Pub Date : 2025-12-19DOI: 10.1016/j.combustflame.2025.114716
Ashlesh Dahake, Anil S. Karthik, Ranjay K. Singh, Ajay V. Singh
<div><div>Ozonolysis — the direct reaction of an unsaturated hydrocarbon with ozone, proceeds rapidly even under ambient conditions due to significantly high rate constants. The current work investigates the impact of ozonolysis on the structure and dynamics of ethylene–oxygen detonations using constant-volume (CV) simulations, ZND computations, and high-fidelity two-dimensional simulations. The two-dimensional simulations, based on reactive Navier–Stokes equations, successfully reproduced the experimentally observed cellular structure for <figure><img></figure> detonations, with a cell width difference of <span><math><mrow><mo>∼</mo><mn>14</mn><mtext>%</mtext></mrow></math></span> at 25 kPa. The CV simulations provided the temporal evolution of the mixture composition and thermodynamic state. Under adiabatic conditions, exothermic ozonolysis reactions preheated the mixture and generated reactive radicals and intermediate species, leading to in situ thermo-chemical pretreatment. The residence time of the reactor, the concentration of ozone, and the initial pressure influenced the extent of this pretreatment. The CV simulations also showed that autoignition could occur in <figure><img></figure> mixtures solely due to ozonolysis under premixed adiabatic conditions. The presence of a finite residence time reactor before the detonation simulations activated the ozonolysis pathways, leading to low-temperature ethylene oxidation. Ozonolysis was found to increase the detonability of the reactive mixture, reducing the ZND induction length and detonation cell size. While sensitivity analysis showed that the dominant post-shock reactions remained largely unchanged, a significant increase in radical concentrations (H, O, OH) was observed for ozonolysis-activated mixtures. The rate of production analysis revealed a nonlinear surge in radical generation immediately behind the shock front. For ozonolysis-activated mixtures, the two-dimensional simulations show that the detonation cell size can be reduced by <span><math><mrow><mo>∼</mo><mn>46</mn><mtext>%</mtext></mrow></math></span> when compared to the non-ozonated case. However, when ozonolysis reactions were omitted from the kinetic model, the detonation cell size was found to decrease by <span><math><mrow><mo>∼</mo><mn>37</mn><mtext>%</mtext></mrow></math></span> when compared to the non-ozonated case. The cellular regularity was also found to improve with ozonolysis due to a reduction in the effective activation energy, primarily driven by increased radical production.</div><div><strong>Novelty and significance statement</strong></div><div>This work presents the first quantitative investigation of the effects of ozonolysis on the multidimensional cellular structure of ethylene–oxygen detonations. Using a combination of CV, ZND, and high-fidelity 2D reactive flow simulations with a detailed chemical kinetic model, the study demonstrates that ozonolysis-induced radical proliferation and in situ thermal-chem
{"title":"Investigating the effect of ozonolysis on the structure and dynamics of ethylene–oxygen–ozone detonations","authors":"Ashlesh Dahake, Anil S. Karthik, Ranjay K. Singh, Ajay V. Singh","doi":"10.1016/j.combustflame.2025.114716","DOIUrl":"10.1016/j.combustflame.2025.114716","url":null,"abstract":"<div><div>Ozonolysis — the direct reaction of an unsaturated hydrocarbon with ozone, proceeds rapidly even under ambient conditions due to significantly high rate constants. The current work investigates the impact of ozonolysis on the structure and dynamics of ethylene–oxygen detonations using constant-volume (CV) simulations, ZND computations, and high-fidelity two-dimensional simulations. The two-dimensional simulations, based on reactive Navier–Stokes equations, successfully reproduced the experimentally observed cellular structure for <figure><img></figure> detonations, with a cell width difference of <span><math><mrow><mo>∼</mo><mn>14</mn><mtext>%</mtext></mrow></math></span> at 25 kPa. The CV simulations provided the temporal evolution of the mixture composition and thermodynamic state. Under adiabatic conditions, exothermic ozonolysis reactions preheated the mixture and generated reactive radicals and intermediate species, leading to in situ thermo-chemical pretreatment. The residence time of the reactor, the concentration of ozone, and the initial pressure influenced the extent of this pretreatment. The CV simulations also showed that autoignition could occur in <figure><img></figure> mixtures solely due to ozonolysis under premixed adiabatic conditions. The presence of a finite residence time reactor before the detonation simulations activated the ozonolysis pathways, leading to low-temperature ethylene oxidation. Ozonolysis was found to increase the detonability of the reactive mixture, reducing the ZND induction length and detonation cell size. While sensitivity analysis showed that the dominant post-shock reactions remained largely unchanged, a significant increase in radical concentrations (H, O, OH) was observed for ozonolysis-activated mixtures. The rate of production analysis revealed a nonlinear surge in radical generation immediately behind the shock front. For ozonolysis-activated mixtures, the two-dimensional simulations show that the detonation cell size can be reduced by <span><math><mrow><mo>∼</mo><mn>46</mn><mtext>%</mtext></mrow></math></span> when compared to the non-ozonated case. However, when ozonolysis reactions were omitted from the kinetic model, the detonation cell size was found to decrease by <span><math><mrow><mo>∼</mo><mn>37</mn><mtext>%</mtext></mrow></math></span> when compared to the non-ozonated case. The cellular regularity was also found to improve with ozonolysis due to a reduction in the effective activation energy, primarily driven by increased radical production.