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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "I1: Fuel".

Deadline for manuscript submissions: 30 June 2025 | Viewed by 8812

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Prof. Dr. Leszek Chybowski

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Guest Editor

Faculty of Marine Engineering, Maritime University of Szczecin, 70-500 Szczecin, Poland
Interests: diesel engines; operation and maintenance; reliability and safety; energy conversion; failure prevention; directed innovations; marine systems; machinery; propulsion systems; TRIZ; inventics; modelling; fault prediction; condition monitoring
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Dear Colleagues,

Ongoing climate change, the depletion of natural resources, and growing energy demands have rendered the production of new types of fuels for energy systems, including combustion engines and boilers, very crucial. Using alternative fuels, either as direct propellants or as additives to classic fossil fuels, may have both positive and negative consequences for energy machines and the environment. The most popular alternative fuels are biofuels, recycled fuels, synthetic fuels, ammonia, ethanol, methanol, ethylene, and hydrogen. Their mixtures with common fuels such as kerosene, gasoline, diesel oil, heating oil, LNG, CNG, LPG, etc., are also often employed.

This SI aims to present the latest research results related to the use of various types of fuels to power combustion engines, boilers and other thermal machines in maritime, road, railway and air transport applications. Additionally, we are interested in the combination of these fuels in stationary power and heating plants. We intend for the studies published in this SI to highlight the impact of alternative fuels and their combinations with other fuels (classic and/or alternative) on the level of exhaust gases emissions (NOx, SOx, PMs, aldehydes, etc.), energy performance (power, torque, speed, energy efficiency), component wear, reliability and safety of operation, cost effectiveness, as well as the functionalities (maintainability, noise, vibrations) of machines and devices powered by these fuels.

Prof. Dr. Leszek Chybowski
Guest Editor

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Keywords

engine
motor
ICE
boiler
fuel
propellant
biofuel
synthetic fuel
recycled fuel
fuel blends
ammonia
hydrogen
ethanol
methanol
ethylene
kerosene
gasoline
fuel oil
diesel oil
gas oil
heating oil
ice
powertrains
transportation
power plant
exhaust gas
emissions
NOx
SOx
PMs
CO₂
noise
vibration
performance
wear
reliability
durability
operational risk
environment
ecology
safety
economy
functionality

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Published Papers (9 papers)

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Research

19 pages, 3200 KiB

Open AccessArticle

Effects of Ethanol–Diesel Blends on Cylinder Pressure, Ignition Delay, and NO_x Emissions in a Diesel Engine

by Krzysztof Górski, Dimitrios Tziourtzioumis, Ruslans Smigins and Rafał Longwic

Energies 2025, 18(9), 2392; https://doi.org/10.3390/en18092392 - 7 May 2025

Viewed by 210

Abstract

This study examined how adding ethanol to diesel fuel affects combustion characteristics, cylinder pressure and NO_x emissions in an AVL engine. The research focused on key engine parameters, including autoignition delay, in-cylinder pressure rise rates, the peaks of the mean in-cylinder temperature and NO_x emissions. Three fuel types were tested: pure diesel (DF) and blends with 10 and 20% ethanol by volume (DF10 and DF20). The results obtained indicate that increasing the ethanol content in diesel fuel significantly affects the combustion process of the fuel mixture, particularly in its early stage, reducing the benefits of the pilot fuel injection. Moreover, it was observed that the combustion of the DF20 mixture leads to a substantially higher pressure increase in the cylinder, exceeding the values recorded for pure diesel fuel by approximately 25%. Furthermore, the study revealed that ethanol addition increases the peaks of the mean in-cylinder temperature, with a recorded difference of up to 60 °C between pure diesel fuel and DF20. Since NO_x formation is highly temperature-dependent, this temperature rise is likely to result in higher NO_x concentration. Additionally, a slight effect of ethanol on increasing the ignition delay angle was observed. This remained minor, and did not exceed approximately 1 CA. These findings highlight the complex relationship between ethanol content in diesel fuel, combustion dynamics, and emissions. They emphasize the need for optimizing the injection process for ethanol–diesel blends to balance the benefits of ethanol addition with potential challenges related to combustion efficiency, engine load and NO_x concentration. Full article

