Atmospheric chemistry research and atmospheric measurement techniques have mutually promoted each other and developed rapidly in China in recent years.Cavity-based absorption spectroscopy,which uses a high-finesse cav...Atmospheric chemistry research and atmospheric measurement techniques have mutually promoted each other and developed rapidly in China in recent years.Cavity-based absorption spectroscopy,which uses a high-finesse cavity to achieve very long absorption path-length,thereby achieving ultra-high detection sensitivity,plays an extremely important role in atmospheric chemistry research.Based on the Beer–Lambert law,this technology has the unique advantages of being non-destructive,chemical-free,and highly selective.It does not require any sample preparation and can quantitatively analyze atmospheric trace gases in real time and in situ.In this paper,we review the following:(1)key technological advances in different cavity-based absorption spectroscopy techniques,including cavity ring-down spectroscopy,cavityenhanced absorption spectroscopy,cavity attenuated phase shift spectroscopy,and their extensions;and(2)applications of these techniques in the detection of atmospheric reactive species,such as total peroxy radical,formaldehyde,and reactive nitrogen(e.g.,NOx,HONO,peroxy nitrates,and alkyl nitrates).The review systematically introduces cavity-based absorption spectroscopy techniques and their applications in atmospheric chemistry,which will help promote further communication and cooperation in the fields of laser spectroscopy and atmospheric chemistry.展开更多
Hystereses and catastrophes were experimentally investigated in a cavity-based scramjet combustor.The inflow Mach number was 3.0.Fuel Equivalence Ratio(ER)was continuously regulated with multi-steps to explore influen...Hystereses and catastrophes were experimentally investigated in a cavity-based scramjet combustor.The inflow Mach number was 3.0.Fuel Equivalence Ratio(ER)was continuously regulated with multi-steps to explore influences of historical regulation directions on combustion states.Two divided hysteresis loops with catastrophes were observed.By 1-D flow estimations,the first loop occurred with shock-free/separated scramjet mode transitions,while the second kept in the separated scramjet mode.This breaks through the traditional knowledge that hysteresis and catastrophe were certainly related to ramjet/scramjet mode transitions.The first hysteresis and catastrophes were attributed to flame stabilization mode transitions between the cavity shearlayer stabilized and the jet-wake stabilized,with flow separation establishment/vanishment upstream the cavities.The obvious variations of flame and shock/separation structures meant large wall-pressure changes in the expansive duct,and generated obvious thrust catastrophes.Besides,transition ER and catastrophe were larger in historical ER-increasing path because combustion efficiency became obviously larger as flow separation established.Difference of critical transition ERs meant the first hysteresis.The second hysteresis and catastrophes in the jet-wake stabilized mode were attributed to flame/shock interaction mode transitions between the flame/shock weak interaction mode and intensive interaction mode.Each transition caused slightly stronger/weaker flame interacting with slightly larger/smaller flow separation,which meant small wall-pressure changes in the expansive duct,and thus thrust catastrophe was unobvious.Hysteresis occurred as the critical transition ER was slightly higher in historical ER-increasing path because of slightly lower combustion efficiency under slightly smaller separation.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.U21A2028,42022051,62275250,42030609,41627810,91644107,and 91544228).
文摘Atmospheric chemistry research and atmospheric measurement techniques have mutually promoted each other and developed rapidly in China in recent years.Cavity-based absorption spectroscopy,which uses a high-finesse cavity to achieve very long absorption path-length,thereby achieving ultra-high detection sensitivity,plays an extremely important role in atmospheric chemistry research.Based on the Beer–Lambert law,this technology has the unique advantages of being non-destructive,chemical-free,and highly selective.It does not require any sample preparation and can quantitatively analyze atmospheric trace gases in real time and in situ.In this paper,we review the following:(1)key technological advances in different cavity-based absorption spectroscopy techniques,including cavity ring-down spectroscopy,cavityenhanced absorption spectroscopy,cavity attenuated phase shift spectroscopy,and their extensions;and(2)applications of these techniques in the detection of atmospheric reactive species,such as total peroxy radical,formaldehyde,and reactive nitrogen(e.g.,NOx,HONO,peroxy nitrates,and alkyl nitrates).The review systematically introduces cavity-based absorption spectroscopy techniques and their applications in atmospheric chemistry,which will help promote further communication and cooperation in the fields of laser spectroscopy and atmospheric chemistry.
基金National Natural Science Foundation of China(Nos.11902325 and 11672309)。
文摘Hystereses and catastrophes were experimentally investigated in a cavity-based scramjet combustor.The inflow Mach number was 3.0.Fuel Equivalence Ratio(ER)was continuously regulated with multi-steps to explore influences of historical regulation directions on combustion states.Two divided hysteresis loops with catastrophes were observed.By 1-D flow estimations,the first loop occurred with shock-free/separated scramjet mode transitions,while the second kept in the separated scramjet mode.This breaks through the traditional knowledge that hysteresis and catastrophe were certainly related to ramjet/scramjet mode transitions.The first hysteresis and catastrophes were attributed to flame stabilization mode transitions between the cavity shearlayer stabilized and the jet-wake stabilized,with flow separation establishment/vanishment upstream the cavities.The obvious variations of flame and shock/separation structures meant large wall-pressure changes in the expansive duct,and generated obvious thrust catastrophes.Besides,transition ER and catastrophe were larger in historical ER-increasing path because combustion efficiency became obviously larger as flow separation established.Difference of critical transition ERs meant the first hysteresis.The second hysteresis and catastrophes in the jet-wake stabilized mode were attributed to flame/shock interaction mode transitions between the flame/shock weak interaction mode and intensive interaction mode.Each transition caused slightly stronger/weaker flame interacting with slightly larger/smaller flow separation,which meant small wall-pressure changes in the expansive duct,and thus thrust catastrophe was unobvious.Hysteresis occurred as the critical transition ER was slightly higher in historical ER-increasing path because of slightly lower combustion efficiency under slightly smaller separation.
