Pub Date : 2024-06-29DOI: 10.1016/j.proci.2024.105249
Abdallah Alhaffar, Véranika Latour, Clément Patat, Daniel Durox, Antoine Renaud, Jean-Bernard Blaisot, Sébastien Candel, Françoise Baillot
One important aspect in the analysis of combustion instabilities in multiple-injector annular systems is that of representing such oscillations with a linear array of injectors. This issue is considered in the present work by comparing flame dynamics in a self-sustained oscillations situation in the annular configuration MICCA-Spray, with experiments carried out in TACC-Spray, a rectangular combustor equipped with five injectors externally modulated by driver units. In the annular system, the coupling mode is azimuthal, and in the linear array, the flames are submitted to a transverse acoustic field. An original method is used to change the limit-cycle pressure oscillations amplitude in the annular system and favor a standing mode with a well-defined nodal line position. It consists in using different arrangements of two types of injectors, leading to various azimuthal staging patterns. The range of pressure oscillation amplitudes is swept in TACC-Spray by changing the external acoustic forcing level. It is thus possible to compare the flame dynamics in forced and self-sustained situations using these two experimental facilities. This is done by examining flame describing functions (FDFs) based on downstream pressure fluctuations measured in the two configurations for different pressure oscillation amplitudes. The trends observed in the two systems are in good agreement, and there is a reasonably good match between the values of the gains and phases determined in the two configurations. The pressure-based FDFs are determined for flames located at different positions with respect to the acoustic mode. It is found that the transverse or azimuthal velocity component has only a weak influence on the pressure-based FDF, the strongest impact being observed in the neighborhood of the velocity antinode. This study demonstrates the ability of a linear-array setup modulated by a transverse mode to reproduce conditions of azimuthal coupling leading to self-sustained limit cycles in an annular combustor.
{"title":"Comparison of pressure-based flame describing functions measured in an annular combustor under self-sustained oscillations and in an externally modulated linear combustor","authors":"Abdallah Alhaffar, Véranika Latour, Clément Patat, Daniel Durox, Antoine Renaud, Jean-Bernard Blaisot, Sébastien Candel, Françoise Baillot","doi":"10.1016/j.proci.2024.105249","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105249","url":null,"abstract":"One important aspect in the analysis of combustion instabilities in multiple-injector annular systems is that of representing such oscillations with a linear array of injectors. This issue is considered in the present work by comparing flame dynamics in a self-sustained oscillations situation in the annular configuration MICCA-Spray, with experiments carried out in TACC-Spray, a rectangular combustor equipped with five injectors externally modulated by driver units. In the annular system, the coupling mode is azimuthal, and in the linear array, the flames are submitted to a transverse acoustic field. An original method is used to change the limit-cycle pressure oscillations amplitude in the annular system and favor a standing mode with a well-defined nodal line position. It consists in using different arrangements of two types of injectors, leading to various azimuthal staging patterns. The range of pressure oscillation amplitudes is swept in TACC-Spray by changing the external acoustic forcing level. It is thus possible to compare the flame dynamics in forced and self-sustained situations using these two experimental facilities. This is done by examining flame describing functions (FDFs) based on downstream pressure fluctuations measured in the two configurations for different pressure oscillation amplitudes. The trends observed in the two systems are in good agreement, and there is a reasonably good match between the values of the gains and phases determined in the two configurations. The pressure-based FDFs are determined for flames located at different positions with respect to the acoustic mode. It is found that the transverse or azimuthal velocity component has only a weak influence on the pressure-based FDF, the strongest impact being observed in the neighborhood of the velocity antinode. This study demonstrates the ability of a linear-array setup modulated by a transverse mode to reproduce conditions of azimuthal coupling leading to self-sustained limit cycles in an annular combustor.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141532307","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 : 2024-06-29DOI: 10.1016/j.proci.2024.105281
Jiun Cai Ong, Kar Mun Pang, Rajavasanth Rajasegar, Ales Srna, Xue-Song Bai, Jens H. Walther
