Radiative imaging of combustion flame in furnace of power plant plays an increasingly important role in combustion diagnosis. This paper presents a new method for calculating the radiative imaging of three-dimensional...Radiative imaging of combustion flame in furnace of power plant plays an increasingly important role in combustion diagnosis. This paper presents a new method for calculating the radiative imaging of three-dimensional (3D) combustion flame based on Monte Carlo method and optical lens imaging. Numerical simulation case was used in this study. Radiative images were calculated and images obtained can not only present the energy distribution on the charge-coupled device (CCD) camera target plane but also reflect the energy distribution condition in the simulation furnace. Finally the relationships between volume ele- ments and energy shares were also discussed.展开更多
The flame propagation processes of MgH_(2)dust clouds with four different particle sizes were recorded by a high-speed camera.The dynamic flame temperature distributions of MgH_(2)dust clouds were reconstructed by the...The flame propagation processes of MgH_(2)dust clouds with four different particle sizes were recorded by a high-speed camera.The dynamic flame temperature distributions of MgH_(2)dust clouds were reconstructed by the two-color pyrometer technique,and the chemical composition of solid combustion residues were analyzed.The experimental results showed that the average flame propagation velocities of 23μm,40μm,60μm and 103μm MgH_(2)dust clouds in the stable propagation stage were 3.7 m/s,2.8 m/s,2.1 m/s and 0.9 m/s,respectively.The dust clouds with smaller particle sizes had faster flame propagation velocity and stronger oscillation intensity,and their flame temperature distributions were more even and the temperature gradients were smaller.The flame structures of MgH_(2)dust clouds were significantly affected by the particle sinking velocity,and the combustion processes were accompanied by micro-explosion of particles.The falling velocities of 23μm and 40μm MgH_(2)particles were 2.24 cm/s and 6.71 cm/s,respectively.While the falling velocities of 60μm and 103μm MgH_(2)particles were as high as 15.07 cm/s and 44.42 cm/s,respectively,leading to a more rapid downward development and irregular shape of the flame.Furthermore,the dehydrogenation reaction had a significant effect on the combustion performance of MgH_(2)dust.The combustion of H_(2)enhanced the ignition and combustion characteristics of MgH_(2)dust,resulting in a much higher explosion power than the pure Mg dust.The micro-structure characteristics and combustion residues composition analysis of MgH_(2)dust indicated that the combustion control mechanism of MgH_(2)dust flame was mainly the heterogeneous reaction,which was affected by the dehydrogenation reaction.展开更多
A scramjet combustor with double cavitybased flameholders was experimentally studied in a directconnected test bed with the inflow conditions of M = 2.64,Pt = 1.84 MPa,Tt = 1 300 K.Successful ignition and selfsustaine...A scramjet combustor with double cavitybased flameholders was experimentally studied in a directconnected test bed with the inflow conditions of M = 2.64,Pt = 1.84 MPa,Tt = 1 300 K.Successful ignition and selfsustained combustion with room temperature kerosene was achieved using pilot hydrogen,and kerosene was vertically injected into the combustor through 4×φ 0.5 mm holes mounted on the wall.For different equivalence ratios and different injection schemes with both tandem cavities and parallel cavities,flow fields were obtained and compared using a high speed camera and a Schlieren system.Results revealed that the combustor inside the flow field was greatly influenced by the cavity installation scheme,cavities in tandem easily to form a single side flame distribution,and cavities in parallel are more likely to form a joint flame,forming a choked combustion mode.The supersonic combustion flame was a kind of diffusion flame and there were two kinds of combustion modes.In the unchoked combustion mode,both subsonic and supersonic combustion regions existed.While in the choked mode,the combustion region was fully subsonic with strong shock propagating upstream.Results also showed that there was a balance point between the boundary separation and shock enhanced combustion,depending on the intensity of heat release.展开更多
