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

Deadline for manuscript submissions: 31 August 2025 | Viewed by 6142

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Prof. Dr. Sławomir Wierzbicki

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Faculty of Technical Sciences, University of Warmia and Mazury in Olsztyn, 46 A, Słoneczna St., 10-710 Olsztyn, Poland
Interests: liquid and gaseous fuels for internal combustion engines; alternative fuels; combustion engines; control algorithms for combustion engines; engine diagnostics
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Dr. Kamil Duda

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Guest Editor

Faculty of Technical Sciences, University of Warmia and Mazury in Olsztyn, 46 A, Słoneczna St., 10-710 Olsztyn, Poland
Interests: alternative fuels production; alternative fuels quality; liquid biofuels; compression ignition engines; exhaust emission; engine performance
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The last decade has seen a stunning rise in the production of renewable fuels, with this sector growing at an average rate of 8% per year. However, this growth is only enough to cover half of the global increase in energy demand. With this growth in demand for energy, combustion engines will remain the prime vehicle power generation method for heavy-duty road and waterborne transport in the coming years. Furthermore, their role in power generation, as fast-response peakers for wind- and solar-based future energetics, is constantly increasing.

Considering the above situation and the CO₂ reduction targets of the 2015 Paris Agreement, there is an immediate need for high-TRL renewable fuels for use in combustion engine technology. This development must be accompanied by intensified combustion research, exploring the potential efficiency and emission co-optimization of new fuels. At the same, the fast phasing-in of renewable fuels requires efficient production methods and price-competitive feedstock. Finally, researchers, investors, legislators, and society require open access to well-organized, up-to-date, and relevant developments in the above fields to support the necessary transition of the fuel market.

This need for systematization and open dissemination of knowledge on renewable fuels for internal combustion engines forms the premise of the present Special Issue of Energies. Experts are encouraged to share their latest findings in the form of original research papers, case studies, or short reviews. Studies targeting all aspects of the value chain are considered necessary, including those covering the following topics: liquid and gaseous fuel production processes, upgrading (catalytic and fractional blending), and end-of-life valorization in combustion engines (conventional and advanced concepts). Also, techno-economic analyses aiming to valorize the value chain holistically are encouraged.

Prof. Dr. Sławomir Wierzbicki
Dr. Kamil Duda
Guest Editors

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Keywords

alternative fuels for internal combustion engines
fuel injection modes
steady and transient operation
combustion control
combustion modeling
innovative combustion concepts
engine performance
engine thermodynamics
emission characteristics
impacts of biofuels for engine components degradation
biofuels blending
biofuel quality examination
additives for alternative fuels biofuel production techniques
biofuel feedstock diversification
economy of biofuel use

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Renewable Fuels for Internal Combustion Engines in Energies (10 articles)

Published Papers (9 papers)

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Research

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31 pages, 4715 KiB

Open AccessArticle

Physical and Energy Properties of Fuel Pellets Produced from Sawdust with Potato Pulp Addition

by Sławomir Obidziński, Paweł Cwalina, Małgorzata Kowczyk-Sadowy, Aneta Sienkiewicz, Małgorzata Krasowska, Joanna Szyszlak-Bargłowicz, Grzegorz Zając, Tomasz Słowik, Jacek Mazur and Marek Jankowski

Energies 2024, 17(16), 3960; https://doi.org/10.3390/en17163960 - 9 Aug 2024

Viewed by 366

Abstract

This paper presents the findings of a study of the pelleting process of pine sawdust with the addition of waste in the form of potato pulp (as a natural binder), in the context of producing fuel pellets. The process of pelleting was carried out for sawdust and for a mixture of sawdust and potato pulp (10, 15, 20, and 25%). The highest moisture content was obtained in the case of pellets produced from a mixture of straw with a 25% potato pulp content, i.e., 26.54% (with a potato pulp moisture content of 85.08%). Increasing the potato pulp content in a mixture with sawdust from 10 to 25% reduced the power demand of the pelletizer by approx. 20% (from 7.35 to 5.92 kW). The obtained density values for pellets made from a mixture of sawdust and potato pulp (over 1000 kg∙m⁻³) with a potato pulp content of 10% make it possible to conclude that the obtained pellets meet the requirements of the ISO 17225-2:2021-11 standard. Increasing the potato pulp content from 0 to 25% caused a slight decrease in the heat of combustion, i.e., from 20.45 to 20.32 MJ∙kg⁻¹, as well as in the calorific value, from 19.02 to 18.83 MJ∙kg⁻¹ (both for dry sawdust matter and the mixture). The results of the laboratory tests were used to verify the densification process of mixtures of sawdust and potato pulp under industrial conditions at the PANBAH plant, using pelleting mixtures with a 5%, 10%, and 25% content of potato pulp. Industrial research also confirmed that the use of the addition of potato pulp in a mixture with sawdust significantly reduces the power demand of the pelletizer, and it also increases the kinetic strength of the obtained pellets. Full article

