Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Aerospace aerospace	2.1	3.4	2014	21.3 Days	CHF 2400
Applied Sciences applsci	2.5	5.3	2011	18.4 Days	CHF 2400
Catalysts catalysts	3.8	6.8	2011	13.9 Days	CHF 2200
Energies energies	3.0	6.2	2008	16.8 Days	CHF 2600
Mathematics mathematics	2.3	4.0	2013	18.3 Days	CHF 2600

25 pages, 1355 KiB

Open AccessArticle

Expanding Known Performance Capabilities of Geared Turbofan Engine When Powered by LNG and Methanol

by Sergios Villette, Alexios Alexiou, Nikolaos Aretakis and Konstantinos Mathioudakis

Aerospace 2025, 12(2), 96; https://doi.org/10.3390/aerospace12020096 - 28 Jan 2025

Viewed by 1055

As aviation demand rises, fossil jet fuel consumption follows, thus increasing focus on sustainable aviation fuels to reduce aircraft greenhouse gas emissions. While advanced technologies and optimized operations play a role, alternative fuels, especially non-drop-in options like Liquefied Natural Gas (LNG) and methanol, [...] Read more.

As aviation demand rises, fossil jet fuel consumption follows, thus increasing focus on sustainable aviation fuels to reduce aircraft greenhouse gas emissions. While advanced technologies and optimized operations play a role, alternative fuels, especially non-drop-in options like Liquefied Natural Gas (LNG) and methanol, offer promising potential for significant emission reductions if used in current aero-engines. LNG, a candidate near-term replacement of fossil jet fuel and methanol, even though a less conventional option in aviation, present advantages. Both fuels showcase the ability to generate the same thrust output by also achieving lower post-combustion temperatures, thereby enhancing component life and reducing emissions. Inversely, requesting equal post-combustion temperature as the baseline kerosene operation of the engine can produce greater thrust output, a much needed result for such fuels with low volumetric energy density, which causes greater take-off thrust demand mainly due to their larger tank requirements. This study uses advanced 0-D engine models coupled with detailed chemistry 1-D burner models and mission analysis tools to assess the aforementioned trends of LNG and methanol used to power a current geared turbofan engine. The aim of this work is to provide insights into the advantages, the limitations and the overall viability of the fuels in question as less polluting aviation fuels, addressing both environmental impact and operational feasibility in future aviation applications. According to findings of this article, when compared with Jet-A, LNG can reduce post-combustion temperature by an average of 1% or increase net-thrust by 3% while lowering

C O_{2}

,

N O_{x}

and

C O

emissions by 20%, 46% and 39%, respectively. Adversely, methanol is capable of lessening post-combustion temperature by 3% or enhancing thrust output by 10% while also reducing

C O_{2}

,

N O_{x}

and

C O

emissions by an average of 6%, 60% and 38%, respectively. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

18 pages, 19256 KiB

Open AccessArticle

Numerical Investigation of the Effect of Equivalent Ratio on Detonation Characteristics and Performance of CH₄/O₂ Rotating Detonation Rocket Engine

by Xiao Xu, Qixiang Han and Yining Zhang

Aerospace 2025, 12(1), 68; https://doi.org/10.3390/aerospace12010068 - 18 Jan 2025

Viewed by 794

Abstract

Equivalent ratio (ER) is an important factor affecting detonation characteristics and propulsion performance of rotating detonation rocket engine (RDRE). In this paper, the effects of different equivalent ratios detonation characteristics and thrust performance of methane-oxygen RDRE were studied by 2D numerical simulation. The [...] Read more.

Equivalent ratio (ER) is an important factor affecting detonation characteristics and propulsion performance of rotating detonation rocket engine (RDRE). In this paper, the effects of different equivalent ratios detonation characteristics and thrust performance of methane-oxygen RDRE were studied by 2D numerical simulation. The premixed reactants were injected through the injection holes to simulate the discrete injection of reactants on the injection panel in actual RDRE, the number of injection holes was 60 and 120. The results show that there is hybrid detonation mode (HDM), co-direction multi-wave detonation mode (CMM) and unstable detonation mode (UDM) in detonation combustion due to the influence of equivalent ratio and the number of injection holes, and the co-directional multi-wave detonation mode is beneficial to the thrust stability of RDRE. At the last, the number of detonation waves in RDRE decreases with the increase in the equivalent ratio, and the specific impulse (I_sp) increases with the increase of the equivalent ratio. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