Recently,plasma-assisted combustion has become a potentially applicable technology in many combustion scenarios.In this paper,a dielectric barrier discharge（DBD） plasma generator is designed to explore the effect of...Recently,plasma-assisted combustion has become a potentially applicable technology in many combustion scenarios.In this paper,a dielectric barrier discharge（DBD） plasma generator is designed to explore the effect of plasma on the CH4 oxidation process,and several properties of combustion are considered.First,in the presence or absence of plasma discharge,physical appearance of the flame is examined and analyzed.Second,the flame propagation velocity is calculated by the flame front extracted from the imaging data with the Bunsen burner method.Finally,the main molecular components and their intensity variation in the flame and the plasma zones are identified with an emission spectrograph to analyze the effect of active species on the combustion process.We also discuss the possible kinetic regime of plasma-assisted combustion.Experimental results imply that plasma discharge applied to the premixed CH_4/O_2/He mixture significantly raises the flame speed with equivalence ratios ranging from 0.85 to 1.10,with the flame speed improved by 17%to 35%.It can be seen that plasma can improve methane oxidation efficiency in the premixed fuel/oxidizer,especially at a low equivalence ratio.展开更多
Various semicokes were obtained from medium-low temperature pyrolysis of Dongrong long flame coal.The proximate analysis,calorific value and Hardgrove grindability index(HGI) of semicokes were determined,and the ignit...Various semicokes were obtained from medium-low temperature pyrolysis of Dongrong long flame coal.The proximate analysis,calorific value and Hardgrove grindability index(HGI) of semicokes were determined,and the ignition temperature,burnout temperature,ignition index,burnout index,burnout ratio,combustion characteristic index of semicokes were measured and analyzed using thermogravimetry analysis(TGA).The effects of pyrolysis temperature,heating rate,and pyrolysis time on yield,composition and calorific value of long flame coal derived semicokes were investigated,especially the influence of pyrolysis temperature on combustion characteristics and grindability of the semicokes was studied combined with X-ray diffraction(XRD) analysis of semicokes.The results show that the volatile content,ash content and calorific value of semicokes pyrolyzed at all process parameters studied meet the technical specifications of the pulverized coal-fired furnaces(PCFF) referring to China Standards GB/T 7562-1998.The pyrolysis temperature is the most influential factor among pyrolysis process parameters.As pyrolysis temperature increases,the yield,ignition index,combustion reactivity and burnout index of semicokes show a decreasing tend,but the ash content increases.In the range of 400 and 450 °C,the grindability of semicokes is rational,especially the grindability of semicokes pyrolyzed at 450 °C is suitable.Except for the decrease of volatile content and increase of ash content,the decrease of combustion performance of semicokes pyrolyzed at higher temperature should be attributed to the improvement of the degree of structural ordering and the increase of aromaticity and average crystallite size of char.It is concluded that the semicokes pyrolyzed at the temperature of 450 °C is the proper fuel for PCFF.展开更多
9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide( DOPO)-based flame retardant( DOPO-DOPC) which contains carbon source was used to improve the flame retardancy of poly( ethylene terephthalate)( PET) fabrics. The pr...9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide( DOPO)-based flame retardant( DOPO-DOPC) which contains carbon source was used to improve the flame retardancy of poly( ethylene terephthalate)( PET) fabrics. The prepared DOPODOPC dispersion was applied onto PET fabrics via two kinds of processes,thermosol process and exhaustion process,and in the later using it alone or together with disperse dyes. The flame retardancy of PET fabrics was determined by limiting oxygen index( LOI) and vertical burning test. The results showed that DOPODOPC could obviously improve the flame retardancy of PET fabrics.The PET fabric treated by 60 g/L DOPO-DOPC dispersion via exhaustion process achieved an LOI value of 32. 3%,for example.The flame retardancy and dyeing performances showed that DOPODOPC dispersion could be used together with a part of disperse dyes in one bath. The thermal stability of DOPO-DOPC and the treated PET fabrics were investigated by thermogravimetric analysis( TGA). And the flame retardant mechanism of DOPO-DOPC treated PET fabrics was further investigated by pyrolysis-gas chromatography/mass spectrometry( Py-GC/MS), Fourier transform infrared spectroscopy( FTIR) and scanning electron microscopy( SEM).展开更多
