Pub Date : 2026-05-01Epub Date: 2026-02-27DOI: 10.1016/j.combustflame.2026.114886
Yichen Zhang , Xiaojing Zheng , Gaoxiang Xiang
The successful operation of oblique detonation wave (ODW) engines is critically dependent on the stability of the detonation wavefront under realistic, non-uniform inflow conditions, a phenomenon that remains inadequately understood. This study employs two-dimensional simulations with a detailed H2/air mechanism to systematically elucidate the dynamic response of ODW structures to both gradient-type and sine-type inhomogeneities in equivalence ratio, pressure, temperature, and velocity. Results reveal that gradient-type inflows induce progressive deflection of the wavefront and alter the transition locus, whereas sine-type non-uniformities trigger periodic modulation, leading to distinctive flame dynamics including cellular patterns and localized extinction-reignition cycles. Crucially, large-amplitude oscillations are found to provoke decoupling of the shock and reaction fronts, defining critical stability boundaries. These findings provide fundamental insights into the coupling between inflow perturbations and detonation combustion, offering vital guidelines for the robust design of hypersonic propulsion systems.
{"title":"The dynamics of oblique detonation waves in non-uniform inflows: Flame structure and stability","authors":"Yichen Zhang , Xiaojing Zheng , Gaoxiang Xiang","doi":"10.1016/j.combustflame.2026.114886","DOIUrl":"10.1016/j.combustflame.2026.114886","url":null,"abstract":"<div><div>The successful operation of oblique detonation wave (ODW) engines is critically dependent on the stability of the detonation wavefront under realistic, non-uniform inflow conditions, a phenomenon that remains inadequately understood. This study employs two-dimensional simulations with a detailed H<sub>2</sub>/air mechanism to systematically elucidate the dynamic response of ODW structures to both gradient-type and sine-type inhomogeneities in equivalence ratio, pressure, temperature, and velocity. Results reveal that gradient-type inflows induce progressive deflection of the wavefront and alter the transition locus, whereas sine-type non-uniformities trigger periodic modulation, leading to distinctive flame dynamics including cellular patterns and localized extinction-reignition cycles. Crucially, large-amplitude oscillations are found to provoke decoupling of the shock and reaction fronts, defining critical stability boundaries. These findings provide fundamental insights into the coupling between inflow perturbations and detonation combustion, offering vital guidelines for the robust design of hypersonic propulsion systems.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114886"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386931","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 : 2026-05-01Epub Date: 2026-03-05DOI: 10.1016/j.combustflame.2026.114869
Spencer V. Taylor , Bodie J. Ziertman , Carmine S. Taglienti , Steven A. Mathe , Jonathan M. Tylka , Stephen F. Peralta , Gregory J. Harrigan , Zachary C. Cordero
Particle impact ignition in high-pressure oxygen poses a significant threat to oxygen-rich turbomachinery, yet current experimental tests cannot access the temperatures and pressures encountered in service, limiting their predictive value. This study addresses this challenge through a combined experimental-numerical approach in which particle impact tests are used to calibrate a multiphysics model that predicts ignition under engine-relevant conditions beyond those explicitly tested. Experiments with 100-µm Ti-6Al-4V particles impacting Al2O3 and Ni targets reveal a critical impact velocity for ignition that decreases with increasing gas temperature and target hardness. At 300 K, no particle ignitions are observed on Ni, while the critical velocity on Al2O3 is 170 m/s; at 500 K, the respective critical velocities are 225 m/s and 84 m/s. The model, anchored by these data, incorporates plasticity, adiabatic heating, and oxidation-driven thermal effects to simulate impact and ignition behaviors. A parametric study over ranges of temperatures, pressures, and particle sizes relevant to rocket engine applications shows that increasing these parameters lowers the critical velocity by enhancing plasticity, oxide rupture, and localized heat generation, with especially high ignition risk above 600 K and 6 MPa, conditions common in oxygen-rich turbomachinery. These findings clarify the governing mechanisms of particle impact ignition, highlight the relative benefits of different mitigations such as soft inert coatings, and establish a predictive framework for ignition risk assessment in high-pressure oxygen systems.
