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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: closed (25 August 2024) | Viewed by 3994

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Prof. Dr. Markus Klein

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Department of Aerospace Engineering, Institute for Applied Mathematics and Scientific Computing, University of the Bundeswehr Munich, 85577 Neubiberg, Germany
Interests: turbulent combustion; multiphase flow; reactive flow; aerodynamics; supersonic flows; gas explosions; computational fluid dynamics (CFD); numerical methods
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Prof. Dr. Nilanjan Chakraborty

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School of Engineering, Newcastle University, Newcastle-upon-Tyne NE1 7RU, UK
Interests: computational fluid dynamics; turbulent flows; turbulent combustion; heat transfer; non-newtonian fluids; multiphase flows
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Prof. Dr. Christian Trapp

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Guest Editor

Department of Vehicle Power Trains, University of Bundeswehr Munich, 85579 Neubiberg, Germany
Interests: new combustion concepts; alternate fuels (Hydrogen, Ammonia, Methanol); ignition concepts; computational fluid dynamics; turbulent flow; turbulent combustion; ignition modelling; reaction kinetics; thermodynamic and optical experimental methods

Special Issue Information

Dear Colleagues,

The transformation of the transport sector into a climate-neutral economy is particularly challenging, because for some applications, there are only few alternatives to high-energy-density liquid fuels. Therefore, conventional or new concepts for thermochemical energy conversion in combination with e-fuels will play an important role during the transition phase towards a future, carbon-free energy landscape and beyond. The need for new biogenic, synthetic, carbon-free or carbon-reduced fuels, together with the development of new combustion concepts, poses considerable challenges to the research community. The design and development of new combustion systems requires extensive multi-scale and multi-physics experimental and numerical analysis.

In recent years, several contributions from the community have been published that deal with the fundamental aspects of high-fidelity modelling and experimental characterization of internal combustion engines. The urgent need for the use of carbon-free fuels, such as hydrogen or ammonia, or e-fuels, like methanol, DME or ethanol, require significant research efforts because all of these fuels have largely different thermo-chemical properties, flame speeds, flame temperatures and flammability limits and are sometimes difficult in terms of emission control. In addition, there is the need to make thermochemical energy conversion more efficient using concepts like RCCI or water injection using two injectors or fuel/water emulsions in combination with carbon-free or synthetic energy careers.

This Special Issue aims to contribute to the fundamental physical understanding and high-fidelity modelling of turbulent combustion using alternative fuels and new energy conversion concepts. Contributions are welcome from specialists with analytical, experimental and numerical backgrounds who are able to provide different perspectives regarding this topic.

Prof. Dr. Markus Klein
Prof. Dr. Nilanjan Chakraborty
Prof. Dr. Christian Trapp
Guest Editors

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Published Papers (5 papers)

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Research

19 pages, 5538 KiB

Open AccessArticle

Modeling of Hydrogen Combustion from a 0D/1D Analysis to Complete 3D-CFD Engine Simulations

by Thomas Gal, Robin Schmelcher, Antonino Vacca, Francesco Cupo, Marco Chiodi and André Casal Kulzer

Energies 2024, 17(22), 5543; https://doi.org/10.3390/en17225543 - 6 Nov 2024

Viewed by 502

Abstract

Hydrogen and its unique properties pose major challenges to the development of innovative combustion engines, while it represents a viable alternative when it is based on renewable energy sources. The present paper deals with the holistic approach of hydrogen combustion modeling from a 0D/1D reactor evaluation with Cantera up to complete engine simulations in the 3D-CFD tool QuickSim. The obtained results are referenced to the current literature and calibrated with experimental data. In particular, the engine simulations are validated against measurements of a single-cylinder research engine, which was specifically adapted for lean hydrogen operation and equipped with port fuel injection and a passive pre-chamber system. Special attention is hereby given to the influence of different engine loads and varying lambda operation. The focus of this work is the complementary numerical investigation of the hydrogen flame speed and its self-ignition resistance under the consideration of various reaction mechanisms. A detailed transfer from laminar propagation under laboratory conditions to turbulent flame development within the single-cylinder engine is hereby carried out. It is found that the relatively simple reaction kinetics of hydrogen can lead to acceptable results for all mechanisms, but there are particular effects with regard to the engine behavior. The laminar flame speed and induction time vary greatly with the inner cylinder conditions and significantly affect the entire engine’s operation. The 3D-CFD environment offers the opportunity to analyze the interactions between mixture formation and combustion progress, which are indispensable to evaluate advanced operating strategies and optimize the performance and efficiency, as well as the reliability, of the engine. Full article