</div><div><strong>Novelty and significance statement</strong></div><div>This work presents the first quantitative investigation of the effects of ozonolysis on the multidimensional cellular structure of ethylene–oxygen detonations. Using a combination of CV, ZND, and high-fidelity 2D reactive flow simulations with a detailed chemical kinetic model, the study demonstrates that ozonolysis-induced radical proliferation and in situ thermal-chem","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114716"},"PeriodicalIF":6.2,"publicationDate":"2025-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789266","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}
Pub Date : 2025-12-18DOI: 10.1016/j.combustflame.2025.114726
Hyein Choi , Amun Jarzembski , Toai Ton-That , Gregory B. Kennedy , Georgia L. Hilburn , Paul E. Specht , Naresh N. Thadhani , David P. Adams , Michael J. Abere
Bimetallic, reactive multilayers are uniformly structured materials composed of alternating nanoscale layers that may be ignited to produce self-propagating intermetallic-formation reactions. When reactive multilayers age, there is a change in local composition and loss of stored chemical energy due to mass transport and rearrangement at the interfaces. To quantify the long-term reliability of commercial Ni(V)/Al multilayers, the effects of accelerated aging on both ignition sensitivity and self-propagating reactions have been examined. Thermally aged samples were characterized using transmission electron microscopy, differential scanning calorimetry, and laser ignition combined with high-speed videography. The analytically quantifiable nature of both continuous wave laser ignition and reactive wave propagation enabled calculations of Arrhenius rate constants for as-received and various heat-treated multilayers. With heat treatment, there is a change in the intermixed thickness and interfacial chemistry that decreases the activation energy for point ignition but increases it for self-propagating reactions. This finding implies that with increased thermal aging, the reaction becomes easier to facilitate in the solid state but harder in the liquid phase.
{"title":"Quantifying the effects of artificial aging on the ignition and self-propagating reactions of Ni(V)/Al multilayers","authors":"Hyein Choi , Amun Jarzembski , Toai Ton-That , Gregory B. Kennedy , Georgia L. Hilburn , Paul E. Specht , Naresh N. Thadhani , David P. Adams , Michael J. Abere","doi":"10.1016/j.combustflame.2025.114726","DOIUrl":"10.1016/j.combustflame.2025.114726","url":null,"abstract":"<div><div>Bimetallic, reactive multilayers are uniformly structured materials composed of alternating nanoscale layers that may be ignited to produce self-propagating intermetallic-formation reactions. When reactive multilayers age, there is a change in local composition and loss of stored chemical energy due to mass transport and rearrangement at the interfaces. To quantify the long-term reliability of commercial Ni(V)/Al multilayers, the effects of accelerated aging on both ignition sensitivity and self-propagating reactions have been examined. Thermally aged samples were characterized using transmission electron microscopy, differential scanning calorimetry, and laser ignition combined with high-speed videography. The analytically quantifiable nature of both continuous wave laser ignition and reactive wave propagation enabled calculations of Arrhenius rate constants for as-received and various heat-treated multilayers. With heat treatment, there is a change in the intermixed thickness and interfacial chemistry that decreases the activation energy for point ignition but increases it for self-propagating reactions. This finding implies that with increased thermal aging, the reaction becomes easier to facilitate in the solid state but harder in the liquid phase.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114726"},"PeriodicalIF":6.2,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789254","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}
Pub Date : 2025-12-18DOI: 10.1016/j.combustflame.2025.114727
Kunzhuo Chang, Mingyan Gu, Yang Wang, Shoujun Zou, Zihao Ouyang, Yanpeng Han, Jingyun Sun
This study investigates the formation mechanisms of soot and nitrogen oxides (NO) in ammonia-doped ethylene diffusion flames using the CoFlame code with a detailed sectional soot model. The results reveal that C-N containing species have inhibitory effect on the formation of soot precursors; in contrast, C–N containing species were found to promote NO formation. As the ammonia blending ratio increased from 0 % to 5 %, 30 %, and 50 %, the peak soot volume fraction decreased non-linearly, with a sharp 43.6 % reduction at 5 % NH₃, plateauing to 65.8 % at 50 % NH₃. Conversely, NO emissions rose dramatically, with peak concentrations increasing by 700 ppm (226 %), 3590 ppm (1158 %), and 4290 ppm (1384 %) for the respective blends. Mechanistic analysis indicates that soot suppression originated from inhibited nucleation, disrupted HACA-mediated surface growth, and reduced soot particle coagulation. The formation of NO was driven by the increased concentrations and reaction rates of fuel-nitrogen precursors (N, NH, HNO) and the reactive C-N intermediates (HCN, HCNO, H2CN) performed a dual function, diverting hydrocarbon species from polycyclic aromatic hydrocarbon (PAH) formation while simultaneously participating in NO-generating reactions, thereby accelerating NO formation rate.