Large eddy simulations of pilot fuel ignited, lean premixed, natural gas engines are performed to study the pilot-ignition process and its subsequent interaction with the premixed charge. The injection pressure () and injection duration () are varied (i.e. 800 bar/, 800 bar/, and 400bar/) to study the impact of the injection process on the subsequent combustion evolution. Open-cycle simulations considering the full engine geometry are used to predict the in-cylinder flows, while combustion is modeled using a finite-rate chemistry model. In-cylinder methane (CH) is shown to delay the low-temperature ignition of the pilot fuel, regardless of the pilot injection setting, which subsequently prolongs the overall pilot fuel ignition delay. Moreover, all simulated cases show the occurrence of back-supported combustion (BSC), where the burning of CH-air mixture is “back-supported” by pilot fuel radicals. Despite both the 800 bar/ and 400 bar/ cases having the same injected pilot fuel mass, the peak in-cylinder pressure and burning rate of the premixed CH-air mixture in the former case are higher. Higher and shorter lead to better mixing between the pilot fuel and the premixed CH-air charge. Subsequently, this forms a larger volume of regions with elevated equivalence ratio due to the presence of pilot fuel () which, consequently promotes the formation of BSC. The impact of in-cylinder flow fields on the dual-fuel combustion process is investigated by performing two closed-cycle 800 bar/ cases with one assuming solid-body rotation and another without solid-body rotation (i.e. zero velocity field). In-cylinder flow field is shown to have a visible impact on the transition stage between the pilot ignition stage and the premixed flame propagation stage, but have an insignificant effect on the pilot fuel ignition process. In the transition stage, slower flame propagation is observed in the zero-velocity case. The results show that this is not only due to the turbulence effect on premixed flame but also due to differences in the volume and distribution of pilot fuels that impacts BSC.
{"title":"LES of pilot n-heptane ignition and its interaction with the lean premixed methane–air mixture in a dual-fuel combustion engine","authors":"Jiun Cai Ong, Kar Mun Pang, Rajavasanth Rajasegar, Ales Srna, Xue-Song Bai, Jens H. Walther","doi":"10.1016/j.proci.2024.105281","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105281","url":null,"abstract":"Large eddy simulations of pilot fuel ignited, lean premixed, natural gas engines are performed to study the pilot-ignition process and its subsequent interaction with the premixed charge. The injection pressure () and injection duration () are varied (i.e. 800 bar/, 800 bar/, and 400bar/) to study the impact of the injection process on the subsequent combustion evolution. Open-cycle simulations considering the full engine geometry are used to predict the in-cylinder flows, while combustion is modeled using a finite-rate chemistry model. In-cylinder methane (CH) is shown to delay the low-temperature ignition of the pilot fuel, regardless of the pilot injection setting, which subsequently prolongs the overall pilot fuel ignition delay. Moreover, all simulated cases show the occurrence of back-supported combustion (BSC), where the burning of CH-air mixture is “back-supported” by pilot fuel radicals. Despite both the 800 bar/ and 400 bar/ cases having the same injected pilot fuel mass, the peak in-cylinder pressure and burning rate of the premixed CH-air mixture in the former case are higher. Higher and shorter lead to better mixing between the pilot fuel and the premixed CH-air charge. Subsequently, this forms a larger volume of regions with elevated equivalence ratio due to the presence of pilot fuel () which, consequently promotes the formation of BSC. The impact of in-cylinder flow fields on the dual-fuel combustion process is investigated by performing two closed-cycle 800 bar/ cases with one assuming solid-body rotation and another without solid-body rotation (i.e. zero velocity field). In-cylinder flow field is shown to have a visible impact on the transition stage between the pilot ignition stage and the premixed flame propagation stage, but have an insignificant effect on the pilot fuel ignition process. In the transition stage, slower flame propagation is observed in the zero-velocity case. The results show that this is not only due to the turbulence effect on premixed flame but also due to differences in the volume and distribution of pilot fuels that impacts BSC.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141527542","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 : 2024-06-29DOI: 10.1016/j.proci.2024.105231
Daniel Vigarinho de Campos, Thibault F. Guiberti, Et-touhami Es-sebbar, Deanna A. Lacoste