(This article belongs to the Special Issue Towards Climate Neutral Thermochemical Energy Conversion)

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17 pages, 2398 KiB

Open AccessFeature PaperArticle

Effects of Water Mist on the Initial Evolution of Turbulent Premixed Hydrogen/Air Flame Kernels

by Riccardo Concetti, Josef Hasslberger, Nilanjan Chakraborty and Markus Klein

Energies 2024, 17(18), 4632; https://doi.org/10.3390/en17184632 - 16 Sep 2024

Viewed by 728

Abstract

In this study, a series of carrier-phase direct numerical simulations are conducted on spherical expanding premixed hydrogen/air flames with liquid water addition. An Eulerian–Lagrangian approach with two-way coupling is employed to describe the liquid–gas interaction. The impacts of preferential diffusion, the equivalence ratio, water loading, and the initial diameter of the water droplets are examined and analyzed in terms of flame evolution. It is observed that liquid water has the potential to influence flame propagation characteristics by reducing the total burning rate, flame area, and burning rate per unit area, attributed to flame cooling effects. However, these effects become discernible only under conditions where water evaporation is sufficiently intense. For the conditions investigated, the influence of preferential diffusion on flame evolution is found to be more significant than the interaction with liquid water. The results suggest that due to the slow evaporation rate of water, which is a result of its high latent heat of evaporation, the water droplets do not disturb the initial flame kernel growth significantly. This has implications for water injection concepts in internal combustion engines and for explosion mitigation. Full article

(This article belongs to the Special Issue Towards Climate Neutral Thermochemical Energy Conversion)

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32 pages, 12297 KiB

Open AccessArticle

A Comparative Study of the Hydrogen Auto-Ignition Process in Oxygen–Nitrogen and Oxygen–Water Vapor Oxidizer: Numerical Investigations in Mixture Fraction Space and 3D Forced Homogeneous Isotropic Turbulent Flow Field

by Lena Caban and Artur Tyliszczak

Energies 2024, 17(17), 4525; https://doi.org/10.3390/en17174525 - 9 Sep 2024

Cited by 1 | Viewed by 479

Abstract

In this paper, we analyze the auto-ignition process of hydrogen in a hot oxidizer stream composed of oxygen–nitrogen and oxygen–water vapor with nitrogen/water vapor mass fractions in a range of 0.1–0.9. The temperature of the oxidizer varies from 1100 K to 1500 K and the temperature of hydrogen is assumed to be 300 K. The research is performed in 1D mixture fraction space and in a forced homogeneous isotropic turbulent (HIT) flow field. In the latter case, the Large Eddy Simulation (LES) method combined with the Eulerian Stochastic Field (ESF) combustion model is applied. The results obtained in mixture fraction space aim to determine the most reactive mixture fraction, maximum flame temperature, and dependence on the scalar dissipation rate. Among others, we found that the ignition in

H_{2}

O_{2}

H_{2} O

mixtures occurs later than in

H_{2}

O_{2}

N_{2}

mixtures, especially at low oxidizer temperatures. On the other hand, for a high oxidizer temperature, the ignitability of