{"title":"Particle impact ignition in high-pressure oxygen: Experiments, mechanisms, and multiphysics modeling","authors":"Spencer V. Taylor , Bodie J. Ziertman , Carmine S. Taglienti , Steven A. Mathe , Jonathan M. Tylka , Stephen F. Peralta , Gregory J. Harrigan , Zachary C. Cordero","doi":"10.1016/j.combustflame.2026.114869","DOIUrl":"10.1016/j.combustflame.2026.114869","url":null,"abstract":"<div><div>Particle impact ignition in high-pressure oxygen poses a significant threat to oxygen-rich turbomachinery, yet current experimental tests cannot access the temperatures and pressures encountered in service, limiting their predictive value. This study addresses this challenge through a combined experimental-numerical approach in which particle impact tests are used to calibrate a multiphysics model that predicts ignition under engine-relevant conditions beyond those explicitly tested. Experiments with 100-µm Ti-6Al-4V particles impacting Al<sub>2</sub>O<sub>3</sub> and Ni targets reveal a critical impact velocity for ignition that decreases with increasing gas temperature and target hardness. At 300 K, no particle ignitions are observed on Ni, while the critical velocity on Al<sub>2</sub>O<sub>3</sub> is 170 m/s; at 500 K, the respective critical velocities are 225 m/s and 84 m/s. The model, anchored by these data, incorporates plasticity, adiabatic heating, and oxidation-driven thermal effects to simulate impact and ignition behaviors. A parametric study over ranges of temperatures, pressures, and particle sizes relevant to rocket engine applications shows that increasing these parameters lowers the critical velocity by enhancing plasticity, oxide rupture, and localized heat generation, with especially high ignition risk above 600 K and 6 MPa, conditions common in oxygen-rich turbomachinery. These findings clarify the governing mechanisms of particle impact ignition, highlight the relative benefits of different mitigations such as soft inert coatings, and establish a predictive framework for ignition risk assessment in high-pressure oxygen systems.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114869"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387009","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 : 2026-05-01Epub Date: 2026-03-06DOI: 10.1016/j.combustflame.2026.114897
Jie Li , Wenyan Song , Zhibo Cao , Bolun Sun , Ziwan Li
This study investigates the spray distribution, droplet lifetime, combustion performance, emissions and flame structure of a centrally staged combustor under conditions ranging from stable operation to near lean blowout (LBO) conditions. The results show that SMD and droplet velocity shift from pilot- to main-stage air control, underscoring the growing main-stage influence along the flow direction. As FAR decreases, the SMD increases and droplet lifetime becomes significantly longer, while the chemical reaction times remain short and change very little. Correspondingly, the spray morphology evolves from weakened radial expansion to contraction. At higher inlet temperatures, atomization is enhanced and the fuel distribution becomes more uniform, whereas at lower temperatures, droplet accumulation and limited evaporation result in dispersed, uneven spray structures. Characteristic time analysis confirms that flame stability is dominated by fuel preparation rather than by chemical kinetics, particularly under low inlet temperature conditions. Combustion efficiency and temperature rise jointly determine FARLBO: temperature rise sets the lower limit, while efficiency dictates how closely that limit can be approached. An optimal FARLBO can be achieved only when the temperature rise is sufficiently low and the combustion efficiency remains high. The CO2 conversion rate and normalized PMT signal intensity were introduced as new indicators. They exhibit a strong linear correlation with FAR across all inlet temperatures and an inverse relationship with CO formation. Therefore, it is more reliable than combustion efficiency under low inlet temperature. High inlet temperature improves atomization, shortens droplet lifetime, anchors the flame at the swirler exit while maintaining radial uniformity, and thereby delays blowout. In contrast, at lower temperatures, evaporation-limited combustion leads to earlier flame bifurcation at high FAR. POD analysis reveals that as LBO approaches, the flame transitions from a stable recirculation-zone mode to localized fuel-rich modes, with the mode 1 energy fraction continuously decreasing at higher inlet temperatures and the flame progressively fragmenting toward extinction.
