Ammonia (NH) has gained increasing attention as a promising carbon-free fuel for compression ignition engines. Nonetheless, its poor combustion characteristics and elevated nitrogen oxides (NO) emissions present substantial obstacles. In the present study, we examine the utility of incorporating NH as a low-reactivity fuel (LRF) in diesel-assisted dual-fuel combustion under Reactivity Controlled Compression Ignition (RCCI) conditions. Three large-eddy simulations (LES) are performed to quantify the effect of varying concentrations of NH as LRF on the ignition characteristics and flame structure. The computational setup corresponds to the Engine Combustion Network (ECN) Spray A configuration, which provides the baseline for the present analysis. The ignition of the dodecane spray is found to be delayed by the presence of NH, which increases with increasing NH content in the ambient. Local flamelets are extracted to examine the evolution of the flame structure starting from ignition at richer mixtures through low-temperature chemistry of dodecane, to finally stabilizing at the stoichiometric conditions. Near ignition, NH oxidation is observed to follow the autoignition behavior of the most reactive mixture fraction, whereas at post-ignition the behavior shifts towards canonical premixed flame propagation. This study shows that using NH as LRF under RCCI conditions offers an effective solution for NH operation in CI engines to reduce carbon emissions.
{"title":"Examining diesel-spray assisted ignition of ammonia under reactivity-controlled conditions using large-eddy simulations","authors":"Pushan Sharma, Davy Brouzet, Wai Tong Chung, Matthias Ihme","doi":"10.1016/j.proci.2024.105317","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105317","url":null,"abstract":"Ammonia (NH) has gained increasing attention as a promising carbon-free fuel for compression ignition engines. Nonetheless, its poor combustion characteristics and elevated nitrogen oxides (NO) emissions present substantial obstacles. In the present study, we examine the utility of incorporating NH as a low-reactivity fuel (LRF) in diesel-assisted dual-fuel combustion under Reactivity Controlled Compression Ignition (RCCI) conditions. Three large-eddy simulations (LES) are performed to quantify the effect of varying concentrations of NH as LRF on the ignition characteristics and flame structure. The computational setup corresponds to the Engine Combustion Network (ECN) Spray A configuration, which provides the baseline for the present analysis. The ignition of the dodecane spray is found to be delayed by the presence of NH, which increases with increasing NH content in the ambient. Local flamelets are extracted to examine the evolution of the flame structure starting from ignition at richer mixtures through low-temperature chemistry of dodecane, to finally stabilizing at the stoichiometric conditions. Near ignition, NH oxidation is observed to follow the autoignition behavior of the most reactive mixture fraction, whereas at post-ignition the behavior shifts towards canonical premixed flame propagation. This study shows that using NH as LRF under RCCI conditions offers an effective solution for NH operation in CI engines to reduce carbon emissions.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141527512","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 : 2024-06-28DOI: 10.1016/j.proci.2024.105284
Laura Donato, M. Mustafa Kamal, Alberto Procacci, Marianna Cafiero, Saurabh Sharma, Chiara Galletti, Axel Coussement, Alessandro Parente
This study presents a data assimilation (DA) framework that combines a simulation-based digital twin (DT) with a sparse sensing (SpS) strategy using experimental data. This approach continuously enhances the DT model with newly available data from numerical simulations and experiments. The DT, built by coupling Proper Orthogonal Decomposition (POD) and Gaussian Process Regression (GPR), is based on 49 Reynolds-averaged Navier–Stokes simulations of a semi-industrial combustion furnace, covering a range of operating conditions in terms of fuel inlet mixture, equivalence ratio, and air inlet velocity. The experimental campaign utilizes Laser Rayleigh Scattering (LRS) to map the temperature field in the combustion furnace. The SpS model is employed to project the experimental data into a low-dimensional manifold. Afterwards, DA is carried out to obtain an updated set of coefficients within that manifold. The assimilated solution leads to a DT with enhanced predictive capabilities. The findings highlight the potential of this approach to improve the accuracy of DTs through the integration of experimental and numerical data.
