انجمن احتراق ایران سوخت و احتراق 2008-3629 18 4 2025 12 22 Numerical investigation of the effects of cavity flameholder geometric parameters on the combustion performance of ramjet and scramjet engines بررسی عددی اثر پارامترهای هندسی شعله‌نگه‌دار حفره‌ای بر عملکرد احتراقی موتورهای رم‌جت و اسکرَم‌جت 1 17 242580 10.22034/jfnc.2026.566615.1453 FA میلاد مهرپویا گروه منهدسی مکانیک، دانشکده مهندسی، دانشگاه فردوسی مشهد، مشهد 0009-0008-4316-0836 سجاد راستگو کروه مهندسی مکانیک، دانشکده مهندسی، دانشگاه فردوسی مشهد، مشهد جواد سپاهی یونسی گروه مهندسی مکانیک، دانشکده مهندسی، دانشگاه فردوسی مشهد، مشهد 0000-0002-8803-1068 Journal Article 2025 10 12 In ramjet and scramjet engines, due to the very high velocity of the incoming flow into the combustion chamber, efficiency and effective fuel–air mixing face significant challenges. One efficient method to increase fuel residence time and create a suitable recirculation zone for stable combustion is the use of cavity flameholders. Despite the widespread application of this method, the effect of cavity geometry on combustion performance in both ramjet and scramjet engines, especially under heated conditions, still requires comprehensive investigation. The aim of this study is to numerically investigate the effect of cavity geometric parameters—including height, length, and ramp angle—on combustion efficiency in both ramjet and scramjet engines. For this purpose, simulations were performed using ANSYS Fluent with the SST k–ω turbulence model in a compressible, hydrogen-fueled combustion configuration. The results indicate that increasing the cavity height in both engines improves combustion efficiency. Reducing the cavity length can also enhance combustion efficiency in both engines. These findings can serve as a basis for optimizing flameholder geometry in future supersonic engines. در موتورهای رم‌جت و اسکرَم‌جت، به دلیل سرعت بسیار بالای جریان ورودی به محفظه احتراق، پایداری شعله و اختلاط مؤثر سوخت و هوا با چالش جدی روبه‌رو است. یکی از روش‌های کارآمد برای افزایش زمان ماند سوخت و ایجاد ناحیه بازچرخشی مناسب جهت افزایش بازده احتراق، استفاده از شعله‌نگه‌دارهای حفره‌ای است. باوجود کاربرد گسترده این روش، تأثیر هندسه حفره بر عملکرد احتراق در هر دو موتور رم‌جت و اسکرَم‌جت، به‌ویژه در شرایط گرم، هنوز نیازمند بررسی جامع است. هدف این پژوهش، مطالعه عددی اثر پارامترهای هندسی حفره شامل ارتفاع، طول و زاویه سطح شیب‌دار انتهایی بر بازده احتراق در دو موتور رم‌جت و اسکرَم‌جت است. برای این منظور، شبیه‌سازی‌ها با استفاده از نرم‌افزار ANSYS Fluent و مدل آشفتگی SST k–ω به‌صورت تراکم‌پذیر، در حالت گرم و با سوخت هیدروژن انجام شده است. نتایج نشان می‌دهد افزایش ارتفاع حفره در هر دو موتور موجب بهبود بازده احتراق می‌شود. کاهش طول حفره نیز می‌تواند بازده احتراق را در هر دو موتور افزایش دهد. این یافته‌ها می‌توانند مبنایی برای بهینه‌سازی هندسه شعله‌نگه‌دار در موتورهای فراصوتی آینده باشند.

