In ground tests of hypersonic scramjet, the highenthalpy airstream produced by burning hydrocarbon fuels often contains contaminants of water vapor and carbon dioxide. The contaminants may change the ignition characte...In ground tests of hypersonic scramjet, the highenthalpy airstream produced by burning hydrocarbon fuels often contains contaminants of water vapor and carbon dioxide. The contaminants may change the ignition characteristics of fuels between ground tests and real flights. In order to properly assess the influence of the contaminants on ignition characteristics of hydrocarbon fuels, the effect of water vapor and carbon dioxide on the ignition delay times of China RP-3 kerosene was studied behind reflected shock waves in a preheated shock tube. Experiments were conducted over a wider temperature range of 800-1 500 K, at a pressure of 0.3 MPa, equivalence ratios of 0.5 and 1, and oxygen concentration of 20%. Ignition delay times were determined from the onset of the excited radical OH emission together with the pressure profile. Ignition delay times were measured for four cases： （1） clean gas, （2） gas vitiated with 10% and 20% water vapor in mole, （3） gas vitiated with 10% carbon dioxide in mole, and （4） gas vitiated with 10% water vapor and 10% carbon dioxide, 20% water vapor and 10% carbon dioxide in mole. The results show that carbon dioxide produces an inhibiting effect at temperatures below 1 300 K when Ф = 0.5, whereas water vapor appears to accelerate the ignition process below a critical temperature of about 1 000 K when Ф = 0.5. When both water vapor and carbon dioxide exist together, a minor inhibiting effect is observed at Ф = 0.5, while no effect is found at Ф = 1.0. The results are also discussed preliminary by considering both the combustion reaction mechanism and the thermophysics properties of the fuel mixtures. The current measurements demonstrate vitiation effects of water vapor and carbon dioxide on the autoignition characteristics of China RP-3 kerosene at air-like O2 concentration. It is important to account for such effects when data are extrapolated from ground testing to real flight conditions.展开更多
Using the outputs from 16 chemistry-climate models(CCMs), the trends of lower- to mid-stratospheric water vapor(WV) during the period 1980–2005 were studied. Comparisons were made between the CCM results and European...Using the outputs from 16 chemistry-climate models(CCMs), the trends of lower- to mid-stratospheric water vapor(WV) during the period 1980–2005 were studied. Comparisons were made between the CCM results and European Centre for Medium-Range Weather Forecasts(ECMWF) Interim Reanalysis(ERA-Interim).The results of most of the CCMs, and those based on ERA-Interim, showed the trends of lower- to mid-stratospheric WV during the period 1980–2005 to be positive, with the extent of the trend increasing with altitude. The trend of lower- to mid-stratospheric WV in the ensemble mean of the CCMs was 0.03 ppmv per decade,which was about twice as large as that based on ERA-Interim. The authors also used a state-of-the-art general circulation model to evaluate the impacts of greenhouse gas(GHG) concentration increases and ozone depletion on stratospheric WV. The simulation results showed that the increases of lower- to mid-stratospheric WV affected by the combined effects of GHG and ozone changes happened mainly via warming of the tropopause and enhancement of the Brewer-Dobson circulation(BDC), with the former being the greater contributor.GHG increase led to a higher and warmer tropopause with stronger BDC, which in turn led to more WV entering the stratosphere; while ozone depletion led to a higher and cooler tropopause, which caused the decreases of lowerto mid-stratospheric WV, despite also causing stronger BDC.展开更多
Laayoune and the Foum El Oued aquifers are in hydraulic communication only at the level of Oued Saguia El Hamra. The present study has accordingly made use of all the hydrogeological, hydrological, geological and geop...Laayoune and the Foum El Oued aquifers are in hydraulic communication only at the level of Oued Saguia El Hamra. The present study has accordingly made use of all the hydrogeological, hydrological, geological and geophysical data that preceded the watershed of Oued Saguia El Hamra in its downstream part. These data are by no means omplementary with the objective of having a better understanding of the boundary line between Laayoune and Foum El Oued aquifers and the origin of feeding the sources of Oued Saguia El Hamra. This study will focus only on the previous geophysical studies where a reinterpretation of electrical soundings has proved useful as a result of the recent well-logging results. It makes it possible to highlight the presence of a significant rise in the truncated marly substratum of Oued Saguia El Hamra and depressions (left and right banks) which could correspond to stream channels or depressed areas. At the level of the Wadi bed, there has been a regular immersion of the conductive level roofs from east to west towards Foum El Oued favoring the flow of wastewater from the zone and spraying the brackish water sources towards the groundwater of Foum El Oued. In the light of the reinterpretation of electric polls, plus as well as the geophysical surveys by electrical tomography and high definition made at the right and left banks of the Oueed Saguia El-Hamra, it was possible to verify the existence of dry ridge separating the two webs of Laayoune and Foum El Oued and stream channels or depressed areas of the left bank for drainage of brackish water to sources located along Oued Saguia El Hamra. The true resistivity models tomography profiles confirm the presence of the backbone at the left and right banks and the graben of the left bank for underground water drainage of the web Laayoune to sources welling the river Saguia El Hamra. They reveal the presence of a quaternary plio-cover (coastal platform Moghrebian) as being heterogeneous and affected by many electrical discontinuities, particularly in the level resistant R2 (coquina sandstone). These discontinuities could correspond to lateral changes in facies and/or synsedimental faults compartmentalizing the plio-quaternary formations into a system of Horsts and Grabens that relies on the whole (D1, Cs) attributed to formations from the Miocene to the Upper Cretaceous. The contours of the map show the distribution of the three families of electrical soundings A, B and C limited by two main electrical discontinuities D and M. East of discontinuity million, this map reflects the look of the wall of the Pliocene-Quaternary resting on the impermeable upper Cretaceous floor. To the west of this electrical discontinuity M, the map reflects the behavior of the roof of marl deposits of Miocene age.展开更多