{"title":"Integrating data assimilation and sparse sensing for updating a digital twin of a semi-industrial furnace","authors":"Laura Donato, M. Mustafa Kamal, Alberto Procacci, Marianna Cafiero, Saurabh Sharma, Chiara Galletti, Axel Coussement, Alessandro Parente","doi":"10.1016/j.proci.2024.105284","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105284","url":null,"abstract":"This study presents a data assimilation (DA) framework that combines a simulation-based digital twin (DT) with a sparse sensing (SpS) strategy using experimental data. This approach continuously enhances the DT model with newly available data from numerical simulations and experiments. The DT, built by coupling Proper Orthogonal Decomposition (POD) and Gaussian Process Regression (GPR), is based on 49 Reynolds-averaged Navier–Stokes simulations of a semi-industrial combustion furnace, covering a range of operating conditions in terms of fuel inlet mixture, equivalence ratio, and air inlet velocity. The experimental campaign utilizes Laser Rayleigh Scattering (LRS) to map the temperature field in the combustion furnace. The SpS model is employed to project the experimental data into a low-dimensional manifold. Afterwards, DA is carried out to obtain an updated set of coefficients within that manifold. The assimilated solution leads to a DT with enhanced predictive capabilities. The findings highlight the potential of this approach to improve the accuracy of DTs through the integration of experimental and numerical data.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141527510","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 : 2024-06-28DOI: 10.1016/j.proci.2024.105201
Nikola Sekularac, Thomas Lesaffre, Davide Laera, Laurent Gicquel
Well-understanding and mastering Sustainable Aviation Fuels (SAF) mixture composition as well as the potential of their initial component concentrations’ impact on flames is clearly of critical importance in today’s effort and energy transition. In this study, the focus lies on conducting Large Eddy Simulations (LES) to comprehend the impact of species concentration changes in well-controlled multi-component fuel blends on flame structures. The SICCA-spray rig from the EM2C laboratory operated with three blends of n-dodecane and n-heptane in varying proportions, is specifically addressed and investigated in light of the available data. To conduct these simulations, the dynamically thickened flame model and an evaporation multi-component sub-model are coupled with a reduced chemistry mechanism for n-heptane and n-dodecane binary blends. Across all investigated blends, the simulated swirling spray flame predictions align well with the experimental measurements confirming the suitability of the proposed modeling. For this configuration, the alterations in species concentration do not appear to significantly impact the overall flame structures and characteristics when observed from an average perspective. However, localized differences are identified, revealing notable composition effects. The simulation outcomes indicate that the early consumption of n-heptane contributes to stabilizing the flame, whereas the vaporization of n-dodecane is the primary factor responsible for combustion occurring further downstream. These effects are closely tied to the evaporation properties of each fuel compound and their concentration proportions within the blend, as expected. This insight highlights the intricate relationship between fuel properties, their concentrations within blends, and the resulting combustion behavior, shedding light on the complexities of multi-component fuel combustion characteristics.
{"title":"Large Eddy Simulations of n-heptane and n-dodecane binary blends in swirling multi-component spray flames","authors":"Nikola Sekularac, Thomas Lesaffre, Davide Laera, Laurent Gicquel","doi":"10.1016/j.proci.2024.105201","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105201","url":null,"abstract":"Well-understanding and mastering Sustainable Aviation Fuels (SAF) mixture composition as well as the potential of their initial component concentrations’ impact on flames is clearly of critical importance in today’s effort and energy transition. In this study, the focus lies on conducting Large Eddy Simulations (LES) to comprehend the impact of species concentration changes in well-controlled multi-component fuel blends on flame structures. The SICCA-spray rig from the EM2C laboratory operated with three blends of n-dodecane and n-heptane in varying proportions, is specifically addressed and investigated in light of the available data. To conduct these simulations, the dynamically thickened flame model and an evaporation multi-component sub-model are coupled with a reduced chemistry mechanism for n-heptane and n-dodecane binary blends. Across all investigated blends, the simulated swirling spray flame predictions align well with the experimental measurements confirming the suitability of the proposed modeling. For this configuration, the alterations in species concentration do not appear to significantly impact the overall flame structures and characteristics when observed from an average perspective. However, localized differences are identified, revealing notable composition effects. The simulation outcomes indicate that the early consumption of n-heptane contributes to stabilizing the flame, whereas the vaporization of n-dodecane is the primary factor responsible for combustion occurring further downstream. These effects are closely tied to the evaporation properties of each fuel compound and their concentration proportions within the blend, as expected. This insight highlights the intricate relationship between fuel properties, their concentrations within blends, and the resulting combustion behavior, shedding light on the complexities of multi-component fuel combustion characteristics.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141527511","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 : 2024-06-27DOI: 10.1016/j.proci.2024.105353
Ning Liu, Bowen Mei, Xingqian Mao, Ziyu Wang, Zijian Sun, Yijie Xu, Zhiyu Shi, Yiguang Ju
Ammonia (NH) has been widely recognized as one of the carbon-neutral fuels. However, ammonia combustion suffers low reactivity and high NO/NO emissions. To overcome these issues, this work reports plasma assisted NH/H oxidation and unveils the kinetics of fuel oxidation and NO/NO formation by combining time-resolved laser diagnostics with plasma modeling. Firstly, we found that the NH consumption is promoted with a H blending ratio of 0.3, due to enhancements of H and OH formation by plasma assisted H dissociation. Secondly, at a high reduced electric field, when the H blending ratio increases, the NH oxidation is promoted due to both the HO formation and strong NO kinetic enhancement via NO-HO and NO-H pathways. In the meantime, it is shown that the NO mole fraction also increases with H blending ratio, because the NO formation is enhanced via N(D)-O pathways, and the DeNO chemistry is weakened with less NH production. By contrast, at a lower reduced electric field, when the H blending ratio increases, the decreased N(D) formation does not produce enough NO to replenish the NO formation drop caused by lower NH concentration. Thirdly, the reduced electric field non-monotonically affects fuel consumption and NO/NO formation by manipulating electron energy deposition pathways. The NH consumption is maximized with an optimal reduced electric field where N* excitation and O dissociation are most efficient. When the reduced electric field deviates from its optimum, the NH consumption decreases due to the discharge energy deposition to either vibrational excitation or dissociation of N. The NO/NO emissions governed by the NH oxidation follow the above NH consumption trend.
