Hydrogen,with its carbon-free composition and the availability of abundant renewable energy sources for its production,holds significant promise as a fuel for internal combustion engines(ICEs).Its wide flammability li...Hydrogen,with its carbon-free composition and the availability of abundant renewable energy sources for its production,holds significant promise as a fuel for internal combustion engines(ICEs).Its wide flammability limits and high flame speeds enable ultra-lean combustion,which is a promising strategy for reducing NOx emissions and improving thermal efficiency.However,lean hydrogen-air flames,characterized by low Lewis numbers,experience thermo-diffusive instabilities that can significantly influence flame propagation and emissions.To address this challenge,it is crucial to gain a deep understanding of the fundamental flame dynamics of hydrogen-fueled engines.This study uses high-speed planar SO_(2)-LIF to investigate the evolutions of the early flame kernels in hydrogen and methane flames,and analyze the intricate interplay between flame characteristics,such as flame curvature,the gradients of SO_(2)-LIF intensity,tortuosity of flame boundary,the equivalent flame speed,and the turbulent flow field.Differential diffusion effects are particularly pronounced in H_(2)flames,resulting in more significant flame wrinkling.In contrast,CH_(4)flames,while exhibiting smoother flame boundaries,are more sensitive to turbulence,resulting in increased wrinkling,especially under stronger turbulence conditions.The higher correlation between curvature and gradient of H_(2)flames indicates enhanced reactivity at the flame troughs,leading to faster flame propagation.However,increased turbulence can mitigate these effects.Hydrogen flames consistently exhibit higher equivalent flame speeds due to their higher thermo-diffusivity,and both hydrogen and methane flames accelerate under high turbulence conditions.These findings provide valuable insights into the distinct flame behaviors of hydrogen and methane,highlighting the importance of understanding the interactions between thermo-diffusive effects and turbulence in hydrogen-fueled engine combustion.展开更多
Accurate digital terrain models(DTMs)are essential for a wide range of geospatial and environmental applications,yet their derivation in forested regions remains a significant challenge.Existing global DTMs,typically ...Accurate digital terrain models(DTMs)are essential for a wide range of geospatial and environmental applications,yet their derivation in forested regions remains a significant challenge.Existing global DTMs,typically generated from satellite stereo photogrammetry or interferometric synthetic aperture radar(InSAR),fail to accurately capture understory terrain due to limited penetration capabilities,resulting in elevation overestimation in densely vegetated areas.While airborne light detection and ranging(LiDAR)can provide high-accuracy DTMs,its limited spatial coverage and high acquisition cost hinder large-scale applications.Thus,there is an urgent need for a scalable and cost-effective approach to extract DTMs directly from satellite-derived digital surface models(DSMs).In this study,we propose a simple,interpretable understory terrain extraction method that utilizes canopy height data from Global Ecosystem Dynamics Investigation(GEDI)and Ice,Cloud,and Land Elevation Satellite-2(ICESat-2)to construct a tree height surface model,which is then subtracted from the stereo-derived DSM to generate the final DTM.By directly incorporating LiDAR constraints,the method avoids error propagation from multiple heterogeneous datasets and reduces reliance on ancillary inputs,ensuring ease of implementation and broad applicability.In contrast to machine learning-based terrain modeling methods,which are often prone to overfitting and data bias,the proposed approach is simple,interpretable,and robust across diverse forested landscapes.The accuracy of the resulting DTM was validated against airborne LiDAR reference data and compared with both the Copernicus Digital Elevation Model(DEM)and the forest and buildings removed DEM(FABDEM),a global bare-earth elevation model corrected for vegetation bias.The results indicate that the proposed DTM consistently outperforms the Copernicus DEM(CopDEM)and achieves accuracy comparable to FABDEM.In addition,its finer spatial resolution of 1 m,compared to the 30 m resolution of FABDEM,allows for more detailed terrain representation and better capture of fine-scale variation.This advantage is most pronounced in gently to moderately sloped areas,where the proposed DTM shows clearly higher accuracy than both the CopDEM and FABDEM.The results confirm that high-resolution DTMs can be effectively extracted from DSMs using spaceborne LiDAR constraints,offering a scalable solution for terrain modeling in forested environments where airborne LiDAR is unavailable.To illustrate the potential utility of the proposed DTM,we applied it to a fire risk mapping application based on topographic parameters such as slope,aspect,and elevation.This case highlights how improved terrain representation can support geospatial hazard assessments.展开更多
1 Background As the basic principle of the world economy,environment,and social development,sustainable development is the focus of the international community today.In the Olympic Agenda 2020 published by the Interna...1 Background As the basic principle of the world economy,environment,and social development,sustainable development is the focus of the international community today.In the Olympic Agenda 2020 published by the International Olympic Committee(IOC),sustainable development was officially listed as one of the core concepts of the Olympic Games.Since the beginning of the bid,the concept of ctathlete-centered,sustainable and economical”was proposed,which was highly consistent with the idea of the Olympic Agenda 2020.To implement the concept of holding“green”Olympic Games and meet the sustainability requirements of the IOC,the Organizing Committee of Beijing Winter Olympic Games issued a series of documents related to the sustainability of sports venues such as Sustainability Policies for 2022 Beijing Winter Olympic Games and Winter Paralympic Games,and strived to realize the sustainable development of sports venues in the whole life cycle of planning and design stage,construction stage,operation stage,and post-game utilization.展开更多
基金supported by the Deutsche Forschungsgemeinschaft through FOR 2687“Cyclic variations in highly optimized spark-ignition engines:experiment and simulation of a multiscale causal chain”(No.423224402).