(This article belongs to the Special Issue Renewable Fuels for Internal Combustion Engines: 2nd Edition)

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20 pages, 3460 KiB

Open AccessArticle

Hydroprocessing Microbial Oils for Advanced Road Transportation, Aviation, and Maritime Drop-In Fuels: Industrially Relevant Scale Validation

by Athanasios Dimitriadis, Loukia P. Chrysikou, Ioanna Kosma, Nikos Tourlakidis and Stella Bezergianni

Energies 2024, 17(15), 3854; https://doi.org/10.3390/en17153854 - 5 Aug 2024

Viewed by 319

Abstract

Triacylglycerides (TAGs) produced via the syngas fermentation of biogenic residues and wastes were evaluated as a potential feedstock for advanced road transportation, aviation, and maritime drop-in fuels via hydroprocessing technology. Due to the limited availability of TAGs, a simulated feedstock (SM TAGs) was utilized by blending various commercial oils, simulating the fatty acid composition of TAGs. At first, the simulated feedstock and the real TAGs were hydrotreated on a TRL 4 (technology readiness level) pilot plant to evaluate the potential of the SM feedstock to simulate the TAGs based on product quality. The hydrotreatment technology was evaluated and optimized on a TRL 4 plant. The research was further extended to a TRL 5 hydrotreatment plant with the optimum operating window for scaling up the technology. The resulting product was fractionated on a batch fractionation unit under vacuum to separate the jet and diesel fractions. The produced fuels were analyzed and evaluated based on the aviation Jet A1, EN590, EN15940, and marine diesel DMA specifications. The results show that the TAG composition was successfully simulated via a blend of vegetable oils. In addition, the hydrotreatment of the real TAGs and simulated feedstock resulted in similar-quality liquid products. The technology was successfully scaled up on a TRL 5 unit, leading to advanced, high-quality aviation and diesel drop-in fuels from TAGs, while the reaction pathways of hydrotreating can be controlled via the operating parameters of pressure, temperature, and H₂/oil ratio. The hydrotreatment process’s optimum conditions were 13.8 MPa pressure, 643 K temperature, 1 h⁻¹ liquid hourly space velocity (LHSV), and 5000 scfb hydrogen-to-oil ratio. Finally, a storage stability study of the hydrotreated liquid product showed that it can be stored for more than 6 months at ambient conditions without any noticeable changes to its properties. Full article

(This article belongs to the Special Issue Renewable Fuels for Internal Combustion Engines: 2nd Edition)

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24 pages, 2500 KiB

Open AccessArticle

Simulation of a Continuous Pyrolysis Reactor for a Heat Self-Sufficient Process and Liquid Fuel Production

by Antonio Chavando, Valter Bruno Silva, Luís A. C. Tarelho, João Sousa Cardoso and Daniela Eusebio

Energies 2024, 17(14), 3526; https://doi.org/10.3390/en17143526 - 18 Jul 2024

Viewed by 347

Abstract

This study investigates the potential of utilizing pyrolysis byproducts, including char and non-condensable gases, as an energy source to promote autothermal pyrolysis. A total of six pyrolysis experiments were conducted at three distinct cracking temperatures, namely, 450 °C, 500 °C, and 550 °C. The experiments utilized two types of biomasses, i.e., 100% pine chips and 75% pine chips mixed with 25% refuse-derived fuels (RDF). The findings from the experiments were subsequently incorporated into a process simulation conducted on Aspen Plus for an energy balance and a techno-economic analysis. The results of the experiments revealed that the energy produced by the byproducts utilizing only pine chips is 1.453 kW/kg, which is enough to fulfill the energy demand of the pyrolysis reactor (1.298 kW/kg). However, when 25% of RDF is added, the energy demand of the reactor decreases to 1.220 kW/kg, and the produced energy increases to 1.750 kW/kg. Furthermore, adding RDF increases bio-oil’s lower heating value (LHV). The techno-economic study proposed three scenarios: optimistic, conservative, and tragic. The optimistic has a payback period (PBP) of 7.5 years and a positive net present value (NPV). However, the other two scenarios were unfavorable, resulting in unfeasibility. Full article