(This article belongs to the Special Issue Advances in Fuel Energy)

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18 pages, 6471 KiB

Open AccessFeature PaperArticle

Evaluation of Rheological and Lubrication Properties of Selected Alcohol Fuels

by Leszek Chybowski, Wojciech Wójcik and Marcin Szczepanek

Energies 2025, 18(5), 1038; https://doi.org/10.3390/en18051038 - 21 Feb 2025

Viewed by 378

Abstract

This article presents the results of a study on the rheological and lubricating properties of selected alcohol fuels. Methanol, ethanol, and 2-propanol are investigated, for which density, kinematic, and dynamic viscosity are determined at selected temperatures in the range of 15–60 °C. In addition, the water content of the studied fuels is determined. Based on the measurements, the coefficient of temperature change for density and the relative percentage decrease in kinematic viscosity with increasing temperature are calculated. Subsequently, regression models are built to describe the value of density and viscosity of the tested liquid alcohol fuels as a function of temperature. Next, the fuels under study are subjected to the evaluation of antiwear properties using a high-frequency reciprocating rig (HFRR). For each fuel, the corrected wear scar size WS_1.4, which is a measure of lubricity, the average coefficient of friction, and the relative percentage decrease in oil FILM thickness during the conduct of the HFRR test under standardized conditions, are determined. The measurements are carried out at a standardized temperature of 25 °C in accordance with standardized methods for a time equal to 75 min. Due to the low lubricity of the tested fuels, additional tests are performed at a reduced time equal to 30 min. In this case, all fuels show a similar WS_1.4 value, which ranges from 384 μm for methanol through 422 μm for 2-propanol to 426 μm for ethanol. The wear marks on the samples after the execution of the test are used to draw additional qualitative conclusions about the lubricating properties of the tested alcohols. The results obtained are summarized, and possibilities for their use in further research are provided. Full article

(This article belongs to the Special Issue Advances in Fuel Energy)

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16 pages, 4736 KiB

Open AccessArticle

Investigation of Water-in-Diesel Emulsion Behavior Formulated for Performance Conditions in a Single-Cylinder Diesel Engine

by Pedro Oliveira, Francisco Brójo, Rogério Serôdio and João Serôdio

Energies 2025, 18(4), 934; https://doi.org/10.3390/en18040934 - 15 Feb 2025

Viewed by 668

Abstract

The search for alternative fuels is driven by increasing environmental and health concerns across the globe. Water-in-diesel emulsions (WiDEs) have been explored over the years as a potential fuel for diesel engines to mitigate emissions of greenhouse gases, especially nitrogen oxides and smoke. Researchers have been developing and testing different formulations of emulsified fuels with the common goal of stabilizing the mixture and minimizing pollutant emissions without significantly compromising engine performance. In this work, a novel approach is taken by developing a hydrophilic emulsion formulation optimized for engine operating temperatures, overcoming the storage-related stability issues that most studies focus on. Two different mixtures of WiDE were heated and supplied to a Hatz 1B40 single-cylinder diesel engine. The engine was coupled to an eddy current dynamometer to measure speed, torque, and power values. Emissions of carbon monoxide (CO), carbon dioxide (CO₂), hydrocarbons (HCs), nitric oxide (NO), and oxygen (O₂) were measured by an AVL DiGas 1000 exhaust gas analyzer. Smoke emissions were measured by an AVL DiSmoke 480. This study represents a contribution to the field of alternative fuels for diesel engines by providing experimental evidence that formulating WiDE for operating temperatures can be advantageous and significantly improve thermal efficiency and reduce emissions of NO and smoke at specific engine operating conditions, with a maximum reduction of 46.86% for NO emissions and a maximum reduction of 83.67% for smoke emissions obtained when compared to diesel. Full article