氨（NH）已被公认为碳中性燃料之一。然而，氨燃烧存在反应活性低和 NO/NO 排放量高的问题。为了克服这些问题，本研究报告了等离子体辅助 NH/H 氧化，并通过结合时间分辨激光诊断和等离子体建模揭示了燃料氧化和 NO/NO 形成的动力学。首先，我们发现当 H 混合比为 0.3 时，NH 的消耗会增加，这是由于等离子体辅助 H 解离会促进 H 和 OH 的形成。其次，在高还原电场下，当 H 混合比增加时，由于 HO 的形成以及通过 NO-HO 和 NO-H 途径产生的 NO 动力性增强，促进了 NH 的氧化。同时，由于通过 N(D)-O 途径促进了 NO 的形成，并且由于 NH 生成较少，DeNO 化学性质减弱，因此 NO 分子分数也会随着 H 混合比的增加而增加。相反，在较低的还原电场中，当 H 混合比增加时，N(D) 形成的减少并不能产生足够的 NO 来补充 NH 浓度降低导致的 NO 形成下降。第三，降低的电场通过操纵电子能量沉积途径对燃料消耗和 NO/NO 形成产生非单调影响。在 N* 激发和 O 解离效率最高的最佳还原电场中，NH 消耗量最大。当还原电场偏离最佳值时，由于放电能量沉积到 N 的振动激发或解离，NH 消耗量会减少。
{"title":"Kinetics of low temperature plasma assisted NH3/H2 oxidation in a nanosecond-pulsed discharge","authors":"Ning Liu, Bowen Mei, Xingqian Mao, Ziyu Wang, Zijian Sun, Yijie Xu, Zhiyu Shi, Yiguang Ju","doi":"10.1016/j.proci.2024.105353","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105353","url":null,"abstract":"Ammonia (NH) has been widely recognized as one of the carbon-neutral fuels. However, ammonia combustion suffers low reactivity and high NO/NO emissions. To overcome these issues, this work reports plasma assisted NH/H oxidation and unveils the kinetics of fuel oxidation and NO/NO formation by combining time-resolved laser diagnostics with plasma modeling. Firstly, we found that the NH consumption is promoted with a H blending ratio of 0.3, due to enhancements of H and OH formation by plasma assisted H dissociation. Secondly, at a high reduced electric field, when the H blending ratio increases, the NH oxidation is promoted due to both the HO formation and strong NO kinetic enhancement via NO-HO and NO-H pathways. In the meantime, it is shown that the NO mole fraction also increases with H blending ratio, because the NO formation is enhanced via N(D)-O pathways, and the DeNO chemistry is weakened with less NH production. By contrast, at a lower reduced electric field, when the H blending ratio increases, the decreased N(D) formation does not produce enough NO to replenish the NO formation drop caused by lower NH concentration. Thirdly, the reduced electric field non-monotonically affects fuel consumption and NO/NO formation by manipulating electron energy deposition pathways. The NH consumption is maximized with an optimal reduced electric field where N* excitation and O dissociation are most efficient. When the reduced electric field deviates from its optimum, the NH consumption decreases due to the discharge energy deposition to either vibrational excitation or dissociation of N. The NO/NO emissions governed by the NH oxidation follow the above NH consumption trend.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141527544","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 : 2024-06-27DOI: 10.1016/j.proci.2024.105392
Jingru Zheng, Longhua Hu, Suk Ho Chung
The effect of ammonia addition on the nanostructure of soot particles was studied experimentally for ethylene diffusion flames. To compensate the thermal effect and nitrogen-containing species production when ammonia was added, the total mole fraction of ammonia and nitrogen was fixed in the fuel stream. Soot particle size, fringe length, and fringe tortuosity were measured through transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). A complementary X-ray photoelectron spectroscopy (XPS) analysis provided information about the chemical bonding of soot. A significant delay in soot growth was observed and the particle size increased with the addition of ammonia. While there was no obvious correlation between the fractal dimension of soot and ammonia mole fraction () or sampling location. With the addition of ammonia, the mean fringe length increased reasonably linearly with and the fringe tortuosity increased up to ≈ 0.17 and then decreased with , which suggested that ammonia addition led to higher graphitization and lower oxidative activity. The soot from ammonia diluted flame exhibited lower reactivity, implying the delay of soot surface growth. With the addition of ammonia, the value of sp/sp (indication of the graphitization degree of soot particles) did not change much for from 0 to 0.17 then increased significantly, which indicated the degree of graphitization of soot particles significantly increased with ammonia addition. The intensity of the N1s peak (indication of the N-containing species in soot) increased with the addition of ammonia. This study confirmed that the addition of NH promotes the graphitization of soot.