Metal particles such as aluminum（ Al）,magnesium（ Mg）,boron（ B） and nickel（ Ni）,as well as Mg/Al alloy（ Mg/Al = 3/4） are currently the most widely used ingredients in modified doublebase propellants. In this ...Metal particles such as aluminum（ Al）,magnesium（ Mg）,boron（ B） and nickel（ Ni）,as well as Mg/Al alloy（ Mg/Al = 3/4） are currently the most widely used ingredients in modified doublebase propellants. In this contribution,the combustion properties of the metal species are studied by means of the high-speed photography technique and the non-contact wavelet-based measurement of flame temperature distribution. The combustion process of the Al,Mg and Mg/Al samples shows both gas phase reaction and surface oxidation,which yield volatile and nonvolatile products,corresponding to the oxide and suboxide respectively. However,the combustion of B and Ni shows only gas phase reaction,due to their high melting point as well as high enthalpy of vaporization. In addition to the experiments,a hypothetical combustion model has been proposed to clarify the combustion characteristics of metal species in modified double-base propellants.展开更多
A one-step method for continuous large-scale synthesis of well-defined hollow titania spheres was established by feeding titanium tetrachloride mixed with ethanol vapor to a facile diffusion flame. A mixture of TiCl4 ...A one-step method for continuous large-scale synthesis of well-defined hollow titania spheres was established by feeding titanium tetrachloride mixed with ethanol vapor to a facile diffusion flame. A mixture of TiCl4 and C2H5OH vapor was transported at 100 m/s into a flame reactor and condensed into mesoscale droplets due to Joule-Thomson cooling and the entrainment of cool gases into the expanding high-speed jet. Hollow crystalline TiO2 spheres with good thermal stability were formed after the hydrolysis of TiCl4 in the H2/air flame at about 1500℃. Structural characterization indicates that the hollow spheres, with uniform diameter of 300 nm and shell thickness of 35 rim, consist of 20-30 nm TiO2 nanocrystallites. A formation mechanism of the hollow spheres was proposed, involving the competition between chemical reaction and diffusion during the flame process. The present study provides a new pathway for continuous and large-scale engineering of hollow nanomaterials.展开更多
In this study, piperazine-modified ammonium polyphosphates（PA-APPs） with hierarchical structure were synthesized through ion exchange reaction. ^1H nuclear magnetic resonance（^1H-NMR）, Fourier transform infrared s...In this study, piperazine-modified ammonium polyphosphates（PA-APPs） with hierarchical structure were synthesized through ion exchange reaction. ^1H nuclear magnetic resonance（^1H-NMR）, Fourier transform infrared spectra（FTIR）, elemental analysis（EA）, and inductively coupled plasma atomic emission spectroscopy（ICP-AES） confirmed that the PA-APPs with different structures were prepared successfully. Then these flame retardants were used alone as monocomponent intumescent flame retardant for low-density polyethylene（LDPE）. Combustion tests demonstrated that the flameretardant efficiency of PA-APP containing about 7 wt% carbon（PA-APP_7） was significantly higher than that of the other PAAPPs with more or less carbon. The flame-retarded LDPE system with 30 wt% PA-APP_7 passed the UL-94 V-0 rating, and had the oxygen index（LOI） of 33.0%. Thermal analysis illustrated that the thermal decomposition behavior of PA-APP changed with incorporating different contents of PA. For all these PA-APPs, PA-APP_7 showed higher thermal stability than the other PA-APP flame retardants. All the experimental results proved that PA-APP_7 could reach the balance of an acid source, a blowing source, and a charring source as a mono-component intumescent flame retardant for LDPE. Further, it led to the formation of a compact intumescent char layer containing the structures of rich P―O―P, P―N―C, C=C, etc. during burning which in turn resulted in the excellent flame-retardant efficiency of PA-APP7.展开更多
Cryogenic propellants LOx/H2 are used at very high pressure in rocket engine combustion. The description of the combustion process in such application is very complex due essentially to the supercritical regime. Ideal...Cryogenic propellants LOx/H2 are used at very high pressure in rocket engine combustion. The description of the combustion process in such application is very complex due essentially to the supercritical regime. Ideal gas law becomes invalid. In order to try to capture the average characteristics of this combustion process, numerical computations are performed using a model based on a one-phase multi-component approach. Such work requires fluid properties and a correct definition of the mixture behavior generally described by cubic equations of state with appropriated thermodynamic relations validated against the NIST data. In this study we consider an alternative way to get the effect of real gas by testing the volume-weighted-mixing-law with association of the component transport properties using directly the NIST library data fitting including the supercritical regime range. The numerical simulations are carried out using 3D RANS approach associated with two tested turbulence models, the standard k-Epsilon model and the realizable k-Epsilon one. The combustion model is also associated with two chemical reaction mechanisms. The first one is a one-step generic chemical reaction and the second one is a two-step chemical reaction. The obtained results like temperature profiles, recirculation zones, visible flame lengths and distributions of OH species are discussed.展开更多