{"title":"Investigation of soot and NO formation pathway and the interaction between C–N species in ammonia-doped ethylene co-flow diffusion flames","authors":"Kunzhuo Chang, Mingyan Gu, Yang Wang, Shoujun Zou, Zihao Ouyang, Yanpeng Han, Jingyun Sun","doi":"10.1016/j.combustflame.2025.114727","DOIUrl":"10.1016/j.combustflame.2025.114727","url":null,"abstract":"<div><div>This study investigates the formation mechanisms of soot and nitrogen oxides (NO) in ammonia-doped ethylene diffusion flames using the CoFlame code with a detailed sectional soot model. The results reveal that C-N containing species have inhibitory effect on the formation of soot precursors; in contrast, C–N containing species were found to promote NO formation. As the ammonia blending ratio increased from 0 % to 5 %, 30 %, and 50 %, the peak soot volume fraction decreased non-linearly, with a sharp 43.6 % reduction at 5 % NH₃, plateauing to 65.8 % at 50 % NH₃. Conversely, NO emissions rose dramatically, with peak concentrations increasing by 700 ppm (226 %), 3590 ppm (1158 %), and 4290 ppm (1384 %) for the respective blends. Mechanistic analysis indicates that soot suppression originated from inhibited nucleation, disrupted HACA-mediated surface growth, and reduced soot particle coagulation. The formation of NO was driven by the increased concentrations and reaction rates of fuel-nitrogen precursors (N, NH, HNO) and the reactive C-N intermediates (HCN, HCNO, H<sub>2</sub>CN) performed a dual function, diverting hydrocarbon species from polycyclic aromatic hydrocarbon (PAH) formation while simultaneously participating in NO-generating reactions, thereby accelerating NO formation rate.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114727"},"PeriodicalIF":6.2,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789258","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}
Pub Date : 2025-12-18DOI: 10.1016/j.combustflame.2025.114724
Zhenyang Ming , Chao Jin , Haifeng Liu , Zongyu Yue , Jeffrey Dankwa Ampah , HaoZhong Huang , Yiyong Han , Zhiqin Jia , Mingfa Yao
Methanol compression ignition serves as a cornerstone of decarbonization in heavy-duty transportation, yet combustion instability remains a critical bottleneck restricting its development. This study fundamentally clarifies the mechanism underlying methanol combustion instability through optical diagnostics combined with chemical reaction kinetics analysis, and addresses this issue via molecular fuel design by adding cetane improvers, namely 2-ethylhexyl nitrate (EHN) and di‑tert‑butyl peroxide (DTBP). Detailed analysis shows that methanol combustion instability arises from the combined effects of poor fuel–air mixture homogeneity, high turbulence intensity, and the absence of a low-temperature exothermic stage. In the specific spray configuration and conditions of this experiment (ambient temperature: 950 K; ambient pressure: 4 MPa), the equivalence ratio of methanol spray is approximately twice that of n-heptane, while its temperature is about 17 % lower, leading to around 47 % of the methanol fuel–air mixture being in a misfiring state. At the same time, mixing in the central region of the methanol spray is highly non-uniform, with a scalar dissipation rate 2.4 times that of n-heptane. The methanol spray flame exhibits almost no low-temperature combustion process. The addition of cetane improvers mitigates these issues. In particular, EHN prolongs the duration of low-temperature chemistry and advances high-temperature combustion significantly, resulting in a more regular flame structure and suppressing flame-edge wrinkling. EHN outperforms DTBP in improvement efficacy because its regenerative NO₂ cycle (NO₂→HONO→NO→NO2) catalytically accelerates methanol dehydrogenation, whereas DTBP’s chain-terminating methyl radicals limit its effectiveness. These results demonstrate that suitably designed cetane improvers can act as molecular catalysts, enabling methanol to achieve diesel-like stability while maintaining near-zero soot emissions, and providing a pathway toward scalable carbon-neutral heavy-duty transportation and marine power.
{"title":"Unravelling the instability mechanism of methanol spray flame and its enhancement by cetane additives","authors":"Zhenyang Ming , Chao Jin , Haifeng Liu , Zongyu Yue , Jeffrey Dankwa Ampah , HaoZhong Huang , Yiyong Han , Zhiqin Jia , Mingfa Yao","doi":"10.1016/j.combustflame.2025.114724","DOIUrl":"10.1016/j.combustflame.2025.114724","url":null,"abstract":"<div><div>Methanol compression ignition serves as a cornerstone of decarbonization in heavy-duty transportation, yet combustion instability remains a critical bottleneck restricting its development. This study fundamentally clarifies the mechanism underlying methanol combustion instability through optical diagnostics combined with chemical reaction kinetics analysis, and addresses this issue via molecular fuel design by adding cetane improvers, namely 2-ethylhexyl nitrate (EHN) and di‑tert‑butyl peroxide (DTBP). Detailed analysis shows that methanol combustion instability arises from the combined effects of poor fuel–air mixture homogeneity, high turbulence intensity, and the absence of a low-temperature exothermic stage. In the specific spray configuration and conditions of this experiment (ambient temperature: 950 K; ambient pressure: 4 MPa), the equivalence ratio of methanol spray is approximately twice that of n-heptane, while its temperature is about 17 % lower, leading to around 47 % of the methanol fuel–air mixture being in a misfiring state. At the same time, mixing in the central region of the methanol spray is highly non-uniform, with a scalar dissipation rate 2.4 times that of n-heptane. The methanol spray flame exhibits almost no low-temperature combustion process. The addition of cetane improvers mitigates these issues. In particular, EHN prolongs the duration of low-temperature chemistry and advances high-temperature combustion significantly, resulting in a more regular flame structure and suppressing flame-edge wrinkling. EHN outperforms DTBP in improvement efficacy because its regenerative NO₂ cycle (NO₂→HONO→NO→NO<sub>2</sub>) catalytically accelerates methanol dehydrogenation, whereas DTBP’s chain-terminating methyl radicals limit its effectiveness. These results demonstrate that suitably designed cetane improvers can act as molecular catalysts, enabling methanol to achieve diesel-like stability while maintaining near-zero soot emissions, and providing a pathway toward scalable carbon-neutral heavy-duty transportation and marine power.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114724"},"PeriodicalIF":6.2,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789256","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}