16 pages, 1979 KiB

Open AccessArticle

Heat Release Rates of Straight Soybean and Diesel Oil Blends in a Compression Ignition Engine

by Nury A. Nieto Garzón, Amir A. Martins Oliveira and Edson Bazzo

Appl. Sci. 2024, 14(20), 9215; https://doi.org/10.3390/app14209215 - 10 Oct 2024

Cited by 1 | Viewed by 1047

Abstract

Straight soybean and diesel oil blends are proposed as alternatives for electricity generation in isolated regions. The compression ignition engine is considered the prime mover and has the attractive potential to distribute electricity generation for supply in isolated regions, as well as for [...] Read more.

Straight soybean and diesel oil blends are proposed as alternatives for electricity generation in isolated regions. The compression ignition engine is considered the prime mover and has the attractive potential to distribute electricity generation for supply in isolated regions, as well as for small applications demanded by the agro-industrial sector. The heat release rate evaluation of straight soybean blends is the main focus of this paper. A single-cylinder compression ignition engine with a nominal power of 14.7 kW/2200 rpm fueled with blends of 50% and 80% v/v straight soybean oil with commercial diesel oil was tested on a dynamometer bench. The heat release rate and ignition delay were determined from in-cylinder pressure measurements using zero-dimensional modeling. The experimental results showed a promising performance and coherent behavior with the physicochemical fuel properties and load conditions tested. The highest fraction of vegetable oil led to a combustion delay, characterized by high diffusive and residual combustion phases, although the fuel oxygen content favored the combustion. Finally, this work allowed observation of the development of the heat release rate of straight soybean blends in a diesel engine, understanding the influence of the fuel properties and in-cylinder gas properties on the combustion process. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

16 pages, 3632 KiB

Open AccessArticle

Numerical Study of High-g Combustion Characteristics in a Channel with Backward-Facing Steps

by Zhen Gong and Hao Tang

Aerospace 2024, 11(9), 767; https://doi.org/10.3390/aerospace11090767 - 19 Sep 2024

Cited by 1 | Viewed by 763

Abstract

High gravity (high-g) combustion can significantly increase flame propagation speed, thereby potentially shortening the axial length of aero-engines and increasing their thrust-to-weight ratio. In this study, we utilized the large eddy simulation model to investigate the combustion characteristics and flame morphology evolution of [...] Read more.

High gravity (high-g) combustion can significantly increase flame propagation speed, thereby potentially shortening the axial length of aero-engines and increasing their thrust-to-weight ratio. In this study, we utilized the large eddy simulation model to investigate the combustion characteristics and flame morphology evolution of premixed propane–air flames in a channel with a backward-facing step. The study reveals that both the increase in centrifugal force and flow velocity can enhance pressure fluctuations during combustion and increase the turbulence intensity. The presence of centrifugal force promotes the occurrence of Rayleigh–Taylor instability (RTI) between hot and cold fluids. The combined effects of RTI and Kelvin–Helmholtz instability (KHI) enhance the disturbance between hot and cold fluids, shorten the fuel combustion time, and intensify the dissipation of large-scale vortices. The increase in fluid flow velocity can raise the flame front’s hydrodynamic stretch rate, thereby enhancing the turbulence level during combustion to a certain extent and increasing the fuel consumption rate. When a strong centrifugal force is applied, the global flame propagation speed can be more than doubled. Within a certain range, the increase in high-g field strength can enhance the intensity of RTI and accelerate the transition of RTI to the nonlinear stage. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

16 pages, 5887 KiB

Open AccessArticle

Numerical Investigation on the Flame Characteristics of Lean Premixed Methane Flame Piloted with Rich Premixed Flame

by Lili Zhang, Yongzhang Cui, Pengfei Yin, Wenlong Mao and Pengzhao Zhang

Energies 2024, 17(14), 3430; https://doi.org/10.3390/en17143430 - 12 Jul 2024

Viewed by 999

Abstract

The introduction of the pilot flame can stabilize the lean premixed flame and promote its industrial application. However, the interaction mechanism between the pilot and main flames is complicated. To reveal the effect of the pilot flame on the main flame, a laminar [...] Read more.