https://www.jfnc.ir/article_242580_b2d6b60e3181079bc8b18b4122015525.pdf

انجمن احتراق ایران سوخت و احتراق 2008-3629 18 4 2025 12 22 Numerical Simulation of the Effects of Inlet Shape on the Combustion Chamber Performance of a Hypersonic Projectile شبیه سازی عددی اثرات شکل ورودی هوا در عملکرد محفظه احتراق یک پرتابه مافوق صوت 18 49 242581 10.22034/jfnc.2026.549461.1444 FA مصطفی محمودی گروه جلوبرنده- دانشگاه مالک اشتر 0009-0000-1754-3966 محسن شجاعی دانشگاه مالک اشتر افشین ولی محمد دانشگاه مالک اشتر Journal Article 2025 10 12 In this study, an air intake was designed for the combustion chamber of a supersonic projectile operating at flight conditions of Mach 3.4 and an altitude of 15 km. Initially, a three-dimensional design methodology for the supersonic air intake is presented. Subsequently, the designed intake was integrated with the combustion chamber, and its performance was evaluated. To ensure the accuracy of the analyses, the simulation process was validated against the results of an existing combustion chamber. The results indicate that the air intake’s performance closely aligns with the calculated theoretical values. The maximum error observed was 6.25%, corresponding to the Mach number at the first section of the intake. The obtained total pressure recovery factor also showed a 2.43% difference compared to the calculated values. The performance of the combustion chamber, using the airflow supplied by the intake, was examined, yielding a combustion temperature of 1298 K and a combustion efficiency of 83.5%. Furthermore, the distance between the air inlet and the fuel injection point was reduced to investigate its effect on combustion. It was determined that at a distance-to-diameter ratio of 1, the combustion efficiency increased by 3.9%. در این پژوهش برای محفظه احتراق یک پرتابه مافوق صوت یک ورودی هوا در شرایط پروازی عدد ماخ 3/4 و ارتفاع پروازی 15 کیلومتر طراحی شده است. در ابتدا یک روش طراحی برای ورودی هوای مافوق صوت به صورت سه بعدی ارائه شده است. در ادامه ورودی هوای طراحی شده به محفظه احتراق متصل شده و عملکرد آن بررسی شده است. به منظور اطمینان از صحت تحلیل‌های انجام شده، روند تحلیل با نتایج یک محفظه احتراق موجود، اعتبارسنجی شد. در ادامه هندسه یکپارچه شده شبکه‌بندی و تحلیل شد. بر اساس نتایج عملکرد ورودی هوا به مقادیر اشاره شده در نتایج محاسبه شده، نزدیک است. بیشترین مقدار خطا به میزان 6/25 درصد، مربوط به عدد ماخ مقطع اول ورودی هوا است. مقدار ضریب بازیابی فشار بدست آمده نیز در مقایسه با مقادیر محاسبه شده، 2/43 خطا دارد. عملکرد محفظه احتراق در مواجهه با هوای دریافتی از ورودی هوا مورد بررسی قرار گرفت که مقدار دمای احتراق 1298 کلوین و بازده احتراق نیز 83/5 درصد محاسبه شد. در ادامه فاصله محل پاشش سوخت و ورودی هوا کاهش یافت تا تأثیر آن بر احتراق بررسی شود که مشخص شد در نسبت فاصله 1 برابر قطر، راندمان احتراق 3/9 درصد افزایش داشته است.

https://www.jfnc.ir/article_242581_cf19cd8b7fd139adc570d505773a1d1d.pdf

انجمن احتراق ایران سوخت و احتراق 2008-3629 18 4 2025 12 22 Analysis and measurement of performance parameters of combustion by adding chamber to a double swirl burner اندازه‌گیری و تحلیل پارامترهای عملکردی احتراق با افزودن محفظه به یک مشعل دوپیچشی 50 80 243197 10.22034/jfnc.2026.564242.1452 FA علی اسدی فرد دانشگاه صنعتی امیرکبیر دانشکده مهندسی هوافضا،تهران، ایران 0009-0008-0406-1501 صادق تابع جماعت دانشگاه صنعتی امیرکبیر دانشکده مهندسی هوافضا،تهران،ایران 0000-0003-0882-9289 عباس زندی لک دانشگاه صنعتی امیرکبیر دانشکده مهندسی هوافضا،تهران،ایران 0009-0005-8471-619X بهراد کریمی دانشگاه صنعتی امیرکبیر دانشکده مهندسی هوافضا، تهران، ایران Journal Article 2025 11 11 Double swirl burners are an advanced type of burner designed to improve combustion and increase flame stability. The burner used consists of two separate swirling air streams. In this paper, various experiments were performed on the burner. Subsequently, the results obtained from the experiments were repeated with a combustion chamber installed around the burner to analyze and investigate the changes that occurred. Key variables include the equivalence ratio, inner swirl number, outer swirl number, and flow split ratio. Double swirl burners are a type of advanced burner designed to improve combustion and increase flame stability and efficiency. The burner used in current consists of two separate swirling air streams. Various experiments have been performed and the results obtained from the tests have been repeated in the case of installing a chamber on the burner to analyze and examine the changes that have occurred. The basic variables include the equivalence ratio, inner swirl number, outer swirl number and flow split ratio. Tests conducted in both cases without a chamber and with a chamber indicate that adding a chamber generally limits the stability of the burner and in some cases results in a longer flame length. In addition, the results show that adding a chamber in some places causes the lean blowout limit to extend to lower equivalence ratios. It is also shown that in certain conditions, increasing the outer flow split ratio leads to a shorter flame length and an increase in flame width; both effects were simultaneously observed in the flame area as well. In addition, at the points that were performed for both configuration (with and without the chamber), with a certain confinement ratio, the flame liftoff height did not change. مشعل‌های دوپیچشی، نوعی مشعل پیشرفته هستند که برای بهبود احتراق و افزایش پایداری و کارایی شعله طراحی شده‌اند. مشعل استفاده ‌شده در این پژوهش، از دو جریان هوای پیچشی مجزا تشکیل شده ‌‌است. آزمایش‌های مختلف بر روی این مشعل، انجام شده است، سپس نتایج به‌دست‌آمده از آزمایش‌ها در حالت تعبیه محفظه روی مشعل نیز تکرار شده است تا تغییرات به وجود آمده مورد تحلیل و بررسی قرار گیرد. متغیرهای اساسی شامل نسبت هم ارزی، عدد پیچش داخلی، عدد پیچش خارجی و نسبت تقسیم جریان است. آزمایش‌های انجام شده در هر دو حالت بدون محفظه و با محفظه حاکی از آن است که افزودن محفظه پایداری مشعل را در حالت کلی محدودتر کرده و در بعضی موارد باعث کشیده‌تر شدن طول شعله می‌شود. ضمناً نتایج نشان می‌دهد که افزودن محفظه در برخی نقاط موجب می‌شود که محدوده خاموشی رقیق به مقادیر نسبت‌هم‌ارزی کمتر توسعه پیدا کند. همچنین در شرایط خاصی نشان داده می‌شود که افزایش نسبت تقسیم خارجی باعث می‌شود که طول شعله کمتر شود و عرض شعله افزایش می‌یابد و هم‌زمان این دو اثر در مساحت شعله نیز دیده‌ شده است. ضمنا در نقاطی که برای هر دو حالت بامحفظه و بدون محفظه انجام شد، با نسبت محصورسازی مشخص، ارتفاع بلندشدگی شعله تغییری نکرد.