(This article belongs to the Special Issue Advances in Fuel Energy)

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19 pages, 3993 KiB

Open AccessArticle

Improvement Efficiency and Emission Reduction in Used Cars for Developing Regions Using Gasoline–Bioethanol Blends

by Alejandro Zacarías, Mario R. Grijalva, José de Jesús Rubio, Guerlin Romage, Violeta Y. Mena, Raúl Hernández, Ignacio Carvajal, Alicia Flores, Orlando Guarneros and Brayan A. Rodríguez

Energies 2025, 18(3), 638; https://doi.org/10.3390/en18030638 - 30 Jan 2025

Viewed by 841

Abstract

Energy demand is continuously increasing owing to rapid technological developments and population growth. Additionally, it has been shown that the consumption of fossil fuels contributes to the emission of gases that increase the greenhouse effect. An alternative for addressing the problems of greenhouse gas emissions and dependence on oil is to replace fossil fuels with biofuels. This article presents the combustion gas emissions and performance assessment of a used car using gasoline–bioethanol blends at concentrations free of mechanical risk to contribute information for energy transition. The tests were carried out using the mixtures E0, E5, and E10 at speeds of 1500, 2500, and 4500 rpm for the evaluation of emissions. Meanwhile, for the performance assessment, the speed was varied from 2500 rpm to 8000 rpm. The vehicle was analyzed under functional operating conditions, and no mechanical modifications were made to the alcohol mixtures. Testing was performed using a gas analyzer with non-dispersive infrared (NDIR) electroluminescence and electrochemical cells to measure the emissions, and a computerized chassis dynamometer was used to measure the torque and speed. From the results shown here, it can be concluded that the use of bioethanol at low concentrations in the range without mechanical risk, such as E0, E5, and E10, can be utilized in used cars and in functional operating conditions, improving the thermal efficiency of the engine by 2% and 1.2% with the E5 and E10 mixtures. The specific consumption increased up to 3% with the E10 mixture owing to the lower energy capacity of the mixture. Meanwhile, HC polluting emissions decreased by up to 8.44%, 20%, and 100 at speeds of 1500 rpm, 2500 rpm, and 4500 rpm, respectively. The nitrogen oxide emissions decreased by up to 5% for mixtures E5 and E10. The results presented in this article may be useful for decision making in the use of biofuels in automobiles used in the energy transition. In addition, our study can be taken as a reference for studies on cars that are more than 20 years old. Full article

(This article belongs to the Special Issue Advances in Fuel Energy)

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18 pages, 4298 KiB

Open AccessArticle

Research and Analysis of Explosion-Proof Diesel Engine Performance Based on Different Exhaust Gas Cooling Systems

by Zhiyuan Shi, Hongxin Wei, Guanghui Li, Yuan Wang, Quanming Li, Xin Zheng, Kunhao Song, Chong Chen, Chi Ma, Samsil Arefin Mozumder and Md Khairul Basher

Energies 2025, 18(3), 610; https://doi.org/10.3390/en18030610 - 28 Jan 2025

Viewed by 807

Abstract

As stringent emission regulations and safety standards for explosion-proof diesel engines become more critical, the demand for efficient exhaust cooling systems has increased. Traditional cooling systems, typically relying on cooling and purification water tanks, have limitations in terms of safety, performance, and emissions control. To address these challenges, a novel dry exhaust gas cooling system was developed, incorporating a heat exchanger and exhaust dilution cooling device, replacing the conventional water-based cooling systems. This study explores the performance of the dry exhaust gas cooling system through a series of experiments including explosion-proof testing of the exhaust system, whole machine explosion-proof testing, exhaust temperature measurements, surface temperature evaluations, and exhaust gas composition analysis. The system’s performance was compared to both wet and combined dry + wet exhaust gas cooling systems. Results showed that the dry exhaust cooling system maintained its explosion-proof integrity during all tests, with the highest exhaust temperature at 68.5 °C and a surface temperature of 130.8 °C—both of which comply with safety standards. Notably, the dry exhaust system also demonstrated improved power output and reduced fuel consumption by over 4% compared to the other systems. Furthermore, it significantly lowered harmful exhaust emissions, reducing CO, HC, NOX, and CO₂ levels by 55%, 71%, 68%, and 82%, respectively, when compared to the wet exhaust cooling system. In comparison to the dry + wet system, these reductions were even more pronounced—63%, 75%, 66%, and 94%, respectively. The findings suggest that the dry exhaust gas cooling system offers a safer, more efficient, and environmentally friendly alternative to conventional exhaust cooling systems in explosion-proof diesel engines. Full article