An experimental investigation on ignition characteristics with air-throttling in an ethylene-fueled scramjet under flight Ma 6.5 conditions was conducted.The dynamic process of air-throttling ignition was explored sys...An experimental investigation on ignition characteristics with air-throttling in an ethylene-fueled scramjet under flight Ma 6.5 conditions was conducted.The dynamic process of air-throttling ignition was explored systematically.The influences of throttling parameters,i.e.,throttling mass rate and duration,were investigated.When the throttling mass rate was 45% of the inflow mass rate,ambient ethylene could be ignited reliably.The delay time from ignition to throttling was about 45–55 ms.There was a threshold of throttling duration under a certain throttling mass rate.It was shorter than 100 ms when the throttling mass rate was 45%.While a 45%throttling mass rate would make the shock train propagate upstream to the isolator entry in about10–15 ms,four lower throttling mass rates were tested,including 30%,25%,20%,and 10%.All of these throttling mass rates could ignite ethylene.However,combustion performances varied with them.A higher throttling mass rate made more ethylene combust and produced higher wall pressure.Through these experiments,some aspects of the relationships between ignition,flame stabilization,combustion efficiency,and air-throttling parameters were brought to light.These results could also be a benchmark for CFD validation.展开更多
基金Project supported by National Natural Science Foundation of China(No. 60534030)Program for Changjiang Scholars and InnovativeResearch Team in University (No. IRT0434)
文摘Radiative imaging of combustion flame in furnace of power plant plays an increasingly important role in combustion diagnosis. This paper presents a new method for calculating the radiative imaging of three-dimensional (3D) combustion flame based on Monte Carlo method and optical lens imaging. Numerical simulation case was used in this study. Radiative images were calculated and images obtained can not only present the energy distribution on the charge-coupled device (CCD) camera target plane but also reflect the energy distribution condition in the simulation furnace. Finally the relationships between volume ele- ments and energy shares were also discussed.
基金supported by the National Natural Science Foundation of China(Grant Nos.12272001,11972046)the Outstanding Youth Project of Natural Science Foundation of Anhui Province(Grant No.2108085Y02)the Major Project of Anhui University Natural Science Foundation(Grant No.KJ2020ZD30)。
文摘The flame propagation processes of MgH_(2)dust clouds with four different particle sizes were recorded by a high-speed camera.The dynamic flame temperature distributions of MgH_(2)dust clouds were reconstructed by the two-color pyrometer technique,and the chemical composition of solid combustion residues were analyzed.The experimental results showed that the average flame propagation velocities of 23μm,40μm,60μm and 103μm MgH_(2)dust clouds in the stable propagation stage were 3.7 m/s,2.8 m/s,2.1 m/s and 0.9 m/s,respectively.The dust clouds with smaller particle sizes had faster flame propagation velocity and stronger oscillation intensity,and their flame temperature distributions were more even and the temperature gradients were smaller.The flame structures of MgH_(2)dust clouds were significantly affected by the particle sinking velocity,and the combustion processes were accompanied by micro-explosion of particles.The falling velocities of 23μm and 40μm MgH_(2)particles were 2.24 cm/s and 6.71 cm/s,respectively.While the falling velocities of 60μm and 103μm MgH_(2)particles were as high as 15.07 cm/s and 44.42 cm/s,respectively,leading to a more rapid downward development and irregular shape of the flame.Furthermore,the dehydrogenation reaction had a significant effect on the combustion performance of MgH_(2)dust.The combustion of H_(2)enhanced the ignition and combustion characteristics of MgH_(2)dust,resulting in a much higher explosion power than the pure Mg dust.The micro-structure characteristics and combustion residues composition analysis of MgH_(2)dust indicated that the combustion control mechanism of MgH_(2)dust flame was mainly the heterogeneous reaction,which was affected by the dehydrogenation reaction.