文摘Hydrogen,with its carbon-free composition and the availability of abundant renewable energy sources for its production,holds significant promise as a fuel for internal combustion engines(ICEs).Its wide flammability limits and high flame speeds enable ultra-lean combustion,which is a promising strategy for reducing NOx emissions and improving thermal efficiency.However,lean hydrogen-air flames,characterized by low Lewis numbers,experience thermo-diffusive instabilities that can significantly influence flame propagation and emissions.To address this challenge,it is crucial to gain a deep understanding of the fundamental flame dynamics of hydrogen-fueled engines.This study uses high-speed planar SO_(2)-LIF to investigate the evolutions of the early flame kernels in hydrogen and methane flames,and analyze the intricate interplay between flame characteristics,such as flame curvature,the gradients of SO_(2)-LIF intensity,tortuosity of flame boundary,the equivalent flame speed,and the turbulent flow field.Differential diffusion effects are particularly pronounced in H_(2)flames,resulting in more significant flame wrinkling.In contrast,CH_(4)flames,while exhibiting smoother flame boundaries,are more sensitive to turbulence,resulting in increased wrinkling,especially under stronger turbulence conditions.The higher correlation between curvature and gradient of H_(2)flames indicates enhanced reactivity at the flame troughs,leading to faster flame propagation.However,increased turbulence can mitigate these effects.Hydrogen flames consistently exhibit higher equivalent flame speeds due to their higher thermo-diffusivity,and both hydrogen and methane flames accelerate under high turbulence conditions.These findings provide valuable insights into the distinct flame behaviors of hydrogen and methane,highlighting the importance of understanding the interactions between thermo-diffusive effects and turbulence in hydrogen-fueled engine combustion.
基金supported by the National Key Research and Development Program of China(Nos.SQ2022YFB3900026 and 2022YFB3903305)supported by the Leading Talents of Guangdong Pearl River Talent Program(No.2021CX02S024)the Guangdong S&T programme(No.2024B1212050011).
文摘Accurate digital terrain models(DTMs)are essential for a wide range of geospatial and environmental applications,yet their derivation in forested regions remains a significant challenge.Existing global DTMs,typically generated from satellite stereo photogrammetry or interferometric synthetic aperture radar(InSAR),fail to accurately capture understory terrain due to limited penetration capabilities,resulting in elevation overestimation in densely vegetated areas.While airborne light detection and ranging(LiDAR)can provide high-accuracy DTMs,its limited spatial coverage and high acquisition cost hinder large-scale applications.Thus,there is an urgent need for a scalable and cost-effective approach to extract DTMs directly from satellite-derived digital surface models(DSMs).In this study,we propose a simple,interpretable understory terrain extraction method that utilizes canopy height data from Global Ecosystem Dynamics Investigation(GEDI)and Ice,Cloud,and Land Elevation Satellite-2(ICESat-2)to construct a tree height surface model,which is then subtracted from the stereo-derived DSM to generate the final DTM.By directly incorporating LiDAR constraints,the method avoids error propagation from multiple heterogeneous datasets and reduces reliance on ancillary inputs,ensuring ease of implementation and broad applicability.In contrast to machine learning-based terrain modeling methods,which are often prone to overfitting and data bias,the proposed approach is simple,interpretable,and robust across diverse forested landscapes.The accuracy of the resulting DTM was validated against airborne LiDAR reference data and compared with both the Copernicus Digital Elevation Model(DEM)and the forest and buildings removed DEM(FABDEM),a global bare-earth elevation model corrected for vegetation bias.The results indicate that the proposed DTM consistently outperforms the Copernicus DEM(CopDEM)and achieves accuracy comparable to FABDEM.In addition,its finer spatial resolution of 1 m,compared to the 30 m resolution of FABDEM,allows for more detailed terrain representation and better capture of fine-scale variation.This advantage is most pronounced in gently to moderately sloped areas,where the proposed DTM shows clearly higher accuracy than both the CopDEM and FABDEM.The results confirm that high-resolution DTMs can be effectively extracted from DSMs using spaceborne LiDAR constraints,offering a scalable solution for terrain modeling in forested environments where airborne LiDAR is unavailable.To illustrate the potential utility of the proposed DTM,we applied it to a fire risk mapping application based on topographic parameters such as slope,aspect,and elevation.This case highlights how improved terrain representation can support geospatial hazard assessments.
文摘1 Background As the basic principle of the world economy,environment,and social development,sustainable development is the focus of the international community today.In the Olympic Agenda 2020 published by the International Olympic Committee(IOC),sustainable development was officially listed as one of the core concepts of the Olympic Games.Since the beginning of the bid,the concept of ctathlete-centered,sustainable and economical”was proposed,which was highly consistent with the idea of the Olympic Agenda 2020.To implement the concept of holding“green”Olympic Games and meet the sustainability requirements of the IOC,the Organizing Committee of Beijing Winter Olympic Games issued a series of documents related to the sustainability of sports venues such as Sustainability Policies for 2022 Beijing Winter Olympic Games and Winter Paralympic Games,and strived to realize the sustainable development of sports venues in the whole life cycle of planning and design stage,construction stage,operation stage,and post-game utilization.