实验研究了乙烯扩散火焰中添加氨对烟尘颗粒纳米结构的影响。为了补偿加入氨气时产生的热效应和含氮物质，固定了燃料流中氨气和氮气的总摩尔分数。通过透射电子显微镜（TEM）和高分辨率透射电子显微镜（HRTEM）测量了烟尘的粒度、条纹长度和条纹曲折度。辅助的 X 射线光电子能谱（XPS）分析提供了有关烟尘化学键的信息。观察到烟尘的生长明显延迟，并且随着氨的加入，颗粒尺寸增大。烟尘的分形维度与氨的摩尔分数（）或取样位置之间没有明显的相关性。随着氨的加入，平均条纹长度呈合理的线性增长，条纹曲折度增加到≈0.17，然后随氨的加入而下降，这表明氨的加入导致了更高的石墨化和更低的氧化活性。氨水稀释火焰产生的烟尘表现出较低的反应活性，这意味着烟尘表面生长的延迟。随着氨的加入，表示烟尘颗粒石墨化程度的 sp/sp 值从 0 到 0.17 变化不大，然后显著增加，这表明随着氨的加入，烟尘颗粒的石墨化程度显著增加。N1s 峰（表示烟尘中的含 N 物种）的强度随着氨的加入而增加。这项研究证实了 NH 的加入会促进烟尘的石墨化。
{"title":"Effect of ammonia addition on nanostructure of soot in laminar coflow diffusion flames of ethylene diluted with nitrogen","authors":"Jingru Zheng, Longhua Hu, Suk Ho Chung","doi":"10.1016/j.proci.2024.105392","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105392","url":null,"abstract":"The effect of ammonia addition on the nanostructure of soot particles was studied experimentally for ethylene diffusion flames. To compensate the thermal effect and nitrogen-containing species production when ammonia was added, the total mole fraction of ammonia and nitrogen was fixed in the fuel stream. Soot particle size, fringe length, and fringe tortuosity were measured through transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). A complementary X-ray photoelectron spectroscopy (XPS) analysis provided information about the chemical bonding of soot. A significant delay in soot growth was observed and the particle size increased with the addition of ammonia. While there was no obvious correlation between the fractal dimension of soot and ammonia mole fraction () or sampling location. With the addition of ammonia, the mean fringe length increased reasonably linearly with and the fringe tortuosity increased up to ≈ 0.17 and then decreased with , which suggested that ammonia addition led to higher graphitization and lower oxidative activity. The soot from ammonia diluted flame exhibited lower reactivity, implying the delay of soot surface growth. With the addition of ammonia, the value of sp/sp (indication of the graphitization degree of soot particles) did not change much for from 0 to 0.17 then increased significantly, which indicated the degree of graphitization of soot particles significantly increased with ammonia addition. The intensity of the N1s peak (indication of the N-containing species in soot) increased with the addition of ammonia. This study confirmed that the addition of NH promotes the graphitization of soot.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141532309","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 : 2024-06-27DOI: 10.1016/j.proci.2024.105356
Jiale Cao, Xinyi Zhou, Run Chen, Shiyan Li, Sanghoon Kook, Tie Li
Understanding the transient heat transfer mechanism of impinging flames is a crucial pathway for further improving the thermal efficiency of already efficient compression ignition (CI) engines. In this paper, the investigation of the transient heat transfer of wall-impinging flames was performed in a high-pressure constant-volume vessel. Fast-response thermocouples were installed in the impinging wall to record the transient heat flux. Two-color pyrometry was employed to estimate the mean temperature inside the flame region. Firstly, the transient heat transfer characteristics were investigated under varied ambient density, oxygen concentration, temperature, and injection pressure conditions. The optical flame velocity calculation method was applied to this extensive dataset to develop a heat transfer correlation between Nu and Re with which transient heat transfer coefficients were calculated and compared with the experimental results. From this analysis, cumulative fuel injection velocity was developed as the new characteristic parameter to characterize the transient heat transfer of the wall-impinging flames. Results indicate that the effect of fuel injection pressure on the heat flux is more significant than that of ambient gas conditions, with higher injection pressure causing higher heat flux through the impinging wall. No obvious linear tendency of transient Nu and Re was found when using the optical measurement results of the wall-impinging flame as the characteristic parameter. Instead, the cumulative fuel injection velocity shows a strong linear trend of transient Nu and Re during the transient heat transfer processes of the wall-impinging flame. Moreover, the heat transfer coefficients from the new cumulative fuel injection velocity well fit the experimental results.