The introduction of the pilot flame can stabilize the lean premixed flame and promote its industrial application. However, the interaction mechanism between the pilot and main flames is complicated. To reveal the effect of the pilot flame on the main flame, a laminar lean premixed flame adjacent to a rich premixed pilot flame on one side and a similar lean premixed flame on the other side was considered. A two-dimensional numerical model was adopted with detailed chemistry and species transport, also with no artificial flame anchoring boundary conditions. The results show that the pilot flame could promote the main flame stabilized in different locations with various shapes, by adjusting the stretch, heat transfer, and preferential diffusion in a complicated manner. The pilot flame improves the local equivalence ratio and transfer more heat to the main flame. The growth of the pilot flame equivalence ratio and inlet velocity enhances the combustion on the rich side of the main flame and helps it anchor closer to the flame wall. Both the curvature and strain rate show a significant effect on the flame root, which contributes to the main flame bending towards the pilot flame. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

15 pages, 458 KiB

Open AccessFeature PaperArticle

Comparisons of Different Representative Species Selection Schemes for Reduced-Order Modeling and Chemistry Acceleration of Complex Hydrocarbon Fuels

by Kevin M. Gitushi and Tarek Echekki

Energies 2024, 17(11), 2604; https://doi.org/10.3390/en17112604 - 28 May 2024

Viewed by 817

Abstract

The simulation of engine combustion processes, such as autoignition, an important process in the co-optimization of fuel-engine design, can be computationally expensive due to the large number of thermo-chemical scalars needed to describe the full chemical system. Yet, the inherent correlations between the [...] Read more.

The simulation of engine combustion processes, such as autoignition, an important process in the co-optimization of fuel-engine design, can be computationally expensive due to the large number of thermo-chemical scalars needed to describe the full chemical system. Yet, the inherent correlations between the different chemical species during oxidation can significantly reduce the complexity of representing this system. One strategy is to select a subset of representative species that accurately captures the combustion process at a fraction of the computational cost of the full system. In this study, we compare the performance of four different techniques to select these species. They include the two-step principal component analysis (PCA) approach, directed relation graphs (DRGs), the global pathway selection (GPS) approach, and the manifold-informed species selection method. A parametric study of the representative species selection is carried out on data from the simulation of homogeneous and perfectly stirred reactors by investigating seven cumulative variances and 47 different cut-off percentages for the two-step PCA, and 65 and 51 thresholds for the DRGs and GPS, respectively. Results show that these selection methods capture key important species that can accurately describe the chemical system and track each stage of oxidation. The two-step PCA is sensitive to the cumulative variance, and DRGs and GPS are sensitive to the choice of target variables. By selecting key representative species and reducing the number of thermo-chemical scalars, these three methods can be used to develop computationally efficient hybrid chemistry schemes. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

35 pages, 6486 KiB

Open AccessFeature PaperReview

A Review on Micro-Combustion Flame Dynamics and Micro-Propulsion Systems

by David M. Dias, Pedro R. Resende and Alexandre M. Afonso

Energies 2024, 17(6), 1327; https://doi.org/10.3390/en17061327 - 10 Mar 2024

Cited by 1 | Viewed by 2617

Abstract

This work presents a state-of-the-art review of micro-combustion flame dynamics and micro propulsion systems. In the initial section, we focus in on the different challenges of micro-combustion, investigating the typical length and time scales involved in micro-combustion and some critical phenomena such as [...] Read more.

This work presents a state-of-the-art review of micro-combustion flame dynamics and micro propulsion systems. In the initial section, we focus in on the different challenges of micro-combustion, investigating the typical length and time scales involved in micro-combustion and some critical phenomena such as flammability limits and the quenching diameter.We present an extensive collection of studies on the principal types of micro-flame dynamics, including flashback, blow-off, steady versus non-steady flames, mild combustion, stable flames, flames with repetitive extinction, and ignition and pulsatory flame burst. In the final part of this review, we focus on micropropulsion systems, their performance metrics, conventional manufacturing methods, and the advancements in Micro-Electro-Mechanical Systems manufacturing. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

15 pages, 3538 KiB

Open AccessArticle

A Data-Based Hybrid Chemistry Acceleration Framework for the Low-Temperature Oxidation of Complex Fuels

by Sultan Alqahtani, Kevin M. Gitushi and Tarek Echekki

Energies 2024, 17(3), 734; https://doi.org/10.3390/en17030734 - 4 Feb 2024

Cited by 1 | Viewed by 1277

Abstract

The oxidation of complex hydrocarbons is a computationally expensive process involving detailed mechanisms with hundreds of chemical species and thousands of reactions. For low-temperature oxidation, an accurate account of the fuel-specific species is required to correctly describe the pyrolysis stage of oxidation. In [...] Read more.

