Regarding the research on alternatives for monopropellant hydrazine, several so called green propellants are currently under investigation or qualification. Aside others, the DLR Institute of Space Propulsion investig...Regarding the research on alternatives for monopropellant hydrazine, several so called green propellants are currently under investigation or qualification. Aside others, the DLR Institute of Space Propulsion investigates a N20/C2I-I4 premixed green propellant. During the research activities, flashback from the rocket combustion chamber into the feeding system has been identified as a major challenge when using the propellant mixture. This paper shows the results of ignition experiments conducted in a cylindrical, optical accessible ignition chamber. During the ignition and flame propagation process, pressure, temperature and high-speed video data were collected. The high speed video data were used to analyze the flame propagation speed. The obtained propagation speed was about 20 rn/s at ignition, while during further propagation of the flame speeds of up to 120 m/s were measured. Additionally, two different porous materials as flame arresting elements were tested： Porous stainless steel and porous bronze material. For both materials Peclet numbers for flashback were derived. The critical Peclet number for the sintered bronze material was around 20, while for the sintered stainless steel the critical Peclet number seems to be larger than 40. Due to the test results, sintered porous materials seem to be suitable as flashback arresters.展开更多
Hydrogen, the cleanest and most promising energy vector, can be produced by solar into chemical energy conversion, either by the photocatalytic direct splitting of water into Hand O, or, more efficiently,in the presen...Hydrogen, the cleanest and most promising energy vector, can be produced by solar into chemical energy conversion, either by the photocatalytic direct splitting of water into Hand O, or, more efficiently,in the presence of sacrificial reagents, e.g., in the so-called photoreforming of organics. Efficient photocatalytic materials should not only be able to exploit solar radiation to produce electron–hole pairs, but also ensure enough charge separation to allow electron transfer reactions, leading to solar energy driven thermodynamically up-hill processes. Recent achievements of our research group in the development and testing of innovative TiO-based photocatalytic materials are presented here, together with an overview on the mechanistic aspects of water photosplitting and photoreforming of organics. Photocatalytic materials were either（i） obtained by surface modification of commercial photocatalysts, or produced（ii） in powder form by different techniques, including traditional sol gel synthesis, aiming at engineering their electronic structure, and flame spray pyrolysis starting from organic solutions of the precursors, or（iii） in integrated form, to produce photoelectrodes within devices, by radio frequency magnetron sputtering or by electrochemical growth of nanotube architectures, or photocatalytic membranes, by supersonic cluster beam deposition.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
Kinetic analysis of coupled effects of CO2 and H2 additions on laminar lean premixed dimethyl ether flames is performed at atmospheric pressure. The coupled effects of H2/CO2 additions on major species, intermediate s...Kinetic analysis of coupled effects of CO2 and H2 additions on laminar lean premixed dimethyl ether flames is performed at atmospheric pressure. The coupled effects of H2/CO2 additions on major species, intermediate stable species and radicals are discussed and analyzed in detail. The dilution, thermal and chemical effects of H2 and CO2 are separated and identified. The results show that H2 addition can slightly mitigate the CO2 chemical effects on decreasing the temperatures, H radical concen- tration, acetylene mole fraction and formaldehyde concentration. After CO2 is added, the H2 chemical effects on increasing the temperatures are enhanced. DME oxidation is promoted by the H2 chemical effects, which is further strengthened by the CO2 addition. Moreover, CO2 addition can reduce the H2 chemical effects on increasing the H radical mole fraction, but strengthen the H2 chemical effects on increasing the production of HO2 and C2H2. CH2O formation can be promoted by the H2 chemical effects, which is enhanced by the CO2 addition. In actually, the H2/CO2 coupled chemical effects almost have no obvious in- fluence on the temperatures and HO2 mole fraction. DME consumption is delayed by the H2/CO2 coupled chemical effects. Furthermore, the H2/CO2 coupled chemical effects can decrease the H radical mole fraction, CH4 concentration, C2H2 mole fraction, CH2O concentration and CHaCHO mole fraction, but increase the CO concentration.展开更多
The two-phase volume-averaged model with the detailed chemistry reaction mechanism GRI 3.0 was adopted in the quasi-steady-state simulation of hydrogen production by CH4-rich filtration combustion in an alumina foam u...The two-phase volume-averaged model with the detailed chemistry reaction mechanism GRI 3.0 was adopted in the quasi-steady-state simulation of hydrogen production by CH4-rich filtration combustion in an alumina foam under fully developed conditions. The relations among the combustion wave velocity, the inlet gas velocity and the equivalence ratio were discussed, and their influences on the distributions of temperature and species in the alumina foam and on H2 yield, CH4 conversion, H2 selectivity and CO selectivity were analyzed in detail. The results show that the combustion wave velocity increases with the increase of equivalence ratio or inlet gas velocity. The H2 yield exceeded 50% with equivalence ratio between 2.0 and 3.0 and combustion wave velocity larger than 0.4 mm/s. The H2 selectivity exceeded 50% with equivalence ratio larger than 2.0 and CO selectivity exceeded 80% with equivalence ratio between 1.8 and 2.0 and combustion wave velocity larger than 0.4 mm/s.展开更多
文摘Regarding the research on alternatives for monopropellant hydrazine, several so called green propellants are currently under investigation or qualification. Aside others, the DLR Institute of Space Propulsion investigates a N20/C2I-I4 premixed green propellant. During the research activities, flashback from the rocket combustion chamber into the feeding system has been identified as a major challenge when using the propellant mixture. This paper shows the results of ignition experiments conducted in a cylindrical, optical accessible ignition chamber. During the ignition and flame propagation process, pressure, temperature and high-speed video data were collected. The high speed video data were used to analyze the flame propagation speed. The obtained propagation speed was about 20 rn/s at ignition, while during further propagation of the flame speeds of up to 120 m/s were measured. Additionally, two different porous materials as flame arresting elements were tested： Porous stainless steel and porous bronze material. For both materials Peclet numbers for flashback were derived. The critical Peclet number for the sintered bronze material was around 20, while for the sintered stainless steel the critical Peclet number seems to be larger than 40. Due to the test results, sintered porous materials seem to be suitable as flashback arresters.