了解撞击火焰的瞬态传热机制是进一步提高高效压燃（CI）发动机热效率的关键途径。本文在高压恒容容器中对撞壁火焰的瞬态传热进行了研究。在撞击壁上安装了快速反应热电偶，以记录瞬态热通量。采用双色高温计估算火焰区域内的平均温度。首先，研究了不同环境密度、氧气浓度、温度和喷射压力条件下的瞬态传热特性。将光学火焰速度计算方法应用于这一广泛的数据集，以建立 Nu 和 Re 之间的传热相关性，从而计算出瞬态传热系数，并将其与实验结果进行比较。分析结果表明，燃料喷射累积速度是表征贴壁火焰瞬态传热的新特征参数。结果表明，与环境气体条件相比，燃料喷射压力对热通量的影响更为显著，喷射压力越高，通过撞壁的热通量越高。将撞壁火焰的光学测量结果作为特征参数时，未发现瞬态 Nu 和 Re 有明显的线性趋势。相反，在撞壁火焰的瞬态传热过程中，燃料喷射累积速度与瞬态 Nu 和 Re 呈强烈的线性趋势。此外，新的累积燃料喷射速度得出的传热系数与实验结果非常吻合。
{"title":"Characteristics of the transient heat transfer of impinging flames and correlation analysis using a new characteristic velocity under CI engine-like conditions","authors":"Jiale Cao, Xinyi Zhou, Run Chen, Shiyan Li, Sanghoon Kook, Tie Li","doi":"10.1016/j.proci.2024.105356","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105356","url":null,"abstract":"Understanding the transient heat transfer mechanism of impinging flames is a crucial pathway for further improving the thermal efficiency of already efficient compression ignition (CI) engines. In this paper, the investigation of the transient heat transfer of wall-impinging flames was performed in a high-pressure constant-volume vessel. Fast-response thermocouples were installed in the impinging wall to record the transient heat flux. Two-color pyrometry was employed to estimate the mean temperature inside the flame region. Firstly, the transient heat transfer characteristics were investigated under varied ambient density, oxygen concentration, temperature, and injection pressure conditions. The optical flame velocity calculation method was applied to this extensive dataset to develop a heat transfer correlation between Nu and Re with which transient heat transfer coefficients were calculated and compared with the experimental results. From this analysis, cumulative fuel injection velocity was developed as the new characteristic parameter to characterize the transient heat transfer of the wall-impinging flames. Results indicate that the effect of fuel injection pressure on the heat flux is more significant than that of ambient gas conditions, with higher injection pressure causing higher heat flux through the impinging wall. No obvious linear tendency of transient Nu and Re was found when using the optical measurement results of the wall-impinging flame as the characteristic parameter. Instead, the cumulative fuel injection velocity shows a strong linear trend of transient Nu and Re during the transient heat transfer processes of the wall-impinging flame. Moreover, the heat transfer coefficients from the new cumulative fuel injection velocity well fit the experimental results.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141527545","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 : 2024-06-27DOI: 10.1016/j.proci.2024.105228
Fanggang Zhang, Dong Han, John Mantzaras, Chung K. Law, Ran Sui
The catalytic total oxidation of propane over platinum was investigated experimentally and numerically at pressures of 1–7 bar and catalyst temperatures up to 700 K. A wire microcalorimeter was employed to determine the global rate parameters of the catalytic reaction within the kinetically controlled regime. For 1 bar pressure, the dissociative adsorption of CH on Pt and its subsequent decomposition were modeled as two lumped steps based on global reaction parameters. A detailed and thermodynamically consistent catalytic mechanism was constructed by incorporating these lumped steps with an existing atmospheric-pressure H-C elementary reaction model. Two-dimensional CFD simulations using the developed global and detailed reaction mechanisms closely reproduced the measured heat release rates. The intricate dependence of catalytic ignition and reactivity on pressure was further elucidated. Ignition temperatures were found to be linearly correlated to pressures, due to the weaker net adsorption of oxygen compared to that of propane, which progressively aggravated at higher pressures and in turn hindered ignition. More importantly, a non-monotonic pressure dependence of the CH catalytic reactivity on Pt, which gradually diminishes with increasing temperatures, is reported for the first time. The temperature range of this non-monotonic behavior (< 650 K) is of special importance for part-load and idling operations of gas turbines using hybrid hetero-/homogeneous combustion approaches and for normal operations of recuperative microreactors. Thus, this work provides key information for the design and optimization of such devices utilizing Pt as catalyst.