{"title":"Experimental investigation of spray and combustion behavior in a centrally staged combustor under stable and near-blowout conditions","authors":"Jie Li , Wenyan Song , Zhibo Cao , Bolun Sun , Ziwan Li","doi":"10.1016/j.combustflame.2026.114897","DOIUrl":"10.1016/j.combustflame.2026.114897","url":null,"abstract":"<div><div>This study investigates the spray distribution, droplet lifetime, combustion performance, emissions and flame structure of a centrally staged combustor under conditions ranging from stable operation to near lean blowout (LBO) conditions. The results show that SMD and droplet velocity shift from pilot- to main-stage air control, underscoring the growing main-stage influence along the flow direction. As FAR decreases, the SMD increases and droplet lifetime becomes significantly longer, while the chemical reaction times remain short and change very little. Correspondingly, the spray morphology evolves from weakened radial expansion to contraction. At higher inlet temperatures, atomization is enhanced and the fuel distribution becomes more uniform, whereas at lower temperatures, droplet accumulation and limited evaporation result in dispersed, uneven spray structures. Characteristic time analysis confirms that flame stability is dominated by fuel preparation rather than by chemical kinetics, particularly under low inlet temperature conditions. Combustion efficiency and temperature rise jointly determine FAR<sub>LBO</sub>: temperature rise sets the lower limit, while efficiency dictates how closely that limit can be approached. An optimal FAR<sub>LBO</sub> can be achieved only when the temperature rise is sufficiently low and the combustion efficiency remains high. The CO<sub>2</sub> conversion rate and normalized PMT signal intensity were introduced as new indicators. They exhibit a strong linear correlation with FAR across all inlet temperatures and an inverse relationship with CO formation. Therefore, it is more reliable than combustion efficiency under low inlet temperature. High inlet temperature improves atomization, shortens droplet lifetime, anchors the flame at the swirler exit while maintaining radial uniformity, and thereby delays blowout. In contrast, at lower temperatures, evaporation-limited combustion leads to earlier flame bifurcation at high FAR. POD analysis reveals that as LBO approaches, the flame transitions from a stable recirculation-zone mode to localized fuel-rich modes, with the mode 1 energy fraction continuously decreasing at higher inlet temperatures and the flame progressively fragmenting toward extinction.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114897"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387012","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 : 2026-05-01Epub Date: 2026-02-20DOI: 10.1016/j.combustflame.2026.114861
Chenyu Li , Haiyue Li , Chung K. Law , Wenkai Liang
Ozone (O3), as a strong oxidizer, demonstrates the potential for influencing and controlling flame propagation speed through altered chemical kinetics. In this study, we investigated flame enhancement by compositionally stratified ozone on the oxidizer side for hydrogen (H2) /air mixtures with =0.6–4.0 and ozone fraction in the oxidant =0–10%. Detailed flame dynamics and structure have been systematically analysed through numerical simulation and kinetics analysis. It is shown that, ozone stratification induces a sustaining effect, i.e., the flame remains fast-propagating even when traveling out of the ozone stratification layer and transiting into the ozone-free regime. Such a sustaining effect shows opposite dependences on the ozone concentration for (fuel-)lean and rich conditions, with a crossing point approximately at equivalence ratio =1.5. Furthermore, ozone stratification exerts much stronger influences on flame propagation through chemical effects compared to thermal effects. The reaction of ozone with H radical is of primary importance, contributing to both flame enhancement and the sustaining effect. Preferential diffusion by ozone can facilitate flame propagation under both lean and rich conditions. This study provides insights into optimizing hydrogen combustion applications by ozone stratification.
{"title":"Facilitated hydrogen/air flame propagation using ozone stratification","authors":"Chenyu Li , Haiyue Li , Chung K. Law , Wenkai Liang","doi":"10.1016/j.combustflame.2026.114861","DOIUrl":"10.1016/j.combustflame.2026.114861","url":null,"abstract":"<div><div>Ozone (O<sub>3</sub>), as a strong oxidizer, demonstrates the potential for influencing and controlling flame propagation speed through altered chemical kinetics. In this study, we investigated flame enhancement by compositionally stratified ozone on the oxidizer side for hydrogen (H<sub>2</sub>) /air mixtures with <span><math><mi>ϕ</mi></math></span>=0.6–4.0 and ozone fraction in the oxidant <span><math><msub><mi>α</mi><msub><mi>O</mi><mn>3</mn></msub></msub></math></span>=0–10%. Detailed flame dynamics and structure have been systematically analysed through numerical simulation and kinetics analysis. It is shown that, ozone stratification induces a sustaining effect, i.e., the flame remains fast-propagating even when traveling out of the ozone stratification layer and transiting into the ozone-free regime. Such a sustaining effect shows opposite dependences on the ozone concentration for (fuel-)lean and rich conditions, with a crossing point approximately at equivalence ratio <span><math><mi>ϕ</mi></math></span>=1.5. Furthermore, ozone stratification exerts much stronger influences on flame propagation through chemical effects compared to thermal effects. The reaction of ozone with H radical is of primary importance, contributing to both flame enhancement and the sustaining effect. Preferential diffusion by ozone can facilitate flame propagation under both lean and rich conditions. This study provides insights into optimizing hydrogen combustion applications by ozone stratification.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114861"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386880","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 : 2026-05-01Epub Date: 2026-03-11DOI: 10.1016/j.combustflame.2026.114920
Weijie Fan , Haoyang Peng , Shijie Liu , Chenglong Yan , Hailong Zhang , Xueqiang Yuan , Shenghui Zhong , Weidong Liu
This study investigates the combustion characteristics of continuous rotating detonation (CRD) in a hollow combustor using synchronous chemiluminescence imaging. Ambient-temperature ethylene and air are employed as propellants, with the air mass flow rate being 35010 g/s. The results show that the high-luminance zone induced by the CRD wave is attached to the outer wall while the low-luminance deflagration combustion occurs in the central region of the hollow combustor. As the nozzle contraction ratio (CR) increases from 1 to 4, the area of the deflagration reaction zone at the center of the combustor gradually expands. However, the chemiluminescence intensity of the detonation reaction zone near the outer wall of the combustor first increases and then decreases as CR increases. Moreover, the axial length and chemiluminescence intensity of the reaction zone of CRD first increase and then decrease as the CR rises. Correspondingly, the axial reaction zone of CRD wave exhibits segmented curved, continuous linear, and loose cluster structures as the CR increases from 1 to 4. An appropriate increase in the nozzle CR enhances the pre-heating effect of the central high-temperature recirculation zone on the fresh combustible mixture, thereby enhancing the CRD intensity. In contrast, excessive parasitic deflagration combustion with a large CR leads to destruction of the combustible mixture layer and further attenuates the CRD intensity. These findings provide comprehensive understanding of the CRD flowfield within a hollow combustor, facilitating an in-depth comprehension of the self-sustaining mechanism of CRD waves.