文摘A scramjet combustor with double cavitybased flameholders was experimentally studied in a directconnected test bed with the inflow conditions of M = 2.64,Pt = 1.84 MPa,Tt = 1 300 K.Successful ignition and selfsustained combustion with room temperature kerosene was achieved using pilot hydrogen,and kerosene was vertically injected into the combustor through 4×φ 0.5 mm holes mounted on the wall.For different equivalence ratios and different injection schemes with both tandem cavities and parallel cavities,flow fields were obtained and compared using a high speed camera and a Schlieren system.Results revealed that the combustor inside the flow field was greatly influenced by the cavity installation scheme,cavities in tandem easily to form a single side flame distribution,and cavities in parallel are more likely to form a joint flame,forming a choked combustion mode.The supersonic combustion flame was a kind of diffusion flame and there were two kinds of combustion modes.In the unchoked combustion mode,both subsonic and supersonic combustion regions existed.While in the choked mode,the combustion region was fully subsonic with strong shock propagating upstream.Results also showed that there was a balance point between the boundary separation and shock enhanced combustion,depending on the intensity of heat release.
基金supported by the Fundamental Research Funds for the Central Universities of China(No.xjj2013086)Natural Science Basic Research Plan in Shaanxi Province of China(No.2014JQ7254)National Natural Science Foundation of China(No.51477135)
文摘Recently,plasma-assisted combustion has become a potentially applicable technology in many combustion scenarios.In this paper,a dielectric barrier discharge（DBD） plasma generator is designed to explore the effect of plasma on the CH4 oxidation process,and several properties of combustion are considered.First,in the presence or absence of plasma discharge,physical appearance of the flame is examined and analyzed.Second,the flame propagation velocity is calculated by the flame front extracted from the imaging data with the Bunsen burner method.Finally,the main molecular components and their intensity variation in the flame and the plasma zones are identified with an emission spectrograph to analyze the effect of active species on the combustion process.We also discuss the possible kinetic regime of plasma-assisted combustion.Experimental results imply that plasma discharge applied to the premixed CH_4/O_2/He mixture significantly raises the flame speed with equivalence ratios ranging from 0.85 to 1.10,with the flame speed improved by 17%to 35%.It can be seen that plasma can improve methane oxidation efficiency in the premixed fuel/oxidizer,especially at a low equivalence ratio.