Pub Date : 2025-12-17DOI: 10.1016/j.combustflame.2025.114718
Guibiao He , Jian Li , Zichun Yu, Saichao Song, Jie Zhong, Yaning Li, Boliang Wang
The detonation characteristics of vapor-liquid two-phase fuel/air aerosol are an essential subject in fuel utilization and vapor explosion prevention. In this study, the effects of isopropyl nitrate (iPN) addition on the detonation initiation characteristics of vapor-liquid two-phase n-heptane (HP)/air aerosol were investigated in a detonation tube. The aerosol was generated by injecting liquid HP/iPN mixture into the test section through 12 sets of dispersion systems. Hydrogen-oxygen pre-detonation served as the initiation source. Chemical reaction kinetics simulation was performed to elucidate the underlying reaction mechanism of iPN/HP mixtures. Experimental results demonstrated that the detonation wave velocity of HP/(iPN)/air aerosol ranged from 1480 to 1820 m/s and the detonation pressure varied from 2.6 to 5.2 MPa, whereas iPN/air aerosol exhibited lower velocity (1260 to 1450 m/s) and comparable detonation pressure (3.2 to 5.3 MPa). iPN addition significantly enhanced the detonation initiation sensitivity of HP/air aerosol and reduced the minimum detonable concentration. This promoting effect intensified with increasing iPN content, though excessive iPN content considerably weakened the detonation intensity. Numerical analysis revealed that iPN facilitated detonation initiation by generating reactive radicals (H, CH3, OH, and O) during the early stage of the ignition induction period, accelerating the establishment of a radical pool for HP reaction and thereby reducing the reaction induction period of HP. Furthermore, iPN addition introduced new consumption pathways for HP and increased the pathways converting intermediate products into the final product CO2. These findings provide valuable insights for fuel formulation optimization and industrial safety management.
{"title":"The promoting effect of isopropyl nitrate on the detonation initiation of vapor-liquid two-phase n-heptane/air aerosol","authors":"Guibiao He , Jian Li , Zichun Yu, Saichao Song, Jie Zhong, Yaning Li, Boliang Wang","doi":"10.1016/j.combustflame.2025.114718","DOIUrl":"10.1016/j.combustflame.2025.114718","url":null,"abstract":"<div><div>The detonation characteristics of vapor-liquid two-phase fuel/air aerosol are an essential subject in fuel utilization and vapor explosion prevention. In this study, the effects of isopropyl nitrate (iPN) addition on the detonation initiation characteristics of vapor-liquid two-phase n-heptane (HP)/air aerosol were investigated in a detonation tube. The aerosol was generated by injecting liquid HP/iPN mixture into the test section through 12 sets of dispersion systems. Hydrogen-oxygen pre-detonation served as the initiation source. Chemical reaction kinetics simulation was performed to elucidate the underlying reaction mechanism of iPN/HP mixtures. Experimental results demonstrated that the detonation wave velocity of HP/(iPN)/air aerosol ranged from 1480 to 1820 m/s and the detonation pressure varied from 2.6 to 5.2 MPa, whereas iPN/air aerosol exhibited lower velocity (1260 to 1450 m/s) and comparable detonation pressure (3.2 to 5.3 MPa). iPN addition significantly enhanced the detonation initiation sensitivity of HP/air aerosol and reduced the minimum detonable concentration. This promoting effect intensified with increasing iPN content, though excessive iPN content considerably weakened the detonation intensity. Numerical analysis revealed that iPN facilitated detonation initiation by generating reactive radicals (H, CH<sub>3</sub>, OH, and O) during the early stage of the ignition induction period, accelerating the establishment of a radical pool for HP reaction and thereby reducing the reaction induction period of HP. Furthermore, iPN addition introduced new consumption pathways for HP and increased the pathways converting intermediate products into the final product CO<sub>2</sub>. These findings provide valuable insights for fuel formulation optimization and industrial safety management.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114718"},"PeriodicalIF":6.2,"publicationDate":"2025-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789259","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}
Pub Date : 2025-12-17DOI: 10.1016/j.combustflame.2025.114713
Marc Le Boursicaud , Jean-Louis Consalvi , Pierre Boivin
The growing interest in hydrogen as an alternative energy vector has raised new technological challenges, in particular regarding its storage. This has motivated increasing attention to ammonia as a hydrogen carrier. In parallel, the use of hydrogen–ammonia blends as combustible fuels has attracted significant interest, as such mixtures can be easier to handle in some applications than pure hydrogen, while still enabling carbon-free combustion.
In this context, the present study focuses on modeling the ignition of arbitrary gaseous hydrogen–ammonia–air blends. First, the minimal chemical description required to accurately capture the ignition delay of these mixtures is identified, revealing three main ignition regimes. Ignition delay formulas are then derived for these regimes by extending methods previously developed for pure hydrogen and syngas. The resulting ignition time expressions are subsequently combined into a unified formulation, valid across a wide range of pressures, temperatures, and fuel compositions. Finally, modifications to a recently published passive scalar model for CFD tools are introduced so as to accurately predict ignition events in hydrogen–ammonia–air mixtures while reducing computational cost.
Novelty and Significance Statement: This work advances the modeling of hydrogen–ammonia–air ignition by deriving analytical ignition time expressions for arbitrary fuel composition and by extending a recently published passive scalar approach, thereby enabling efficient CFD-based ignition prediction across a broad range of conditions.