{"title":"Combustion characteristics of continuous rotating detonation in the hollow combustor through synchronous chemiluminescence imaging","authors":"Weijie Fan , Haoyang Peng , Shijie Liu , Chenglong Yan , Hailong Zhang , Xueqiang Yuan , Shenghui Zhong , Weidong Liu","doi":"10.1016/j.combustflame.2026.114920","DOIUrl":"10.1016/j.combustflame.2026.114920","url":null,"abstract":"<div><div>This study investigates the combustion characteristics of continuous rotating detonation (CRD) in a hollow combustor using synchronous chemiluminescence imaging. Ambient-temperature ethylene and air are employed as propellants, with the air mass flow rate being 350<span><math><mo>±</mo></math></span>10 g/s. The results show that the high-luminance zone induced by the CRD wave is attached to the outer wall while the low-luminance deflagration combustion occurs in the central region of the hollow combustor. As the nozzle contraction ratio (CR) increases from 1 to 4, the area of the deflagration reaction zone at the center of the combustor gradually expands. However, the chemiluminescence intensity of the detonation reaction zone near the outer wall of the combustor first increases and then decreases as CR increases. Moreover, the axial length and chemiluminescence intensity of the reaction zone of CRD first increase and then decrease as the CR rises. Correspondingly, the axial reaction zone of CRD wave exhibits segmented curved, continuous linear, and loose cluster structures as the CR increases from 1 to 4. An appropriate increase in the nozzle CR enhances the pre-heating effect of the central high-temperature recirculation zone on the fresh combustible mixture, thereby enhancing the CRD intensity. In contrast, excessive parasitic deflagration combustion with a large CR leads to destruction of the combustible mixture layer and further attenuates the CRD intensity. These findings provide comprehensive understanding of the CRD flowfield within a hollow combustor, facilitating an in-depth comprehension of the self-sustaining mechanism of CRD waves.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114920"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386888","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 : 2026-05-01Epub Date: 2026-02-27DOI: 10.1016/j.combustflame.2026.114838
Yegor D. Bugrov, Vladimir V. Karasev, Oleg G. Glotov
The study focuses on phenomena accompanying asymmetric combustion of aluminum particles in gaseous media, including particle rotation, sinusoidal tracks, abrupt trajectory swerves, helical smoke tail formation, and the dependence of rotation frequency on droplet size, ambient temperature, and oxidizer concentration. An extensive literature review, combined with original high‑speed video observations, reveals two rotation modes with a transition diameter near 30 µm. For larger particles, the mean rotation frequency scales as dp–1.7, and for smaller ones as dp–0.15, where dp denotes particle diameter. This disparity arises from the difference in combustion regimes of coarse and fine particles. Rotation frequency follows a characteristic "two‑humped" temporal pattern and increases with oxidizer concentration and temperature. Swerves occur without fragmentation, and smoke helix diameter scales linearly with Al/Al2O3 droplet size. The chemical interaction between molten alumina and aluminum can produce either discrete bubbles beneath the oxide cap (at high pressure above 5–20 atm) or a “quasi-cleft” (at lower pressure). The transition from bubbles to the quasi‑cleft resembles that from nucleate boiling to film boiling. The developed semi-analytical quasi-cleft model describes jet outflow beneath the oxide cap, linking rotation dynamics, swerve onset, and helical tail formation. The growth of the oxide cap on the aluminum droplet surface leads to the emergence of the “two-humped” frequency-time dependence, with a trajectory swerve occurring near the minimum rotation frequency. This can cause detrimental deposition of oxide residues on a combustion chamber wall. A number of additives in Al-based composite induce and enhance rotation. Assessments based on the literature support that the burning rate increases appreciably due to rotating convection, particularly under conditions of high ambient temperature and oxidizer concentration at pressures below ∼10 atm, typical for ramjet mode.
