Proceedings of the Combustion Institute最新文献

{"title":"Flame characteristics and lift-off dependencies of flames stabilized on a multi hydrogen jet in swirled crossflow burner","authors":"Lars Koch,&nbsp;Julian Bajrami,&nbsp;Friedrich Dinkelacker","doi":"10.1016/j.proci.2025.105878","DOIUrl":"10.1016/j.proci.2025.105878","url":null,"abstract":"<div><div>This study investigates the stabilization and lift-off behaviour of flames on a multi-hydrogen jet in a swirled crossflow burner under thermal powers ranging from 3 to 17 kW, equivalence ratios from 0.1 to 1.2, and swirl numbers from 0 to 1.79. Depending on the operational conditions, five different flame types can be stabilized. These flames can be distinguished by their anchoring: either anchored at the jet orifices or lifted and stabilized aerodynamically within the shear layer of hydrogen and air. The transitional behaviour of these flame architypes was examined using OH-PLIF, visible chemiluminescence images and stereo-PIV data of the isothermal flow field. Flame shapes during anchoring are primarily influenced by the formation of an inner recirculation zone (IRZ), determined by the crossflow swirl and the equivalence ratio. The imparted swirling motion of the crossflow is reduced due to the radial injection of hydrogen, resulting in an effective swirl number that governs the vortex breakdown. This promotes the formation of an additional reaction zone within the IRZ. Lift-off occurs by increasing the crossflow velocity until the anchored jet flames blow out and an edge flame stabilizes in low-velocity regions of the hydrogen-air shear layer. The lift-off behaviour is similarly governed by the effective swirl number. Increasing the effective swirl number causes a tangential deflection of the anchored flame jets, resulting in a spiral jet path. This motion increases jet-to-jet interactions, leading to merging of several flame jets and increased stability, leading to higher crossflow velocities required to detach the flame. The study’s results highlight the importance of carefully balancing the advantages of increased crossflow swirl, such as enhanced mixing, flame compactness and stability, against the diminished operational range in the lifted regime and proposes an effective swirl number as guidance for the injector design using multi-jet in a swirl crossflow configuration.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105878"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145216409","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental and numerical investigation of non-premixed ammonia flames stabilized on a heated slot burner","authors":"Daniel Kretzler ,&nbsp;Rishabh Puri ,&nbsp;Björn Stelzner ,&nbsp;Thorsten Zirwes ,&nbsp;Fabian P. Hagen ,&nbsp;Oliver T. Stein ,&nbsp;Dimosthenis Trimis","doi":"10.1016/j.proci.2025.105854","DOIUrl":"10.1016/j.proci.2025.105854","url":null,"abstract":"<div><div>In this study, non-premixed laminar ammonia/air flames are investigated using a custom-designed heated slot burner developed at KIT. This innovative setup enables investigations into ammonia decomposition and pollutant formation processes through in-situ diagnostics, numerical simulations, and global performance analyses, providing a unique dataset. Experiments are conducted at three oven temperatures (T = 1073 K, 1123 K, and 1173 K) and two thermal loads (0.2 and 0.6 kW) at a global equivalence ratio of <span><math><mrow><mi>Φ</mi><mo>=</mo><mn>1</mn></mrow></math></span>. Inlet temperatures, as well as qualitative insights into NH*, NH₂*, and OH* along the flame are obtained using thermocouples and emission spectroscopy. To assess global combustion characteristics, gas analyzers measure exhaust species, including NO, NO₂, N₂O, NH₃, and O₂. The experimental setup is reconstructed in two dimensions for numerical simulations using an in-house OpenFOAM solver. Flame and emission characteristics are investigated for different operating conditions and chemical mechanisms. While experiments and simulations agree well regarding flame length, flame stability, and chemiluminescence profiles, some deviations in exhaust gas emissions remain. These are attributed to experimental uncertainty from the assumption of flow symmetry, boundary conditions, and uncertainty due to the choice of chemical reaction mechanism at elevated temperatures. Emissions are strongly influenced by oven temperature and flow velocity, with lowest NH₃, N₂O, and NO_x levels observed at high oven temperatures. The non-premixed configuration achieves NO_x emissions down to 335 ppmv at <span><math><mrow><mi>Φ</mi><mo>=</mo><mn>1</mn></mrow></math></span>, significantly below values from premixed combustion, which typically exceed several thousand ppmv. Pathway analysis reveals that the investigated reaction mechanisms predict routes with different relative contributions to NO production, but provide similar trends for NO consumption. The results highlight the suitability of the platform for systematic ammonia combustion studies and the potential of non-premixed strategies for NO_x mitigation.