Ammonia is an easy solution for the transportation and storage of hydrogen. To achieve combustion properties similar to those of methane, ammonia can be partially cracked on site to introduce hydrogen and nitrogen in the fuel mixture. In this work, an atmospheric pressure dual-swirl ammonia-hydrogen burner is used to study different configurations of stratified flames of ammonia cracked at 28 %. First, flame stabilization is evaluated in terms of the overall equivalence ratio and the distribution of air between the hydrogen and ammonia streams. This is done for both cases where either hydrogen or ammonia occupies the central part of the burner or its periphery. The configuration of the burner is adjusted in such a way that several stratification levels are scrutinized, depending on where the two streams meet. Seven types of flames are identified and described. A stability map is measured. The results show that the configuration with ammonia flowing centrally and hydrogen occupying the periphery enhances stability. Second, measurements of NOx, NO, unburnt ammonia, and unburnt hydrogen in the exhaust gases are performed. Full stratification reduces NOx emissions, but both lean overall equivalence ratio and lean ammonia equivalence ratio increase NO emissions. The flame with ammonia in the center and hydrogen at the periphery with an overall equivalence ratio of 0.55 gives the best results in terms of stability and low pollutant emissions. This condition is further investigated by changing the reactants temperature. The reactants preheating is beneficial for NO emissions but comes with a strong NOx penalty.
{"title":"Effects of reactants stratification and pre-heating on the stabilization and emissions of partially cracked ammonia swirl flames","authors":"Daniel Vigarinho de Campos, Thibault F. Guiberti, Et-touhami Es-sebbar, Deanna A. Lacoste","doi":"10.1016/j.proci.2024.105231","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105231","url":null,"abstract":"Ammonia is an easy solution for the transportation and storage of hydrogen. To achieve combustion properties similar to those of methane, ammonia can be partially cracked on site to introduce hydrogen and nitrogen in the fuel mixture. In this work, an atmospheric pressure dual-swirl ammonia-hydrogen burner is used to study different configurations of stratified flames of ammonia cracked at 28 %. First, flame stabilization is evaluated in terms of the overall equivalence ratio and the distribution of air between the hydrogen and ammonia streams. This is done for both cases where either hydrogen or ammonia occupies the central part of the burner or its periphery. The configuration of the burner is adjusted in such a way that several stratification levels are scrutinized, depending on where the two streams meet. Seven types of flames are identified and described. A stability map is measured. The results show that the configuration with ammonia flowing centrally and hydrogen occupying the periphery enhances stability. Second, measurements of NOx, NO, unburnt ammonia, and unburnt hydrogen in the exhaust gases are performed. Full stratification reduces NOx emissions, but both lean overall equivalence ratio and lean ammonia equivalence ratio increase NO emissions. The flame with ammonia in the center and hydrogen at the periphery with an overall equivalence ratio of 0.55 gives the best results in terms of stability and low pollutant emissions. This condition is further investigated by changing the reactants temperature. The reactants preheating is beneficial for NO emissions but comes with a strong NOx penalty.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141527543","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 : 2024-06-29DOI: 10.1016/j.proci.2024.105344
Geveen Arumapperuma, Yihao Tang, Antonio Attili, Wang Han
The dynamics of soot evolution in a swirl-stabilized model aero-engine combustor are studied using Large-Eddy Simulation (LES) and state-of-the-art combustion and soot models. The simulated combustor is a dual-swirl combustor with and without secondary oxidation air at a pressure of 3 bar. The comparison with experimental data shows that the simulation accurately captures the gas-phase statistics. Overall, soot statistics are well captured, particularly in the shear layers, although underpredicted in other locations. Three locations in the combustor: Shear Layer (SL), Inner Recirculation Zone (IRZ), and Outer Recirculation Zone (ORZ) are probed to obtain velocity, temperature, and soot volume fraction signals. Lomb–Scargle spectral analysis on the probed signals reveals that soot evolution in the SL is characterized by high-frequency dynamics, whereas in the IRZ and ORZ, it is characterized by low-frequency dynamics. Within the SL, couplings between the soot and flow dynamics are observed, with the soot volume fraction and velocity sharing a common dominant frequency. However, in the IRZ and ORZ, such couplings are not evident. Additionally, the wavelet transform is applied to the probed signals to study the temporal distribution of the frequencies. The analysis indicates that, in the SL, the dominant frequency of the velocity occurs continuously throughout the entire time series, while higher frequencies occur in short bursts. Conversely, for the soot volume fraction, both the dominant frequency and higher frequencies appear in short bursts. In the ORZ and IRZ, the soot volume fraction scalogram shows that low frequencies dominate and occur continuously throughout the time series. Finally, the phase space reconstructions show that the trajectory of the soot dynamics shows a circular pattern, indicative of periodic behavior. The center of attraction remains stationary over a relatively large time scale, suggesting stability in the dynamics as they evolve.
