large Eddy Simulation
  • Reynolds averaged of Navier-Stocks equations
  • Diesel Engine
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