The oxidation of complex hydrocarbons is a computationally expensive process involving detailed mechanisms with hundreds of chemical species and thousands of reactions. For low-temperature oxidation, an accurate account of the fuel-specific species is required to correctly describe the pyrolysis stage of oxidation. In this study, we develop a hybrid chemistry framework to model and accelerate the low-temperature oxidation of complex hydrocarbon fuels. The framework is based on a selection of representative species that capture the different stages of ignition, heat release, and final products. These species are selected using a two-step principal component analysis of the reaction rates of simulation data. Artificial neural networks (ANNs) are used to model the source terms of the representative species during the pyrolysis stage up to the transition time. This ANN-based model is coupled with C₀–C₄ foundational chemistry, which is used to model the remaining species up to the transition time and all species beyond the transition time. Coupled with the USC II mechanism as foundational chemistry, this framework is demonstrated using simple reactor homogeneous chemistry and perfectly stirred reactor (PSR) calculations for n-heptane oxidation over a range of composition and thermodynamic conditions. The hybrid chemistry framework accurately captures correct physical behavior and reproduces the results obtained using detailed chemistry at a fraction of the computational cost. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

14 pages, 6242 KiB

Open AccessArticle

The Effects of Parameter Settings on Triggering Time and Climb Rate during Lean-Premixed Combustion Thermoacoustic Oscillations

by Chengfei Tao, Rongyue Sun, Yichen Wang, Liang Zhang, Jiangming Ye and Shaohua Liang

Appl. Sci. 2024, 14(2), 806; https://doi.org/10.3390/app14020806 - 17 Jan 2024

Cited by 1 | Viewed by 951

Abstract

This study theoretically explored the effects of parameter settings on thermoacoustic oscillations with a low-order model. Three factors were explored—combustor length, inlet gas temperature and thermal power. The research findings indicate that optimizing the parameter settings can yield better thermoacoustic oscillation suppression results. [...] Read more.

This study theoretically explored the effects of parameter settings on thermoacoustic oscillations with a low-order model. Three factors were explored—combustor length, inlet gas temperature and thermal power. The research findings indicate that optimizing the parameter settings can yield better thermoacoustic oscillation suppression results. The sound pressure amplitude decreased from 3.2 × 10⁵ Pa to 2.1 × 10⁵ Pa as the combustor length increased from 1.2 m to 6.0 m. The triggering time increased from 0.32 s to 0.91 s when the combustion chamber length increased. The climb rate declined from 23.38 × 10⁵ Pa/s to 3.75 × 10⁵ Pa/s when the combustor length was elongated. The sound pressure amplitude decreased from 3.44 × 10⁵ Pa to 2.4 × 10⁵ Pa as the gas temperature rose from 0 to 100 °C. The triggering time and climb rate variation tendency were similar when the gas temperature increased—both declined as the gas temperature rose. The sound pressure amplitude experienced a slight fluctuation when the thermal power rose. However, the triggering time decreased from 0.26 s to 0.043 s when the thermal power improved. The climb rate increased from 18.72 × 10⁵ Pa/s to 27.65 × 10⁵ Pa/s when the thermal power rose. The oscillation frequency presented was completely different in three cases that had different wavelengths and oscillation intensities. The triggering time and climb rate fluctuated extensively in varying conditions, and the above two factors were interrelated and contradictory to each other when thermoacoustic oscillation was excited. This study explored parameters’ effects on triggering time and climb rate, thereby providing references for constructing a model-based control system for thermoacoustic oscillation feedback control. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

24 pages, 10369 KiB

Open AccessArticle

The Influence of Co-Firing Coal with Biomass Syngas on the Thermodynamic Parameters of a Boiler

by Jin Wang, Qiaopeng Yao, Xiaoling Jin and Lei Deng

Appl. Sci. 2023, 13(20), 11477; https://doi.org/10.3390/app132011477 - 19 Oct 2023

Cited by 1 | Viewed by 1399

Abstract

Biomass syngas can be considered as a supplementary fuel to partially substitute coal, which is beneficial to CO₂ emission reduction. For the case study, the influences of co-firing typical biomass syngas (gasification from palm, straw, and wood) with coal on the thermodynamic [...] Read more.