基金support from the Allocated Section of the Basic Fund for the Scientific Research and Operation of Central Universities of China (No.2009KH10)
文摘Various semicokes were obtained from medium-low temperature pyrolysis of Dongrong long flame coal.The proximate analysis,calorific value and Hardgrove grindability index(HGI) of semicokes were determined,and the ignition temperature,burnout temperature,ignition index,burnout index,burnout ratio,combustion characteristic index of semicokes were measured and analyzed using thermogravimetry analysis(TGA).The effects of pyrolysis temperature,heating rate,and pyrolysis time on yield,composition and calorific value of long flame coal derived semicokes were investigated,especially the influence of pyrolysis temperature on combustion characteristics and grindability of the semicokes was studied combined with X-ray diffraction(XRD) analysis of semicokes.The results show that the volatile content,ash content and calorific value of semicokes pyrolyzed at all process parameters studied meet the technical specifications of the pulverized coal-fired furnaces(PCFF) referring to China Standards GB/T 7562-1998.The pyrolysis temperature is the most influential factor among pyrolysis process parameters.As pyrolysis temperature increases,the yield,ignition index,combustion reactivity and burnout index of semicokes show a decreasing tend,but the ash content increases.In the range of 400 and 450 °C,the grindability of semicokes is rational,especially the grindability of semicokes pyrolyzed at 450 °C is suitable.Except for the decrease of volatile content and increase of ash content,the decrease of combustion performance of semicokes pyrolyzed at higher temperature should be attributed to the improvement of the degree of structural ordering and the increase of aromaticity and average crystallite size of char.It is concluded that the semicokes pyrolyzed at the temperature of 450 °C is the proper fuel for PCFF.
基金National High Technology Research and Development Program 863 Project,China(No.2013AA06A307)
文摘9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide( DOPO)-based flame retardant( DOPO-DOPC) which contains carbon source was used to improve the flame retardancy of poly( ethylene terephthalate)( PET) fabrics. The prepared DOPODOPC dispersion was applied onto PET fabrics via two kinds of processes,thermosol process and exhaustion process,and in the later using it alone or together with disperse dyes. The flame retardancy of PET fabrics was determined by limiting oxygen index( LOI) and vertical burning test. The results showed that DOPODOPC could obviously improve the flame retardancy of PET fabrics.The PET fabric treated by 60 g/L DOPO-DOPC dispersion via exhaustion process achieved an LOI value of 32. 3%,for example.The flame retardancy and dyeing performances showed that DOPODOPC dispersion could be used together with a part of disperse dyes in one bath. The thermal stability of DOPO-DOPC and the treated PET fabrics were investigated by thermogravimetric analysis( TGA). And the flame retardant mechanism of DOPO-DOPC treated PET fabrics was further investigated by pyrolysis-gas chromatography/mass spectrometry( Py-GC/MS), Fourier transform infrared spectroscopy( FTIR) and scanning electron microscopy( SEM).
基金Supported by the Science and Technology on Combustion and Explosion Laboratory Foundation(9140C350319140C35161)
文摘Metal particles such as aluminum（ Al）,magnesium（ Mg）,boron（ B） and nickel（ Ni）,as well as Mg/Al alloy（ Mg/Al = 3/4） are currently the most widely used ingredients in modified doublebase propellants. In this contribution,the combustion properties of the metal species are studied by means of the high-speed photography technique and the non-contact wavelet-based measurement of flame temperature distribution. The combustion process of the Al,Mg and Mg/Al samples shows both gas phase reaction and surface oxidation,which yield volatile and nonvolatile products,corresponding to the oxide and suboxide respectively. However,the combustion of B and Ni shows only gas phase reaction,due to their high melting point as well as high enthalpy of vaporization. In addition to the experiments,a hypothetical combustion model has been proposed to clarify the combustion characteristics of metal species in modified double-base propellants.
基金supported by the National Natural Science Foundation of China (20925621, 20706015, 20906027)the Program of Shanghai Subject Chief Scientist (08XD1401500)+2 种基金the Shanghai Shuguang Scholars Tracking Program (08GG09)the Special Projects for Key Laboratories in Shanghai (09DZ2202000)the Special Projects for Nanotechnology of Shanghai (0852nm02000,0952nm02100)
文摘A one-step method for continuous large-scale synthesis of well-defined hollow titania spheres was established by feeding titanium tetrachloride mixed with ethanol vapor to a facile diffusion flame. A mixture of TiCl4 and C2H5OH vapor was transported at 100 m/s into a flame reactor and condensed into mesoscale droplets due to Joule-Thomson cooling and the entrainment of cool gases into the expanding high-speed jet. Hollow crystalline TiO2 spheres with good thermal stability were formed after the hydrolysis of TiCl4 in the H2/air flame at about 1500℃. Structural characterization indicates that the hollow spheres, with uniform diameter of 300 nm and shell thickness of 35 rim, consist of 20-30 nm TiO2 nanocrystallites. A formation mechanism of the hollow spheres was proposed, involving the competition between chemical reaction and diffusion during the flame process. The present study provides a new pathway for continuous and large-scale engineering of hollow nanomaterials.