{"title":"Prediction of hydrogen–ammonia blends autoignition","authors":"Marc Le Boursicaud , Jean-Louis Consalvi , Pierre Boivin","doi":"10.1016/j.combustflame.2025.114713","DOIUrl":"10.1016/j.combustflame.2025.114713","url":null,"abstract":"<div><div>The growing interest in hydrogen as an alternative energy vector has raised new technological challenges, in particular regarding its storage. This has motivated increasing attention to ammonia as a hydrogen carrier. In parallel, the use of hydrogen–ammonia blends as combustible fuels has attracted significant interest, as such mixtures can be easier to handle in some applications than pure hydrogen, while still enabling carbon-free combustion.</div><div>In this context, the present study focuses on modeling the ignition of arbitrary gaseous hydrogen–ammonia–air blends. First, the minimal chemical description required to accurately capture the ignition delay of these mixtures is identified, revealing three main ignition regimes. Ignition delay formulas are then derived for these regimes by extending methods previously developed for pure hydrogen and syngas. The resulting ignition time expressions are subsequently combined into a unified formulation, valid across a wide range of pressures, temperatures, and fuel compositions. Finally, modifications to a recently published passive scalar model for CFD tools are introduced so as to accurately predict ignition events in hydrogen–ammonia–air mixtures while reducing computational cost.</div><div><strong>Novelty and Significance Statement</strong>: This work advances the modeling of hydrogen–ammonia–air ignition by deriving analytical ignition time expressions for arbitrary fuel composition and by extending a recently published passive scalar approach, thereby enabling efficient CFD-based ignition prediction across a broad range of conditions.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114713"},"PeriodicalIF":6.2,"publicationDate":"2025-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789270","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}
<div><div>Combustion-generated soot harms health and the climate; adding ammonia (NH<sub>3</sub>) is being explored as a low-carbon countermeasure. This study explores the effects of NH<sub>3</sub> addition on soot and polycyclic aromatic hydrocarbons (PAHs) formation in n-decane laminar co-flow diffusion flames. Laser induced incandescence and laser induced fluorescence are used to measure soot, PAHs and OH. A detailed kinetic mechanism is developed to simulate soot formation and the chemical role of NH<sub>3</sub>. Increasing the NH<sub>3</sub> blending ratio from 0 % to 40 % leads to a marked reduction in soot and PAH signals. The soot peak moves upward and becomes more radially diffuse. The LIF intensities of A1, A2-A3 and A4 decrease by about 45 %, 20 % and 15 %, while the OH-PLIF peak also decreases with little change in shape. A cross fuel comparison with methane, ethylene and n-heptane data shows that, at similar NH<sub>3</sub> levels, soot and large PAHs are suppressed much less in n-decane flames than in small fuel flames. Numerical simulations based on rate-of-production and sensitivity analyses demonstrate that NH<sub>3</sub> changes the routes that control aromatic formation. The dominant A1 formation reaction via propargyl recombination is notably weakened in NH<sub>3</sub>-containing flames. At the same time, the oxidation of C<sub>3</sub>H<sub>3</sub> by OH and the decomposition of C<sub>3</sub>H<sub>5</sub> to C<sub>2</sub>H<sub>2</sub> and CH<sub>3</sub> are enhanced, promoting the consumption of PAH intermediates. Sensitivity analysis reveals that these inhibitory reactions exhibit increased negative sensitivity under NH<sub>3</sub>-rich conditions, indicating that NH<sub>3</sub> strengthens the influence of reactions unfavorable to aromatic growth. Additionally, NH<sub>3</sub> consumes reactive radicals such as H, OH, and CH<sub>3</sub>, reducing their availability for hydrocarbon chain propagation and ring formation. This means that the main control of A1 changes from C<sub>3</sub> and C<sub>4</sub> growth reactions to C<sub>3</sub> consumption reactions. Correspondingly, the concentrations of key precursors C<sub>2</sub>H<sub>2</sub> and C<sub>3</sub>H<sub>3</sub> are significantly reduced with increasing NH<sub>3</sub> blending ratio. Model results further show that moderate NH<sub>3</sub> fractions already give most of the soot reduction, whereas higher fractions mainly increase NO, NO<sub>2</sub> and N<sub>2</sub>O, revealing a soot-NO<sub>X</sub> trade off. The present work clarifies how ammonia influences soot formation and offers insights for controlling soot in zero-carbon combustion.</div></div><div><h3>Novelty and significance statement</h3><div>This study presents the first combined OH-PLIF and LII diagnostics applied to n-decane/ ammonia laminar diffusion flames, systematically investigating how ammonia addition affects soot and polycyclic aromatic hydrocarbons formation. Additionally, a kinetic model consisting o
{"title":"An experimental and kinetic modeling study of NH3/n-decane laminar diffusion flames","authors":"Jingyang Jia , Xu He , Qi Xiang , Zhiwei Zhang , Zhen-Yu Tian","doi":"10.1016/j.combustflame.2025.114703","DOIUrl":"10.1016/j.combustflame.2025.114703","url":null,"abstract":"<div><div>Combustion-generated soot harms health and the climate; adding ammonia (NH<sub>3</sub>) is being explored as a low-carbon countermeasure. This study explores the effects of NH<sub>3</sub> addition on soot and polycyclic aromatic hydrocarbons (PAHs) formation in n-decane laminar co-flow diffusion flames. Laser induced incandescence and laser induced fluorescence are used to measure soot, PAHs and OH. A detailed kinetic mechanism is developed to simulate soot formation and the chemical role of NH<sub>3</sub>. Increasing the NH<sub>3</sub> blending ratio from 0 % to 40 % leads to a marked reduction in soot and PAH signals. The soot peak moves upward and