{"title":"Spectral analysis of soot dynamics in an aero-engine model combustor","authors":"Geveen Arumapperuma, Yihao Tang, Antonio Attili, Wang Han","doi":"10.1016/j.proci.2024.105344","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105344","url":null,"abstract":"The dynamics of soot evolution in a swirl-stabilized model aero-engine combustor are studied using Large-Eddy Simulation (LES) and state-of-the-art combustion and soot models. The simulated combustor is a dual-swirl combustor with and without secondary oxidation air at a pressure of 3 bar. The comparison with experimental data shows that the simulation accurately captures the gas-phase statistics. Overall, soot statistics are well captured, particularly in the shear layers, although underpredicted in other locations. Three locations in the combustor: Shear Layer (SL), Inner Recirculation Zone (IRZ), and Outer Recirculation Zone (ORZ) are probed to obtain velocity, temperature, and soot volume fraction signals. Lomb–Scargle spectral analysis on the probed signals reveals that soot evolution in the SL is characterized by high-frequency dynamics, whereas in the IRZ and ORZ, it is characterized by low-frequency dynamics. Within the SL, couplings between the soot and flow dynamics are observed, with the soot volume fraction and velocity sharing a common dominant frequency. However, in the IRZ and ORZ, such couplings are not evident. Additionally, the wavelet transform is applied to the probed signals to study the temporal distribution of the frequencies. The analysis indicates that, in the SL, the dominant frequency of the velocity occurs continuously throughout the entire time series, while higher frequencies occur in short bursts. Conversely, for the soot volume fraction, both the dominant frequency and higher frequencies appear in short bursts. In the ORZ and IRZ, the soot volume fraction scalogram shows that low frequencies dominate and occur continuously throughout the time series. Finally, the phase space reconstructions show that the trajectory of the soot dynamics shows a circular pattern, indicative of periodic behavior. The center of attraction remains stationary over a relatively large time scale, suggesting stability in the dynamics as they evolve.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141527540","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 : 2024-06-29DOI: 10.1016/j.proci.2024.105216
Balázs Vincze, Clément Mocquard, Jérôme Dombard, Laurent Gicquel, Thierry Poinsot
Two-phase reactive turbulent Large-Eddy Simulations (LES) of the single flameholder postcombustion test rig of Georgia Tech (Cross et al., 2011) are presented and compared to experimental measurements with and without combustion. Postcombustion differs from usual turbulent flames in many ways: the inlet oxidizer stream is hot ( K), the flow speeds and Reynolds numbers are high (U , Re ), the fuel injection systems are specific and only found in reheat chambers. As a result, LES models that were developed and calibrated for conventional turbulent flames, such as those found in primary chambers of gas turbines are not adapted to reheat combustion. This study presents a collection of models specifically developed for reheat flows. The chemical scheme and the turbulent combustion model are changed to take high temperature and vitiated flow conditions into account. The Lagrangian injection methodology for the liquid jets in crossflow is modified to account for the unusually strong crossflow conditions. A modified version of the Droplet Deformation and Breakup (DDB) drag model (Ibrahim et al., 1993) is implemented to improve the drag force prediction through drop deformation. As a result, the LES shows good agreement with the experimental results both for liquid and gaseous phases, with and without combustion. Based on such results, more details about the combustion regimes and dynamics are extracted. Right downstream of the injection zone, at the bluff body trailing edge, rich premixed flames are observed along with pockets of diffusion flames in the bluff body recirculation zone, due to the highly three dimensional nature of the flow. Further downstream however, combustion takes place mainly in two diffusion flame sheets in the shear layers between the evaporated fuel, and the two vitiated air streams.