基金financially supported by the National Natural Science Foundation of China(No.51421061)the Program for Changjiang Scholars and Innovative Research Team in University(No.IRT1026)
文摘In this study, piperazine-modified ammonium polyphosphates（PA-APPs） with hierarchical structure were synthesized through ion exchange reaction. ^1H nuclear magnetic resonance（^1H-NMR）, Fourier transform infrared spectra（FTIR）, elemental analysis（EA）, and inductively coupled plasma atomic emission spectroscopy（ICP-AES） confirmed that the PA-APPs with different structures were prepared successfully. Then these flame retardants were used alone as monocomponent intumescent flame retardant for low-density polyethylene（LDPE）. Combustion tests demonstrated that the flameretardant efficiency of PA-APP containing about 7 wt% carbon（PA-APP_7） was significantly higher than that of the other PAAPPs with more or less carbon. The flame-retarded LDPE system with 30 wt% PA-APP_7 passed the UL-94 V-0 rating, and had the oxygen index（LOI） of 33.0%. Thermal analysis illustrated that the thermal decomposition behavior of PA-APP changed with incorporating different contents of PA. For all these PA-APPs, PA-APP_7 showed higher thermal stability than the other PA-APP flame retardants. All the experimental results proved that PA-APP_7 could reach the balance of an acid source, a blowing source, and a charring source as a mono-component intumescent flame retardant for LDPE. Further, it led to the formation of a compact intumescent char layer containing the structures of rich P―O―P, P―N―C, C=C, etc. during burning which in turn resulted in the excellent flame-retardant efficiency of PA-APP7.
文摘Cryogenic propellants LOx/H2 are used at very high pressure in rocket engine combustion. The description of the combustion process in such application is very complex due essentially to the supercritical regime. Ideal gas law becomes invalid. In order to try to capture the average characteristics of this combustion process, numerical computations are performed using a model based on a one-phase multi-component approach. Such work requires fluid properties and a correct definition of the mixture behavior generally described by cubic equations of state with appropriated thermodynamic relations validated against the NIST data. In this study we consider an alternative way to get the effect of real gas by testing the volume-weighted-mixing-law with association of the component transport properties using directly the NIST library data fitting including the supercritical regime range. The numerical simulations are carried out using 3D RANS approach associated with two tested turbulence models, the standard k-Epsilon model and the realizable k-Epsilon one. The combustion model is also associated with two chemical reaction mechanisms. The first one is a one-step generic chemical reaction and the second one is a two-step chemical reaction. The obtained results like temperature profiles, recirculation zones, visible flame lengths and distributions of OH species are discussed.
基金supported by the National Natural Science Foundation of China(No.51406222 and No.51376194)
文摘An experimental investigation on ignition characteristics with air-throttling in an ethylene-fueled scramjet under flight Ma 6.5 conditions was conducted.The dynamic process of air-throttling ignition was explored systematically.The influences of throttling parameters,i.e.,throttling mass rate and duration,were investigated.When the throttling mass rate was 45% of the inflow mass rate,ambient ethylene could be ignited reliably.The delay time from ignition to throttling was about 45–55 ms.There was a threshold of throttling duration under a certain throttling mass rate.It was shorter than 100 ms when the throttling mass rate was 45%.While a 45%throttling mass rate would make the shock train propagate upstream to the isolator entry in about10–15 ms,four lower throttling mass rates were tested,including 30%,25%,20%,and 10%.All of these throttling mass rates could ignite ethylene.However,combustion performances varied with them.A higher throttling mass rate made more ethylene combust and produced higher wall pressure.Through these experiments,some aspects of the relationships between ignition,flame stabilization,combustion efficiency,and air-throttling parameters were brought to light.These results could also be a benchmark for CFD validation.