{"title":"An experimental study and modeling of aluminum particle asymmetric combustion","authors":"Yegor D. Bugrov, Vladimir V. Karasev, Oleg G. Glotov","doi":"10.1016/j.combustflame.2026.114838","DOIUrl":"10.1016/j.combustflame.2026.114838","url":null,"abstract":"<div><div>The study focuses on phenomena accompanying asymmetric combustion of aluminum particles in gaseous media, including particle rotation, sinusoidal tracks, abrupt trajectory swerves, helical smoke tail formation, and the dependence of rotation frequency on droplet size, ambient temperature, and oxidizer concentration. An extensive literature review, combined with original high‑speed video observations, reveals two rotation modes with a transition diameter near 30 µm. For larger particles, the mean rotation frequency scales as <em>d</em><sub><em>p</em></sub><sup>–1.7</sup>, and for smaller ones as <em>d</em><sub><em>p</em></sub><sup>–0.15</sup>, where <em>d</em><sub><em>p</em></sub> denotes particle diameter. This disparity arises from the difference in combustion regimes of coarse and fine particles. Rotation frequency follows a characteristic \"two‑humped\" temporal pattern and increases with oxidizer concentration and temperature. Swerves occur without fragmentation, and smoke helix diameter scales linearly with Al/Al<sub>2</sub>O<sub>3</sub> droplet size. The chemical interaction between molten alumina and aluminum can produce either discrete bubbles beneath the oxide cap (at high pressure above 5–20 atm) or a “quasi-cleft” (at lower pressure). The transition from bubbles to the quasi‑cleft resembles that from nucleate boiling to film boiling. The developed semi-analytical quasi-cleft model describes jet outflow beneath the oxide cap, linking rotation dynamics, swerve onset, and helical tail formation. The growth of the oxide cap on the aluminum droplet surface leads to the emergence of the “two-humped” frequency-time dependence, with a trajectory swerve occurring near the minimum rotation frequency. This can cause detrimental deposition of oxide residues on a combustion chamber wall. A number of additives in Al-based composite induce and enhance rotation. Assessments based on the literature support that the burning rate increases appreciably due to rotating convection, particularly under conditions of high ambient temperature and oxidizer concentration at pressures below ∼10 atm, typical for ramjet mode.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114838"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386932","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 : 2026-05-01Epub Date: 2026-02-27DOI: 10.1016/j.combustflame.2026.114892
Geveen Arumapperuma, Antonio Attili
<div><div>This study investigates the formation, evolution, and modelling of polycyclic aromatic hydrocarbons (PAH) using large-scale three-dimensional direct numerical simulations (DNS) of spatially evolving turbulent non-premixed ethylene/air flames. Finite rate chemistry is used with a detailed chemical mechanism for ethylene oxidation with naphthalene as the PAH species. Three cases are analysed: two at the same Reynolds number with different Damköhler numbers and one at a higher Reynolds number with the same Damköhler number as one of the lower Reynolds number cases. A strong correlation is observed between the mean PAH field and the mean scalar dissipation rate, while the correlation between the local instantaneous values is extremely weak. For a given streamwise location of the flame, if the mean scalar dissipation rate is the same between the simulations, the mean PAH concentration is also the same, irrespective of the Damköhler number. It was also shown that the mean scalar dissipation rate, conditioned on the mixture fraction, can be used to retrieve the PAH mass fraction accurately from a table build using steady flamelets. These observations suggest that highly fluctuating quantities like PAHs in turbulent flames, despite being uncorrelated to the local turbulent and mixing fields, are however related to the mean fields. Moreover, the PAH is found to be insensitive to the Reynolds number, as no significant difference in the PAH field can be observed between the two flames with different Reynolds numbers. An <em>a priori</em> analysis revealed that the PAH source terms deviate considerably from the steady flamelet solution and a linear scaling of the PAH consumption term based on the local PAH concentration leads to significant errors. In addition to the DNS, an LES with tabulated chemistry of the higher Reynolds number flame is performed for an <em>a posteriori</em> analysis of the PAH modelling errors. The PAH is modelled using a transport equation where the source term is read from a flamelet table. Two separate LESs are performed, one with a unity Lewis number flamelet table and the other with a table generated with mixture-averaged transport. Both LESs capture the spatial distribution of PAH with reasonable accuracy. However, the unity Lewis number LES significantly underpredicts the magnitude of PAH by about an order of magnitude. The non-unity Lewis number LES shows an improvement, albeit still underpredicting the DNS results. It is observed that the prediction errors are mostly associated with the errors in the PAH source terms from the flamelet model and highlights the need to improve the model. Finally, the idea of using the mean scalar dissipation to parametrise PAH in LES is tested <em>a posteriori</em> and it is found that this can be a viable approach.</div><div><strong>Novelty and significance statement</strong></div><div>A novel, large-scale direct numerical simulation dataset of a realistic flame configuration was gene