本文介绍了佐治亚理工学院（Cross 等人，2011 年）单焰座后燃烧试验台的两相反应湍流大型埃迪模拟（LES），并与有燃烧和无燃烧的实验测量结果进行了比较。燃烧后火焰在许多方面不同于通常的湍流火焰：入口氧化剂流很热 ( K)，流速和雷诺数很高 (U , Re )，燃料喷射系统很特殊，而且只存在于再热室中。因此，针对传统湍流火焰（如燃气轮机初级燃烧室中的火焰）开发和校准的 LES 模型并不适合再热燃烧。本研究介绍了一系列专门为再热气流开发的模型。对化学方案和湍流燃烧模型进行了修改，以将高温和虚流条件考虑在内。修改了横流中液体喷射的拉格朗日喷射方法，以考虑异常强烈的横流条件。对液滴变形和破裂（DDB）阻力模型（Ibrahim 等，1993 年）进行了修改，以通过液滴变形改进阻力预测。因此，无论是液相还是气相，无论是有燃烧还是无燃烧，LES 与实验结果都显示出良好的一致性。在这些结果的基础上，提取了更多有关燃烧状态和动力学的细节。在喷射区的右下方，也就是崖体后缘，可以观察到丰富的预混合火焰，以及崖体再循环区的扩散火焰，这是由于气流的高度三维特性造成的。但在更下游的地方，燃烧主要发生在蒸发燃料和两股减弱气流之间的剪切层中的两片扩散火焰中。
{"title":"Models for Large-Eddy Simulation of reheat combustion","authors":"Balázs Vincze, Clément Mocquard, Jérôme Dombard, Laurent Gicquel, Thierry Poinsot","doi":"10.1016/j.proci.2024.105216","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105216","url":null,"abstract":"Two-phase reactive turbulent Large-Eddy Simulations (LES) of the single flameholder postcombustion test rig of Georgia Tech (Cross et al., 2011) are presented and compared to experimental measurements with and without combustion. Postcombustion differs from usual turbulent flames in many ways: the inlet oxidizer stream is hot ( K), the flow speeds and Reynolds numbers are high (U , Re ), the fuel injection systems are specific and only found in reheat chambers. As a result, LES models that were developed and calibrated for conventional turbulent flames, such as those found in primary chambers of gas turbines are not adapted to reheat combustion. This study presents a collection of models specifically developed for reheat flows. The chemical scheme and the turbulent combustion model are changed to take high temperature and vitiated flow conditions into account. The Lagrangian injection methodology for the liquid jets in crossflow is modified to account for the unusually strong crossflow conditions. A modified version of the Droplet Deformation and Breakup (DDB) drag model (Ibrahim et al., 1993) is implemented to improve the drag force prediction through drop deformation. As a result, the LES shows good agreement with the experimental results both for liquid and gaseous phases, with and without combustion. Based on such results, more details about the combustion regimes and dynamics are extracted. Right downstream of the injection zone, at the bluff body trailing edge, rich premixed flames are observed along with pockets of diffusion flames in the bluff body recirculation zone, due to the highly three dimensional nature of the flow. Further downstream however, combustion takes place mainly in two diffusion flame sheets in the shear layers between the evaporated fuel, and the two vitiated air streams.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141527508","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.2024.105241
M. Srinivasarao, Giancarlo Sorrentino, Mara de Joannon, V. Mahendra Reddy
Ammonia combustion has gained significant attention due to its high hydrogen content and zero carbon emissions. It poses a challenge for stabilization due to their low energy content and limited flammability range, with the added concern of fuel NOx emissions. In the current study, a novel burner design equipped with four series of reactors is proposed to achieve stable pure ammonia-air flames with reduced NOx emissions. The impact of thermal intensity (∼0.7 MW/m to ∼4 MW/m), number of stages, equivalence ratio (0.5–1.2), and fuel staging on flame stabilization and emissions were investigated in the proposed burner. Comprehensive emissions analysis is performed at various burner levels. Numerical simulations incorporating Large Eddy Simulation (LES) modeling are employed to enhance understanding of the impact of thermal intensity and equivalence ratios on ammonia dissociation, mixedness, and NO emissions. The results indicated that the present burner design improved reactant mixing, and flame stability, reduced NH emissions (∼ 0 PPM), and lowered NOx levels in non-premixed ammonia-air flames. The computational and experimental results demonstrated that the implementation of fuel staging is crucial for reducing NOx emissions for the flames with lean global equivalence ratios. Lower NO emissions were identified at a global equivalence ratio of 1.1 for all the considered flames in the range of 0.5–1.2. In the four-stage