Biomass syngas can be considered as a supplementary fuel to partially substitute coal, which is beneficial to CO₂ emission reduction. For the case study, the influences of co-firing typical biomass syngas (gasification from palm, straw, and wood) with coal on the thermodynamic parameters of a 300 MW tangentially fired boiler are evaluated through a thermal calculation based on the principles of mass conservation, heat conservation, and heat transfer. The effects of boiler loads, biomass syngas species, and consumption rates are discussed. The results show that the introduction of biomass syngas weakens the radiative characteristics of the flame and reduces the furnace exit flue-gas temperature. As 3 × 10⁴ m³ h⁻¹ of wood syngas is introduced, the decrement of thermal efficiency reaches 0.4%, while that of the coal consumption rate is 5.1%. The retrofitting of the boiler was not necessary and the corrosion of the low-temperature heating surface did not appear. The CO₂ annual emission reduction could achieve 0.001 to 0.095 million tons for palm syngas, 0.005 to 0.069 million tons for straw syngas, and 0.013 to 0.107 million tons for wood syngas with increasing biomass syngas consumption rates under the full load. Moreover, the main thermodynamic parameters changed more significantly under the low loads. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

19 pages, 54763 KiB

Open AccessArticle

The Effects of Cracking Ratio on Ammonia/Air Non-Premixed Flames under High-Pressure Conditions Using Large Eddy Simulations

by Chengming Wang, Haiou Wang, Kun Luo and Jianren Fan

Energies 2023, 16(19), 6985; https://doi.org/10.3390/en16196985 - 7 Oct 2023

Cited by 8 | Viewed by 1872

Abstract

Ammonia is a promising carbon-free fuel. However, one of the main challenges for ammonia combustion is the high level of

NO

emissions. In this study, simulations were conducted for ammonia/air laminar counterflow flames and turbulent non-premixed jet flames in the KAUST high-pressure combustion [...] Read more.

Ammonia is a promising carbon-free fuel. However, one of the main challenges for ammonia combustion is the high level of

NO

emissions. In this study, simulations were conducted for ammonia/air laminar counterflow flames and turbulent non-premixed jet flames in the KAUST high-pressure combustion duct (HPCD) at a pressure of 5 bar, with two ammonia cracking ratios of 14% and 28%. The influence of ammonia cracking ratio on the flame structure and

NO

formation mechanism were examined. The laminar counterflow flame results showed that

HNO

is one of the most critical species related to

NO

formation and

NO

is mainly generated through the path of

{NH}_{2} \to NH \to HNO \to NO

. For the turbulent flames, the flamelet/progress variable (FPV) approach was employed in the context of large eddy simulations (LES) for high-fidelity simulations. The simulation results were compared with the measured data with promising agreements, which proves the accuracy of the FPV method for the present flames. It was shown that with increasing cracking ratio, not only the flame reactivity is enhanced, but also the generation of

NO

is increased. The correlation between

NO

and

HNO

is weaker when compared to that between

NO

and radicals such as

O

,

H

and

OH

in the entire flame. Through the distribution of

NO

source terms, it was found that the

NO

source term has a higher absolute value in the upstream region and the absolute value rapidly decreases with increasing streamwise distance. The total

NO

source term is positive in the fuel-lean zone and shows negative values in the fuel-rich zone. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

24 pages, 6315 KiB

Open AccessFeature PaperArticle

Investigating the Ignition and Stability Limits of Premixed Methane/Air Combustion in Micro-Channels

by Almoutazbellah Kutkut, Mohsen Ayoobi, Marc E. Baumgardner and V’yacheslav Akkerman

Energies 2023, 16(18), 6752; https://doi.org/10.3390/en16186752 - 21 Sep 2023

Cited by 3 | Viewed by 1366

Abstract

Understanding and improving the performance of miniature devices powered by micro-combustion have been the focus of continued attention of researchers recently. The goal of the present work is to investigate the behavior of premixed methane–air combustion in a quartz microreactor with an externally [...] Read more.