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105854"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145154443","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Kinetic coupling effects on the extinction limits of diffusion flames of hydrocarbons blended with ammonia","authors":"Min Kyeong Yoon ,&nbsp;Frederick L. Dryer ,&nbsp;Michael P. Burke ,&nbsp;Sang Hee Won","doi":"10.1016/j.proci.2025.105801","DOIUrl":"10.1016/j.proci.2025.105801","url":null,"abstract":"<div><div>Chemical kinetic coupling effects between NH₃ and liquid hydrocarbon fuels on extinction limits of diffusion flames are experimentally and numerically investigated. Three n-alkanes (n-heptane, n-decane, and n-dodecane), isooctane as a representative fully branched isoalkane, and toluene as a representative mono-aromatic are each tested, along with their blends with NH₃. The measured extinction strain rates are analyzed, employing transport-weighted enthalpy and radical index to demonstrate relative changes of chemical kinetic potentials for each fuel evaluated. The results show a significantly lower chemical kinetic potential for NH₃, compared to hydrocarbon fuels. Comparison of extinction limits as a function of transport-weighted enthalpy multiplied by radical index for fuel/NH₃ mixtures shows potential promotive effects for n-alkanes and no significant coupling for isooctane and toluene. Planar laser-induced fluorescence is applied to quantify OH concentrations for n-heptane, isooctane, and their mixtures with NH₃, and data are modeled to test the fidelity of chemical kinetic model predictions. It is found that including interaction reactions of n-alkyl and isoalkyl fragments with NH₂, and the reactions involving methylamine and cyanide are critical to predicting OH production rates, as well as extinction limits for hydrocarbon/NH₃ blends. Promotive effects of NH₃ blending on n-alkanes diffusion flame extinction limits are primarily from higher flame temperatures due to the reduced fraction of CO₂ found in the flame products. In the case of isooctane blended with NH₃, the formation of two main isoalkyl fragments, CH₃ and C₃H₆, are found to interact with NH₂, resulting in the suppression of the reactive radical pool population and kinetic inhibition. A significantly weaker reactive radical pool in toluene oxidation leads to more significant inhibitive kinetic coupling from NH₃-related reactions.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105801"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144830201","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Propagation modes and statistics of near-limit hydrocarbon detonations","authors":"Liliana Berson,&nbsp;Anthony Morales,&nbsp;Rachel Hytovick,&nbsp;Robyn Cideme,&nbsp;Kareem Ahmed","doi":"10.1016/j.proci.2025.105808","DOIUrl":"10.1016/j.proci.2025.105808","url":null,"abstract":"<div><div>Universal propagation mechanisms and structural dynamics of hydrocarbon detonations near the detonation limit are investigated using MHz-rate shadowgraph and CH* chemiluminescence imaging to capture the coupled shock and reaction front. A total of 310 realizations of methane-oxygen and ethylene-oxygen mixtures with varied nitrogen dilution were conducted in a fully automated thin-channel detonation facility. Spatial wavefront velocity fields were extracted from high-speed imagery to compute ensemble statistics, including probability density functions, and the mean, variance, skewness, and kurtosis. The transition from freely propagating detonations to the onset of spin is distinctly separated into four propagation regimes: CJ multiheaded, transitional multiheaded, weak multiheaded, and singleheaded. These regimes are defined by the emergence and eventual dominance of transverse detonation waves, which compensate for weakening cellular instabilities by driving local velocities significantly above the Chapman-Jouguet velocity. This shift in mechanism is shown to be clearly linked to the lack of prompt autoignition by the leading shock indicated by the increasing induction length. The modes are shown to be separable statistically with the combination of the mean velocity and the coefficient of variation (standard deviation scaled by the mean). Transverse detonations are observed to form through the autoignition of large unreacted gas pockets in transverse wave collisions. The induction length is shown to govern the transition, with increasing length correlating to broader velocity distributions (higher variance and skewness) and a shift toward sub-Chapman-Jouguet velocities. Elevated kurtosis values mark the presence of overdriven transverse detonations as statistical outliers. The product of the activation energy and the Von Neumann density ratio, which effectively captures the effects of the activation energy and molecular collisions, were shown to differentiate the modes.