becomes more radially diffuse. The LIF intensities of A1, A2-A3 and A4 decrease by about 45 %, 20 % and 15 %, while the OH-PLIF peak also decreases with little change in shape. A cross fuel comparison with methane, ethylene and n-heptane data shows that, at similar NH<sub>3</sub> levels, soot and large PAHs are suppressed much less in n-decane flames than in small fuel flames. Numerical simulations based on rate-of-production and sensitivity analyses demonstrate that NH<sub>3</sub> changes the routes that control aromatic formation. The dominant A1 formation reaction via propargyl recombination is notably weakened in NH<sub>3</sub>-containing flames. At the same time, the oxidation of C<sub>3</sub>H<sub>3</sub> by OH and the decomposition of C<sub>3</sub>H<sub>5</sub> to C<sub>2</sub>H<sub>2</sub> and CH<sub>3</sub> are enhanced, promoting the consumption of PAH intermediates. Sensitivity analysis reveals that these inhibitory reactions exhibit increased negative sensitivity under NH<sub>3</sub>-rich conditions, indicating that NH<sub>3</sub> strengthens the influence of reactions unfavorable to aromatic growth. Additionally, NH<sub>3</sub> consumes reactive radicals such as H, OH, and CH<sub>3</sub>, reducing their availability for hydrocarbon chain propagation and ring formation. This means that the main control of A1 changes from C<sub>3</sub> and C<sub>4</sub> growth reactions to C<sub>3</sub> consumption reactions. Correspondingly, the concentrations of key precursors C<sub>2</sub>H<sub>2</sub> and C<sub>3</sub>H<sub>3</sub> are significantly reduced with increasing NH<sub>3</sub> blending ratio. Model results further show that moderate NH<sub>3</sub> fractions already give most of the soot reduction, whereas higher fractions mainly increase NO, NO<sub>2</sub> and N<sub>2</sub>O, revealing a soot-NO<sub>X</sub> trade off. The present work clarifies how ammonia influences soot formation and offers insights for controlling soot in zero-carbon combustion.</div></div><div><h3>Novelty and significance statement</h3><div>This study presents the first combined OH-PLIF and LII diagnostics applied to n-decane/ ammonia laminar diffusion flames, systematically investigating how ammonia addition affects soot and polycyclic aromatic hydrocarbons formation. Additionally, a kinetic model consisting o","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114703"},"PeriodicalIF":6.2,"publicationDate":"2025-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789267","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}
Pub Date : 2025-12-17DOI: 10.1016/j.combustflame.2025.114728
Sanket Girhe, Raymond Langer, Francesca Loffredo, Heinz Pitsch
<div><div>Kinetic models are essential for describing combustion chemistry and play a central role in developing cleaner combustion technologies. Their predictive accuracy is crucial for performing reliable combustion simulations, which support the design and optimization of these application systems. Model parameter optimization is often employed to improve the predictive accuracy of the kinetic models. For certain fuels like ammonia, where key reaction sensitivities span a broad range of temperatures, optimizing all three Arrhenius parameters (the pre-exponential factor <span><math><mi>A</mi></math></span>, the temperature exponent <span><math><mi>n</mi></math></span>, and the activation energy <span><math><mi>E</mi></math></span>) yields significantly higher predictive accuracy than conventional <span><math><mi>A</mi></math></span>-factor optimization, owing to the additional degrees of freedom. However, the inherent correlations among the Arrhenius parameters pose challenges to the accuracy of response surface modeling, a commonly used strategy for efficient optimization. We present a novel optimization approach involving the projection of Arrhenius parameters into the uncorrelated principal component (PC) space. An artificial neural network-based response surface is employed. A significant improvement in the accuracy of the response surface model is observed when using PCs instead of the Arrhenius parameters. The objective function uses the curve-matching score, which quantifies both local and global agreement between experimental data and model predictions. Our optimization approach is applied to the NH<sub>3</sub>/NO combustion system as a test case, yielding an optimized thermal DeNO<span><math><msub><mrow></mrow><mrow><mtext>x</mtext></mrow></msub></math></span> model that exhibits a significantly improved predictive accuracy. A comparison between Arrhenius-based and PC-based optimization revealed superior performance with the PC-based approach. The optimized results allowed us to improve the understanding of key reactions in NH<sub>3</sub> combustion, including <figure><img></figure> , <figure><img></figure> , and <figure><img></figure> , which sensitively impact the NH<sub>3</sub>/NO combustion process.</div><div><strong>Novelty and significance statement</strong></div><div>This study introduces a novel principal component-based optimization methodology for refining kinetic models, fundamentally distinct from traditional Arrhenius parameter optimization. By transforming correlated Arrhenius parameters into an orthogonal principal component space, this approach enhances the accuracy of surrogate response surfaces, resulting in an optimized model with superior predictive performance. Additionally, the novel integration of an ANN-based response surface and a CM score-based objective function in our framework addresses shortcomings of conventional techniques, marking a significant advancement in kinetic model optimization. Its successful a