Understanding and improving the performance of miniature devices powered by micro-combustion have been the focus of continued attention of researchers recently. The goal of the present work is to investigate the behavior of premixed methane–air combustion in a quartz microreactor with an externally controlled wall temperature. Specifically, the impacts of the flow inlet velocity, the equivalence ratio, and the microreactor channel size are examined. This study is conducted by means of computational simulations, and the results are validated against prior experimental data, as well as by other similar studies in the literature. Utilizing simulation results with detailed chemistry, the present work provides more in-depth insight into a variety of phenomena, such as ignition, flame propagation, flames with repetitive extinctions and ignitions (FREI), and flame stabilization. In particular, the ignition, the flame span, and the FREI-related characteristics are scrutinized to understand the underlying physics of the flame stability/instability modes. It is shown that the flames appear stable at higher inlet velocities, while the FREI mode is detected at a lower inlet velocity, depending on the equivalence ratio and the channel size. The findings also explain how different operating conditions impact the flame characteristics in both stability modes. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

20 pages, 12780 KiB

Open AccessArticle

Combustion Regimes in Turbulent Non-Premixed Flames for Space Propulsion

by Daniel Martinez-Sanchis, Andrej Sternin, Oskar Haidn and Martin Tajmar

Aerospace 2023, 10(8), 671; https://doi.org/10.3390/aerospace10080671 - 28 Jul 2023

Cited by 4 | Viewed by 1980

Abstract

Direct numerical simulations of non-premixed fuel-rich methane–oxygen flames at 20 bar are conducted to investigate the turbulent mixing burning of gaseous propellants in rocket engines. The reacting flow is simulated by using an EBI-DNS solver within an OpenFOAM frame. The transport of species [...] Read more.

Direct numerical simulations of non-premixed fuel-rich methane–oxygen flames at 20 bar are conducted to investigate the turbulent mixing burning of gaseous propellants in rocket engines. The reacting flow is simulated by using an EBI-DNS solver within an OpenFOAM frame. The transport of species is resolved with finite-rate chemistry by using a complex skeletal mechanism that entails 21 species. Two different flames at low and high Reynolds numbers are considered to study the sensitivity of the flame dynamics to turbulence. Regime markers are used to measure the probability of the flow to burn in premixed and non-premixed conditions at different regions. The local heat release statistics are studied in order to understand the drivers in the development of the turbulent diffusion flame. Despite the eminent non-premixed configuration, a significant amount of combustion takes place in premixed conditions. Premixed combustion is viable in both lean and fuel-rich regions, relatively far from the stoichiometric line. It has been found that a growing turbulent kinetic energy is detrimental to combustion in fuel-rich premixed conditions. This is motivated by the disruption of the local premixed flame front, which promotes fuel transport into the diffusion flame. In addition, at downstream positions, higher turbulence enables the advection of methane into the lean core of the flame, enhancing the burning rates in these regions. Therefore, the primary effect of turbulence is to increase the fraction of propellants burnt in oxygen-rich and near-stoichiometric conditions. Consequently, the mixture fraction of the products shifts towards lean conditions, influencing combustion completion at downstream positions. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

34 pages, 8147 KiB

Open AccessArticle

Performance and Weight Parameters Calculation for Hydrogen- and Battery-Powered Aircraft Concepts

by Michal Janovec, Viktor Babčan, Branislav Kandera, Kristína Šajbanová, Filip Škultéty and Ľuboš Halvoň

Aerospace 2023, 10(5), 482; https://doi.org/10.3390/aerospace10050482 - 18 May 2023

Cited by 3 | Viewed by 3424

Abstract

This article describes the creation of a program that would be useful for calculating mathematical models in order to estimate the weight of aircraft components. Using several parameters, it can calculate other parameters of civil transport aircraft powered by batteries or fuel cells. [...] Read more.