{"title":"Analysis and modelling of PAHs in turbulent non-premixed jet flames","authors":"Geveen Arumapperuma, Antonio Attili","doi":"10.1016/j.combustflame.2026.114892","DOIUrl":"10.1016/j.combustflame.2026.114892","url":null,"abstract":"<div><div>This study investigates the formation, evolution, and modelling of polycyclic aromatic hydrocarbons (PAH) using large-scale three-dimensional direct numerical simulations (DNS) of spatially evolving turbulent non-premixed ethylene/air flames. Finite rate chemistry is used with a detailed chemical mechanism for ethylene oxidation with naphthalene as the PAH species. Three cases are analysed: two at the same Reynolds number with different Damköhler numbers and one at a higher Reynolds number with the same Damköhler number as one of the lower Reynolds number cases. A strong correlation is observed between the mean PAH field and the mean scalar dissipation rate, while the correlation between the local instantaneous values is extremely weak. For a given streamwise location of the flame, if the mean scalar dissipation rate is the same between the simulations, the mean PAH concentration is also the same, irrespective of the Damköhler number. It was also shown that the mean scalar dissipation rate, conditioned on the mixture fraction, can be used to retrieve the PAH mass fraction accurately from a table build using steady flamelets. These observations suggest that highly fluctuating quantities like PAHs in turbulent flames, despite being uncorrelated to the local turbulent and mixing fields, are however related to the mean fields. Moreover, the PAH is found to be insensitive to the Reynolds number, as no significant difference in the PAH field can be observed between the two flames with different Reynolds numbers. An <em>a priori</em> analysis revealed that the PAH source terms deviate considerably from the steady flamelet solution and a linear scaling of the PAH consumption term based on the local PAH concentration leads to significant errors. In addition to the DNS, an LES with tabulated chemistry of the higher Reynolds number flame is performed for an <em>a posteriori</em> analysis of the PAH modelling errors. The PAH is modelled using a transport equation where the source term is read from a flamelet table. Two separate LESs are performed, one with a unity Lewis number flamelet table and the other with a table generated with mixture-averaged transport. Both LESs capture the spatial distribution of PAH with reasonable accuracy. However, the unity Lewis number LES significantly underpredicts the magnitude of PAH by about an order of magnitude. The non-unity Lewis number LES shows an improvement, albeit still underpredicting the DNS results. It is observed that the prediction errors are mostly associated with the errors in the PAH source terms from the flamelet model and highlights the need to improve the model. Finally, the idea of using the mean scalar dissipation to parametrise PAH in LES is tested <em>a posteriori</em> and it is found that this can be a viable approach.</div><div><strong>Novelty and significance statement</strong></div><div>A novel, large-scale direct numerical simulation dataset of a realistic flame configuration was gene","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114892"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386933","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 : 2026-05-01Epub Date: 2026-03-01DOI: 10.1016/j.combustflame.2026.114898
Xin-xing Zeng , Jing-an Xiang , Xing-quan Zhang , Hai-fu Wang , Jun Wang
Boron (B) fuel has great potential in solid propellant owing to its high oxidation reaction heat. Unfortunately, low combustion efficiency and energy release rate result from the inert oxide layer (B2O3) and combustion production aggregation. Herein, fluorine and oxygen were integrated to microparticle of B@PTFE-AP containing core-shell B@PTFE with different PTFE contents. The excellent performance originates from oxidation and fluorination reactions of boron, and high interfacial effect from B@PTFE-AP with uniform microstructure and component for gas-liquid-solid reaction and energy release. Compared to B-AP and physical mixed B@PTFE/AP, the combustion speed and pressure output of B@PTFE-AP increased to 10.11 mm/s, 379.64 kPa. Furthermore, B@PTFE-AP based solid propellant has an elevated combustion rate (5.15 mm/s) and smaller particles size of condensed combustion products. The above results demonstrated that our work provides a viable approach to overcome the low combustion reaction and energy output efficiency of boron for the practical applications in solid propellants.