(This article belongs to the Special Issue Renewable Fuels for Internal Combustion Engines: 2nd Edition)

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17 pages, 1081 KiB

Open AccessArticle

Compatibility of Methanol-Hydrotreated Vegetable Oil Blends with Chosen Steels and Aluminum

by Huaying Wang-Alho, Katriina Sirviö, Carolin Nuortila, Jonna Kaivosoja, Maciej Mikulski and Seppo Niemi

Energies 2024, 17(14), 3423; https://doi.org/10.3390/en17143423 - 11 Jul 2024

Viewed by 442

Abstract

Methanol and hydrotreated vegetable oil (HVO) are complementary in the context of achieving ultra-low emission levels via low temperature combustion. HVO is a high-quality fuel fully compatible with compression ignition engines. Standalone methanol combustion is relatively straight-forward according to the Otto principle, with a spark ignited or in conventional dual-fuel (“liquid spark”) engines. These two fuels have by far the largest reactivity span amongst commercially available alternatives, allowing to secure controllable partially premixed compression ignition with methanol–HVO emulsification. This study investigates the corrosion of aluminum, carbon steel, stainless steel, and a special alloy of MoC210M/25CrMo4+SH, exposed to different combinations of HVO, HVO without additives (HVOr), methanol, and emulsion stabilizing additives (1-octanol or 1-dodecanol). General corrosive properties are well determined for all these surrogates individually, but their mutual interactions have not been researched in the context of relevant engine components. The experimental research involved immersion of metal samples into the fuels at room temperature for a duration of 60 days. The surfaces of the metals were inspected visually and the dissolution of the metals into fuels was evaluated by analyzing the fuels’ trace metal concentrations before and after the immersion test. Furthermore, this study compared the alterations in the chemical and physical properties of the fuels, such as density, kinematic viscosity, and distillation properties, due to possible corrosion products. Based on these results, methanol as 100% fuel or as blending component slightly increases the corrosion risk. Methanol had slight dissolving effect on aluminum (dissolving Al) and carbon steel (dissolving Zn). HVO, HVOr, and methanol–HVOr–co-solvents were compatible with the metals. No fuels induced visible corrosion on the metals’ surfaces. If corrosion products were formed in the fuel samples, they did not affect fuel parameters. Full article

(This article belongs to the Special Issue Renewable Fuels for Internal Combustion Engines: 2nd Edition)

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18 pages, 2358 KiB

Open AccessEditor’s ChoiceArticle

Automotive e-Fuels via Hydrocracking of FT-Wax: e-Gasoline and e-Diesel Production

by Athanasios Dimitriadis, Loukia P. Chrysikou and Stella Bezergianni

Energies 2024, 17(11), 2756; https://doi.org/10.3390/en17112756 - 5 Jun 2024

Viewed by 530

Abstract

The main goal of this research is the production of e-fuels in gasoline- and diesel-range hydrocarbons via the hydrocracking of wax from Fischer–Tropsch (FT-wax) synthesis. The hydrogen for the hydrocracking process originated from solar energy via water electrolysis, thus, the produced fuels were called e-fuels. The FT-wax was produced via the Fischer–Tropsch synthesis of syngas stream from the chemical looping gasification (CLG) of biogenic residues. For the hydrocracking tests, a continuous-operation TRL3 (Technology Readiness Level) pilot plant was utilized. At first, hydrocracking catalyst screening was performed for the upgrading of the FT-wax. Three hydrocracking catalysts were investigated (Ni-W, Ni-W zeolite-supported, and Ni-W Al₂O₃-supported catalyst) via various operating conditions to identify the optimal operating window for each one. These three catalysts were selected, as they are typical catalysts that are used in the petroleum refinery industry. The optimal catalyst was found to be the NiW catalyst, as it led to high e-fuel yields (38 wt% e-gasoline and 47 wt% e-diesel) with an average hydrogen consumption. The optimum operating window was found at a 603 K reactor temperature, 8.3 MPa system pressure, 1 hr⁻¹ LHSV, and 2500 scfb H₂/oil ratio. In the next phase, the production of 5 L of hydrocracked wax was performed utilizing the optimum NiW catalyst and the optimal operating parameters. The liquid product was further fractionated to separate the fractions of e-gasoline, e-diesel, and e-heavy fuel. The e-gasoline and e-diesel fractions were qualitatively assessed, indicating that they fulfilled almost all EN 228 and EN 590 for petroleum-based gasoline and diesel, respectively. Furthermore, a 12-month storage study showed that the product can be stored for a period of 4 months in ambient conditions. In general, green transportation e-fuels with favorable properties that met most of the fossil fuels specifications were produced successfully from the hydrocracking of FT-wax. Full article