https://www.jfnc.ir/article_243197_2a30855c69a104f06d3ec40cbb0f52dd.pdf

انجمن احتراق ایران سوخت و احتراق 2008-3629 18 4 2025 12 22 Development of a Rapid-Response Code Based on a Chemical Reactor Network for the Analysis of a Turbine Combustor توسعه کد پاسخ سریع مبتنی بر شبکه رآکتور شیمیایی و تحلیل محفظه احتراق توربینی 81 102 245174 10.22034/jfnc.2026.559273.1446 FA امیررضا احمدی تنکابنی ایران، تهران، دانشگاه تهران، دانشکدگان علوم و فناوری‌های میان‌رشته‌ای، دانشکده مهندسی هوافضا مسعود عیدی عطارزاده ایران، تهران، دانشگاه تهران، دانشکدگان علوم و فناوری‌های میان‌رشته‌ای، دانشکده مهندسی هوافضا Journal Article 2025 11 25 The gas turbine combustion chamber, as one of the key components, has been extensively studied. The temperature distribution in the combustion chamber is of great importance because it can not only lead to changes in the composition of exhaust gases but also cause significant damage to the chamber walls or turbine blades. Among the methods for investigating combustion chambers, analytical methods, with appropriate accuracy and high simplicity and computational speed, can provide an effective assessment of combustion chamber performance. In this research, the distribution of inlet air to a laboratory-scale cylindrical combustion chamber was initially investigated and validated using a one-dimensional code developed in the MATLAB environment. Subsequently, combustion and temperature distributions along the chamber were simulated and validated using the CANTERA software through a Chemical Reactor Network (CRN). Following this, the sensitivity of control parameters such as the number of reactors, the initial reactor temperature, and the number of time steps in the chamber was investigated. The results showed that increasing the number of reactors up to 50, although providing a more detailed temperature distribution along the combustion chamber, did not improve solution accuracy and even led to computational errors due to an excessive reduction in reactor size. Varying the initial temperature up to 2300 K had no noticeable effect on solution accuracy. In addition, a 50 fold increase in the number of time steps from 100 to 5000 showed no improvement in solution accuracy but resulted in an approximately twofold increase in computational time. محفظه احتراق توربین گاز به‌عنوان یکی از اجزا اصلی همواره مورد مطالعه و بررسی بوده است. توزیع دما در محفظه احتراق از آن جهت دارای اهمیت است که نهتنها میتواند منجر به تغییر ترکیب گازهای خروجی شود بلکه با آسیب به دیواره و یا پره های توربین خسارت زیادی به بار آورد. در میان روش های بررسی محفظه احتراق، روش تحلیلی بادقت مناسب و سهولت و سرعت بالا میتواند پاسخ مناسبی از عملکرد محفظه احتراق ارائه دهد. در این پژوهش در ابتدا توزیع هوای ورودی به محفظه احتراق استوانه‌ای آزمایشگاهی، توسط کد یک‌بعدی توسعه‌یافته بر بستر برنامه MATLAB مورد بررسی و اعتبارسنجی قرار گرفته است. سپس احتراق و توزیع دما در راستای محفظه توسط برنامه CANTERA و به‌وسیله شبکه رآکتورهای شیمیایی (CRN) حل شده و اعتبارسنجی شده است. در ادامه حساسیت پارامترهای کنترلی نظیر تعداد رآکتورها، دمای اولیه رآکتور، تعداد گام زمانی محفظه مورد بررسی قرار گرفت که نشان داد افزایش تعداد رآکتور تا 50 عدد اگر چه توزیع دمای بیشتری در راستای محفظه احتراق نشان می دهد، اما در دقت حل بی تأثیر بوده و حتی با کوچک شدن بیش از حد رآکتور باعث خطای محاسباتی می‌شود. تغییر دمای اولیه تا 2300 کلوین در دقت حل موثر نبود. همچنین افزایش 50 برابری گام زمانی از 100 تا 5000 گام تأثیری در دقت حل نشان نداد اما منجر به با افزایش 2 برابری، زمان پاسخ‌گویی برنامه شد.

https://www.jfnc.ir/article_245174_269b4f70a39a338c4b3fa768c148738a.pdf

انجمن احتراق ایران سوخت و احتراق 2008-3629 18 4 2025 12 22 Experimental Evaluation of Burner Geometry Performance and its flame structure on Heating Rate of a MILD Steel Reheating Furnace ارزیابی تجربی عملکرد هندسه مشعل و ساختار شعله آن در سرعت گرمایش کوره احتراق بدون شعله گرمایش قطعات فولادی 103 123 246841 10.22034/jfnc.2026.579786.1457 FA علی عاشوری دانشکده مهنسدی مکانیک - دانشگاه تربیت مدرس 0000-0003-3138-5874 سروش صرافان صادقی دانشکده مهندسی مکانیک - دانشگاه تربیت مدرس 0009-0008-0010-3794 محمد ضابطیان طرقی تربیت مدرس مهندسی مکانیک 0000-0001-5622-2639 Journal Article 2025 11 27 MILD combustion has emerged as a promising technology for achieving uniform temperature distribution, reduced pollutant formation, and improved thermal efficiency in industrial reheating furnaces. However, the performance of different burner geometries under MILD conditions—particularly in full-scale steel‑heating scenarios—has not been adequately characterized. In this study, the thermal behavior of three burner configurations, namely a co‑flow axial burner, a swirl burner, and a perforated lining burner, was experimentally investigated in a laboratory-scale MILD furnace developed at Tarbiat Modares University. The primary objective was to Steel reheating furnaces are critical in metallurgical industries for preparing billets or slabs prior to hot forming. Conventional combustion systems in these furnaces often create large temperature gradients and emit high levels of nitrogen oxides (NOₓ). Flameless oxidation, also known as Moderate or Intense Low‑oxygen Dilution (MILD) combustion, has emerged as a promising alternative. By strongly diluting fuel and oxidizer with recirculated combustion products before ignition, MILD combustion suppresses visible flame formation, reduces peak temperatures, and promotes a more uniform thermal field within the furnace volume. Despite these advantages, the performance of MILD combustion systems is highly sensitive to burner geometry and the resulting mixing characteristics of fuel and oxidizer streams. Different burner configurations can produce distinct flow structures, internal recirculation rates, and temperature distributions. Therefore, systematic experimental evaluation of burner designs is essential for optimizing industrial reheating furnaces operating under MILD conditions. The present work addresses this need by experimentally comparing three burner types—co‑flow axial, swirl, and perforated lining—in a purpose‑built laboratory‑scale MILD furnace. The study focuses on both heating rate and flame stability, providing practical insights for burner selection in steel reheating applications. Methodology Laboratory‑Scale MILD Furnace Experiments were conducted in a laboratory‑scale flameless oxidation furnace designed and constructed at the National Combustion Laboratory of Tarbiat Modares University. The furnace was scaled down from a 7 MW industrial steel reheating furnace using the constant residence time (CRT) scaling method, resulting in a 10 kW laboratory model. Key dimensions of the scaled furnace are 919 mm (length) × 513 mm (width) × 293 mm (height). The furnace walls and roof were insulated with multi‑layer refractory materials (cordierite‑mullite, lightweight firebrick, and perlite) to maintain external surface temperatures below 80 °C during operation up to 1600 °C. Burner Configurations Three distinct burner geometries were fabricated and tested: · Co‑flow axial burner: A 1‑inch diameter burner with an axially adjustable fuel tube. The fuel nozzle could be positioned upstream or downstream of the air exit to control premixing and flame stability. Optimal stability was achieved with the fuel tube retracted by 2.5 cm relative to the air outlet. · Swirl burner: A 1‑inch burner featuring a helical swirler (4 cm pitch) along the fuel tube. Air flowing over this spiral acquires a tangential velocity component, inducing a swirling motion at approximately 45° relative to the burner axis. This enhances mixing, flame volume, and stability. · Perforated lining burner: A 1‑inch burner consisting of a perforated inner tube (½‑inch, 16 holes of 3 mm diameter) enclosed within a perforated outer casing (1‑inch, holes of ~1.5 mm, porosity ≈ 0.26). The design promotes distributed, multi‑point injection for uniform heating and increased power capacity (up to 30 kW). Instrumentation and Procedure Each burner was installed separately in the furnace, and tests were performed under comparable firing rates and air preheating conditions. Fuel (natural gas) and air flow rates were controlled via calibrated rotameters and pressure regulators. Temperatures were measured using S‑type thermocouples (for high‑temperature regions up to 1600 °C) and J‑type thermocouples (for stack and lower‑temperature zones). Thermocouples were arranged in a 9‑column, 3‑row grid on the sidewall to capture spatial temperature distributions. A CCD camera recorded flame behavior, and RGB image analysis was employed