(This article belongs to the Special Issue Advances in Fuel Energy)

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13 pages, 1807 KiB

Open AccessArticle

Dielectric Constant Predictions for Jet-Range Hydrocarbons: Evaluating the Clausius–Mossotti Relation and Correcting for Molecular Dipole Moments

by Conor Faulhaber, David C. Bell, Randall Boehm and Joshua Heyne

Energies 2024, 17(18), 4700; https://doi.org/10.3390/en17184700 - 21 Sep 2024

Viewed by 1040

Abstract

The dielectric constant of aviation turbine fuel is leveraged by aircraft fuel quantity indicator systems (FQISs) using the Clausius–Mossotti relation, which assumes no significant dipole moments. For fossil-derived jet fuel containing relatively consistent fractions of polar aromatic molecules, this is appropriate. However, the interest in sustainable aviation fuels (SAFs) to reduce the carbon intensity of commercial aviation has brought attention to the uncertainty of the FQISs’ compatibility for low- or zero-aromatic fuels exhibiting dielectric constant values outside of the conventional Jet-A range. A dielectric constant model accounting for the varying dipole moments of both aromatic and non-aromatic jet-range hydrocarbons improves the community’s understanding of fuel composition on FQISs’ operability and provides a tool suitable for fuel performance property optimizations while maintaining compatibility with current aircraft systems. Here, the Clausius–Mossotti relation is first evaluated against a training dataset of 240 dielectric constant and density measurements (48 neat hydrocarbons each measured at five temperatures). Then, the dipole moment is calculated for each species of interest using open-source computational chemistry software, and a second-degree binomial regression is performed over the training data to correct for the error in the Clausius–Mossotti relation. The Clausius–Mossotti relation exhibited an R² value of 0.54, which increased to 0.92 when terms for the dipole correction were added to the model. The improved accuracy from this model establishes a computationally inexpensive framework for modeling theoretical fuel compositions that demonstrate improved performance characteristics (sooting propensity, thermal management, aircraft efficiency, etc.) while remaining within key limiting property constraints, such as the dielectric constant. Full article

(This article belongs to the Special Issue Advances in Fuel Energy)

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17 pages, 2144 KiB

Open AccessArticle

Decarbonization in Shipping—The Hopes and Doubts on the Way to Hydrogen Use

by Jerzy Herdzik and Anna Lesnau

Energies 2024, 17(18), 4668; https://doi.org/10.3390/en17184668 - 19 Sep 2024

Cited by 3 | Viewed by 1108

Abstract

This article presents the initial processes of changing ship fuels aimed at reducing emissions of carbon dioxide and other greenhouse gases. A significant reduction in GHG emissions is only possible by using carbon-free fuels. The process of reducing CO₂ emissions was forced by legal regulations introduced in recent years by the International Maritime Organization and the Parliament of the European Union. The year 2050 was set as the target year for achieving the intended goals, but intermediate goals should be achieved already in 2030 and 2040. This article attempts to analyze the ongoing changes in the fuel market in maritime transport on the way to achieving the threshold of climate neutrality with this form of transport. A number of hopes related to this were indicated but also so were obstacles that may slow down this process. In 2023, there was an increased interest among shipowners in adapting ship engines to burn more ecological ship fuels. However, it is far from our expectations. Meeting the gradually increasing emission limits through imposed regulations was possible in the years 2020–2023 by using dual-fuel engines in which gaseous fuels, mainly LNG and LPG, were used for long periods of operation. The next step is the use of biofuels or synthetic fuels, which, however, will not meet the requirements after 2030. Interest is moving towards the use of ammonia and, ultimately, after 2040, hydrogen. The aim of this article is to analyze the ongoing processes and assess the directions of changes that justify the sense of the actions taken. Full article