(This article belongs to the Special Issue Renewable Fuels for Internal Combustion Engines: 2nd Edition)

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25 pages, 5904 KiB

Open AccessArticle

Start of Injection Influence on In-Cylinder Fuel Distribution, Engine Performance and Emission Characteristic in a RCCI Marine Engine

by Alireza Kakoee, Maciej Mikulski, Aneesh Vasudev, Martin Axelsson, Jari Hyvönen, Mohammad Mahdi Salahi and Amin Mahmoudzadeh Andwari

Energies 2024, 17(10), 2370; https://doi.org/10.3390/en17102370 - 14 May 2024

Cited by 1 | Viewed by 758

Abstract

Reactivity-controlled compression ignition (RCCI) is a promising new combustion technology for marine applications. It has offered the potential to achieve low NO_x emissions and high thermal efficiency, which are both important considerations for marine engines. However, the performance of RCCI engines is sensitive to a number of factors, including the start of injection. This study used computational fluid dynamics (CFD) to investigate the effects of start of ignition (SOI) on the performance of a marine RCCI engine. The CFD model was validated against experimental data, and the results showed that the SOI has a significant impact on the combustion process. In particular, the SOI affected the distribution of fuel and air in the combustion chamber, which in turn affected the rate of heat release and the formation of pollutants. Ten different SOIs were implemented on a validated closed-loop CFD model from 96 to 42 CAD bTDC (crank angle degree before top dead center) at six-degree intervals. A chemical kinetic mechanism of 54 species and 269 reactions tuned and used for simulation of in-cylinder combustion. The results show that in early injection, high-reactivity fuel was distributed close to the liner. This distribution was around the center of late injection angles. A homogeneity study was carried out to investigate the local equivalence ratio. It showed a more homogenous mixture in early injection until 66 CAD bTDC, after which point, earlier injection timing had no effect on homogeneity. Maximum indicated mean effective pressure (IMEP) was achieved at SOI 48 CAD bTDC, and minimum amounts of THC (total hydrocarbons) and NO_x were observed with middle injection timing angles around 66 CAD bTDC. Full article

(This article belongs to the Special Issue Renewable Fuels for Internal Combustion Engines: 2nd Edition)

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20 pages, 7192 KiB

Open AccessEditor’s ChoiceArticle

Advanced Flame front Detection in Combustion Processes Using Autoencoder Approach

by Federico Ricci and Francesco Mariani

Energies 2024, 17(7), 1759; https://doi.org/10.3390/en17071759 - 6 Apr 2024

Viewed by 927

Abstract

This research explores the detection of flame front evolution in spark-ignition engines using an innovative neural network, the autoencoder. High-speed camera images from an optical access engine were analyzed under different air excess coefficient λ conditions to evaluate the autoencoder’s performance. This study compared this new approach (AE) with an established method used by the same research group (BR) across multiple combustion cycles. Results revealed that the AE method outperformed the BR in accurately identifying flame pixels and significantly reducing overestimations outside the flame boundary. AE exhibited higher sensitivity levels, indicating its superior ability to identify pixels and minimize errors compared to the BR method. Additionally, AE’s accuracy in representing combustion evolution was notably improved, offering a more detailed depiction of the process. AE’s strength lies in its independence from specific threshold searches, a requirement in the BR method. By relying on learned representations within its latent space, AE eliminates laborious threshold exploration, ensuring reliability and reducing workload pressures. Comparative analyses consistently confirmed AE’s superior performance in accurately reproducing and delineating combustion evolution compared to BR. This study highlights AE’s potential as a promising technique for precise flame front detection in combustion processes. Its ability to autonomously extract features, minimize errors, and enhance overall accuracy signifies a significant step forward in analyzing flame fronts. AE’s reliability, reduced need for manual intervention, and adaptability across various conditions suggest a promising future for improving combustion analysis techniques in spark-ignition engines with optical access. Full article