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105808"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144830203","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Soot formation and precursor chemistry in Counterflow flames of aviation fuel surrogates","authors":"Chiara Saggese ,&nbsp;Russell Whitesides ,&nbsp;Scott W. Wagnon ,&nbsp;Tanusree Chatterjee ,&nbsp;Fabian P. Hagen ,&nbsp;Petros Vlavakis ,&nbsp;Nils Schraud ,&nbsp;Dimosthenis Trimis","doi":"10.1016/j.proci.2025.105816","DOIUrl":"10.1016/j.proci.2025.105816","url":null,"abstract":"<div><div>To meet market demands, the aviation sector is interested in utilizing drop-in Synthetic Aviation Turbine Fuels (SATF), either as neat fuels or in blends with conventional Jet A. SATF currently approved in standard specifications may have lower aromatic content with significant fractions of normal, branched, and cyclo-alkanes. Fundamental studies on soot formation from aviation fuels (Jet A, SATF) and their surrogate components are essential to understand how fuel composition influences soot and soot precursor formation. This study reports new measurements of polycyclic aromatic hydrocarbons (PAH) and soot in counterflow diffusion flames (CDFs) of aviation fuel surrogates. Both intrusive and non-intrusive diagnostics are employed to determine the profiles of temperature, gas phase species, PAHs (up to C16), and soot volume fraction (SVF) in CDFs of iso-octane and surrogate mixtures. These measurements shed light on the transition of soot precursors to primary soot particles. In addition to serving as a common surrogate component in Jet A surrogate mixtures, iso-octane is a template species for larger, less volatile branched alkanes found in SATF mixtures. The newly developed Lawrence Livermore National Laboratory (LLNL) PAH and soot model successfully captures temperature, precursor species, and SVF profiles for the mixtures and conditions discussed in this work. Finally, a high-fidelity surrogate for Jet A is proposed that matches targeted physical and chemical properties well, while leveraging the wide range of candidate fuel molecules available in the LLNL detailed chemical model. The proposed surrogate formulation is validated against newly acquired measurements of the surrogate and literature measurements of Jet A. These new experiments and simulations provide critical insights into the PAH and soot formation from aviation fuels. Reaction pathways which require further investigation are highlighted, such that future work may bridge the remaining quantitative gaps in predicting soot formation from aviation fuel surrogates and surrogate components.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105816"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144860421","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Data assimilation of state-indirect observations for constraining detonation wave dynamics","authors":"James J. Hansen ,&nbsp;Davy Brouzet ,&nbsp;Matthias Ihme","doi":"10.1016/j.proci.2025.105812","DOIUrl":"10.1016/j.proci.2025.105812","url":null,"abstract":"<div><div>This study investigates the integration of sparse experimental observations into numerical simulations of detonation waves through data assimilation (DA). We extend a two-step local ensemble transform Kalman filter (LETKF) framework to assimilate numerically generated Schlieren and chemiluminescence images into simulations of a methane–oxygen detonation wave with detailed chemistry. Using an ensemble of 30 simulations, we demonstrate that the method can effectively constrain detonation wave dynamics despite the chaotic and highly nonlinear nature of the complex shock system. Results show that the LETKF reduces errors in unobserved state variables by up to 70%, successfully reconstructing key detonation structures including triple points, Mach stems, and transverse waves. The framework exhibits robustness across multiple assimilation cycles with a 50 kHz observational cadence, maintaining consistent state estimation even as ensemble members naturally diverge. While the method excels at constraining structural features like density and temperature fields, we observe that intermediate species distributions require more frequent observation due to their localized spatial distribution. This work demonstrates the potential of DA techniques for advancing pressure-gain combustion research by enabling the fusion of limited experimental diagnostics with high-fidelity numerical simulations, providing a framework for enhanced understanding of detonation dynamics in practical systems.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105812"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145060349","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Determining the reaction enthalpy in pyrolysis and combustion at realistic process conditions","authors":"Raymond Chen,&nbsp;Ewa J. Marek","doi":"10.1016/j.proci.2025.105890","DOIUrl":"10.1016/j.proci.2025.105890","url":null,"abstract":"<div><div>Understanding and optimising processes during combustion or converting biomass to carbon materials requires information about reaction enthalpies, ideally determined experimentally at industrially relevant conditions. However, more complicated experimental set-ups exploring newer technologies often do not allow simultaneous measurement of reaction enthalpy, <em>e.g.