rich-lean combustion strategy employed in this study; it was observed that higher thermal intensity (4 MW/m) with fuel staging resulted in lower NOx emissions per kW of energy input compared to lower thermal intensities 0.7 MW/m. This finding underscores the significance of achieving uniform mixtures and ensuring local flame in rich conditions for achieving low NOx emissions in ammonia combustion. Exhaust gas analysis is conducted at three stages of the burner to enhance the understanding of emissions at various levels of the burner. The proposed combustor design has achieved a substantial reduction in NOx to ∼1 PPM/kW and ∼2.8 PPM/kW with and without fuel staging, respectively. This impressive outcome is attributed to the controlled ammonia consumption facilitated by uniform mixing generated through the use of tangential air inlets.
{"title":"Pure ammonia flames with high thermal intensities through fuel and air staging under extreme rich-to-lean conditions","authors":"M. Srinivasarao, Giancarlo Sorrentino, Mara de Joannon, V. Mahendra Reddy","doi":"10.1016/j.proci.2024.105241","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105241","url":null,"abstract":"Ammonia combustion has gained significant attention due to its high hydrogen content and zero carbon emissions. It poses a challenge for stabilization due to their low energy content and limited flammability range, with the added concern of fuel NOx emissions. In the current study, a novel burner design equipped with four series of reactors is proposed to achieve stable pure ammonia-air flames with reduced NOx emissions. The impact of thermal intensity (∼0.7 MW/m to ∼4 MW/m), number of stages, equivalence ratio (0.5–1.2), and fuel staging on flame stabilization and emissions were investigated in the proposed burner. Comprehensive emissions analysis is performed at various burner levels. Numerical simulations incorporating Large Eddy Simulation (LES) modeling are employed to enhance understanding of the impact of thermal intensity and equivalence ratios on ammonia dissociation, mixedness, and NO emissions. The results indicated that the present burner design improved reactant mixing, and flame stability, reduced NH emissions (∼ 0 PPM), and lowered NOx levels in non-premixed ammonia-air flames. The computational and experimental results demonstrated that the implementation of fuel staging is crucial for reducing NOx emissions for the flames with lean global equivalence ratios. Lower NO emissions were identified at a global equivalence ratio of 1.1 for all the considered flames in the range of 0.5–1.2. In the four-stage rich-lean combustion strategy employed in this study; it was observed that higher thermal intensity (4 MW/m) with fuel staging resulted in lower NOx emissions per kW of energy input compared to lower thermal intensities 0.7 MW/m. This finding underscores the significance of achieving uniform mixtures and ensuring local flame in rich conditions for achieving low NOx emissions in ammonia combustion. Exhaust gas analysis is conducted at three stages of the burner to enhance the understanding of emissions at various levels of the burner. The proposed combustor design has achieved a substantial reduction in NOx to ∼1 PPM/kW and ∼2.8 PPM/kW with and without fuel staging, respectively. This impressive outcome is attributed to the controlled ammonia consumption facilitated by uniform mixing generated through the use of tangential air inlets.","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":"141532308","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}
For applications in optics, energy storage, and semiconductors etc., spherical non-aggregated particles are desired for better flowability, molding capability and homogeneous densification. Spray flame synthesis has attracted widespread attention with its excellent ability for atomic-level mixing/doping and good potential for scale-up production. However, spray flame synthesis usually produces aggregates due to the known collision-coalescence growth. In this paper, we propose a two-step strategy of suspension-fed spray-flame synthesis. The first step involves the synthesis of aggregated nanoparticles, followed by a second step where these aggregates are reconstructed into