(This article belongs to the Special Issue Renewable Fuels for Internal Combustion Engines: 2nd Edition)

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Review

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32 pages, 6774 KiB

Open AccessReview

A Comprehensive Review on the Hydrogen–Natural Gas–Diesel Tri-Fuel Engine Exhaust Emissions

by Hassan Sadah Muhssen, Máté Zöldy and Ákos Bereczky

Energies 2024, 17(15), 3862; https://doi.org/10.3390/en17153862 - 5 Aug 2024

Viewed by 430

Abstract

Natural gas (NG) is favored for transportation due to its availability and lower CO₂ emissions than fossil fuels, despite drawbacks like poor lean combustion ability and slow burning. According to a few recent studies, using hydrogen (H₂) alongside NG and diesel in Tri-fuel mode addresses these drawbacks while enhancing efficiency and reducing emissions, making it a promising option for diesel engines. Due to the importance and novelty of this, the continuation of ongoing research, and insufficient literature studies on HNG–diesel engine emissions that are considered helpful to researchers, this research has been conducted. This review summarizes the recent research on the HNG–diesel Tri-fuel engines utilizing hydrogen-enriched natural gas (HNG). The research methodology involved summarizing the effect of engine design, operating conditions, fuel mixing ratios and supplying techniques on the CO, CO₂, NO_x and HC emissions separately. Previous studies show that using natural gas with diesel increases CO and HC emissions while decreasing NO_x and CO₂ compared to pure diesel. However, using hydrogen with diesel reduces CO, CO₂, and HC emissions but increases NO_x. On the other hand, HNG–diesel fuel mode effectively mitigates the disadvantages of using these fuels separately, resulting in decreased emissions of CO, CO₂, HC, and NO_x. The inclusion of hydrogen improves combustion efficiency, reduces ignition delay, and enhances heat release and in-cylinder pressure. Additionally, operational parameters such as engine power, speed, load, air–fuel ratio, compression ratio, and injection parameters directly affect emissions in HNG–diesel Tri-fuel engines. Overall, the Tri-fuel approach offers promising emissions benefits compared to using natural gas or hydrogen separately as dual-fuels. Full article

(This article belongs to the Special Issue Renewable Fuels for Internal Combustion Engines: 2nd Edition)

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35 pages, 2809 KiB

Open AccessReview

Advancements and Challenges of Ammonia as a Sustainable Fuel for the Maritime Industry

by Antonio Chavando, Valter Silva, João Cardoso and Daniela Eusebio

Energies 2024, 17(13), 3183; https://doi.org/10.3390/en17133183 - 28 Jun 2024

Viewed by 1597

Abstract

The maritime industry needs sustainable, low-emission fuels to reduce the environmental impact. Ammonia is one of the most promising alternative fuels because it can be produced from renewable energy, such as wind and solar. Furthermore, ammonia combustion does not emit carbon. This review article covers the advantages and disadvantages of using ammonia as a sustainable marine fuel. We start by discussing the regulations and environmental concerns of the shipping sector, which is responsible for around 2% to 3% of global energy-related CO₂ emissions. These emissions may increase as the maritime industry grows at a compound annual growth rate of 4.33%. Next, we analyze the use of ammonia as a fuel in detail, which presents several challenges. These challenges include the high price of ammonia compared to other fossil fuels, the low reactivity and high toxicity of ammonia, NOx, and N₂O emissions resulting from incomplete combustion, an inefficient process, and NH₃ slipping. However, we emphasize how to overcome these challenges. We discuss techniques to reduce NOx and N₂O emissions, co-combustion to improve reactivity, waste heat recovery strategies, the regulatory framework, and safety conditions. Finally, we address the market trends and challenges of using ammonia as a sustainable marine fuel. Full article

(This article belongs to the Special Issue Renewable Fuels for Internal Combustion Engines: 2nd Edition)

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