基金supported by the National Natural Science Foundation of China(90916017)
文摘In ground tests of hypersonic scramjet, the highenthalpy airstream produced by burning hydrocarbon fuels often contains contaminants of water vapor and carbon dioxide. The contaminants may change the ignition characteristics of fuels between ground tests and real flights. In order to properly assess the influence of the contaminants on ignition characteristics of hydrocarbon fuels, the effect of water vapor and carbon dioxide on the ignition delay times of China RP-3 kerosene was studied behind reflected shock waves in a preheated shock tube. Experiments were conducted over a wider temperature range of 800-1 500 K, at a pressure of 0.3 MPa, equivalence ratios of 0.5 and 1, and oxygen concentration of 20%. Ignition delay times were determined from the onset of the excited radical OH emission together with the pressure profile. Ignition delay times were measured for four cases： （1） clean gas, （2） gas vitiated with 10% and 20% water vapor in mole, （3） gas vitiated with 10% carbon dioxide in mole, and （4） gas vitiated with 10% water vapor and 10% carbon dioxide, 20% water vapor and 10% carbon dioxide in mole. The results show that carbon dioxide produces an inhibiting effect at temperatures below 1 300 K when Ф = 0.5, whereas water vapor appears to accelerate the ignition process below a critical temperature of about 1 000 K when Ф = 0.5. When both water vapor and carbon dioxide exist together, a minor inhibiting effect is observed at Ф = 0.5, while no effect is found at Ф = 1.0. The results are also discussed preliminary by considering both the combustion reaction mechanism and the thermophysics properties of the fuel mixtures. The current measurements demonstrate vitiation effects of water vapor and carbon dioxide on the autoignition characteristics of China RP-3 kerosene at air-like O2 concentration. It is important to account for such effects when data are extrapolated from ground testing to real flight conditions.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41225018 and 41305036)
文摘Using the outputs from 16 chemistry-climate models(CCMs), the trends of lower- to mid-stratospheric water vapor(WV) during the period 1980–2005 were studied. Comparisons were made between the CCM results and European Centre for Medium-Range Weather Forecasts(ECMWF) Interim Reanalysis(ERA-Interim).The results of most of the CCMs, and those based on ERA-Interim, showed the trends of lower- to mid-stratospheric WV during the period 1980–2005 to be positive, with the extent of the trend increasing with altitude. The trend of lower- to mid-stratospheric WV in the ensemble mean of the CCMs was 0.03 ppmv per decade,which was about twice as large as that based on ERA-Interim. The authors also used a state-of-the-art general circulation model to evaluate the impacts of greenhouse gas(GHG) concentration increases and ozone depletion on stratospheric WV. The simulation results showed that the increases of lower- to mid-stratospheric WV affected by the combined effects of GHG and ozone changes happened mainly via warming of the tropopause and enhancement of the Brewer-Dobson circulation(BDC), with the former being the greater contributor.GHG increase led to a higher and warmer tropopause with stronger BDC, which in turn led to more WV entering the stratosphere; while ozone depletion led to a higher and cooler tropopause, which caused the decreases of lowerto mid-stratospheric WV, despite also causing stronger BDC.
文摘Laayoune and the Foum El Oued aquifers are in hydraulic communication only at the level of Oued Saguia El Hamra. The present study has accordingly made use of all the hydrogeological, hydrological, geological and geophysical data that preceded the watershed of Oued Saguia El Hamra in its downstream part. These data are by no means omplementary with the objective of having a better understanding of the boundary line between Laayoune and Foum El Oued aquifers and the origin of feeding the sources of Oued Saguia El Hamra. This study will focus only on the previous geophysical studies where a reinterpretation of electrical soundings has proved useful as a result of the recent well-logging results. It makes it possible to highlight the presence of a significant rise in the truncated marly substratum of Oued Saguia El Hamra and depressions (left and right banks) which could correspond to stream channels or depressed areas. At the level of the Wadi bed, there has been a regular immersion of the conductive level roofs from east to west towards Foum El Oued favoring the flow of wastewater from the zone and spraying the brackish water sources towards the groundwater of Foum El Oued. In the light of the reinterpretation of electric polls, plus as well as the geophysical surveys by electrical tomography and high definition made at the right and left banks of the Oueed Saguia El-Hamra, it was possible to verify the existence of dry ridge separating the two webs of Laayoune and Foum El Oued and stream channels or depressed areas of the left bank for drainage of brackish water to sources located along Oued Saguia El Hamra. The true resistivity models tomography profiles confirm the presence of the backbone at the left and right banks and the graben of the left bank for underground water drainage of the web Laayoune to sources welling the river Saguia El Hamra. They reveal the presence of a quaternary plio-cover (coastal platform Moghrebian) as being heterogeneous and affected by many electrical discontinuities, particularly in the level resistant R2 (coquina sandstone). These discontinuities could correspond to lateral changes in facies and/or synsedimental faults compartmentalizing the plio-quaternary formations into a system of Horsts and Grabens that relies on the whole (D1, Cs) attributed to formations from the Miocene to the Upper Cretaceous. The contours of the map show the distribution of the three families of electrical soundings A, B and C limited by two main electrical discontinuities D and M. East of discontinuity million, this map reflects the look of the wall of the Pliocene-Quaternary resting on the impermeable upper Cretaceous floor. To the west of this electrical discontinuity M, the map reflects the behavior of the roof of marl deposits of Miocene age.