在压力为 1-7 巴、催化剂温度高达 700 K 的条件下，对铂上丙烷的催化全氧化反应进行了实验和数值研究。在 1 bar 压力下，根据全局反应参数，将 CH 在铂上的离解吸附及其随后的分解模拟为两个一次性步骤。通过将这些一次性步骤与现有的常压 H-C 基本反应模型相结合，构建了一个详细的、热力学上一致的催化机制。使用所开发的全局和详细反应机制进行的二维 CFD 模拟密切再现了所测量的热释放率。催化点火和反应性对压力的复杂依赖关系得到了进一步阐明。研究发现，点火温度与压力呈线性相关，这是由于氧气的净吸附力弱于丙烷，在压力较高时，净吸附力逐渐增强，进而阻碍了点火。更重要的是，首次报道了铂对 CH 催化反应活性的非单调压力依赖性，即随着温度的升高而逐渐减弱。这种非单调行为的温度范围（小于 650 K）对于采用异质/均质混合燃烧方法的燃气轮机的部分负荷和空转运行以及再生式微反应器的正常运行具有特别重要的意义。因此，这项工作为利用铂作为催化剂的此类装置的设计和优化提供了关键信息。
{"title":"Surface kinetics and pressure dependence of propane oxidation over platinum","authors":"Fanggang Zhang, Dong Han, John Mantzaras, Chung K. Law, Ran Sui","doi":"10.1016/j.proci.2024.105228","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105228","url":null,"abstract":"The catalytic total oxidation of propane over platinum was investigated experimentally and numerically at pressures of 1–7 bar and catalyst temperatures up to 700 K. A wire microcalorimeter was employed to determine the global rate parameters of the catalytic reaction within the kinetically controlled regime. For 1 bar pressure, the dissociative adsorption of CH on Pt and its subsequent decomposition were modeled as two lumped steps based on global reaction parameters. A detailed and thermodynamically consistent catalytic mechanism was constructed by incorporating these lumped steps with an existing atmospheric-pressure H-C elementary reaction model. Two-dimensional CFD simulations using the developed global and detailed reaction mechanisms closely reproduced the measured heat release rates. The intricate dependence of catalytic ignition and reactivity on pressure was further elucidated. Ignition temperatures were found to be linearly correlated to pressures, due to the weaker net adsorption of oxygen compared to that of propane, which progressively aggravated at higher pressures and in turn hindered ignition. More importantly, a non-monotonic pressure dependence of the CH catalytic reactivity on Pt, which gradually diminishes with increasing temperatures, is reported for the first time. The temperature range of this non-monotonic behavior (< 650 K) is of special importance for part-load and idling operations of gas turbines using hybrid hetero-/homogeneous combustion approaches and for normal operations of recuperative microreactors. Thus, this work provides key information for the design and optimization of such devices utilizing Pt as catalyst.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141527513","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 : 2024-06-27DOI: 10.1016/j.proci.2024.105363
Jiaye Li, Zhenshan Li
Chemical looping combustion (CLC) of solid fuel is a promising technology with inherent CO separation and low energy penalty for CO capture. Syngas is main intermediate species of solid fuel conversion in CLC, the reduction kinetics of oxygen carriers with syngas play a crucial role in CLC systems. However, the current research obtains the reaction rate constants by fitting the apparent models with the experimental data, and cannot explain the reduction kinetics behavior from a microscopic level. It remains a challenge to compute the reduction kinetics of oxygen carriers with syngas directly from first-principles density functional theory (DFT) without fitting experimental data. This study proposes a first-principle-based rate equation (1pRE) theory and integrates it into the random pore model (RPM) to predict the kinetics of FeO reduction by syngas in CLC. The developed 1pRE theory utilizes DFT calculations to search for reaction pathways and energy barriers of elementary reactions. Then the DFT data are introduced into the statistical mechanics partition function and transition state theory (TST) to calculate the reaction rate constants. Microkinetic rate equations of elementary reactions occurring at the surface scale are developed to describe the change of surface coverage of different surface species. The 1pRE theory is integrated into the RPM to account for the influence of particle-scale structural changes on the overall conversion rate during the reduction process. The theory can predict the reduction kinetics of oxygen carriers without fitting experimental data and establishes a connection between microscopic insights and macroscopic phenomena. The accuracy was validated by experimental data of FeO oxygen carriers obtained from the thermogravimetric analyzer (TGA) in the atmosphere of syngas. The developed 1pRE predicts the reduction kinetics of oxygen carriers accurately and can be used to optimize the design of oxygen carrier materials and the scale up of CLC reactors.