spherical non-aggregated particles while retaining the advantage of atomic-level homogeneous mixing. It is found that for aggregated YO nanoparticles, the critical point for reconstructing into spherical particles occurs when the flame temperature exceeds the melting point. The spherical particle size increases with the solid concentration of the suspension by a power of about 0.28. Assuming that droplets do not undergo micro-explosions and instead follow a one droplet to one particle route results in an overestimation of particle size by a factor of 6 to 8. This discrepancy suggests that micro-explosions may play certain role in the new suspension-fed flame synthesis, and largely reduces the final particle size. Furthermore, the AlO-YO and MgO-YO particles are selected for the multicomponent suspension-fed synthesis, representing the miscible and immiscible systems, respectively. The results show that for the AlO-YO system, uniformly mixed spherical non-aggregated particles are obtained. For the MgO-YO system, both composite spherical particles with pinning structure and MgO nanoparticles are identified, indicating that for obtaining spherical multi-component non-aggregated particles, the flame temperature needs to be higher than not only the eutectic component's melting point but also any single component's melting point. Overall, suspension-fed spray flame synthesis opens up a new pathway for the low-cost industrial-scale production of spherical non-aggregated multi-component particles.
{"title":"A two-step strategy for production of spherical non-aggregated multi-component particles by suspension-fed spray flame","authors":"Shuting Lei, Yiyang Zhang, Zhu Fang, Tianyi Wu, Xing Jin, Shuiqing Li","doi":"10.1016/j.proci.2024.105350","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105350","url":null,"abstract":"For applications in optics, energy storage, and semiconductors etc., spherical non-aggregated particles are desired for better flowability, molding capability and homogeneous densification. Spray flame synthesis has attracted widespread attention with its excellent ability for atomic-level mixing/doping and good potential for scale-up production. However, spray flame synthesis usually produces aggregates due to the known collision-coalescence growth. In this paper, we propose a two-step strategy of suspension-fed spray-flame synthesis. The first step involves the synthesis of aggregated nanoparticles, followed by a second step where these aggregates are reconstructed into spherical non-aggregated particles while retaining the advantage of atomic-level homogeneous mixing. It is found that for aggregated YO nanoparticles, the critical point for reconstructing into spherical particles occurs when the flame temperature exceeds the melting point. The spherical particle size increases with the solid concentration of the suspension by a power of about 0.28. Assuming that droplets do not undergo micro-explosions and instead follow a one droplet to one particle route results in an overestimation of particle size by a factor of 6 to 8. This discrepancy suggests that micro-explosions may play certain role in the new suspension-fed flame synthesis, and largely reduces the final particle size. Furthermore, the AlO-YO and MgO-YO particles are selected for the multicomponent suspension-fed synthesis, representing the miscible and immiscible systems, respectively. The results show that for the AlO-YO system, uniformly mixed spherical non-aggregated particles are obtained. For the MgO-YO system, both composite spherical particles with pinning structure and MgO nanoparticles are identified, indicating that for obtaining spherical multi-component non-aggregated particles, the flame temperature needs to be higher than not only the eutectic component's melting point but also any single component's melting point. Overall, suspension-fed spray flame synthesis opens up a new pathway for the low-cost industrial-scale production of spherical non-aggregated multi-component particles.","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":"141527509","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}
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}
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