</em> using differential scanning calorimetry (DSC). Therefore, we developed a method for <em>in-situ</em> measurement of the reaction enthalpy, requiring only minimal equipment of a sample holder, two thermocouples, and a furnace. To obtain the momentary reaction enthalpy, the heating rate of the sample upon insertion into the furnace was recorded and compared to the heating rate of an empty sample holder. Integrating the results led to the total reaction enthalpy in the temperature interval of interest. To correct for artefacts from radiative heat flux of the sample holder, a correction term was introduced, improving the accuracy of the method. To validate our method, the enthalpy of the phase changes from water and tin was measured and compared to values from literature, with the relative error being 9% and 19%, respectively. Additionally, the reaction enthalpy of birch and beech wood spheres and <em>Sargassum</em> powder were measured, revealing the properties and presentation of the sample to influence the precision of this method. From the momentary reaction enthalpy curve, the corresponding temperature range, in which the reaction occurred, was also determined. Overall, the developed method presents a simple and inexpensive approach for measuring the reaction enthalpy during thermal processing of biomass, providing an option that can work in setups incompatible with DSC.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105890"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145262387","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An extended G-equation formulation for simulating thermodiffusively unstable hydrogen flames","authors":"Hongchao Chu ,&nbsp;Vignesh Varatharajan ,&nbsp;Benjamin Pehlivanlar ,&nbsp;Terence Lehmann ,&nbsp;Lukas Berger ,&nbsp;Dominik Golc ,&nbsp;Stefania Esposito ,&nbsp;Thomas L. Howarth ,&nbsp;Emanuele B. Porcelli ,&nbsp;Davide Laera ,&nbsp;Marco Günther ,&nbsp;Michael Gauding ,&nbsp;Joachim Beeckmann ,&nbsp;Stefan Pischinger ,&nbsp;Heinz Pitsch","doi":"10.1016/j.proci.2025.105945","DOIUrl":"10.1016/j.proci.2025.105945","url":null,"abstract":"<div><div>Hydrogen flames featuring thermodiffusive instabilities are challenging to model in large eddy simulations (LES) and Reynolds-averaged Navier–Stokes (RANS) simulations, where the relevant scales of the instability are typically not resolved. Approaches for modeling thermodiffusively unstable flames have mostly been formulated and validated for laminar flames, where interactions with turbulence are not considered. This study aims to extend the <span><math><mi>G</mi></math></span>-equation model for turbulent thermodiffusively unstable hydrogen flames in the context of RANS simulations. Despite the rise of the available computational resources and the development in high-fidelity LES and direct numerical simulations (DNS), RANS simulations are still the most employed approach in industrial applications, especially for design and operation optimization. In this study, the formulation of the turbulent flame speed as part of the <span><math><mi>G</mi></math></span>-equation combustion model was modified by coupling the empirical scaling relations for flame speed and thickness, which were derived from DNS of turbulent hydrogen flames and consider the effects of thermodiffusive instabilities and their interactions with turbulence. Here, a new relation is proposed to account for cases with high Karlovitz numbers, where increasing turbulence intensity leads to suppression of thermodiffusive instabilities. The derived model was applied to RANS simulations of two hydrogen flame configurations. The first configuration corresponds to a DNS database of two premixed turbulent jet flames. One accounts for thermodiffusive instabilities, while the other disables them by setting the Lewis numbers of all species to unity. The second configuration is performed for a research hydrogen engine, where two operating conditions were considered: one with a stoichiometric mixture and the other with a lean mixture representing conditions without and with strong thermodiffusive instabilities, respectively. Significant improvement in the prediction of the flame length of the jet flame and the in-cylinder pressure of the research engine was achieved with the extended model. The super-adiabatic temperatures due to thermodiffusive instabilities cannot be captured by the extended model, indicating a potential for further improvement for cases where the temperature distribution is of interest.