This article describes the creation of a program that would be useful for calculating mathematical models in order to estimate the weight of aircraft components. Using several parameters, it can calculate other parameters of civil transport aircraft powered by batteries or fuel cells. The main goals of this research were to add the missing dimensions and parameters to the aircraft database, create a simple but effective program for creating mathematical models, and use this program to find technological barriers to battery or hydrogen fuel-cell-powered aircraft concepts. The article introduces the reader to the problem of calculating OEW (operating empty weight) using Breguet–Leduc equations. A calculation model was created for OEW calculation. The result of this work is the verification of a mathematical model for battery-powered electric aircraft of the CS-23 (European Aviation Safety Agency Certification Specification for Normal, Utility, Aerobatic, and Commuter Category Aeroplanes) category by comparing the program’s outputs with real aircraft. Subsequently, the results of mathematical models are shown in graphs that specify the space of possible concepts of aircraft powered by batteries or fuel cells, sorted by the number of passengers and the range of the aircraft, delimited by two or three criteria, respectively. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

14 pages, 4573 KiB

Open AccessArticle

Effect of Zr Modification on NH₃-SCR Reaction Performance of Cu-Ce/SAPO-34 Catalysts

by Chongfei Liu, Xuetao Wang, Lili Xing, Xingxing Cheng, Xingyu Zhang, Haojie Li and Mengjie Liu

Appl. Sci. 2023, 13(8), 4763; https://doi.org/10.3390/app13084763 - 10 Apr 2023

Cited by 4 | Viewed by 2263

Abstract

Molecular sieve catalysts containing transition metals have been attracting attention for their potential applications in various fields, including environmental and industrial catalysis. A Cu-Ce-Zr/SAPO-34 series of molecular sieve catalysts were prepared by the impregnation method, and the effect of Zr introduction on the [...] Read more.

Molecular sieve catalysts containing transition metals have been attracting attention for their potential applications in various fields, including environmental and industrial catalysis. A Cu-Ce-Zr/SAPO-34 series of molecular sieve catalysts were prepared by the impregnation method, and the effect of Zr introduction on the selective catalytic reduction of NO by Cu-Ce/SAPO-34 molecular sieve catalysts was explored. Through various characterization methods, the physical and chemical properties of the catalysts were analyzed, and the denitration mechanism of the molecular sieve catalyst was discussed. This study found that the total acid content of the acid sites on the catalyst surface decreased with the introduction of Zr, leading to a decrease in the denitration efficiency of the catalyst. At 350–400 °C, the denitration efficiency of the 4Cu-4Ce-4Zr/SAPO-34 catalyst was over 80%, and at 400–500 °C, it was over 99%. Moreover, excessive metal Zr could destroy its CHA structure and decrease the denitration efficiency of the catalyst. This study analyzed the reaction mechanism of NH₃-SCR of Zr-modified polymetallic zeolites and the effect of Zr modification on the NH3-SCR reaction results. This study contributes to the understanding of the performance of molecular sieve catalysts containing transition metals. Reliable conclusions were obtained, which offer data support for future research in the field of NH₃-SCR. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

19 pages, 3577 KiB

Open AccessArticle

Numerical Study of the Influence of the Thermal Gas Expansion on the Boundary Layer Flame Flashback in Channels with Different Wall Thermal Conditions

by Kai Huang, Damir M. Valiev, Hongtao Zhong and Wenhu Han

Energies 2023, 16(4), 1844; https://doi.org/10.3390/en16041844 - 13 Feb 2023

Cited by 2 | Viewed by 1881

Abstract

In recent years, boundary layer flame flashback (BLF) has re-emerged as a technological and operational issue due to the more widespread use of alternative fuels as a part of a global effort to promote carbon neutrality. While much understanding has been achieved in [...] Read more.