{"title":"Principal component-based approach for kinetic model optimization","authors":"Sanket Girhe, Raymond Langer, Francesca Loffredo, Heinz Pitsch","doi":"10.1016/j.combustflame.2025.114728","DOIUrl":"10.1016/j.combustflame.2025.114728","url":null,"abstract":"<div><div>Kinetic models are essential for describing combustion chemistry and play a central role in developing cleaner combustion technologies. Their predictive accuracy is crucial for performing reliable combustion simulations, which support the design and optimization of these application systems. Model parameter optimization is often employed to improve the predictive accuracy of the kinetic models. For certain fuels like ammonia, where key reaction sensitivities span a broad range of temperatures, optimizing all three Arrhenius parameters (the pre-exponential factor <span><math><mi>A</mi></math></span>, the temperature exponent <span><math><mi>n</mi></math></span>, and the activation energy <span><math><mi>E</mi></math></span>) yields significantly higher predictive accuracy than conventional <span><math><mi>A</mi></math></span>-factor optimization, owing to the additional degrees of freedom. However, the inherent correlations among the Arrhenius parameters pose challenges to the accuracy of response surface modeling, a commonly used strategy for efficient optimization. We present a novel optimization approach involving the projection of Arrhenius parameters into the uncorrelated principal component (PC) space. An artificial neural network-based response surface is employed. A significant improvement in the accuracy of the response surface model is observed when using PCs instead of the Arrhenius parameters. The objective function uses the curve-matching score, which quantifies both local and global agreement between experimental data and model predictions. Our optimization approach is applied to the NH<sub>3</sub>/NO combustion system as a test case, yielding an optimized thermal DeNO<span><math><msub><mrow></mrow><mrow><mtext>x</mtext></mrow></msub></math></span> model that exhibits a significantly improved predictive accuracy. A comparison between Arrhenius-based and PC-based optimization revealed superior performance with the PC-based approach. The optimized results allowed us to improve the understanding of key reactions in NH<sub>3</sub> combustion, including <figure><img></figure> , <figure><img></figure> , and <figure><img></figure> , which sensitively impact the NH<sub>3</sub>/NO combustion process.</div><div><strong>Novelty and significance statement</strong></div><div>This study introduces a novel principal component-based optimization methodology for refining kinetic models, fundamentally distinct from traditional Arrhenius parameter optimization. By transforming correlated Arrhenius parameters into an orthogonal principal component space, this approach enhances the accuracy of surrogate response surfaces, resulting in an optimized model with superior predictive performance. Additionally, the novel integration of an ANN-based response surface and a CM score-based objective function in our framework addresses shortcomings of conventional techniques, marking a significant advancement in kinetic model optimization. Its successful a","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114728"},"PeriodicalIF":6.2,"publicationDate":"2025-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789262","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}
Pub Date : 2025-12-16DOI: 10.1016/j.combustflame.2025.114711
Bo Yin , Aksel Ånestad , Eirik Æsøy , Nicholas A. Worth , Larry K.B. Li
Thermoacoustic instabilities are a key challenge in developing sustainable combustion systems. In this experimental study, we present the first application of a data-driven machine learning algorithm based on genetic programming (GP) to suppress self-excited thermoacoustic oscillations in a turbulent premixed combustor operating with hydrogen-enriched fuels. The GP algorithm evolves model-free control laws via genetic operations such as replication, mutation, and crossover. Its performance is optimized through a cost function that balances the thermoacoustic amplitude reduction against the actuator power consumption. We evaluate GP in both closed-loop and open-loop configurations, benchmarking these against traditional open-loop time-periodic actuation. We find that GP closed-loop control proves superior in every metric evaluated, achieving the highest amplitude reduction with the lowest power consumption. This efficient suppression is physically achieved via synchronous quenching without resonant amplification, where GP actuation synchronizes the acoustic field and disrupts its coupling with the heat-release-rate (HRR) fluctuations of the flame. This disruption inhibits the formation of large-scale coherent vortices, resulting in a steadier HRR field decoupled from the acoustics, as evidenced by phase drifting and reduced Rayleigh index values. We also find that the GP algorithm is robust across varying reactant flow velocities, combustor lengths, and hydrogen concentrations, consistently yielding thermoacoustic amplitude reductions of 80%–94%. These findings establish GP as an effective, efficient and robust data-driven strategy for controlling thermoacoustic instabilities in turbulent combustion systems, including those fueled with hydrogen-enriched mixtures, advancing the development of sustainable energy technology.
Novelty and significance statement:
This experimental study is the first to apply genetic programming (GP) in both closed-loop and open-loop forms to suppress self-excited thermoacoustic oscillations in a turbulent combustor fueled by hydrogen- enriched mixtures. The GP algorithm discovers model-free control laws that achieve synchronous quenching (SQ) of the thermoacoustic mode by disrupting the flame–acoustic coupling, without resonant amplification of the actuation signal. GP closed-loop control outperforms both GP open-loop and conventional time-periodic forcing, achieving 80%–94% amplitude reduction across a range of Reynolds numbers, combustor lengths, and hydrogen power fractions while minimizing the actuation power. These results establish GP as an effective, efficient and robust strategy for active control of thermoacoustic instabilities in turbulent combustion systems, advancing sustainable energy technology.
