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Towards Cleaner and More Efficient Combustion

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "B: Energy and Environment".

Deadline for manuscript submissions: closed (15 January 2026) | Viewed by 6614

Special Issue Editor


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Guest Editor
Mechanical and Industrial Engineering, College of Engineering, Sultan Qaboos University, Muscat 123, Oman
Interests: thermo-fluids; thermodynamics; cogeneration systems; fuels and combustion; internal combustion engines; diesel combustion
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Special Issue Information

Dear Colleagues,

The global push towards sustainable energy has highlighted the critical importance of cleaner and more efficient combustion technologies. Traditional combustion processes, while essential for energy production, transportation, and industrial activities, are major sources of pollutants, including carbon dioxide (CO2), nitrogen oxides (NOx), sulfur oxides (SOx), and particulate matter. These emissions have significant adverse effects on environmental and public health, contributing to climate change, acid rain, and respiratory illnesses. As the world grapples with the dual challenge of meeting growing energy demands while minimizing environmental impact, there is an urgent need for innovative solutions that make combustion processes cleaner and more efficient. Advances in this field not only contribute to reducing greenhouse gas emissions but also enhance energy security and promote the use of renewable and alternative fuels. This Special Issue on "Towards Cleaner and More Efficient Combustion" seeks to bring together the latest research and development efforts that address these critical challenges. By fostering collaboration and knowledge sharing among researchers, engineers, and industry professionals, we aim to accelerate the transition to cleaner and more efficient combustion technologies and support the global drive towards a more sustainable energy future. We are pleased to announce a Special Issue titled "Towards Cleaner and More Efficient Combustion" in the journal Energies. This Special Issue aims to gather cutting-edge research and developments in the field of cleaner and more efficient combustion technologies, addressing the urgent need for reducing emissions and improving energy efficiency in combustion processes. As the world strives towards sustainable energy solutions, advancements in cleaner and more efficient combustion are crucial for mitigating environmental impact and enhancing fuel utilization.  We invite researchers and industry experts to submit original research articles, review papers, and case studies on, but not limited to, the following topics:

  • Advanced Combustion Technologies: Innovations in combustion methods that enhance efficiency and reduce pollutant formation.
  • Alternative Fuels: Research on biofuels, synthetic fuels, and other alternative energy sources that contribute to cleaner combustion.
  • Emission Control Technologies: Development and optimization of technologies for reducing NOx, SOx, CO2, and particulate emissions.
  • Combustion Diagnostics and Monitoring: Advanced techniques for real-time monitoring and diagnostics of combustion processes.
  • Numerical Simulation and Modeling: Computational studies that provide insights into combustion dynamics and pollutant formation.
  • Catalytic Combustion: Innovations in catalytic materials and processes to facilitate cleaner combustion.
  • Engine and Burner Design: Design improvements in engines and burners aimed at reducing emissions and enhancing performance.
  • Waste-to-Energy Combustion: Technologies and methods for converting waste materials into energy through cleaner combustion.
  • Combustion in Industrial Applications: Case studies and research on cleaner combustion in industrial settings such as power plants, refineries, and manufacturing.

Dr. Ahmed Elwardany
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

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Keywords

  • thermo-fluids
  • thermodynamics
  • cogeneration systems
  • fuels and combustion
  • internal combustion engines
  • diesel combustion

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Published Papers (3 papers)

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Research

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21 pages, 3195 KB  
Article
The Effect of Changing Exhaust Nozzle Geometry on Temperature Distribution and Emissions of Methane Diffusion Flame Under Air/Fuel Swirl Flows
by Salim Al Hamdani, Abdullah Al-Janabi, Sulaiman Al-Obidani, Ali Al-Hinaai and Ahmed Elwardany
Energies 2026, 19(8), 1889; https://doi.org/10.3390/en19081889 - 13 Apr 2026
Viewed by 613
Abstract
The performance of diffusion flame (DF) burners strongly depends on how effectively combustion gases mix and retain heat, yet the influence of exhaust nozzle geometry on these processes remains insufficiently characterized. This study examines how varying exhaust nozzle angle affects the thermal behavior [...] Read more.
The performance of diffusion flame (DF) burners strongly depends on how effectively combustion gases mix and retain heat, yet the influence of exhaust nozzle geometry on these processes remains insufficiently characterized. This study examines how varying exhaust nozzle angle affects the thermal behavior and emissions of a methane (CH4) diffusion flame under atmospheric conditions. A laboratory-scale burner with interchangeable exhaust nozzles (0°, 25°, and 50°) was operated at 1.8 kW using a fixed methane flow of 3 L/min and co-swirled air and fuel at 30°, across equivalence ratios (Φ) of 1.0, 0.7, and 0.5. Axial temperature measurements and exhaust gas analyses (Carbon dioxide (CO2) and Carbon monoxide (CO)) were conducted to assess mixing, heat retention, and post-flame oxidation. Results show that exhaust nozzle geometry notably influences flame position and heat distribution, producing non-monotonic temperature trends with equivalence ratio. The 25° nozzle angle yielded the highest near-stoichiometric downstream and flue temperatures, reaching about 204 °C at x = 45 cm and 277 °C in the flue, compared with 72 °C and 177 °C for the 0° nozzle. In contrast, the 50° nozzle produced more uniform downstream temperatures (about 150–160 °C) and the lowest CO emissions, approaching zero near Φ ≈ 1.0. These findings demonstrate that coordinated control of swirl and exhaust nozzle angle can enhance thermal response and CO reduction in diffusion flame burners without significantly changing CO2 levels. Full article
(This article belongs to the Special Issue Towards Cleaner and More Efficient Combustion)
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36 pages, 23568 KB  
Article
Evaluation of the Reliability of Thermogravimetric Indices for Predicting Coal Performance in Utility Systems
by Krzysztof M. Czajka
Energies 2025, 18(13), 3473; https://doi.org/10.3390/en18133473 - 1 Jul 2025
Cited by 1 | Viewed by 1257
Abstract
A thorough understanding of fuel behaviour is essential for designing and operating thermochemical systems. Thermogravimetric analysis (TGA) is among the most widely used fuel characterization methods, offering parameters like reactivity and ignition temperature, and enabling comprehensive fuel behaviour assessment through combined indices. This [...] Read more.
A thorough understanding of fuel behaviour is essential for designing and operating thermochemical systems. Thermogravimetric analysis (TGA) is among the most widely used fuel characterization methods, offering parameters like reactivity and ignition temperature, and enabling comprehensive fuel behaviour assessment through combined indices. This study critically examines the applicability of TGA-based indices for predicting coal performance in industrial processes such as gasification and combustion, where devolatilization, ignition, and burnout stages are key. TGA-derived data are compared with results from established methods, including drop tube furnace (DTF), pulse ignition (PI), and entrained flow reactor (EFR) tests. Findings indicate that the Volatile Matter Release Index (D2) effectively predicts DTF behaviour (R2 = 0.938, max residuals: 4.1 pp), proving useful for fast devolatilization analysis. The Flammability Index (C1) and Ignition Index (C3) correlate well with PI results (R2 = 0.927 and 0.931, max residuals: 53.3a °C), making them reliable ignition indicators. While TGA tools showed limited accuracy in burnout prediction, the proposed Modified Burnout Characteristic Index (B1′) achieved reasonable performance (R2 = 0.734, max residuals: 0.062%∙°C−1). Overall, selected TGA-based indices offer strong predictive potential for key thermochemical conversion stages. Full article
(This article belongs to the Special Issue Towards Cleaner and More Efficient Combustion)
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Review

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26 pages, 7439 KB  
Review
A Review of Marine Dual-Fuel Engine New Combustion Technology: Turbulent Jet-Controlled Premixed-Diffusion Multi-Mode Combustion
by Jianlin Cao, Zebang Liu, Hao Shi, Dongsheng Dong, Shuping Kang and Lingxu Bu
Energies 2025, 18(15), 3903; https://doi.org/10.3390/en18153903 - 22 Jul 2025
Cited by 5 | Viewed by 3983
Abstract
Driven by stringent emission regulations, advanced combustion modes utilizing turbulent jet ignition technology are pivotal for enhancing the performance of marine low-speed natural gas dual-fuel engines. This review focuses on three novel combustion modes, yielding key conclusions: (1) Compared to the conventional DJCDC [...] Read more.
Driven by stringent emission regulations, advanced combustion modes utilizing turbulent jet ignition technology are pivotal for enhancing the performance of marine low-speed natural gas dual-fuel engines. This review focuses on three novel combustion modes, yielding key conclusions: (1) Compared to the conventional DJCDC mode, the TJCDC mode exhibits a significantly higher swirl ratio and turbulence kinetic energy in the main chamber during initial combustion. This promotes natural gas jet development and combustion acceleration, leading to shorter ignition delay, reduced combustion duration, and a combustion center (CA50) positioned closer to the Top Dead Center (TDC), alongside higher peak cylinder pressure and a faster early heat release rate. Energetically, while TJCDC incurs higher heat transfer losses, it benefits from lower exhaust energy and irreversible exergy loss, indicating greater potential for useful work extraction, albeit with slightly higher indicated specific NOx emissions. (2) In the high-compression ratio TJCPC mode, the Liquid Pressurized Natural Gas (LPNG) injection parameters critically impact performance. Delaying the start of injection (SOI) or extending the injection duration degrades premixing uniformity and increases unburned methane (CH4) slip, with the duration effects showing a load dependency. Optimizing both the injection timing and duration is, therefore, essential for emission control. (3) Increasing the excess air ratio delays the combustion phasing in TJCPC (longer ignition delay, extended combustion duration, and retarded CA50). However, this shift positions the heat release more optimally relative to the TDC, resulting in significantly improved indicated thermal efficiency. This work provides a theoretical foundation for optimizing high-efficiency, low-emission combustion strategies in marine dual-fuel engines. Full article
(This article belongs to the Special Issue Towards Cleaner and More Efficient Combustion)
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