In recent years, boundary layer flame flashback (BLF) has re-emerged as a technological and operational issue due to the more widespread use of alternative fuels as a part of a global effort to promote carbon neutrality. While much understanding has been achieved in experiments and simulations of BLF in the past decades, the theoretical modeling of BLF still largely relies on the progress made as early as the 1940s, when the critical gradient model (CGM) for the laminar flame flashback was proposed by Lewis and von Elbe. The CGM does not account for the modification of the upstream flow by the flame, which has been recently shown to play a role in BLF. The aim of the present work is to gain additional insight into the effects of thermal gas expansion and confinement on the flame-flow interaction in laminar BLF. Two-dimensional simulations of the confined laminar BLF in a channel are performed in this work. The parametric study focuses on the channel width, the thermal gas expansion coefficient, and the heat losses to the wall. This study evaluates the influence of these factors on the critical condition for the flame flashback. By varying the channel width, it is demonstrated that at the critical condition, the incoming flow in narrow channels is modified globally by the thermal gas expansion, while in wider channels, the flow modification by the flame tends to be more local. In narrow channels, a non-monotonic dependence of the critical-condition centerline velocity on the channel width has been identified. The variation of the heat loss to the wall confirms that the wall’s thermal conditions can significantly alter the flashback limit, with the flashback propensity being larger when the thermal resistance of the wall is high. To assess the general applicability of the CGM, the flame consumption speed and the flow velocity near the wall are quantified. The results confirm that the assumption of flame having no influence on the upstream flow, employed in the CGM, is not fulfilled under confinement for a realistic thermal gas expansion. This results in a general disagreement between the simulations and the CGM, which implies that the thermal expansion effects should be accounted for when considering the confined boundary layer flashback limits. It is shown that the critical velocity gradient increases with the gas expansion coefficient for the given channel width and wall thermal condition. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

21 pages, 9140 KiB

Open AccessArticle

Comparative Study of Spark-Ignited and Pre-Chamber Hydrogen-Fueled Engine: A Computational Approach

by Hammam Aljabri, Mickael Silva, Moez Ben Houidi, Xinlei Liu, Moaz Allehaibi, Fahad Almatrafi, Abdullah S. AlRamadan, Balaji Mohan, Emre Cenker and Hong G. Im

Energies 2022, 15(23), 8951; https://doi.org/10.3390/en15238951 - 26 Nov 2022

Cited by 17 | Viewed by 3298

Abstract

Hydrogen is a promising future fuel to enable the transition of transportation sector toward carbon neutrality. The direct utilization of H₂ in internal combustion engines (ICEs) faces three major challenges: high NO_x emissions, severe pressure rise rates, and pre-ignition at mid [...] Read more.

Hydrogen is a promising future fuel to enable the transition of transportation sector toward carbon neutrality. The direct utilization of H₂ in internal combustion engines (ICEs) faces three major challenges: high NO_x emissions, severe pressure rise rates, and pre-ignition at mid to high loads. In this study, the potential of H₂ combustion in a truck-size engine operated in spark ignition (SI) and pre-chamber (PC) mode was investigated. To mitigate the high pressure rise rate with the SI configuration, the effects of three primary parameters on the engine combustion performance and NO_x emissions were evaluated, including the compression ratio (CR), the air–fuel ratio, and the spark timing. In the simulations, the severity of the pressure rise was evaluated based on the maximum pressure rise rate (MPRR). Lower compression ratios were assessed as a means to mitigate the auto-ignition while enabling a wider range of engine operation. The study showed that by lowering CR from 16.5:1 to 12.5:1, an indicated thermal efficiency of 47.5% can be achieved at 9.4 bar indicated mean effective pressure (IMEP) conditions. Aiming to restrain the auto-ignition while maintaining good efficiency, growth in λ was examined under different CRs. The simulated data suggested that higher CRs require a higher λ, and due to practical limitations of the boosting system, λ at 4.0 was set as the limit. At a fixed spark timing, using a CR of 13.5 combined with λ at 3.33 resulted in an indicated thermal efficiency of 48.6%. It was found that under such lean conditions, the exhaust losses were high. Thus, advancing the spark time was assessed as a possible solution. The results demonstrated the advantages of advancing the spark time where an indicated thermal efficiency exceeding 50% was achieved while maintaining a very low NO_x level. Finally, the optimized case in the SI mode was used to investigate the effect of using the PC. For the current design of the PC, the results indicated that even though the mixture is lean, the flame speed of H₂ is sufficiently high to burn the lean charge without using a PC. In addition, the PC design used in the current work induced a high MPRR inside the PC and MC, leading to an increased tendency to engine knock. The operation with PC also increased the heat transfer losses in the MC, leading to lower thermal efficiency compared to the SI mode. Consequently, the PC combustion mode needs further optimizations to be employed in hydrogen engine applications. Full article

(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)

► Show Figures

Figure 1

Topic Menu

Topic Editors

Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion

Topic Information

Keywords

Participating Journals

Published Papers (17 papers)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI