Measurements of column-averaged dry-air mole fractions of carbon dioxide and carbon monoxide,CO_(2)(XCO_(2))and CO(XCO),were performed throughout 2019 at an urban site in Beijing using a compact Fourier Transform Spec...Measurements of column-averaged dry-air mole fractions of carbon dioxide and carbon monoxide,CO_(2)(XCO_(2))and CO(XCO),were performed throughout 2019 at an urban site in Beijing using a compact Fourier Transform Spectrometer(FTS)EM27/SUN.This data set is used to assess the characteristics of combustion-related CO_(2)emissions of urban Beijing by analyzing the correlated daily anomalies of XCO and XCO_(2)(e.g.,ΔXCO andΔXCO_(2)).The EM27/SUN measurements were calibrated to a 125HR-FTS at the Xianghe station by an extra EM27/SUN instrument transferred between two sites.The ratio ofΔXCO overΔXCO_(2)(ΔXCO:ΔXCO_(2))is used to estimate the combustion efficiency in the Beijing region.A high correlation coefficient(0.86)betweenΔXCO andΔXCO_(2)is observed.The CO:CO_(2)emission ratio estimated from inventories is higher than the observedΔXCO:ΔXCO_(2)(10.46±0.11 ppb ppm^(−1))by 42.54%-101.15%,indicating an underestimation in combustion efficiency in the inventories.DailyΔXCO:ΔXCO_(2)are influenced by transportation governed by weather conditions,except for days in summer when the correlation is low due to the terrestrial biotic activity.By convolving the column footprint[ppm(μmol m-2 s-1)-1]generated by the Weather Research and Forecasting-X-Stochastic Time-Inverted Lagrangian Transport models(WRF-X-STILT)with two fossil-fuel emission inventories(the Multi-resolution Emission Inventory for China(MEIC)and the Peking University(PKU)inventory),the observed enhancements of CO_(2)and CO were used to evaluate the regional emissions.The CO_(2)emissions appear to be underestimated by 11%and 49%for the MEIC and PKU inventories,respectively,while CO emissions were overestimated by MEIC(30%)and PKU(35%)in the Beijing area.展开更多
The combustion of aluminum particles in solid rocket motor plays an important role in energy release of propellants. However, due to the limited residence time, aluminum particles may not be burned completely, thus hi...The combustion of aluminum particles in solid rocket motor plays an important role in energy release of propellants. However, due to the limited residence time, aluminum particles may not be burned completely, thus hindering the improvement of specific impulse. This study aims to explore the characteristics of aluminum combustion efficiency and its influencing factors by experiments and numerical simulations, providing a guideline for engine performance improvement. As an input of simulation, the initial agglomerate size was measured by a high pressure system. Meanwhile, the size distribution of the particles in plume was measured by ground firing test to validate the numerical model. Then, a two-phase flow model coupling combustion of micro aluminum particle was developed, by which the detailed effects of particle size, detaching position and nozzle convergent section structure on aluminum combustion efficiency were explored. The results suggest that the average combustion temperature in the chamber drops with increasing initial particle size,while the maximum temperature increases slightly. In the tested motors, the aluminum particle burns completely as its diameter is smaller than 50 μm, and beyond 50 μm the combustion efficiency decreases obviously with the increase of initial size. As the diameter approaches to 75 μm, the combustion efficiency becomes more sensitive to particle size. The combustion efficiency of aluminum particle escaping from end-burning surfaces is significantly higher than that from internal burning surface, where the particle combustion efficiency decreases during approaching the convergent section. Furthermore, the combustion efficiency decreases slightly with increasing nozzle convergent section angle. And theoretically it is feasible to improve combustion efficiency of aluminum particles by designing the convergent profile of nozzle.展开更多
Improving the combustion efficiency of fuels is essential to reducing pollutant emissions in the iron ore sintering process.The sintering bed surface steam-injection technology has attracted significant research inter...Improving the combustion efficiency of fuels is essential to reducing pollutant emissions in the iron ore sintering process.The sintering bed surface steam-injection technology has attracted significant research interest for its potential advantages in low-energy consumption and low emission.The effect of steam injection on fuel combustion efficiency and CO emission was studied by comparing the thermodynamic response from the sintering process before and after steam injection.The mechanism of improving combustion efficiency was also revealed.The results indicated that the sintering gas medium of H_(2)O-H_(2)-N_(2)-O_(2) with the blown steam improved the heat transfer conditions of fuel combustion and promoted the water gas reaction.The optimum state of steam injection was achieved at 15 min after ignition with 0.02 m^(3) min^(-1).The CO emission reduction is 10.91% compared with the base case.The combustion efficiency was 88.83%,6.15% higher than conventional sintering,and the solid fuel consumption was reduced by 1.15 kg t^(-1).It was indicated that steam injection would improve combustion efficiency and reduce solid fuel consumption.Meanwhile,the steam injection could improve the combustion kinetic conditions in the zone of unburned fuel and low oxygen partial pressure.It was conducive to the reaction of H_(2)O with C and CO to convert the CO of reducing atmosphere to CO_(2),which in turn realized the complete combustion of fuel and CO and improved the efficiency of fuel combustion.展开更多
Experiments were conducted to determine the effects of the mixing section configurations on the Mg-CO_(2)Martian ramjet combustion efficiency.It was carried out at a mainstream mass flow rate of 110 g/s and a temperat...Experiments were conducted to determine the effects of the mixing section configurations on the Mg-CO_(2)Martian ramjet combustion efficiency.It was carried out at a mainstream mass flow rate of 110 g/s and a temperature of 810 K.The chamber pressure was measured under different configurations and Oxidizer to Fuel(O/F)ratios.Results showed that the engine achieved self-sustaining combustion and worked stably during experiments.The pre-combustion chamber is needed to increase the combustion efficiency and promote the full combustion of the powder.After the configuration of the pre-combustion chamber,the best combustion efficiency reached 80%when radial powder injection and lateral carbon dioxide intake were used.In addition,the O/F ratio in the pre-combustion chamber decreased from 0.67 to 0.31,resulting in an 8%increase in the combustion efficiency.It was speculated that different mixing section configurations and the variations in an O/F ratio within the pre-combustion chamber impacted the combustion efficiency and in essence,all affected the flow velocity and residence time of the two-phase flow in the com-bustion chamber.展开更多
The carbon content in the fly ash from most Chinese circulating fluidized bed (CFB) boilers is much higher than expected, thus directly influencing the combustion efficiency. In the present paper, carbon burnout was i...The carbon content in the fly ash from most Chinese circulating fluidized bed (CFB) boilers is much higher than expected, thus directly influencing the combustion efficiency. In the present paper, carbon burnout was investigated both in field tests and laboratory experiments. The effect of coal property, operation condition, gas-solid mixing, char deactivation, residence time and cyclone performance are analyzed seriatim based on large amount of experimental results. A coal index is proposed to describe the coal rank, defined by the ratio of the volatile content to the coal heat value, is a useful parameter to analyze the char burnout. The carbon content in the fly ash depends on the coal rank strongly. CFB boilers burning anthracite, which has low coal index, usually have high carbon content in the fly ash. On the contrary, the CFB boilers burning brown coal, which has high coal index, normally have low carbon content. Poor gas-solid mixing in the furnace is another important reason of the higher carbon content in the fly ash. Increasing the velocity and rigidity of the secondary air could extend the penetration depth and induce more oxygen into the furnace center. Better gas solid mixing will decrease the lean oxygen core area and increase char combustion efficiency. The fine char particles could be divided into two groups according to their reactivity. One group is 'fresh' char particles with high reactivity and certain amount of volatile content. The other group of char particles has experienced sufficient combustion time both in the furnace and in the cyclone, with nearly no volatile. These 'old' chars in the fly ash will be deactivated during combustion of large coal particles and have very low carbon reactivity. The generated fine inert char particles by attrition of large coal particles could not easily burn out even with the fly ash recirculation. The fraction of large coal particles in coal feed should be reduced during fuel preparation process. The cyclone efficiency controls the particle residence time in CFB loop, especially for that of the fine particles. So the cyclone efficiency, especially the cut size, will greatly influence the carbon content in the fly ash.展开更多
A scramjet engine combustion efficiency measure system was designed.The combustion efficiency was measured by chromatography method,and the results of chromatography method were compared with those of temperature meth...A scramjet engine combustion efficiency measure system was designed.The combustion efficiency was measured by chromatography method,and the results of chromatography method were compared with those of temperature method.The results indicate that the combustion efficiency measured by chromatography method was 80.7%,lower than the combustion efficiency of 84.5%measured by temperature method;the combustion efficiency could be measured more precisely by chromatogram method than by temperature method.The combustion efficiency measure system based on chromatogram method can work well,and thus can be used to measure the combustion efficiency of scramjet engine.展开更多
Nanothermites have been employed as fuel additives in energetic formulations due to their higher energy density over CHNO energetics. Nevertheless, sintering and degradation of nanoparticles significantly limit the pr...Nanothermites have been employed as fuel additives in energetic formulations due to their higher energy density over CHNO energetics. Nevertheless, sintering and degradation of nanoparticles significantly limit the practical use of nanothermites. In this work, combustion characteristic and aging behavior of aluminum/iron oxide(Al/Fe2O3) nanothermite mixtures were investigated in the presence of micron-scale nickel aimed to produce bimetal thermite powders. The results showed that the alumina content in the combustion residue increased from 88.3% for Al/Fe2O3 nanothermite to 96.5% for the nanothermite mixture containing 20 wt% nickel. Finer particle sizes of combustion residue were obtained for the nanothermite mixtures containing nickel, indicative of the reduced agglomeration. Both results suggested a more complete combustion in the bimetal thermite powders. Aging behavior of the nanothermite mixture was also assessed by measuring the heat of combustion of the mixture before and after aging process. The reduction in heat of combustion of nanothermite mixtures containing nickel was less severe as compared to a significant decrease for the nanothermite mixture without nickel, indicating better aging resistance of the bimetal thermite powders.展开更多
Plasma jet has been widely used in supersonic combustor as an effective ignition and combustion assisted method,but currently it is mostly combined with the traditional wall fuel injection method,while the application...Plasma jet has been widely used in supersonic combustor as an effective ignition and combustion assisted method,but currently it is mostly combined with the traditional wall fuel injection method,while the application combined with the central fuel injection method is less.In order to expand the combustion range,the plasma jet was introduced into a strut-cavity combustor with an alternating-wedge.The effects of total pressure of strut fuel injection,total pressure of cavity fuel injection,total pressure of plasma jet injection and plasma jet media on the combustion characteristics were analyzed in supersonic flow by numerical calculations in a three-dimensional domain.The combustion field structure,wall pressure distribution,combustion efficiency and distribution of H2O at the exit of the combustor with different injection conditions were analyzed.The results show that the combustion efficiency decreases with the increase of the strut fuel injection total pressure.However,the combustion area downstream increases when the total pressure of the strut fuel injection increases within the proper range.The combustion range is expanded and the combustion efficiency is improved when the cavity fuel injection total pressure is increased within the range of 0.5−2.0 MPa,but a sharp drop in combustion efficiency can be found due to limited fuel mixing when the total injection pressure of the cavity fuel is excessively increased.With the increased total injection pressure of the plasma jet,the height of the cavity shear layer is raised and the equivalence ratio of the gas mixture in the cavity is improved.When the total pressure of the plasma jet is 1.25 MPa,the combustion efficiency reaches a maximum of 82.1%.The combustion-assisted effect of different plasma jet media is significantly different.When the medium of the plasma jet is O2,the combustion-assisted effect on the combustor is most significant.展开更多
In order to address typical problems due to the huge demand of oil for consumption in traditional internal combustion engines,a new more efficient combustion mode is proposed and studied in the framework of Computatio...In order to address typical problems due to the huge demand of oil for consumption in traditional internal combustion engines,a new more efficient combustion mode is proposed and studied in the framework of Computational Fluid Dynamics(CFD).Moreover,a Non-dominated Sorting Genetic Algorithm(NSGA-Ⅱ)is applied to optimize the related parameters,namely,the engine methanol ratio,the fuel injection time,the initial temperature,the Exhaust Gas Re-Circulation(EGR)rate,and the initial pressure.The so-called Conventional Diesel Combustion(CDC),Homogeneous Charge Compression Ignition(HCCI)and the Reactivity Controlled Compression Ignition(RCCI)combustion modes are compared.The results show that RCCI has a higher methanol ratio and an earlier injection timing with moderate EGR rate and higher initial pressure.The initial temperature increases as the methanol ratio increases.In comparison,CDC has the lowest hydrocarbon and CO emissions and the highest combustion efficiency.At different crankshaft rotation angles corresponding to 50%of the combustion amount(CA50),the combustion temperature and boundary layer temperature of HCCI change significantly,while those of RCCI undergo limited variations.At the same CA50,the exergy losses of HCCI and RCCI are lower than that of the CDC.On the basis of these findings,it can be concluded that the methanol/diesel RCCI engine can be used to obtain a clean and efficient combustion process,which should be regarded as a promising combustion mode.展开更多
The aim of the present study is to develop the biomass furnace combustor which can effectively employ four unused biomasses, i.e., wood bark, wood branch, bamboo, and grass as a fuel. Emphasis is placed on the combust...The aim of the present study is to develop the biomass furnace combustor which can effectively employ four unused biomasses, i.e., wood bark, wood branch, bamboo, and grass as a fuel. Emphasis is placed on the combustion gas components and combustion gas temperature in the combustor. It is found from the study that： （1） Four unused biomasses can take plate self combustion and the stable combustion yield; （2） Different combustion temperature distribution appears in combustor and is affected by each biomass; （3） The concentrations of nitrogen oxide and sulfur oxides are lower than the discharge standard value; （4） Higher thermal efficiency yields for bark, bamboo and grass.展开更多
A novel constant-pressure and constant-quenching distance Condensed Combustion Products(CCPs)collection system was developed,coupled with a timing control system,to collect the CCPs formed in the course of burning of ...A novel constant-pressure and constant-quenching distance Condensed Combustion Products(CCPs)collection system was developed,coupled with a timing control system,to collect the CCPs formed in the course of burning of aluminum-based composite propellants.The effects of adiabatic graphite plating,collection zone,quenching distance,time series of collection,and propellant burning rate on the microscopic morphology,particle size distribution and unburned aluminum content of CCPs were investigated.It was verified that the graphite plating can provide a high-fidelity high-temperature environment for propellant combustion.The combustion efficiency is improved by 2.44% compared to the bare propellant case.The time series of collection has a significant effect on the combustion efficiency of aluminum,and the combustion efficiency of aluminum in the thermal state(1.2-2.4 s)is 2.75% higher than that in the cold state(0-1.2 s).Similarly,the characteristics of the CCPs in different collection zones are different.At the quenching distance of 5 mm,the combustion efficiency of aluminum in the core zone(85.39%)is much lower than that in the outer zone(92.07%),while the particle size of the CCPs in the core zone(172μm)is larger than that in the outer zone(41μm).This indicates that the core zone is more likely to produce large-sized and incompletely burned agglomerates during the propellant combustion process.Different burning rates also lead to a significant difference in particle size distribution and combustion efficiency.High burning rates result in higher combustion efficiency.A detailed sequence of the elaborative collection process of CCPs is proposed,mainly including the setting of ignition delay time,burning rate,working pressure,plating length and time series of collection.The findings of this study are expected to provide a reliable tool for the evaluation of the combustion efficiency of solid propellants.展开更多
This review examines the potential of hydrogen,ammonia,and biodiesel as alternative fuels,focusing on spray dynamics,droplet evaporation,combustion,and emissions.Hydrogen offers superior combustion characteristics but...This review examines the potential of hydrogen,ammonia,and biodiesel as alternative fuels,focusing on spray dynamics,droplet evaporation,combustion,and emissions.Hydrogen offers superior combustion characteristics but faces challenges in NO_(x)emissions.Strategies like nonpremixed direct injection,increased intake boost pressure,and low-pressure EGR are suggested for robust hydrogen combustion in compression-ignition engines.Control of hydrogen start of injection(SOI)and water injection(WI)are identified as effective techniques for reducing NO_(x)emissions.Ammonia shows inferior combustion and higher NO_(x)and unburned NH_(3)emissions in the same conditions as conventional fuels with conventional engines.Understanding ammonia spray and evaporation conditions is significant for optimizing an ammonia-air mixture and minimizing wall impingement and ammonia trap in the crevice,thereby improving combustion and emission reduction.Increasing intake pressure,injection pressure,and EGR rate,employing a turbulent jet,and preheating ammonia improve efficiency and reduce NO_(x)emissions.Utilizing ammonia combustion requires the implementation of after-treatment systems such as NH_(3)adsorber and De NO_(x)catalysts to mitigate unburned NH_(3)and NO_(x)emissions.Biodiesel affects the fuel supply system,combustion,and emission characteristics according to its viscosity and density.Increasing injection pressure and blending with volatile fuels enhance spray and combustion.Optimum biodiesel preheating temperatures for the injection pump and injector are crucial for achieving the best pump capacity and spray formation.By utilizing biodiesel-PODE blends and investigating low-temperature biodiesel combustions,there is potential to improve thermal efficiency and PMNO_(x)trade-off.Therefore,carbon-neutral fuel adoption should be accelerated to mitigate CO_(2)emissions,highlighting the importance of combustion techniques and emissions reduction strategies.展开更多
Thermochemical recuperation heat recovery is an advanced waste heat utilization technology that can effectively recover exhaust waste heat from oxy-fuel Stirling engines.The novel combustor of a Stirling engine with t...Thermochemical recuperation heat recovery is an advanced waste heat utilization technology that can effectively recover exhaust waste heat from oxy-fuel Stirling engines.The novel combustor of a Stirling engine with thermochemical recuperation heat recovery system is expected to utilize both reformed gas and diesel fuels as sources of combustion.In this research,the effects of various factors,including the H_(2)O addition,fuel distribution ratio(FDR),excess oxygen coefficient,and cyclone structure on the temperature distribution in the combustor,combustion emissions,and external combustion system efficiency of the Stirling engine were experimentally investigated.With the increase of steam-to-carbon ratio(S/C),the temperature difference between the upper and lower heating tubes reduces and the circumferential temperature fluctuation decreases,and the combustion of diesel and reformed gas remains close to complete combustion.At S/C=2,the external combustion efficiency is 80.6%,indicating a 1.6%decrease compared to conventional combustion.With the increase of FDR,the temperature uniformity of the heater tube is improved,and the CO and HC emissions decrease.However,the impact of the FDR on the maximum temperature difference and temperature fluctuation across the heater is insignificant.When the FDR rises from 21%to 38%,the external combustion efficiency increases from 87.4%to92.3%.The excess oxygen coefficient plays a secondary role in influencing temperature uniformity and temperature difference,and the reformed gas and diesel fuel can be burned efficiently at a low excess oxygen coefficient of 1.04.With an increase in the cyclone angle,the heater tube temperature increases,while the maximum temperature difference at the lower part decreases,and the temperature fluctuation increases.Simultaneously,the CO and HC emissions increase,and the external combustion efficiency experiences a decrease.A cyclone angle of 30°is found to be an appropriate value for achieving optimal mixing between reformed gas and diesel fuel.The research findings present valuable new insights that can be utilized to enhance the performance optimization of Stirling engines.展开更多
Aluminum is an attractive alternative fuel,but it burns very inefficiently due to the formation of a dense Al_(2)O_(3)layer which prevents O_(2)from diffusion to the surface of Al particles.In previous experiments,the...Aluminum is an attractive alternative fuel,but it burns very inefficiently due to the formation of a dense Al_(2)O_(3)layer which prevents O_(2)from diffusion to the surface of Al particles.In previous experiments,the combustion of millimeter-sized Al(mAl)particles in the fluidized bed has achieved a substantial increase in the combustion efficiency,but further improvements are still needed.In this study,the effects of reaction atmosphere on the fluidized combustion of mAl particles were investigated.The experiments with different O_(2)/H_(2)O/CO_(2)concentrations were conducted.The experimental results indicate that the combustion efficiency of mAl particles in fluidized bed increases as the mole fraction of O_(2),H_(2)O or CO_(2)increases,and the highest combustion efficiency can reach 38.7%.After the analysis of the oxide film on the surface of aluminum particles,it was found that it is easier to generate the unstableθ-Al_(2)O_(3)under CO_(2)atmosphere,and it is easier to generate the unstableγ-Al_(2)O_(3)andθ-Al_(2)O_(3)under H_(2)O atmosphere.The unstable Al_(2)O_(3)film is more likely to be abraded in the fluidized bed,which leads to the effective improvement of the combustion efficiency.展开更多
Supersonic model combustors using two-stage injections of supercritical kerosene were experimentally investigated in both Mach 2.5 and 3.0 model combustors with stagnation temperatures of approximately 1,750 K. Superc...Supersonic model combustors using two-stage injections of supercritical kerosene were experimentally investigated in both Mach 2.5 and 3.0 model combustors with stagnation temperatures of approximately 1,750 K. Supercritical kerosene of approximately 760 K was prepared and injected in the overall equivalence ratio range of 0.5-1.46. Two pairs of integrated injector/flameholder cavity modules in tandem were used to facilitate fuel-air mixing and stable combustion. For single-stage fuel injection at an upstream location, it was found that the boundary layer separation could propagate into the isolator with increasing fuel equivalence ratio due to excessive local heat release, which in turns changed the entry airflow conditions. Moving the fuel injection to a further downstream location could alleviate the problem, while it would result in a decrease in combustion efficiency due to shorter fuel residence time. With two-stage fuel injections the overall combustor performance was shown to be improved and kerosene injections at fuel rich conditions could be reached without the upstream propagation of the boundary layer separation into the isolator. Furthermore, effects of the entry Mach number and pilot hydrogen on combustion performance were also studied.展开更多
This study was performed to estimate the emission of non-CO 2 greenhouse gases(GHGs) from biomass burning at a large fire area.The extended methodology adopted the IPCC Guidelines(2003) equation for use on data from t...This study was performed to estimate the emission of non-CO 2 greenhouse gases(GHGs) from biomass burning at a large fire area.The extended methodology adopted the IPCC Guidelines(2003) equation for use on data from the Samcheok forest fire gathered using 30 m resolution Landsat TM satellite imagery,digital forest type maps,and growing stock information per hectare by forest type in 1999.Normalized burn ratio(NBR) technique was employed to analyze the area and severity of the Samcheok forest fire that occurred in 2000.The differences between NBR from pre-and post-fire datasets are examined to determine the extent and degree of change detected from burning.The results of burn severity analysis by dNBR of the Samcheok forest fire area revealed that a total of 16,200 ha of forest were burned.The proportion of the area characterized by a 'Low' burn severity(dNBR below 152) was 35%,with 'Moderate'(dNBR 153-190) and 'High'(dNBR 191-255) areas were at 33% and 32%,respectively.The combustion efficiency for burn severity was calculated as 0.43 for crown fire where burn severity was 'High',as 0.40 for 'Moderate' severity,and 0.15 for 'Low' severity surface fire.The emission factors for estimating non-CO 2 GHGs were separately applied to CO 130,CH 4 9,NO x 0.7 and N 2 O 0.11.Non-CO 2 GHGs emissions from biomass burning in the Samcheok forest fire area were estimated to be CO 44.100,CH 4 3.053,NO x 0.238 and N 2 O 0.038 Gg.展开更多
The structure of the trapped-vortex cavity and radial flameholder can maintain stable combustion under severe conditions,such as sub-atmospheric pressure and high inlet velocity.This article reports a complete study o...The structure of the trapped-vortex cavity and radial flameholder can maintain stable combustion under severe conditions,such as sub-atmospheric pressure and high inlet velocity.This article reports a complete study of combustion characteristics for this design.The flow field of the physical model was obtained by numerical simulation.The pilot combustion characteristics,including the combustion process,combustion efficiency,and wall temperature distribution,were studied by experiments.The pilot combustion can be divided into three modes under different fuel flow rates and inlet conditions.In“cavity maintained(CM)”mode,pilot flame exists at both sides of the cavity zone,rotating with the main vortex.In“cavity-flameholder maintained(CFM)”mode,the combustion process occurs both inside the cavity and behind the flameholder.While in“flameholder maintained(FM)”mode,the cavity will quench,and the combustion is maintained by the radial flameholder only.Due to the difference in the flow field,the flame pattern and propagation direction vary under different combustion modes.The combustion efficiency,influenced by combustion modes,shows an increase-decrease-increase curve.The wall temperature distribution is also affected;the cavity wall temperature decreases under large fuel flux while the temperature of the burner-back plate continues to rise to a maximum value.展开更多
Iron ore sintering process is the main CO_(2) emission source throughout the integrate steelworks,which primarily comes from the combustion of solid fuels.Improving the combustion efficiency and reducing the solid fue...Iron ore sintering process is the main CO_(2) emission source throughout the integrate steelworks,which primarily comes from the combustion of solid fuels.Improving the combustion efficiency and reducing the solid fuel consumption are important ways to reduce the CO_(2) emission in the sintering process.Around the efficient combustion of fuel,the migration behavior and combustion characteristics of solid fuel in the granulation process were investigated.The results indicated that during the granulation process,fuel particles with size less than 0.5 mm mainly migrated into the granules with grain size of 1-3,3-5 and 5-8 mm;fuel particles with size of 0.5^(-1)mm mainly migrated into granules of 1-3 mm;fuel particles with size of 1-3,3-5 and 5-8 mm mainly entered the granules with the same grain size.With the increase in fuel particles grain size from-0.5 to+8 mm,the combustion efficiency exhibited a firstly-increasing and then decreasing tendency,while the NO_(x) exhibited a decreasing tendency.Potential reason can be described that finer fuel particles(-1 mm)easily distributed in the outer layer of the granules,which combusted fiercely due to its larger specific surface area,leading to the development of incomplete combustion and the conversion of fuel nitrogen;the combustion efficiency of larger fuel particles was restricted by the inner diffusion of O_(2),which then contributed to the reduction of NO_(x) under the inadequate combustion atmosphere.展开更多
On-road tailpipe ammonia (NH3) emissions contribute to urban secondary organic aerosol formation and have direct or indirect adverse impacts on the environment and human health. To understand the tailpipe NH3 emission...On-road tailpipe ammonia (NH3) emissions contribute to urban secondary organic aerosol formation and have direct or indirect adverse impacts on the environment and human health. To understand the tailpipe NH3 emission characteristics, we performed comprehensive chassis dynamometer measurements of NH3 emission from two China 5 and two China 6 light-duty gasoline vehicles (LDGVs) equipped with three-way catalytic converters (TWCs). The results showed that the distance-based emission factors (EFs) were 12.72 ± 2.68 and 3.18 ± 1.37 mg/km for China 5 and China 6 LDGVs, respectively. Upgrades in emission standards were associated with a reduction in tailpipe NH3 emission. In addition, high NH3 EFs were observed during the engine warm-up period in cold-start cases owing to the intensive emissions of incomplete combustion products and suitable catalytic temperature in the TWCs. Notably, based on the instantaneous NH3 emission rate, distinct NH3–emitting events were detected under high/extra high velocity or rapid acceleration. Furthermore, NH3 emission rates correlated well with engine speed, vehicle specific power, and modified combustion efficiency, which were more easily accessible. These strong correlations were applied to reproduce NH3 emissions from China 5/6 LDGVs. The predicted NH3 EFs under different dynamometer and real-world cycles agreed well with existing measurement and prediction results, revealing that the NH3 EFs of LDGVs in urban routes were within 8.55–11.62 mg/km. The results presented here substantially contribute to improving the NH3 emission inventory for LDGVs and predicting on-road NH3 emissions in China.展开更多
This paper presents the combustion characteristics in hybrid rocket motors with multisegmented grain through three-dimensional numerical simulations.Multi-segmented grain is composed of several thin grains with two or...This paper presents the combustion characteristics in hybrid rocket motors with multisegmented grain through three-dimensional numerical simulations.Multi-segmented grain is composed of several thin grains with two or more ports.The numerical model consists of Navier-Stokes equations with turbulence,solid fuel pyrolysis,chemical reactions,a fluid–solid coupling model and a regression rate model.The simulations adopt 90%Hydrogen Peroxide(HP)and PolyEthylene(PE)as the propellant combination.The effects of the rotation,port number,fuel grain segment number and mid-chamber length on the flow field and combustion performances are analyzed.The results indicate that the multi-segmented grain configuration can strengthen the flow field,and the regression rate and combustion efficiency are enhanced.Take the cases with two grain segments and three ports for example,the regression rate is increased by 32.4%-45.1%and the combustion efficiency increases by 6%-8.6%in different rotation angles.展开更多
基金supported by grants from the National Key Research and Development Program of China(Grant No.2017YFB0504000)National Natural Science Foundation of China(Grant No.41875043)+2 种基金the Strategic Priority Research 275 Program of the Chinese Academy of Sciences(Grant No.XDA17010102)External Cooperation Program of the Chinese Academy of Science(Grant No.GJHZ1802)Youth Innovation Promotion Association,CAS.
文摘Measurements of column-averaged dry-air mole fractions of carbon dioxide and carbon monoxide,CO_(2)(XCO_(2))and CO(XCO),were performed throughout 2019 at an urban site in Beijing using a compact Fourier Transform Spectrometer(FTS)EM27/SUN.This data set is used to assess the characteristics of combustion-related CO_(2)emissions of urban Beijing by analyzing the correlated daily anomalies of XCO and XCO_(2)(e.g.,ΔXCO andΔXCO_(2)).The EM27/SUN measurements were calibrated to a 125HR-FTS at the Xianghe station by an extra EM27/SUN instrument transferred between two sites.The ratio ofΔXCO overΔXCO_(2)(ΔXCO:ΔXCO_(2))is used to estimate the combustion efficiency in the Beijing region.A high correlation coefficient(0.86)betweenΔXCO andΔXCO_(2)is observed.The CO:CO_(2)emission ratio estimated from inventories is higher than the observedΔXCO:ΔXCO_(2)(10.46±0.11 ppb ppm^(−1))by 42.54%-101.15%,indicating an underestimation in combustion efficiency in the inventories.DailyΔXCO:ΔXCO_(2)are influenced by transportation governed by weather conditions,except for days in summer when the correlation is low due to the terrestrial biotic activity.By convolving the column footprint[ppm(μmol m-2 s-1)-1]generated by the Weather Research and Forecasting-X-Stochastic Time-Inverted Lagrangian Transport models(WRF-X-STILT)with two fossil-fuel emission inventories(the Multi-resolution Emission Inventory for China(MEIC)and the Peking University(PKU)inventory),the observed enhancements of CO_(2)and CO were used to evaluate the regional emissions.The CO_(2)emissions appear to be underestimated by 11%and 49%for the MEIC and PKU inventories,respectively,while CO emissions were overestimated by MEIC(30%)and PKU(35%)in the Beijing area.
基金supported by the National Natural Science Foundation of China(Nos.11972087 and U20B2018)the Domain Foundation of Equipment Advance Research of 13th Five-year Plan,China(No.61407200201).
文摘The combustion of aluminum particles in solid rocket motor plays an important role in energy release of propellants. However, due to the limited residence time, aluminum particles may not be burned completely, thus hindering the improvement of specific impulse. This study aims to explore the characteristics of aluminum combustion efficiency and its influencing factors by experiments and numerical simulations, providing a guideline for engine performance improvement. As an input of simulation, the initial agglomerate size was measured by a high pressure system. Meanwhile, the size distribution of the particles in plume was measured by ground firing test to validate the numerical model. Then, a two-phase flow model coupling combustion of micro aluminum particle was developed, by which the detailed effects of particle size, detaching position and nozzle convergent section structure on aluminum combustion efficiency were explored. The results suggest that the average combustion temperature in the chamber drops with increasing initial particle size,while the maximum temperature increases slightly. In the tested motors, the aluminum particle burns completely as its diameter is smaller than 50 μm, and beyond 50 μm the combustion efficiency decreases obviously with the increase of initial size. As the diameter approaches to 75 μm, the combustion efficiency becomes more sensitive to particle size. The combustion efficiency of aluminum particle escaping from end-burning surfaces is significantly higher than that from internal burning surface, where the particle combustion efficiency decreases during approaching the convergent section. Furthermore, the combustion efficiency decreases slightly with increasing nozzle convergent section angle. And theoretically it is feasible to improve combustion efficiency of aluminum particles by designing the convergent profile of nozzle.
基金support from the National Natural Science Foundation of China (NSFC) (Grant No.52174290)the China Scholarship Council (CSC)via the Joint-Training Ph.D.Program (Grant No.202008340093)for supportingthis research.
文摘Improving the combustion efficiency of fuels is essential to reducing pollutant emissions in the iron ore sintering process.The sintering bed surface steam-injection technology has attracted significant research interest for its potential advantages in low-energy consumption and low emission.The effect of steam injection on fuel combustion efficiency and CO emission was studied by comparing the thermodynamic response from the sintering process before and after steam injection.The mechanism of improving combustion efficiency was also revealed.The results indicated that the sintering gas medium of H_(2)O-H_(2)-N_(2)-O_(2) with the blown steam improved the heat transfer conditions of fuel combustion and promoted the water gas reaction.The optimum state of steam injection was achieved at 15 min after ignition with 0.02 m^(3) min^(-1).The CO emission reduction is 10.91% compared with the base case.The combustion efficiency was 88.83%,6.15% higher than conventional sintering,and the solid fuel consumption was reduced by 1.15 kg t^(-1).It was indicated that steam injection would improve combustion efficiency and reduce solid fuel consumption.Meanwhile,the steam injection could improve the combustion kinetic conditions in the zone of unburned fuel and low oxygen partial pressure.It was conducive to the reaction of H_(2)O with C and CO to convert the CO of reducing atmosphere to CO_(2),which in turn realized the complete combustion of fuel and CO and improved the efficiency of fuel combustion.
基金supported by the Fund of Advance Research Projects of Manned Spaceflight,China(No.050303).
文摘Experiments were conducted to determine the effects of the mixing section configurations on the Mg-CO_(2)Martian ramjet combustion efficiency.It was carried out at a mainstream mass flow rate of 110 g/s and a temperature of 810 K.The chamber pressure was measured under different configurations and Oxidizer to Fuel(O/F)ratios.Results showed that the engine achieved self-sustaining combustion and worked stably during experiments.The pre-combustion chamber is needed to increase the combustion efficiency and promote the full combustion of the powder.After the configuration of the pre-combustion chamber,the best combustion efficiency reached 80%when radial powder injection and lateral carbon dioxide intake were used.In addition,the O/F ratio in the pre-combustion chamber decreased from 0.67 to 0.31,resulting in an 8%increase in the combustion efficiency.It was speculated that different mixing section configurations and the variations in an O/F ratio within the pre-combustion chamber impacted the combustion efficiency and in essence,all affected the flow velocity and residence time of the two-phase flow in the com-bustion chamber.
文摘The carbon content in the fly ash from most Chinese circulating fluidized bed (CFB) boilers is much higher than expected, thus directly influencing the combustion efficiency. In the present paper, carbon burnout was investigated both in field tests and laboratory experiments. The effect of coal property, operation condition, gas-solid mixing, char deactivation, residence time and cyclone performance are analyzed seriatim based on large amount of experimental results. A coal index is proposed to describe the coal rank, defined by the ratio of the volatile content to the coal heat value, is a useful parameter to analyze the char burnout. The carbon content in the fly ash depends on the coal rank strongly. CFB boilers burning anthracite, which has low coal index, usually have high carbon content in the fly ash. On the contrary, the CFB boilers burning brown coal, which has high coal index, normally have low carbon content. Poor gas-solid mixing in the furnace is another important reason of the higher carbon content in the fly ash. Increasing the velocity and rigidity of the secondary air could extend the penetration depth and induce more oxygen into the furnace center. Better gas solid mixing will decrease the lean oxygen core area and increase char combustion efficiency. The fine char particles could be divided into two groups according to their reactivity. One group is 'fresh' char particles with high reactivity and certain amount of volatile content. The other group of char particles has experienced sufficient combustion time both in the furnace and in the cyclone, with nearly no volatile. These 'old' chars in the fly ash will be deactivated during combustion of large coal particles and have very low carbon reactivity. The generated fine inert char particles by attrition of large coal particles could not easily burn out even with the fly ash recirculation. The fraction of large coal particles in coal feed should be reduced during fuel preparation process. The cyclone efficiency controls the particle residence time in CFB loop, especially for that of the fine particles. So the cyclone efficiency, especially the cut size, will greatly influence the carbon content in the fly ash.
文摘A scramjet engine combustion efficiency measure system was designed.The combustion efficiency was measured by chromatography method,and the results of chromatography method were compared with those of temperature method.The results indicate that the combustion efficiency measured by chromatography method was 80.7%,lower than the combustion efficiency of 84.5%measured by temperature method;the combustion efficiency could be measured more precisely by chromatogram method than by temperature method.The combustion efficiency measure system based on chromatogram method can work well,and thus can be used to measure the combustion efficiency of scramjet engine.
文摘Nanothermites have been employed as fuel additives in energetic formulations due to their higher energy density over CHNO energetics. Nevertheless, sintering and degradation of nanoparticles significantly limit the practical use of nanothermites. In this work, combustion characteristic and aging behavior of aluminum/iron oxide(Al/Fe2O3) nanothermite mixtures were investigated in the presence of micron-scale nickel aimed to produce bimetal thermite powders. The results showed that the alumina content in the combustion residue increased from 88.3% for Al/Fe2O3 nanothermite to 96.5% for the nanothermite mixture containing 20 wt% nickel. Finer particle sizes of combustion residue were obtained for the nanothermite mixtures containing nickel, indicative of the reduced agglomeration. Both results suggested a more complete combustion in the bimetal thermite powders. Aging behavior of the nanothermite mixture was also assessed by measuring the heat of combustion of the mixture before and after aging process. The reduction in heat of combustion of nanothermite mixtures containing nickel was less severe as compared to a significant decrease for the nanothermite mixture without nickel, indicating better aging resistance of the bimetal thermite powders.
基金Project(51606220)supported by the National Natural Science Foundation of ChinaProject(1194028)supported by the Beijing Natural Science Foundation,China。
文摘Plasma jet has been widely used in supersonic combustor as an effective ignition and combustion assisted method,but currently it is mostly combined with the traditional wall fuel injection method,while the application combined with the central fuel injection method is less.In order to expand the combustion range,the plasma jet was introduced into a strut-cavity combustor with an alternating-wedge.The effects of total pressure of strut fuel injection,total pressure of cavity fuel injection,total pressure of plasma jet injection and plasma jet media on the combustion characteristics were analyzed in supersonic flow by numerical calculations in a three-dimensional domain.The combustion field structure,wall pressure distribution,combustion efficiency and distribution of H2O at the exit of the combustor with different injection conditions were analyzed.The results show that the combustion efficiency decreases with the increase of the strut fuel injection total pressure.However,the combustion area downstream increases when the total pressure of the strut fuel injection increases within the proper range.The combustion range is expanded and the combustion efficiency is improved when the cavity fuel injection total pressure is increased within the range of 0.5−2.0 MPa,but a sharp drop in combustion efficiency can be found due to limited fuel mixing when the total injection pressure of the cavity fuel is excessively increased.With the increased total injection pressure of the plasma jet,the height of the cavity shear layer is raised and the equivalence ratio of the gas mixture in the cavity is improved.When the total pressure of the plasma jet is 1.25 MPa,the combustion efficiency reaches a maximum of 82.1%.The combustion-assisted effect of different plasma jet media is significantly different.When the medium of the plasma jet is O2,the combustion-assisted effect on the combustor is most significant.
文摘In order to address typical problems due to the huge demand of oil for consumption in traditional internal combustion engines,a new more efficient combustion mode is proposed and studied in the framework of Computational Fluid Dynamics(CFD).Moreover,a Non-dominated Sorting Genetic Algorithm(NSGA-Ⅱ)is applied to optimize the related parameters,namely,the engine methanol ratio,the fuel injection time,the initial temperature,the Exhaust Gas Re-Circulation(EGR)rate,and the initial pressure.The so-called Conventional Diesel Combustion(CDC),Homogeneous Charge Compression Ignition(HCCI)and the Reactivity Controlled Compression Ignition(RCCI)combustion modes are compared.The results show that RCCI has a higher methanol ratio and an earlier injection timing with moderate EGR rate and higher initial pressure.The initial temperature increases as the methanol ratio increases.In comparison,CDC has the lowest hydrocarbon and CO emissions and the highest combustion efficiency.At different crankshaft rotation angles corresponding to 50%of the combustion amount(CA50),the combustion temperature and boundary layer temperature of HCCI change significantly,while those of RCCI undergo limited variations.At the same CA50,the exergy losses of HCCI and RCCI are lower than that of the CDC.On the basis of these findings,it can be concluded that the methanol/diesel RCCI engine can be used to obtain a clean and efficient combustion process,which should be regarded as a promising combustion mode.
文摘The aim of the present study is to develop the biomass furnace combustor which can effectively employ four unused biomasses, i.e., wood bark, wood branch, bamboo, and grass as a fuel. Emphasis is placed on the combustion gas components and combustion gas temperature in the combustor. It is found from the study that： （1） Four unused biomasses can take plate self combustion and the stable combustion yield; （2） Different combustion temperature distribution appears in combustor and is affected by each biomass; （3） The concentrations of nitrogen oxide and sulfur oxides are lower than the discharge standard value; （4） Higher thermal efficiency yields for bark, bamboo and grass.
基金supported by the National Natural Science Foundation of China(Nos.22375164,21975066 and U2241250)the Key Research and Development Program of Shaanxi,China(No.2023KJXX-005)。
文摘A novel constant-pressure and constant-quenching distance Condensed Combustion Products(CCPs)collection system was developed,coupled with a timing control system,to collect the CCPs formed in the course of burning of aluminum-based composite propellants.The effects of adiabatic graphite plating,collection zone,quenching distance,time series of collection,and propellant burning rate on the microscopic morphology,particle size distribution and unburned aluminum content of CCPs were investigated.It was verified that the graphite plating can provide a high-fidelity high-temperature environment for propellant combustion.The combustion efficiency is improved by 2.44% compared to the bare propellant case.The time series of collection has a significant effect on the combustion efficiency of aluminum,and the combustion efficiency of aluminum in the thermal state(1.2-2.4 s)is 2.75% higher than that in the cold state(0-1.2 s).Similarly,the characteristics of the CCPs in different collection zones are different.At the quenching distance of 5 mm,the combustion efficiency of aluminum in the core zone(85.39%)is much lower than that in the outer zone(92.07%),while the particle size of the CCPs in the core zone(172μm)is larger than that in the outer zone(41μm).This indicates that the core zone is more likely to produce large-sized and incompletely burned agglomerates during the propellant combustion process.Different burning rates also lead to a significant difference in particle size distribution and combustion efficiency.High burning rates result in higher combustion efficiency.A detailed sequence of the elaborative collection process of CCPs is proposed,mainly including the setting of ignition delay time,burning rate,working pressure,plating length and time series of collection.The findings of this study are expected to provide a reliable tool for the evaluation of the combustion efficiency of solid propellants.
基金supported by the Laboratory of Space Utilization and D-Drive Project,Hokkaido University,Japan。
文摘This review examines the potential of hydrogen,ammonia,and biodiesel as alternative fuels,focusing on spray dynamics,droplet evaporation,combustion,and emissions.Hydrogen offers superior combustion characteristics but faces challenges in NO_(x)emissions.Strategies like nonpremixed direct injection,increased intake boost pressure,and low-pressure EGR are suggested for robust hydrogen combustion in compression-ignition engines.Control of hydrogen start of injection(SOI)and water injection(WI)are identified as effective techniques for reducing NO_(x)emissions.Ammonia shows inferior combustion and higher NO_(x)and unburned NH_(3)emissions in the same conditions as conventional fuels with conventional engines.Understanding ammonia spray and evaporation conditions is significant for optimizing an ammonia-air mixture and minimizing wall impingement and ammonia trap in the crevice,thereby improving combustion and emission reduction.Increasing intake pressure,injection pressure,and EGR rate,employing a turbulent jet,and preheating ammonia improve efficiency and reduce NO_(x)emissions.Utilizing ammonia combustion requires the implementation of after-treatment systems such as NH_(3)adsorber and De NO_(x)catalysts to mitigate unburned NH_(3)and NO_(x)emissions.Biodiesel affects the fuel supply system,combustion,and emission characteristics according to its viscosity and density.Increasing injection pressure and blending with volatile fuels enhance spray and combustion.Optimum biodiesel preheating temperatures for the injection pump and injector are crucial for achieving the best pump capacity and spray formation.By utilizing biodiesel-PODE blends and investigating low-temperature biodiesel combustions,there is potential to improve thermal efficiency and PMNO_(x)trade-off.Therefore,carbon-neutral fuel adoption should be accelerated to mitigate CO_(2)emissions,highlighting the importance of combustion techniques and emissions reduction strategies.
基金supported by the Ministry of Science and Technology of China(Grant No.2022YFE0209000)the Shanghai Rising-Star Program(Grant No.21QB1403900)Shanghai Municipal Commission of Science and Technology(Grant No.22170712600)。
文摘Thermochemical recuperation heat recovery is an advanced waste heat utilization technology that can effectively recover exhaust waste heat from oxy-fuel Stirling engines.The novel combustor of a Stirling engine with thermochemical recuperation heat recovery system is expected to utilize both reformed gas and diesel fuels as sources of combustion.In this research,the effects of various factors,including the H_(2)O addition,fuel distribution ratio(FDR),excess oxygen coefficient,and cyclone structure on the temperature distribution in the combustor,combustion emissions,and external combustion system efficiency of the Stirling engine were experimentally investigated.With the increase of steam-to-carbon ratio(S/C),the temperature difference between the upper and lower heating tubes reduces and the circumferential temperature fluctuation decreases,and the combustion of diesel and reformed gas remains close to complete combustion.At S/C=2,the external combustion efficiency is 80.6%,indicating a 1.6%decrease compared to conventional combustion.With the increase of FDR,the temperature uniformity of the heater tube is improved,and the CO and HC emissions decrease.However,the impact of the FDR on the maximum temperature difference and temperature fluctuation across the heater is insignificant.When the FDR rises from 21%to 38%,the external combustion efficiency increases from 87.4%to92.3%.The excess oxygen coefficient plays a secondary role in influencing temperature uniformity and temperature difference,and the reformed gas and diesel fuel can be burned efficiently at a low excess oxygen coefficient of 1.04.With an increase in the cyclone angle,the heater tube temperature increases,while the maximum temperature difference at the lower part decreases,and the temperature fluctuation increases.Simultaneously,the CO and HC emissions increase,and the external combustion efficiency experiences a decrease.A cyclone angle of 30°is found to be an appropriate value for achieving optimal mixing between reformed gas and diesel fuel.The research findings present valuable new insights that can be utilized to enhance the performance optimization of Stirling engines.
基金supported by the National Key R&D Program of China(grant No.2020YFC1910000).
文摘Aluminum is an attractive alternative fuel,but it burns very inefficiently due to the formation of a dense Al_(2)O_(3)layer which prevents O_(2)from diffusion to the surface of Al particles.In previous experiments,the combustion of millimeter-sized Al(mAl)particles in the fluidized bed has achieved a substantial increase in the combustion efficiency,but further improvements are still needed.In this study,the effects of reaction atmosphere on the fluidized combustion of mAl particles were investigated.The experiments with different O_(2)/H_(2)O/CO_(2)concentrations were conducted.The experimental results indicate that the combustion efficiency of mAl particles in fluidized bed increases as the mole fraction of O_(2),H_(2)O or CO_(2)increases,and the highest combustion efficiency can reach 38.7%.After the analysis of the oxide film on the surface of aluminum particles,it was found that it is easier to generate the unstableθ-Al_(2)O_(3)under CO_(2)atmosphere,and it is easier to generate the unstableγ-Al_(2)O_(3)andθ-Al_(2)O_(3)under H_(2)O atmosphere.The unstable Al_(2)O_(3)film is more likely to be abraded in the fluidized bed,which leads to the effective improvement of the combustion efficiency.
基金supported by the National Natural Science Foundation of China (10672169, 10621202)
文摘Supersonic model combustors using two-stage injections of supercritical kerosene were experimentally investigated in both Mach 2.5 and 3.0 model combustors with stagnation temperatures of approximately 1,750 K. Supercritical kerosene of approximately 760 K was prepared and injected in the overall equivalence ratio range of 0.5-1.46. Two pairs of integrated injector/flameholder cavity modules in tandem were used to facilitate fuel-air mixing and stable combustion. For single-stage fuel injection at an upstream location, it was found that the boundary layer separation could propagate into the isolator with increasing fuel equivalence ratio due to excessive local heat release, which in turns changed the entry airflow conditions. Moving the fuel injection to a further downstream location could alleviate the problem, while it would result in a decrease in combustion efficiency due to shorter fuel residence time. With two-stage fuel injections the overall combustor performance was shown to be improved and kerosene injections at fuel rich conditions could be reached without the upstream propagation of the boundary layer separation into the isolator. Furthermore, effects of the entry Mach number and pilot hydrogen on combustion performance were also studied.
文摘This study was performed to estimate the emission of non-CO 2 greenhouse gases(GHGs) from biomass burning at a large fire area.The extended methodology adopted the IPCC Guidelines(2003) equation for use on data from the Samcheok forest fire gathered using 30 m resolution Landsat TM satellite imagery,digital forest type maps,and growing stock information per hectare by forest type in 1999.Normalized burn ratio(NBR) technique was employed to analyze the area and severity of the Samcheok forest fire that occurred in 2000.The differences between NBR from pre-and post-fire datasets are examined to determine the extent and degree of change detected from burning.The results of burn severity analysis by dNBR of the Samcheok forest fire area revealed that a total of 16,200 ha of forest were burned.The proportion of the area characterized by a 'Low' burn severity(dNBR below 152) was 35%,with 'Moderate'(dNBR 153-190) and 'High'(dNBR 191-255) areas were at 33% and 32%,respectively.The combustion efficiency for burn severity was calculated as 0.43 for crown fire where burn severity was 'High',as 0.40 for 'Moderate' severity,and 0.15 for 'Low' severity surface fire.The emission factors for estimating non-CO 2 GHGs were separately applied to CO 130,CH 4 9,NO x 0.7 and N 2 O 0.11.Non-CO 2 GHGs emissions from biomass burning in the Samcheok forest fire area were estimated to be CO 44.100,CH 4 3.053,NO x 0.238 and N 2 O 0.038 Gg.
基金supported by the National Science and Technology Major Project(No.2017-III-0008-0034)。
文摘The structure of the trapped-vortex cavity and radial flameholder can maintain stable combustion under severe conditions,such as sub-atmospheric pressure and high inlet velocity.This article reports a complete study of combustion characteristics for this design.The flow field of the physical model was obtained by numerical simulation.The pilot combustion characteristics,including the combustion process,combustion efficiency,and wall temperature distribution,were studied by experiments.The pilot combustion can be divided into three modes under different fuel flow rates and inlet conditions.In“cavity maintained(CM)”mode,pilot flame exists at both sides of the cavity zone,rotating with the main vortex.In“cavity-flameholder maintained(CFM)”mode,the combustion process occurs both inside the cavity and behind the flameholder.While in“flameholder maintained(FM)”mode,the cavity will quench,and the combustion is maintained by the radial flameholder only.Due to the difference in the flow field,the flame pattern and propagation direction vary under different combustion modes.The combustion efficiency,influenced by combustion modes,shows an increase-decrease-increase curve.The wall temperature distribution is also affected;the cavity wall temperature decreases under large fuel flux while the temperature of the burner-back plate continues to rise to a maximum value.
基金supported by the National Natural Science Foundation of China(No.52274344)Provincial Natural Science Foundation of Hunan(No.2022JJ30723)+1 种基金Independent Exploration and Innovation Project of graduate students of Central South University,Hunan Provincial Science and Technology Achievement Transformation and Industrialization Program(No.2020GK4055)China Baowu Low Carbon Metallurgy Innovation Foundation(No.BWLCF202118).
文摘Iron ore sintering process is the main CO_(2) emission source throughout the integrate steelworks,which primarily comes from the combustion of solid fuels.Improving the combustion efficiency and reducing the solid fuel consumption are important ways to reduce the CO_(2) emission in the sintering process.Around the efficient combustion of fuel,the migration behavior and combustion characteristics of solid fuel in the granulation process were investigated.The results indicated that during the granulation process,fuel particles with size less than 0.5 mm mainly migrated into the granules with grain size of 1-3,3-5 and 5-8 mm;fuel particles with size of 0.5^(-1)mm mainly migrated into granules of 1-3 mm;fuel particles with size of 1-3,3-5 and 5-8 mm mainly entered the granules with the same grain size.With the increase in fuel particles grain size from-0.5 to+8 mm,the combustion efficiency exhibited a firstly-increasing and then decreasing tendency,while the NO_(x) exhibited a decreasing tendency.Potential reason can be described that finer fuel particles(-1 mm)easily distributed in the outer layer of the granules,which combusted fiercely due to its larger specific surface area,leading to the development of incomplete combustion and the conversion of fuel nitrogen;the combustion efficiency of larger fuel particles was restricted by the inner diffusion of O_(2),which then contributed to the reduction of NO_(x) under the inadequate combustion atmosphere.
基金support of the National Natural Science Foundation of China(Nos.51978404,42105100,and 41977180)the Guangdong Basic and Applied Basic Research Foundation(China)(Nos.2021A1515110297 and 2022A1515010866)the Basic Research of Shenzhen Science and Technology Innovation Commission(China)(No.JCYJ20190808145218827).
文摘On-road tailpipe ammonia (NH3) emissions contribute to urban secondary organic aerosol formation and have direct or indirect adverse impacts on the environment and human health. To understand the tailpipe NH3 emission characteristics, we performed comprehensive chassis dynamometer measurements of NH3 emission from two China 5 and two China 6 light-duty gasoline vehicles (LDGVs) equipped with three-way catalytic converters (TWCs). The results showed that the distance-based emission factors (EFs) were 12.72 ± 2.68 and 3.18 ± 1.37 mg/km for China 5 and China 6 LDGVs, respectively. Upgrades in emission standards were associated with a reduction in tailpipe NH3 emission. In addition, high NH3 EFs were observed during the engine warm-up period in cold-start cases owing to the intensive emissions of incomplete combustion products and suitable catalytic temperature in the TWCs. Notably, based on the instantaneous NH3 emission rate, distinct NH3–emitting events were detected under high/extra high velocity or rapid acceleration. Furthermore, NH3 emission rates correlated well with engine speed, vehicle specific power, and modified combustion efficiency, which were more easily accessible. These strong correlations were applied to reproduce NH3 emissions from China 5/6 LDGVs. The predicted NH3 EFs under different dynamometer and real-world cycles agreed well with existing measurement and prediction results, revealing that the NH3 EFs of LDGVs in urban routes were within 8.55–11.62 mg/km. The results presented here substantially contribute to improving the NH3 emission inventory for LDGVs and predicting on-road NH3 emissions in China.
文摘This paper presents the combustion characteristics in hybrid rocket motors with multisegmented grain through three-dimensional numerical simulations.Multi-segmented grain is composed of several thin grains with two or more ports.The numerical model consists of Navier-Stokes equations with turbulence,solid fuel pyrolysis,chemical reactions,a fluid–solid coupling model and a regression rate model.The simulations adopt 90%Hydrogen Peroxide(HP)and PolyEthylene(PE)as the propellant combination.The effects of the rotation,port number,fuel grain segment number and mid-chamber length on the flow field and combustion performances are analyzed.The results indicate that the multi-segmented grain configuration can strengthen the flow field,and the regression rate and combustion efficiency are enhanced.Take the cases with two grain segments and three ports for example,the regression rate is increased by 32.4%-45.1%and the combustion efficiency increases by 6%-8.6%in different rotation angles.