Novelty and significance statement
Boron (B) has great potential in the solid propellant owing to its high reaction heat. Unfortunately, it shows low combustion efficiency and energy release rate resulting from the inert oxide layer (B2O3) and combustion product aggregation. Herein, fluorine and oxygen were integrated to form B@PTFE-AP microparticle containing core-shell B@PTFE for high combustion reactivity and energy release, which originated from oxidation and fluorination reactions of boron, and high interfacial effects from B@PTFE-AP with a uniform micro-structure and component for gas-liquid-solid reaction. Additionally, B@PTFE-AP has been applied in the solid propellant, which has an elevated combustion rate and smaller particles size of condensed combustion products. This work provides an effective approach to overcome the low combustion reaction and energy output efficiency of boron for practical applications.
{"title":"An engineering approach to enhance combustion process and energy of boron for applications in solid propellant","authors":"Xin-xing Zeng , Jing-an Xiang , Xing-quan Zhang , Hai-fu Wang , Jun Wang","doi":"10.1016/j.combustflame.2026.114898","DOIUrl":"10.1016/j.combustflame.2026.114898","url":null,"abstract":"<div><div>Boron (B) fuel has great potential in solid propellant owing to its high oxidation reaction heat. Unfortunately, low combustion efficiency and energy release rate result from the inert oxide layer (B<sub>2</sub>O<sub>3</sub>) and combustion production aggregation. Herein, fluorine and oxygen were integrated to microparticle of B@PTFE-AP containing core-shell B@PTFE with different PTFE contents. The excellent performance originates from oxidation and fluorination reactions of boron, and high interfacial effect from B@PTFE-AP with uniform microstructure and component for gas-liquid-solid reaction and energy release. Compared to B-AP and physical mixed B@PTFE/AP, the combustion speed and pressure output of B@PTFE-AP increased to 10.11 mm/s, 379.64 kPa. Furthermore, B@PTFE-AP based solid propellant has an elevated combustion rate (5.15 mm/s) and smaller particles size of condensed combustion products. The above results demonstrated that our work provides a viable approach to overcome the low combustion reaction and energy output efficiency of boron for the practical applications in solid propellants.</div></div><div><h3>Novelty and significance statement</h3><div>Boron (B) has great potential in the solid propellant owing to its high reaction heat. Unfortunately, it shows low combustion efficiency and energy release rate resulting from the inert oxide layer (B<sub>2</sub>O<sub>3</sub>) and combustion product aggregation. Herein, fluorine and oxygen were integrated to form B@PTFE-AP microparticle containing core-shell B@PTFE for high combustion reactivity and energy release, which originated from oxidation and fluorination reactions of boron, and high interfacial effects from B@PTFE-AP with a uniform micro-structure and component for gas-liquid-solid reaction. Additionally, B@PTFE-AP has been applied in the solid propellant, which has an elevated combustion rate and smaller particles size of condensed combustion products. This work provides an effective approach to overcome the low combustion reaction and energy output efficiency of boron for practical applications.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114898"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386885","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 : 2026-05-01Epub Date: 2026-02-25DOI: 10.1016/j.combustflame.2026.114870
Chenyu Li , Chung K. Law , Wenkai Liang
This study investigates the effects of ozone addition on autoignition-assisted hydrogen-air flames with detailed kinetics and transport. For homogeneous ignition, a critical temperature () was identified that significantly influences the reaction pathways and ignition characteristics. It is shown that below , the system exhibits a distinct two-stage reaction process during autoignition, characterized by initial ozone decomposition followed by high-temperature hydrogen-oxygen reactions. Above , the two ignition stages merge, leading to drastically reduced ignition delay time—a small temperature difference near can result in a hundredfold reduction. For the auto-ignitive flames, similar transition in terms of flame speeds occurs near the critical temperature, for which the proposed scaling law based on Damköhler number holds for both conditions below and above . Comparative analysis of zero-dimensional (0D) and one-dimensional (1D) simulations reveals pronounced differences in the evolution of key species such as H2, H, HO2 and O3. In 1D flames, transport processes lead to more efficient radical buildup and earlier ozone consumption compared to the 0D case. The spatial coupling of the H2 diffusion zones with O3 consumption zones above was found to enhance the overall combustion process. The effects of elevated pressure have also been illustrated. These findings underscore the critical influence of transport effects and subtle temperature variations on radical accumulation, reaction pathways, and flame dynamics in ozone-assisted hydrogen combustion.
