Fuel and Combustion

Fuel and Combustion

Scalable Design of Flameless Combustion Furnaces Based on Dimensionless Groups and Three-Dimensional Numerical Analysis for Preserving the Distributed Reaction Regime

Document Type : Original Article

Authors
Mohamad-Amin Zamani
Alireza Asgharzadeh Karamshahlu
Mohammad Hassan Saidi
Department of Mechanical Engineering, Sharif University of Technology،Iran،Tehran
10.22034/jfnc.2026.562641.1450
Abstract
IIn this study, a new unified framework for scaling flameless combustion furnaces is developed based on π-Buckingham dimensional analysis and an integrated energy–exergy evaluation. The objective of the framework is to preserve the distributed reaction regime during the scale-up from a 10 kW laboratory furnace to a 10 MW industrial system. Accordingly, a set of geometric, flow, heat-transfer, and reaction-kinetics parameters is selected, and six independent dimensionless groups are derived. Three-dimensional CFD simulations employing the EDC combustion model, the GRI-Mech 3.0 mechanism, and the DO radiation model indicate that the proposed scaling method can reproduce the peak temperature with only a 1.7% deviation and the mean temperature with 1.8% deviation. Furthermore, CO emissions decrease from 64 to 41 mg/kJ and NO emissions from 53 to 27 mg/kJ in the scaled-up configuration. Analysis of Ret and Da confirms that this method provides the closest match in reproducing turbulence-chemistry interaction. Energy and exergy assessments also show that the efficiencies remain nearly unchanged between the laboratory and industrial scales. Overall, the results demonstrate that the proposed framework offers a reliable approach for designing low-emission and thermally stable industrial furnaces operating in the flameless combustion regime.

Highlights

A physics-based, dimensionless scaling framework was developed to scale flameless combustion furnaces from laboratory to industrial conditions. By selecting the dominant variables and deriving six independent dimensionless groups, the method inherently preserves the requirements for regime stability. Comparative assessments of temperature fields, pollutant distributions (CO/NO), streamlines, internal flue-gas recirculation (FGR), turbulence-chemistry indicators (Ret, Da), and energy/exergy efficiencies confirm successful regime preservation during scale-up. The scaled furnace shows improved thermal uniformity, predicts mean and peak temperatures with less than 2% deviation, keeps CO and NO within EPA limits, increases internal FGR by more than  6 times, and yields a 36% reduction in reaction-zone thickness while maintaining first and second-law efficiencies.

The framework’s performance is mainly attributed to preserving nozzle geometry and velocity profiles, which sustain effective mixing and distributed heat release, and to reproducing turbulence-chemistry similarity via the closest match in Ret×Da relative to the laboratory reference. Overall, stable flameless scale-up depends on: (i) sufficient FGR through appropriate diameter-to-length similarity (residence time/recirculation), (ii) maintaining Ret and Da within stable ranges to balance mixing and kinetics, and (iii) ensuring thermal uniformity to suppress localized flame fronts. Unlike empirical scale-up approaches, the proposed method preserves these constraints intrinsically, providing a reliable design tool for low-emission, stable industrial flameless furnaces

Keywords
Combustion scaling
Flameless combustion
Dimensional analysis
Energy&‌‌‌‌‌ndash
exergy analysis
Flue gas recirculation
Subjects

در این مطالعه، یک چارچوب نوآورانه و مبتنی بر اصول فیزیکی برای مقیاس‌گذاری کوره‌های احتراق بدون شعله از مقیاس آزمایشگاهی به مقیاس صنعتی ارائه شد. این چارچوب با تعریف مجموعه‌ای از متغیرهای کلیدی و استخراج شش عدد بدون‌بُعد مستقل توانست شرایط لازم برای حفظ رژیم احتراق توزیع‌شده را در ابعاد مختلف تضمین کند. به طور خلاصه، تحلیل مقایسه‌ای میدان دما، توزیع آلاینده‌ها، الگوهای خطوط جریان، پروفایل‌های بازچرخانی داخلی، اعداد رینولدز توربولانسی و دامکوهلر و همچنین بازده‌های انرژی-اگزرژی در روش‌ مقیاس‌گذاری ارائه‌شده نشان می‌دهد که این روش قادر است ضمن اینکه رژیم احتراق بدون شعله را در گذار از مقیاس آزمایشگاهی به مقیاس صنعتی با موفقیت حفظ کند، یکنواختی دما را بهبود بخشیده، توزیع دمای میانگین و بیشینه را با اختلاف کمتر از 2% پیش‌بینی نموده، انتشار CO و NO را در محدوده مجاز استاندارد آلایندگی EPA به حداقل رسانده و شدت بازچرخانی داخلی گازهای احتراق (FGR) را بیش از شش برابر افزایش می‌دهد. همچنین کاهش 36% در ضخامت ناحیه واکنش و حفظ بازده قانون اول و دوم ترمودینامیک، عملکرد برتر این روش در مقیاس‌گذاری را اعتبارسنجی می‌کند. این برتری عمدتاً ناشی از حفظ مطلوب پروفایل‌های سرعت و هندسه نازل در این روش است که در کنار یکدیگر، اختلاط مؤثر سوخت و هوا و آزادسازی حرارت را به‌صورت توزیع‌شده تضمین می‌کند. علاوه بر این، ارزیابی اعداد رینولدز توربولانسی و دامکوهلر تأیید می‌کند که روش مقیاس‌گذاری ارائه شده به نزدیک‌ترین مقدار Ret×Da در کوره آزمایشگاهی دست می‌یابد و بدین ترتیب تعادل صحیح میان مقیاس‌های زمانی اختلاط و شیمیایی را بازتولید می‌کند. این یافته‌ها تأیید می‌کنند که روش‌ مقیاس‌گذاری مبتنی بر تحلیل بدون بُعد، در ترکیب با طراحی آگاهانه ساختارهای جریان و بازچرخانی، برای دستیابی به پایداری رژیم در سامانه‌های احتراق بدون شعله، ضروری است. به طور کلی، نتایج نشان می‌دهند که حفظ احتراق بدون شعله در فرایند مقیاس‌گذاری به طور حیاتی به سه عامل کلیدی بستگی دارد:

1.         دستیابی به FGR کافی از طریق تناسب قطر به طول و بدین ترتیب حفظ زمان ماند و افزایش شدت بازچرخانی.

2.         حفظ اعداد رینولدز توربولانسی و دامکوهلر در محدوده‌های پایدار برای ایجاد تعادل در برهم‌کنش‌های آشفتگی-شیمی.

3.         تضمین یکنواختی حرارتی برای مهار ایجاد گرادیان در جبهه‌های موضعی شعله.

در حالی که روش‌های تجربی مرسوم اغلب این پارامترها را نادیده می‌گیرند، چارچوب پیشنهادی به طور ذاتی آن‌ها را حفظ کرده که عملکرد برتر این روش را توضیح می‌دهد. در مجموع، چارچوب ارائه‌شده ابزاری قدرتمند و قابل‌اتکا برای طراحی و توسعه کوره‌های صنعتی کم‌آلاینده و پایدار در رژیم احتراق بدون شعله بوده و می‌تواند پایه‌ای برای گسترش فناوری‌های پاک و کارآمد در کاربردهای صنعتی آینده فراهم آورد.

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