H_{2}

O_{2}

H_{2} O

mixtures is extended, i.e., the ignition occurs for a larger content of

H_{2} O

and takes place faster. The 3D LES-ESF results show that the ignition time is virtually independent of initial conditions, e.g., randomness of an initial flow field and turbulence intensity. The latter parameter, however, strongly affects the flame evolution. It is shown that the presence of water vapor decreases ignitability and makes flames more prone to extinction. Full article

(This article belongs to the Special Issue Towards Climate Neutral Thermochemical Energy Conversion)

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14 pages, 2147 KiB

Open AccessFeature PaperArticle

Performance of a Methanol-Fueled Direct-Injection Compression-Ignition Heavy-Duty Engine under Low-Temperature Combustion Conditions

by Mark Treacy, Leilei Xu, Hesameddin Fatehi, Ossi Kaario and Xue-Song Bai

Energies 2024, 17(17), 4307; https://doi.org/10.3390/en17174307 - 28 Aug 2024

Viewed by 906

Abstract

Low-temperature combustion (LTC) concepts, such as homogeneous charge compression ignition (HCCI) and partially premixed combustion (PPC), aim to reduce in-cylinder temperatures in internal combustion engines, thereby lowering emissions of nitrogen oxides (NO_x) and soot. These LTC concepts are particularly attractive for decarbonizing conventional diesel engines using renewable fuels such as methanol. This paper uses numerical simulations and a finite-rate chemistry model to investigate the combustion and emission processes in LTC engines operating with pure methanol. The aim is to gain a deeper understanding of the physical and chemical processes in the engine and to identify optimal engine operation in terms of efficiency and emissions. The simulations replicated the experimentally observed trends for CO, unburned hydrocarbons (UHCs), and NO_x emissions, the required intake temperature to achieve consistent combustion phasing at different injection timings, and the distinctively different combustion heat release processes at various injection timings. It was found that the HCCI mode of engine operation required a higher intake temperature than PPC operation due to methanol’s low ignition temperature in fuel-richer mixtures. In the HCCI mode, the engine exhibited ultra-low NO_x emissions but higher emissions of UHC and CO, along with lower combustion efficiency compared to the PPC mode. This was attributed to poor combustion efficiency in the near-wall regions and engine crevices. Low emissions and high combustion efficiency are achievable in PPC modes with a start of injection around a crank angle of 30° before the top dead center. The fundamental mechanism behind the engine performance is analyzed. Full article

(This article belongs to the Special Issue Towards Climate Neutral Thermochemical Energy Conversion)

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16 pages, 5933 KiB

Open AccessEditor’s ChoiceArticle

Learning Flame Evolution Operator under Hybrid Darrieus Landau and Diffusive Thermal Instability

by Rixin Yu, Erdzan Hodzic and Karl-Johan Nogenmyr

Energies 2024, 17(13), 3097; https://doi.org/10.3390/en17133097 - 23 Jun 2024

Viewed by 862

Abstract

Recent advancements in the integration of artificial intelligence (AI) and machine learning (ML) with physical sciences have led to significant progress in addressing complex phenomena governed by nonlinear partial differential equations (PDEs). This paper explores the application of novel operator learning methodologies to unravel the intricate dynamics of flame instability, particularly focusing on hybrid instabilities arising from the coexistence of Darrieus–Landau (DL) and Diffusive–Thermal (DT) mechanisms. Training datasets encompass a wide range of parameter configurations, enabling the learning of parametric solution advancement operators using techniques such as parametric Fourier Neural Operator (pFNO) and parametric convolutional neural networks (pCNNs). Results demonstrate the efficacy of these methods in accurately predicting short-term and long-term flame evolution across diverse parameter regimes, capturing the characteristic behaviors of pure and blended instabilities. Comparative analyses reveal pFNO as the most accurate model for learning short-term solutions, while all models exhibit robust performance in capturing the nuanced dynamics of flame evolution. This research contributes to the development of robust modeling frameworks for understanding and controlling complex physical processes governed by nonlinear PDEs. Full article

(This article belongs to the Special Issue Towards Climate Neutral Thermochemical Energy Conversion)

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