{"title":"Ozone-affected auto-ignitive hydrogen-air flames: Transitions near critical temperatures","authors":"Chenyu Li , Chung K. Law , Wenkai Liang","doi":"10.1016/j.combustflame.2026.114870","DOIUrl":"10.1016/j.combustflame.2026.114870","url":null,"abstract":"<div><div>This study investigates the effects of ozone addition on autoignition-assisted hydrogen-air flames with detailed kinetics and transport. For homogeneous ignition, a critical temperature (<span><math><msub><mi>T</mi><mi>c</mi></msub></math></span>) was identified that significantly influences the reaction pathways and ignition characteristics. It is shown that below <span><math><msub><mi>T</mi><mi>c</mi></msub></math></span>, the system exhibits a distinct two-stage reaction process during autoignition, characterized by initial ozone decomposition followed by high-temperature hydrogen-oxygen reactions. Above <span><math><msub><mi>T</mi><mi>c</mi></msub></math></span>, the two ignition stages merge, leading to drastically reduced ignition delay time—a small temperature difference near <span><math><msub><mi>T</mi><mi>c</mi></msub></math></span> can result in a hundredfold reduction. For the auto-ignitive flames, similar transition in terms of flame speeds occurs near the critical temperature, for which the proposed scaling law based on Damköhler number holds for both conditions below and above <span><math><msub><mi>T</mi><mi>c</mi></msub></math></span>. Comparative analysis of zero-dimensional (0D) and one-dimensional (1D) simulations reveals pronounced differences in the evolution of key species such as H<sub>2</sub>, H, HO<sub>2</sub> and O<sub>3</sub>. In 1D flames, transport processes lead to more efficient radical buildup and earlier ozone consumption compared to the 0D case. The spatial coupling of the H<sub>2</sub> diffusion zones with O<sub>3</sub> consumption zones above <span><math><msub><mi>T</mi><mi>c</mi></msub></math></span> was found to enhance the overall combustion process. The effects of elevated pressure have also been illustrated. These findings underscore the critical influence of transport effects and subtle temperature variations on radical accumulation, reaction pathways, and flame dynamics in ozone-assisted hydrogen combustion.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114870"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386926","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}
This paper reports the characterization of propellant containing hydroxyl-terminated polybutadiene (HTPB) modified with nitro (NO) group. Two propellants named Mix 1 and Mix 2 were prepared using ammonium perchlorate (AP) as an oxidizer with a solid loading of 80%. Mix 1 propellant contained conventional HTPB, while Mix 2 used nitro-modified HTPB (nitro-HTPB). The rheology of nitro-HTPB binder was studied during curing process. The curing agent used was toulene diisocyante. The thermal decomposition of the propellant was studied using thermogravimetric analysis (TGA/DTA) which revealed energetic nature of propellant containing nitro-HTPB. The burn rate was measured in the pressure range of 1–7 MPa using a standard Crawford bomb. The burn rate of Mix 1 and Mix 2 was found to be 10.7 mm/s and 11.78 mm/s at 7 MPa. The pressure index of Mix 2 was observed to be much lower compared to Mix 1. Static motor testing was conducted to determine the combustion efficiency and nozzle efficiency. Characteristic velocity of Mix 2 and Mix 1 was found to be 1425 m/s and 1392 m/s respectively, in the motor test. Burn rates from the strand burner were validated with the burn rate obtained from static motor tests.
{"title":"Ballistic and rheological properties of nitro-HTPB composite propellant","authors":"Deepak Govindaraju , Argha Bhattacharjee , Kumar Nagendra","doi":"10.1016/j.combustflame.2026.114894","DOIUrl":"10.1016/j.combustflame.2026.114894","url":null,"abstract":"<div><div>This paper reports the characterization of propellant containing hydroxyl-terminated polybutadiene (HTPB) modified with nitro (<img>NO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>) group. Two propellants named Mix 1 and Mix 2 were prepared using ammonium perchlorate (AP) as an oxidizer with a solid loading of 80%. Mix 1 propellant contained conventional HTPB, while Mix 2 used nitro-modified HTPB (nitro-HTPB). The rheology of nitro-HTPB binder was studied during curing process. The curing agent used was toulene diisocyante. The thermal decomposition of the propellant was studied using thermogravimetric analysis (TGA/DTA) which revealed energetic nature of propellant containing nitro-HTPB. The burn rate was measured in the pressure range of 1–7 MPa using a standard Crawford bomb. The burn rate of Mix 1 and Mix 2 was found to be 10.7 mm/s and 11.78 mm/s at 7 MPa. The pressure index of Mix 2 was observed to be much lower compared to Mix 1. Static motor testing was conducted to determine the combustion efficiency and nozzle efficiency. Characteristic velocity of Mix 2 and Mix 1 was found to be 1425 m/s and 1392 m/s respectively, in the motor test. Burn rates from the strand burner were validated with the burn rate obtained from static motor tests.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114894"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386934","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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