{"title":"First principle based rate equation (1pRE) for reduction kinetics of Fe2O3 with syngas in chemical looping","authors":"Jiaye Li, Zhenshan Li","doi":"10.1016/j.proci.2024.105363","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105363","url":null,"abstract":"Chemical looping combustion (CLC) of solid fuel is a promising technology with inherent CO separation and low energy penalty for CO capture. Syngas is main intermediate species of solid fuel conversion in CLC, the reduction kinetics of oxygen carriers with syngas play a crucial role in CLC systems. However, the current research obtains the reaction rate constants by fitting the apparent models with the experimental data, and cannot explain the reduction kinetics behavior from a microscopic level. It remains a challenge to compute the reduction kinetics of oxygen carriers with syngas directly from first-principles density functional theory (DFT) without fitting experimental data. This study proposes a first-principle-based rate equation (1pRE) theory and integrates it into the random pore model (RPM) to predict the kinetics of FeO reduction by syngas in CLC. The developed 1pRE theory utilizes DFT calculations to search for reaction pathways and energy barriers of elementary reactions. Then the DFT data are introduced into the statistical mechanics partition function and transition state theory (TST) to calculate the reaction rate constants. Microkinetic rate equations of elementary reactions occurring at the surface scale are developed to describe the change of surface coverage of different surface species. The 1pRE theory is integrated into the RPM to account for the influence of particle-scale structural changes on the overall conversion rate during the reduction process. The theory can predict the reduction kinetics of oxygen carriers without fitting experimental data and establishes a connection between microscopic insights and macroscopic phenomena. The accuracy was validated by experimental data of FeO oxygen carriers obtained from the thermogravimetric analyzer (TGA) in the atmosphere of syngas. The developed 1pRE predicts the reduction kinetics of oxygen carriers accurately and can be used to optimize the design of oxygen carrier materials and the scale up of CLC reactors.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141532310","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 : 2024-06-27DOI: 10.1016/j.proci.2024.105218
Jeongwon Kim, Eric Mayhew, Vincent Coburn, Jacob Temme, Chol-Bum Kweon
This study experimentally investigates the effects of pilot injection on first stage and overall ignition behavior for different fuel blends. A conventional petroleum-derived fuel (F-24) with a Derived Cetane Number (DCN) of 48.5 and gasoline (GAS), which has a low DCN of 21.4 but high volatility, were blended at different volumetric ratios. These blends were injected into a high temperature, pressure vessel using either a single or pilot-main injection strategy. Four optical diagnostics (formaldehyde PLIF, OH* chemiluminescence, schlieren, and Mie scattering) were employed to visualize the ignition process and to evaluate liquid length, penetration distance, heat release rate, the first stage, and overall ignition delays. It is shown that the higher GAS blend ratios result in longer ignition delay and less overall heat release attributed to the poor reactivity of GAS. In such cases, the contributions of the extended first stage ignition delay to the extended overall ignition delay decrease with GAS blend ratio. Furthermore, some of the high GAS blend fuels exhibit no overall ignition at all due to the excessive fuel-air mixing. The study then shows that this decrease in ignition performance with GAS can be mitigated by introducing pilot injection, which shortens the ignition delays and provides more overall heat release. Specifically, at low GAS blend ratios, the ignition exhibits mixing controlled combustion where the ignition of pilot fuel-air mixture induces the main fuel ignition. For pilot-main injections, the decrease in first stage ignition delay accounts for the average of 87 % of the reduced overall ignition delay, suggesting that the reduced ignition delay with pilot injection is primarily due to the reduced time for fuel atomization, vaporization, and decomposition of the main fuel. These results will contribute to the development of ignition models capable of capturing the impact of fuel composition and pilot injection on ignition performance.
本研究通过实验研究了不同混合燃料的先导喷射对第一阶段和整体点火行为的影响。一种衍生十六烷值（DCN）为 48.5 的传统石油衍生燃料（F-24）和一种衍生十六烷值（DCN）为 21.4 但挥发性较高的汽油（GAS）以不同的体积比混合。这些混合物被注入高温高压容器中，采用单次或先导-主注入策略。采用了四种光学诊断方法（甲醛 PLIF、OH* 化学发光、schlieren 和 Mie 散射）来观察点火过程，并评估液体长度、穿透距离、热释放率、第一阶段和整体点火延迟。结果表明，由于 GAS 反应性差，GAS 混合比率越高，点火延迟时间越长，总体热量释放越少。在这种情况下，延长的第一阶段点火延迟对延长的整体点火延迟的贡献随瓦斯混合比的增加而减少。此外，由于燃料与空气的过度混合，一些高 GAS 混合燃料根本没有整体点火。随后的研究表明，引入先导喷射可以缩短点火延迟，并提供更多的整体热量释放，从而缓解 GAS 点火性能下降的问题。具体来说，在较低的天然气混合比例下，点火表现为混合控制燃烧，即先导燃料-空气混合物的点火诱导主燃料的点火。对于先导-主喷射，第一阶段点火延迟的减少平均占整体点火延迟减少量的 87%，这表明先导喷射点火延迟的减少主要是由于燃料雾化、汽化和主燃料分解时间的减少。这些结果将有助于开发能够捕捉燃料成分和先导喷射对点火性能影响的点火模型。