(This article belongs to the Special Issue Advances in Fuel Energy)

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13 pages, 20258 KiB

Open AccessArticle

Influence of In-Cylinder Turbulence Kinetic Energy on the Mixing Uniformity within Gaseous-Fuel Engines under Various Intake Pressure Conditions

by Tianbo Wang, Yu Wang, Lanchun Zhang, Yan Zheng, Ranran Liu, Chengmin Wang and Wu Gong

Energies 2024, 17(13), 3321; https://doi.org/10.3390/en17133321 - 6 Jul 2024

Viewed by 1266

Abstract

To explore the potential for further enhancing the gas mixing uniformity of natural gas (NG) engines, this paper identifies turbulent kinetic energy (TKE), which has an essential impact on gas mixing, as the entry point of the research. After establishing a computational fluid dynamics (CFD) model for NG engines’ direct injection and mixing processes, the inlet pressure is selected as the experimental variable to investigate the influence of TKE on gas mixing uniformity. In particular, by proposing the theoretical concept of the core mixing stage, the numerical variation rule between the best mixture concentration region (BMCR) percentage and the mean turbulent kinetic energy (MTKE) of the core mixing stage is analyzed under certain injection timing conditions. The results indicate that, with identical intake pressures, an advanced gas injection timing elevates the total turbulence kinetic energy (TTKE) during the core mixing stage, thereby amplifying the uniformity of the gas mixture at the ignition. In specific scenarios, as the intake pressure increases, the decreasing trend in the BMCR proportion closely resembles the diminishing trend in the MTKE during the core mixing stage. Scrutinizing the variation trend in either parameter allows for an approximate prediction of the variation trend in the other parameter. When the intake pressure is gradually raised from the naturally aspirated state, the adequacy of the gas jet development is progressively reduced by the increasing back pressure in the cylinder. Full article

(This article belongs to the Special Issue Advances in Fuel Energy)

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17 pages, 4226 KiB

Open AccessEditor’s ChoiceArticle

Performance Analysis Based on Fuel Valve Train Control Optimization of Ammonia-Fuel Ships

by Lim Seungtaek, Lee Hosaeng and Seo Youngkyun

Energies 2024, 17(10), 2272; https://doi.org/10.3390/en17102272 - 8 May 2024

Viewed by 1517

Abstract

In order to reduce carbon emissions, which are currently a problem in the shipping and offshore plant sectors, the international community is strengthening regulations such as the Energy Efficiency Design Index (EEDI) and Energy Efficiency Existing Ship Index (EEXI). To cope with this, eco-friendly fuel propulsion technology is being developed, and the development of an ammonia fuel supply system is in progress. Among them, fuel valve train (FVT) technology was researched for the final supply and cutoff of fuel and purging through nitrogen for ammonia engines. In this paper, we analyzed the change in ammonia supply due to FVT opening and the change in nitrogen supply due to closure. In addition, a plan to minimize risk factors was presented by applying a control method to remove residual fuel in FVT. According to the presented FVT model, the difference in the flow rate of supplied fuel was as much as 17.8 kg/s. Additionally, by opening the gas bleed valve at intervals during the closing process and purging about 0.28 kg of nitrogen, the internal fuel could be completely discharged. This is expected to have an impact on improving the marine environment through the application of eco-friendly fuels and the development of fuel supply system technology. Full article

(This article belongs to the Special Issue Advances in Fuel Energy)

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