to assess flame uniformity and thermal structure. Results and Discussion Flame Structure and Stability The co‑flow axial burner produced a long, narrow flame (≈35 cm) with relatively low momentum. The flame exhibited sensitivity to hot gas recirculation from the furnace rear wall, leading to intermittent instabilities. Due to insufficient mixing at an equivalence ratio of ~1.1, unburned gases were observed in the furnace. In contrast, the swirl burner generated a voluminous, helical flame (≈40 cm) with significantly enhanced mixing and momentum. The swirling motion stabilized the flame, prevented lift‑off, and improved heat transfer to the furnace walls. However, increased turbulence led to moderate flame oscillations over time. The perforated lining burner, when operated at 18.4 kW, produced a uniform, continuous flame sheet across its surface. During initial startup, distinct flame plumes were visible, but as the burner body heated up, the plumes diminished, and combustion transitioned toward a distributed, nearly flameless regime—characteristic of high‑temperature air combustion (HiCOT). Unfortunately, prolonged exposure to high temperatures caused severe surface oxidation and eventual localized fracture of the burner tube, as shown in Figure 12 of the full manuscript. Thermal Performance and Heating Rate Figure 14 of the original study illustrates the temporal response of furnace roof temperature for each burner: · The co‑flow axial burner (10 kW) required approximately 450 minutes (7.5 hours) to reach 500 °C and exhibited no further temperature increase, indicating limited thermal capacity. · The perforated lining burner (18.4 kW) rapidly heated the furnace, reaching 550 °C in just 150 minutes (2 hours 33 minutes). However, the test was terminated prematurely due to burner structural failure. · The swirl burner (10 kW) achieved 550 °C after approximately 7 hours and surpassed 600 °C after 10 hours, with a continuing upward trend. This demonstrates reliable and sustained heating capability. Stack gas temperature measurements (Figure 15) corroborated these trends: the swirl burner achieved the highest exhaust temperature (~213 °C) with an ongoing rising trend, whereas the co‑flow burner plateaued at lower values. RGB Image Analysis RGB intensity scatter plots (Figure 13) provided quantitative insight into flame uniformity. The co‑flow burner displayed the most concentrated and consistent color distribution, suggesting a homogeneous thermal field at the captured moment, though long‑term stability remained problematic. The swirl burner showed increased scatter—particularly in the blue channel—indicating the presence of turbulent, multi‑temperature zones. The perforated lining burner exhibited the widest dispersion, reflecting significant local temperature fluctuations inherent to its multi‑jet design. Conclusions This experimental investigation compared the performance of co‑flow axial, swirl, and perforated lining burners in a laboratory‑scale MILD furnace for steel reheating. The following conclusions are drawn: · Co‑flow axial burner: Produces an elongated flame but suffers from low momentum and instability when exposed to recirculating hot gases. Its heating capacity is insufficient for reaching target temperatures within a reasonable timeframe. · Perforated lining burner: Offers the fastest heating rate, achieving 550 °C in 2 hours 33 minutes. However, severe oxidation and structural failure at elevated temperatures render it unsuitable for long‑term industrial use without expensive alloy upgrades. · Swirl burner: Provides the most stable and uniform heating performance. Although its heating rate is slower than that of the linear burner, it reliably attains and exceeds 600 °C without structural degradation. Scaling this design to larger diameters (e.g., 1.5–2 inches) could further improve heating rate while maintaining stability. Overall, the swirl burner emerges as the most practical and robust option for industrial MILD furnaces, balancing thermal uniformity, operational safety, and long‑term durability. The findings underscore the critical influence of burner geometry on furnace startup time and temperature distribution, offering valuable guidance for optimizing burner selection in steel reheating applications. Author Contributions Ali Ashouri: Conceptualization, Methodology, Investigation, Formal analysis, Writing – original draft, Writing – review & editing, Visualization, Project administration. Soroush Sarrafan Sadeghi: Investigation, Formal analysis, Data curation, Writing – review & editing, Visualization. Mohammad Zabetian Targhi: Supervision, Conceptualization, Resources, Writing – review & editing, Funding acquisition. Funding This research received no specific grant from any funding agency in the public, commercial, or not‑for‑profit sectors. The study was conducted entirely at Tarbiat Modares University, Tehran, Iran, using the facilities of the National Combustion Laboratory. Conflict of Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Steel