基金supported by Fondazione Cariplo through Grants 2009-2477 and 2013-0615
文摘Hydrogen, the cleanest and most promising energy vector, can be produced by solar into chemical energy conversion, either by the photocatalytic direct splitting of water into Hand O, or, more efficiently,in the presence of sacrificial reagents, e.g., in the so-called photoreforming of organics. Efficient photocatalytic materials should not only be able to exploit solar radiation to produce electron–hole pairs, but also ensure enough charge separation to allow electron transfer reactions, leading to solar energy driven thermodynamically up-hill processes. Recent achievements of our research group in the development and testing of innovative TiO-based photocatalytic materials are presented here, together with an overview on the mechanistic aspects of water photosplitting and photoreforming of organics. Photocatalytic materials were either（i） obtained by surface modification of commercial photocatalysts, or produced（ii） in powder form by different techniques, including traditional sol gel synthesis, aiming at engineering their electronic structure, and flame spray pyrolysis starting from organic solutions of the precursors, or（iii） in integrated form, to produce photoelectrodes within devices, by radio frequency magnetron sputtering or by electrochemical growth of nanotube architectures, or photocatalytic membranes, by supersonic cluster beam deposition.
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(Grant Nos.51576100&51306091)the Jiangsu Provincial Natural Science Foundation of China(Grant Nos.BK20140034&BK20130758)+1 种基金Jiangsu “Shuangchuang Program”the Jiangsu Provincial Project of “Six Talent Summit”(Grant No.2014-XNY-002)
文摘Kinetic analysis of coupled effects of CO2 and H2 additions on laminar lean premixed dimethyl ether flames is performed at atmospheric pressure. The coupled effects of H2/CO2 additions on major species, intermediate stable species and radicals are discussed and analyzed in detail. The dilution, thermal and chemical effects of H2 and CO2 are separated and identified. The results show that H2 addition can slightly mitigate the CO2 chemical effects on decreasing the temperatures, H radical concen- tration, acetylene mole fraction and formaldehyde concentration. After CO2 is added, the H2 chemical effects on increasing the temperatures are enhanced. DME oxidation is promoted by the H2 chemical effects, which is further strengthened by the CO2 addition. Moreover, CO2 addition can reduce the H2 chemical effects on increasing the H radical mole fraction, but strengthen the H2 chemical effects on increasing the production of HO2 and C2H2. CH2O formation can be promoted by the H2 chemical effects, which is enhanced by the CO2 addition. In actually, the H2/CO2 coupled chemical effects almost have no obvious in- fluence on the temperatures and HO2 mole fraction. DME consumption is delayed by the H2/CO2 coupled chemical effects. Furthermore, the H2/CO2 coupled chemical effects can decrease the H radical mole fraction, CH4 concentration, C2H2 mole fraction, CH2O concentration and CHaCHO mole fraction, but increase the CO concentration.
基金Supported by the China Postdoctoral Science Foundation (Grant No. 20080440713)the National Hi-Tech Research and Development Program ("863" Project) (Grant Nos. 2007AA05Z105, 2007AA05Z236)the National Natural Science Foundation of China (Grant No. 50776036)
文摘The two-phase volume-averaged model with the detailed chemistry reaction mechanism GRI 3.0 was adopted in the quasi-steady-state simulation of hydrogen production by CH4-rich filtration combustion in an alumina foam under fully developed conditions. The relations among the combustion wave velocity, the inlet gas velocity and the equivalence ratio were discussed, and their influences on the distributions of temperature and species in the alumina foam and on H2 yield, CH4 conversion, H2 selectivity and CO selectivity were analyzed in detail. The results show that the combustion wave velocity increases with the increase of equivalence ratio or inlet gas velocity. The H2 yield exceeded 50% with equivalence ratio between 2.0 and 3.0 and combustion wave velocity larger than 0.4 mm/s. The H2 selectivity exceeded 50% with equivalence ratio larger than 2.0 and CO selectivity exceeded 80% with equivalence ratio between 1.8 and 2.0 and combustion wave velocity larger than 0.4 mm/s.