{"title":"Effects of pilot injection on ignition performance for F-24/Gasoline fuel blends","authors":"Jeongwon Kim, Eric Mayhew, Vincent Coburn, Jacob Temme, Chol-Bum Kweon","doi":"10.1016/j.proci.2024.105218","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105218","url":null,"abstract":"This study experimentally investigates the effects of pilot injection on first stage and overall ignition behavior for different fuel blends. A conventional petroleum-derived fuel (F-24) with a Derived Cetane Number (DCN) of 48.5 and gasoline (GAS), which has a low DCN of 21.4 but high volatility, were blended at different volumetric ratios. These blends were injected into a high temperature, pressure vessel using either a single or pilot-main injection strategy. Four optical diagnostics (formaldehyde PLIF, OH* chemiluminescence, schlieren, and Mie scattering) were employed to visualize the ignition process and to evaluate liquid length, penetration distance, heat release rate, the first stage, and overall ignition delays. It is shown that the higher GAS blend ratios result in longer ignition delay and less overall heat release attributed to the poor reactivity of GAS. In such cases, the contributions of the extended first stage ignition delay to the extended overall ignition delay decrease with GAS blend ratio. Furthermore, some of the high GAS blend fuels exhibit no overall ignition at all due to the excessive fuel-air mixing. The study then shows that this decrease in ignition performance with GAS can be mitigated by introducing pilot injection, which shortens the ignition delays and provides more overall heat release. Specifically, at low GAS blend ratios, the ignition exhibits mixing controlled combustion where the ignition of pilot fuel-air mixture induces the main fuel ignition. For pilot-main injections, the decrease in first stage ignition delay accounts for the average of 87 % of the reduced overall ignition delay, suggesting that the reduced ignition delay with pilot injection is primarily due to the reduced time for fuel atomization, vaporization, and decomposition of the main fuel. These results will contribute to the development of ignition models capable of capturing the impact of fuel composition and pilot injection on ignition performance.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141527583","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 : 2024-06-27DOI: 10.1016/j.proci.2024.105229
Long Qin, Qiang Cheng, John Mantzaras, Chung K. Law, Ran Sui
The catalytic (heterogeneous) and coupled catalytic-gaseous (hetero-/homogeneous) combustion of fuel-lean hydrogen/air mixtures (equivalence ratio = 0.4) in palladium- and rhodium-coated catalytic microchannels was numerically investigated in planar microchannels having a canonical geometry of 10 mm length and 1 mm height. Steady, extinction-induced combustion stability limits were demarcated as a function of inlet velocity and external heat loss at pressures of 1 and 5 bar, with wall thermal conductivities of 1 and 16 W/mK. In each case, interplays between the catalytic and gas-phase chemical reaction pathways, and their impact on the stability limits were identified. The stability results were further compared with literature data for platinum. The simulations indicated that Pd was more resilient against extinction than Rh and had a stronger surface reactivity when competing with gas-phase chemistry in the channel. Similar to Pt, the strong H surface reactivity on Pd resulted in wide stability limits purely determined by surface reactions and independent of gas-phase chemistry. In stark contrast, the presence of gas-phase combustion significantly expanded the stability limits of the Rh channel. The stability limits of Rh at 5 bar were consistently broader than those at 1 bar under all investigated conditions, which was also a behavior different to that of Pd and Pt channels, whose stability limit curves had crossover points between the two pressures. Additional simulations were performed in a Surface Perfectly Stirred Reactor (SPSR), providing comprehensive chemistry information, including sensitivity analyses of key reactions and surface coverages. When approaching extinction, OH(s) was a major surface species on Pd, while the Rh surface was primarily blocked by O(s).
{"title":"Surface-gas chemistry coupling and stability limits of hydrogen/air combustion in catalytic microchannels","authors":"Long Qin, Qiang Cheng, John Mantzaras, Chung K. Law, Ran Sui","doi":"10.1016/j.proci.2024.105229","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105229","url":null,"abstract":"The catalytic (heterogeneous) and coupled catalytic-gaseous (hetero-/homogeneous) combustion of fuel-lean hydrogen/air mixtures (equivalence ratio = 0.4) in palladium- and rhodium-coated catalytic microchannels was numerically investigated in planar microchannels having a canonical geometry of 10 mm length and 1 mm height. Steady, extinction-induced combustion stability limits were demarcated as a function of inlet velocity and external heat loss at pressures of 1 and 5 bar, with wall thermal conductivities of 1 and 16 W/mK. In each case, interplays between the catalytic and gas-phase chemical reaction pathways, and their impact on the stability limits were identified. The stability results were further compared with literature data for platinum. The simulations indicated that Pd was more resilient against extinction than Rh and had a stronger surface reactivity when competing with gas-phase chemistry in the channel. Similar to Pt, the strong H surface reactivity on Pd resulted in wide stability limits purely determined by surface reactions and independent of gas-phase chemistry. In stark contrast, the presence of gas-phase combustion significantly expanded the stability limits of the Rh channel. The stability limits of Rh at 5 bar were consistently broader than those at 1 bar under all investigated conditions, which was also a behavior different to that of Pd and Pt channels, whose stability limit curves had crossover points between the two pressures. Additional simulations were performed in a Surface Perfectly Stirred Reactor (SPSR), providing comprehensive chemistry information, including sensitivity analyses of key reactions and surface coverages. When approaching extinction, OH(s) was a major surface species on Pd, while the Rh surface was primarily blocked by O(s).","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141527566","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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