reheating furnaces are critical in metallurgical industries for preparing billets or slabs prior to hot forming. Conventional combustion systems in these furnaces often create large temperature gradients and emit high levels of nitrogen oxides (NOₓ). Flameless oxidation, also known as Moderate or Intense Low‑oxygen Dilution (MILD) combustion, has emerged as a promising alternative. By strongly diluting fuel and oxidizer with recirculated combustion products before ignition, MILD combustion suppresses visible flame formation, reduces peak temperatures, and promotes a more uniform thermal field within the furnace volume. Despite these advantages, the performance of MILD combustion systems is highly sensitive to burner geometry and the resulting mixing characteristics of fuel and oxidizer streams. Different burner configurations can produce distinct flow structures, internal recirculation rates, and temperature distributions. Therefore, systematic experimental evaluation of burner designs is essential for optimizing industrial reheating furnaces operating under MILD conditions. The present work addresses this need by experimentally comparing three burner types—co‑flow axial, swirl, and perforated lining—in a purpose‑built laboratory‑scale MILD furnace. The study focuses on both heating rate and flame stability, providing practical insights for burner selection in steel reheating applications. Methodology Laboratory‑Scale MILD Furnace Experiments were conducted in a laboratory‑scale flameless oxidation furnace designed and constructed at the National Combustion Laboratory of Tarbiat Modares University. The furnace was scaled down from a 7 MW industrial steel reheating furnace using the constant residence time (CRT) scaling method, resulting in a 10 kW laboratory model. Key dimensions of the scaled furnace are 919 mm (length) × 513 mm (width) × 293 mm (height). The furnace walls and roof were insulated with multi‑layer refractory materials (cordierite‑mullite, lightweight firebrick, and perlite) to maintain external surface temperatures below 80 °C during operation up to 1600 °C. Burner Configurations Three distinct burner geometries were fabricated and tested: · Co‑flow axial burner: A 1‑inch diameter burner with an axially adjustable fuel tube. The fuel nozzle could be positioned upstream or downstream of the air exit to control premixing and flame stability. Optimal stability was achieved with the fuel tube retracted by 2.5 cm relative to the air outlet. · Swirl burner: A 1‑inch burner featuring a helical swirler (4 cm pitch) along the fuel tube. Air flowing over this spiral acquires a tangential velocity component, inducing a swirling motion at approximately 45° relative to the burner axis. This enhances mixing, flame volume, and stability. · Perforated lining burner: A 1‑inch burner consisting of a perforated inner tube (½‑inch, 16 holes of 3 mm diameter) enclosed within a perforated outer casing (1‑inch, holes of ~1.5 mm, porosity ≈ 0.26). The design promotes distributed, multi‑point injection for uniform heating and increased power capacity (up to 30 kW). Instrumentation and Procedure Each burner was installed separately in the furnace, and tests were performed under comparable firing rates and air preheating conditions. Fuel (natural gas) and air flow rates were controlled via calibrated rotameters and pressure regulators. Temperatures were measured using S‑type thermocouples (for high‑temperature regions up to 1600 °C) and J‑type thermocouples (for stack and lower‑temperature zones). Thermocouples were arranged in a 9‑column, 3‑row grid on the sidewall to capture spatial temperature distributions. A CCD camera recorded flame behavior, and RGB image analysis was employed to assess flame uniformity and thermal structure. Results and Discussion Flame Structure and Stability The co‑flow axial burner produced a long, narrow flame (≈35 cm) with relatively low momentum. The flame exhibited sensitivity to hot gas recirculation from the furnace rear wall, leading to intermittent instabilities. Due to insufficient mixing at an equivalence ratio of ~1.1, unburned gases were observed in the furnace. In contrast, the swirl burner generated a voluminous, helical flame (≈40 cm) with significantly enhanced mixing and momentum. The swirling motion stabilized the flame, prevented lift‑off, and improved heat transfer to the furnace walls. However, increased turbulence led to moderate flame oscillations over time. The perforated lining burner, when operated at 18.4 kW, produced a uniform, continuous flame sheet across its surface. During initial startup, distinct flame plumes were visible, but as the burner body heated up, the plumes diminished, and combustion transitioned toward a distributed, nearly flameless regime—characteristic of high‑temperature air combustion (HiCOT). Unfortunately, prolonged exposure to high temperatures caused severe surface oxidation and eventual localized fracture of the burner tube, as shown in Figure 12 of the full manuscript. Thermal Performance and