{"title":"Genetic programming control of self-excited thermoacoustic oscillations in a turbulent hydrogen–methane combustor","authors":"Bo Yin , Aksel Ånestad , Eirik Æsøy , Nicholas A. Worth , Larry K.B. Li","doi":"10.1016/j.combustflame.2025.114711","DOIUrl":"10.1016/j.combustflame.2025.114711","url":null,"abstract":"<div><div>Thermoacoustic instabilities are a key challenge in developing sustainable combustion systems. In this experimental study, we present the first application of a data-driven machine learning algorithm based on genetic programming (GP) to suppress self-excited thermoacoustic oscillations in a turbulent premixed combustor operating with hydrogen-enriched fuels. The GP algorithm evolves model-free control laws via genetic operations such as replication, mutation, and crossover. Its performance is optimized through a cost function that balances the thermoacoustic amplitude reduction against the actuator power consumption. We evaluate GP in both closed-loop and open-loop configurations, benchmarking these against traditional open-loop time-periodic actuation. We find that GP closed-loop control proves superior in every metric evaluated, achieving the highest amplitude reduction with the lowest power consumption. This efficient suppression is physically achieved via synchronous quenching without resonant amplification, where GP actuation synchronizes the acoustic field and disrupts its coupling with the heat-release-rate (HRR) fluctuations of the flame. This disruption inhibits the formation of large-scale coherent vortices, resulting in a steadier HRR field decoupled from the acoustics, as evidenced by phase drifting and reduced Rayleigh index values. We also find that the GP algorithm is robust across varying reactant flow velocities, combustor lengths, and hydrogen concentrations, consistently yielding thermoacoustic amplitude reductions of 80%–94%. These findings establish GP as an effective, efficient and robust data-driven strategy for controlling thermoacoustic instabilities in turbulent combustion systems, including those fueled with hydrogen-enriched mixtures, advancing the development of sustainable energy technology.</div><div><strong>Novelty and significance statement:</strong></div><div>This experimental study is the first to apply genetic programming (GP) in both closed-loop and open-loop forms to suppress self-excited thermoacoustic oscillations in a turbulent combustor fueled by hydrogen- enriched mixtures. The GP algorithm discovers model-free control laws that achieve synchronous quenching (SQ) of the thermoacoustic mode by disrupting the flame–acoustic coupling, without resonant amplification of the actuation signal. GP closed-loop control outperforms both GP open-loop and conventional time-periodic forcing, achieving 80%–94% amplitude reduction across a range of Reynolds numbers, combustor lengths, and hydrogen power fractions while minimizing the actuation power. These results establish GP as an effective, efficient and robust strategy for active control of thermoacoustic instabilities in turbulent combustion systems, advancing sustainable energy technology.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114711"},"PeriodicalIF":6.2,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789255","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}
Pub Date : 2025-12-16DOI: 10.1016/j.combustflame.2025.114721
Guangwei Ma, Guoyan Zhao, Mingbo Sun, Chenxiang Zhao, Fan Li, JiaJian Zhu, Yixin Yang
This study delves into the effects of shock waves on ethylene self-ignition and combustion transition characteristics under Mach 8 flight-equivalent conditions. The shock waves were generated by a wedge with negligible flow loss. Multiple diagnostic techniques, including CH* chemiluminescence, schlieren, and wall pressure measurements, were employed to resolve the flow structures and combustion dynamics. The self-ignition is achieved and the flame kernel consistently appears within the cavity under all test conditions. Both the introduction of shock waves and an increase in the equivalence ratio promote the entrainment of more low-temperature fuel into the cavity, which could suppress the self-ignition process. The self-ignition delay time increased by 9∼33 ms after shock waves implementation, and the initial flame growth rate inside the cavity decreased. Once heat release within the cavity reached a certain high level, the enhanced fuel mixing promoted by shock waves facilitated ignition of the fuel jet outside the cavity. Combustion heat release gradually accumulated during a long period, eventually inducing boundary layer separation and initiating the combustion transition. The shock-induced mainstream deceleration and enhanced fuel mixing together accelerated flame propagation in combustion transition and suppressed intermittent flame flashback. Moreover, the shock-assisted steady combustion exhibited higher flame intensity and shifted to a more robust combustion mode.
{"title":"The shock-assisted self-ignition behavior and combustion transition mechanisms in a Mach 8 scramjet combustor","authors":"Guangwei Ma, Guoyan Zhao, Mingbo Sun, Chenxiang Zhao, Fan Li, JiaJian Zhu, Yixin Yang","doi":"10.1016/j.combustflame.2025.114721","DOIUrl":"10.1016/j.combustflame.2025.114721","url":null,"abstract":"<div><div>This study delves into the effects of shock waves on ethylene self-ignition and combustion transition characteristics under Mach 8 flight-equivalent conditions. The shock waves were generated by a wedge with negligible flow loss. Multiple diagnostic techniques, including CH* chemiluminescence, schlieren, and wall pressure measurements, were employed to resolve the flow structures and combustion dynamics. The self-ignition is achieved and the flame kernel consistently appears within the cavity under all test conditions. Both the introduction of shock waves and an increase in the equivalence ratio promote the entrainment of more low-temperature fuel into the cavity, which could suppress the self-ignition process. The self-ignition delay time increased by 9∼33 ms after shock waves implementation, and the initial flame growth rate inside the cavity decreased. Once heat release within the cavity reached a certain high level, the enhanced fuel mixing promoted by shock waves facilitated ignition of the fuel jet outside the cavity. Combustion heat release gradually accumulated during a long period, eventually inducing boundary layer separation and initiating the combustion transition. The shock-induced mainstream deceleration and enhanced fuel mixing together accelerated flame propagation in combustion transition and suppressed intermittent flame flashback. Moreover, the shock-assisted steady combustion exhibited higher flame intensity and shifted to a more robust combustion mode.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114721"},"PeriodicalIF":6.2,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789264","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}
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