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105945"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145412612","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental and numerical analysis of the knock phenomenon inside ammonia–hydrogen internal combustion engine","authors":"Florian Hurault ,&nbsp;Pierre Brequigny ,&nbsp;Fabrice Foucher ,&nbsp;Christine Mounaïm-Rousselle","doi":"10.1016/j.proci.2025.105901","DOIUrl":"10.1016/j.proci.2025.105901","url":null,"abstract":"<div><div>Ammonia is one of the most promising carbon-free fuels for decarbonising sectors reliant on thermal energy conversion, such as power generation and transportation. However, its distinct combustion properties – low laminar burning velocity, narrow flammability limits, and high autoignition temperature – present challenges for stable and efficient ignition in internal combustion engines. To address these limitations, high-compression-ratio engines are often paired with ignition promoters such as hydrogen, which can be produced on-board through ammonia cracking. Nevertheless, the addition of hydrogen increases the risk of knock occurrence under such conditions. This study aims to improve the understanding of knock formation by investigating the chemical kinetics in the unburned gases during the engine cycle. Before engine testing, ignition delay times (IDTs) were measured in a Rapid Compression Machine for ammonia and partially cracked ammonia (PCA) mixtures (90% NH₃, 10% <span><math><mrow><mi>P</mi><mi>C</mi><mi>A</mi></mrow></math></span>: 7.5% H<span><math><mrow><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub><mo>+</mo><mn>2</mn><mo>.</mo><mn>5</mn></mrow></math></span>% N<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>) under engine-representative conditions (40–70 bar, 950–1000 K, <span><math><mrow><mi>Φ</mi><mo>=</mo></mrow></math></span> 0.5–1.5). Combined with previous IDT data for pure NH₃ and NH₃/10% H₂, the Stagni 2023 mechanism was selected for detailed chemical analysis. Experiments were conducted on a spark-assisted compression ignition engine (CR = 16.4) with fuel blends of pure NH₃, NH₃/10% H₂, and 10% <span><math><mrow><mi>P</mi><mi>C</mi><mi>A</mi></mrow></math></span>. Only the hydrogen-containing blends exhibited knock. The Chemkin Pro SI Engine Zonal Model was employed to simulate in-cylinder chemical evolution. Results indicated that the key reactions driving knock are the consumption of H₂ via H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> <span><math><mo>+</mo></math></span> NH<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> <span><math><mo>↔</mo></math></span> H <span><math><mo>+</mo></math></span> NH<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> and H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> <span><math><mo>+</mo></math></span> OH <span><math><mo>↔</mo></math></span> H <span><math><mo>+</mo></math></span> H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O in the end gases. These pathways contribute significantly to pre-ignition heat release, triggering knock, and explain the absence of knock in pure NH₃ cycles unless sufficient hydrogen is present through residuals or in-situ cracking.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105901"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145463003","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Structure of the standing detonation wave induced by area constriction","authors":"Ruben A. Fernandez,&nbsp;Sebastian S. Abisleiman,&nbsp;Venkat Raman","doi":"10.1016/j.proci.2025.105818","DOIUrl":"10.1016/j.proci.2025.105818","url":null,"abstract":"<div><div>In this study, the stability and propagation of standing detonation waves in an inward-turning channel configuration are investigated. A numerical simulation is conducted using a compressible reacting flow solver with finite-rate chemistry. Adaptive mesh refinement of a stoichiometric ethylene–air mixture with a resolution of <span><math><mrow><mn>6</mn><mo>.</mo><mn>1</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span> at the finest level is used to provide 41 grid cells across the detonation structure. An axisymmetric inward-facing ramp is employed to generate a Mach stem within a confined channel, thereby enhancing compression. Consequently, a Mach stem forms at flow deflection angles that are less than those predicted by two-dimensional theory. This configuration ensures that the conditions following the shock are adequate for detonation. A cyclical quasi-steady-state solution is observed with a single detonation cell pulsing forward into a three-dimensional Mach stem before decoupling, followed by an ignition and a repeat of this process. Transverse wave interaction with the sliplines containing the detonation allows the detonation surface to grow, reducing the reflection of transverse waves back into the reaction front and reducing the geometric dependence on the instability development. The single detonation cell system shows a bias to form detonation cells on one half of the front, inducing counter-rotating modes and a spinning detonation. Instabilities form and propagate radially inward along the detonation surface until a single detonation cell becomes dominant.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105818"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145216404","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}