Heating Rate Figure 14 of the original study illustrates the temporal response of furnace roof temperature for each burner: · The co‑flow axial burner (10 kW) required approximately 450 minutes (7.5 hours) to reach 500 °C and exhibited no further temperature increase, indicating limited thermal capacity. · The perforated lining burner (18.4 kW) rapidly heated the furnace, reaching 550 °C in just 150 minutes (2 hours 33 minutes). However, the test was terminated prematurely due to burner structural failure. · The swirl burner (10 kW) achieved 550 °C after approximately 7 hours and surpassed 600 °C after 10 hours, with a continuing upward trend. This demonstrates reliable and sustained heating capability. Stack gas temperature measurements (Figure 15) corroborated these trends: the swirl burner achieved the highest exhaust temperature (~213 °C) with an ongoing rising trend, whereas the co‑flow burner plateaued at lower values. RGB Image Analysis RGB intensity scatter plots (Figure 13) provided quantitative insight into flame uniformity. The co‑flow burner displayed the most concentrated and consistent color distribution, suggesting a homogeneous thermal field at the captured moment, though long‑term stability remained problematic. The swirl burner showed increased scatter—particularly in the blue channel—indicating the presence of turbulent, multi‑temperature zones. The perforated lining burner exhibited the widest dispersion, reflecting significant local temperature fluctuations inherent to its multi‑jet design. Conclusions This experimental investigation compared the performance of co‑flow axial, swirl, and perforated lining burners in a laboratory‑scale MILD furnace for steel reheating. The following conclusions are drawn: · Co‑flow axial burner: Produces an elongated flame but suffers from low momentum and instability when exposed to recirculating hot gases. Its heating capacity is insufficient for reaching target temperatures within a reasonable timeframe. · Perforated lining burner: Offers the fastest heating rate, achieving 550 °C in 2 hours 33 minutes. However, severe oxidation and structural failure at elevated temperatures render it unsuitable for long‑term industrial use without expensive alloy upgrades. · Swirl burner: Provides the most stable and uniform heating performance. Although its heating rate is slower than that of the linear burner, it reliably attains and exceeds 600 °C without structural degradation. Scaling this design to larger diameters (e.g., 1.5–2 inches) could further improve heating rate while maintaining stability. Overall, the swirl burner emerges as the most practical and robust option for industrial MILD furnaces, balancing thermal uniformity, operational safety, and long‑term durability. The findings underscore the critical influence of burner geometry on furnace startup time and temperature distribution, offering valuable guidance for optimizing burner selection in steel reheating applications. Author Contributions Ali Ashouri: Conceptualization, Methodology, Investigation, Formal analysis, Writing – original draft, Writing – review & editing, Visualization, Project administration. Soroush Sarrafan Sadeghi: Investigation, Formal analysis, Data curation, Writing – review & editing, Visualization. Mohammad Zabetian Targhi: Supervision, Conceptualization, Resources, Writing – review & editing, Funding acquisition. Funding This research received no specific grant from any funding agency in the public, commercial, or not‑for‑profit sectors. The study was conducted entirely at Tarbiat Modares University, Tehran, Iran, using the facilities of the National Combustion Laboratory. Conflict of Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. احتراق بدون شعله (MILD) به‌عنوان یک فناوری نوظهور و کارآمد است که باعث توزیع یکنواخت دما، کاهش تشکیل آلاینده‌ها و بهبود بازدهی حرارتی در کوره‌های صنعتی پیش‌گرم می‌شود. با این حال، عملکرد هندسه‌های مختلف مشعل در شرایط احتراق بدون شعله مخصوصا برای گرمایش کوره عملیات حرارتی قطعات فولادی بررسی نشده است. در این پژوهش، عملکرد سه نوع مشعل جریان همسو محوری، چرخشی و خطی سوراخ‌دار در یک کوره آزمایشگاهی احتراق بدون شعله در دانشگاه تربیت مدرس به‌صورت تجربی مورد ارزیابی قرار گرفت. هدف اصلی، مقایسه توانایی این مشعل‌ها در ایجاد گرمایش پایدار برای قطعات فولادی و نیز بررسی زمان گرمایش کوره تا رسیدن به دمای هدف اولیه ۶۰۰ درجه سلسیوس بود. نتایج نشان داد که مشعل جریان همسو محوری به دلیل تکانه پایین و اختلاط محدود، شعله‌ای کشیده و کم‌پایدار ایجاد کرد و در برابر بازگشت گازهای داغ حساس بود. در مقابل، مشعل چرخشی با ایجاد مؤلفه گردابه‌ای، اختلاط سوخت و هوا را بهبود داد، شعله‌ای حجیم‌تر و پایدارتر شکل داد و عملکرد حرارتی بهتری نسبت به مشعل همسو محوری ارائه کرد. مشعل خطی سوراخ‌دار یکنواخت‌ترین ساختار شعله را ایجاد کرد و سریع‌ترین گرمایش را به‌دست آورد. با این حال، این مشعل در دماهای بالا با اکسایش شدید سطحی و شکست موضعی بدنه مواجه شد. به‌طور کلی، نتایج نشان می‌دهد که نوع مشعل نقش تعیین‌کننده‌ای در پایداری احتراق، یکنواختی حرارتی و زمان راه‌اندازی کوره‌های MILD دارد و مشعل چرخشی از نظر عملکرد ایمن و پایدار برتری بیشتری نشان داد.

https://www.jfnc.ir/article_246841_bfa9a98ebe2de6b153b85c2989472de5.pdf

انجمن احتراق ایران سوخت و احتراق 2008-3629 18 4 2025 12 22 Thermodynamic Equilibrium Investigation of Sustainable Dimethyl Ether Green Fuel Production from Syngas by Gibbs Free Energy Minimization بررسی تعادل ترمودینامیکی تولید پایدار سوخت سبز دی متیل اتر از گاز سنتز به روش حداقل سازی انرژی آزاد گیبس 124 143 248165 10.22034/jfnc.2026.545105.1454 FA رضا خوش بین پژوهشکده فناوری های شیمیایی، سازمان پژوهش های علمی و صنعتی ایران 0000-0003-3432-441X محمد حقیقی دانشکده مهندسی شیمی، دانشگاه صنعتی سهند، شهر جدید سهند، تبریز، ایران 0000-0001-6683-097X Journal Article 2025 11 11 Dimethyl ether (DME) is a clean fuel with a high cetane number and soot-free combustion, making it a suitable substitute for fossil fuels. However, optimizing the direct DME synthesis process from syngas (STD) requires a deep understanding of equilibrium limitations and the interaction of operating conditions. In this study, with the aim of determining the optimal thermodynamic conditions as well as evaluating the final product quality from a combustion perspective, the equilibrium of the STD process was analyzed using the Gibbs free energy minimization method. Calculations were performed using Aspen Plus software and the Peng Robinson equation of state over a temperature range of 100 to 500 °C, a pressure range of 1 to 50 bar, H₂/CO molar ratios from 0.5 to 4, and CO₂/CO ratios from 0 to 2. The effects of adding steam and inert gas (N₂) on conversion and selectivity were also evaluated. All calculations were based on the assumption of single-phase gas equilibrium. At 250 °C and 40 bar, CO conversion reached about 95% and DME selectivity exceeded 92%. Increasing the temperature to 500 °C reduced DME selectivity to below 70% and increased CO₂ selectivity to above 30%. Adding 20% steam to the feed increased hydrogen production by up to 20% but decreased DME selectivity by about 12%. In contrast, adding excess CO₂ reduced DME selectivity without significantly changing hydrogen conversion. Comparison of the direct and indirect routes showed that CO conversion in the direct route exceeds 95%, while in the indirect route it remains below 50%. دی‌متیل اتر (DME) به عنوان یک سوخت پاک با عدد ستان بالا و قابلیت احتراق بدون دوده، جایگزین مناسبی برای سوخت‌های فسیلی است. با این حال، بهینه‌سازی فرایند تولید مستقیم DME از گاز سنتز (STD) مستلزم درک عمیق از محدودیت‌های تعادلی و اثر متقابل شرایط عملیاتی است. در این پژوهش، با هدف تعیین شرایط بهینه ترمودینامیکی و همچنین ارزیابی کیفیت محصول نهایی از دیدگاه احتراق، تعادل فرایند STD به روش حداقل‌سازی انرژی آزاد گیبس تحلیل شده است. محاسبات با نرم‌افزار Aspen Plus و معادله حالت Peng‑Robinson در محدوده دمایی ۱۰۰ تا ۵۰۰ درجه سلسیوس، فشاری ۱ تا ۵۰ بار، نسبت مولی H₂/CO از 0/5 تا ۴ و نسبت CO₂/CO از ۰ تا ۲ انجام شد. همچنین اثر افزودن بخار آب و گاز بی‌اثر (N₂) بر تبدیل و انتخاب‌پذیری ارزیابی شد. کلیه محاسبات بر پایه فرض تعادل تک‌فاز گاز انجام شده است. در دمای °C۲۵۰ و فشار ۴۰ بار، تبدیل CO به حدود 95% و انتخاب‌پذیری DME به بیش از 92% رسید. افزایش دما به °C50۰ ، انتخاب‌پذیری DME را به کمتر از 70% کاهش و انتخاب‌پذیری CO₂ را به بیش از 30% افزایش داد. افزودن 20% بخار آب به خوراک، تولید هیدروژن را تا 20% افزایش ولی انتخاب‌پذیری DME را حدود 12% کاهش داد. در مقابل، افزودن CO₂ اضافی بدون تغییر محسوس در تبدیل هیدروژن، انتخاب‌پذیری DME را کاهش داد. مقایسه مسیر مستقیم و غیرمستقیم نشان داد که تبدیل CO در مسیر مستقیم بیش از 95% است در حالی که در مسیر غیرمستقیم کمتر از 50% باقی می‌ماند.

https://www.jfnc.ir/article_248165_4dedcb6e3e14bf8b99621d6736f1ea81.pdf