Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
  • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N2021/1793—Remote sensing
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
  • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
  • G01N2021/3513—Open path with an instrumental source

Definitions

• the present invention relates to apparatus and method for analysing the constituents of a gas or a gas like cloud or plume (hereafter referred to as a plume).
• Measurement of the gaseous constituents of a motor vehicle exhaust plume, or other similar exhaust plumes is desirable to determine the environmental impact of the exhaust gas.
• some constituents of the exhaust gas plume are of greater interest than others, typically carbon monoxide, oxides of nitrogen, unburned or partially burned hydrocarbons.
• these constituents are usually present in very low concentrations and so cannot be easily determined.
• the device integrates optical absorbance over a path which includes not only the plume but also a large distance through ambient air.
• the net result of applying Beer's law is a calculated concentration, which appears much lower than, and is not wholly representative of that which would be found in the core of the plume itself. This is a consequence of the length of the beam path not being the same as the length of the path within the plume.
• the ratio of optical absorbance for a constituent of interest e.g. NO 2
• optical absorbance for a reference constituent e.g. CO 2
• the ratio reflects gas composition in the plume and is unaffected by the part of the beam path passing through ambient air so long as the concentrations of both reference and constituent of interest in the ambient air are zero or low enough to be acceptable sources of error.
• the determined ratio of optical absorbances is multiplied by the ratio of the absorption coefficients, determined as a calibration step, such that the ratio becomes a ratio of concentrations, independent of path length.
• the ratio of NO 2 to CO 2 E.g. for the ratio of NO 2 to CO 2 :
• the most useful measures for assessing the environmental impact of emissions are not concentrations of emitted gases, however, but measures of the mass of the pollutant emitted.
• Environmental impact assessments relating to transport require data in terms of mass of pollutant emitted per second or per kilometre travelled by the vehicle.
• the effects of fully dispersed emissions in terms of ambient background concentrations of pollutants are usually measured in terms of mass of polluting constituent per cubic metre of ambient air. This is a significant differentiation - while concentrations of gases can provide general information regarding the efficiency of a process, e.g. the state of performance of an engine and catalyst system, only mass emission data can indicate what the effect of the process may be on air quality and related issues such as atmospheric damage or public health.
• the present invention is arranged to address the above problems.
• the present invention provides apparatus for analysing the constituents of a plume comprising: optical absorbance determining apparatus for determining the optical absorbance of a first constituent of the plume along a path through the plume and, spatial variation deteirnining apparatus for determining the spatial variation in mass of a second constituent over at least one dimension within said plume, whereby the total mass of said first constituent of said plume may be calculated by relating the extent of said plume sampled by the optical absorbance determining apparatus to the spatial extent of the plume as determined by the spatial variation determining apparatus.
• the present invention provides apparatus for measuring the constituents of a plume comprising: concentration dete ⁇ nining apparatus for determining the ratio of concentrations of a first and a second constituent of the plume along a path through the plume and, spatial variation determining apparatus for determining the spatial variation in concentration of the second constituent over at least one dimension within the plume, and calculation means to determining the concentration of the first constituent in the plume.
• concentration dete ⁇ nining apparatus for determining the ratio of concentrations of a first and a second constituent of the plume along a path through the plume
• spatial variation determining apparatus for determining the spatial variation in concentration of the second constituent over at least one dimension within the plume
• calculation means to determining the concentration of the first constituent in the plume.
• said spatial variation determining apparatus determines the total amount of the said second constituent in the said plume.
• An advantage of these arrangements is that the constituents of the plume which are of interest, typically carbon monoxide, oxides of nitrogen, unburaed or partially burned hydrocarbons (i.e. the second constituent in the above paragraphs), are usually present in very low concentrations and so cannot be easily quantified in terms of detecting them across the whole transverse cross-section. It is normally necessary to detect them only along a defined path though the core of the plume. It is usually easier, however, to quantify the spatial distribution of carbon dioxide in the plume (i.e. the first constituent in the above paragraphs) which is present in the exhaust in relatively high concentration, and this may be used to determine the spatial extent of the plume by said spatial variation determining apparatus.
• Said apparatus for determining the optical absorbances of a first constituent along a path or ratios of a first and second constituent may comprise beam passing apparatus for passing a beam of electromagnetic radiation through the plume along said path and means to measure changes in the optical intensity at predetermined wavelengths (the predetermined wavelength relating to the chosen second constituent).
• Said beam of electromagnetic radiation is preferably of a limited wavelength range (e.g. monochromatic) and said apparatus for determining the spatial distribution of the second constituent may therefore comprise an appropriate monochromatic source for illumination of the plume or alternatively one or an array of sensors tuned using wavelength selective means, e.g. optical filters, to determine the spatial location and extent of the plume in at least one dimension.
• a limited wavelength range e.g. monochromatic
• said apparatus for determining the spatial distribution of the second constituent may therefore comprise an appropriate monochromatic source for illumination of the plume or alternatively one or an array of sensors tuned using wavelength selective means, e.g. optical filters, to determine the spatial location and extent of the plume in at least one dimension.
• the array of sensors may be provided in a line to determine the spatial distribution of the second constituent in a place (which may extend across the path of a vehicle being remotely monitored)
• said spatial variation determining apparatus for determining the total amount of the second constituent across plume may operate in three dimensions. Furthermore this measurement may be carried out over time so as to determine the change of the plume with time.
• the second constituent may comprise CO 2 or H 2 O
• the first constituent may comprise the constituent of interest, for example the oxides of nitrogen, NO 2 or
• the apparatus of the invention may be provided in a controlled environment, for example in a laboratory to test the exhaust emissions of a motor car under test, or in a semi-controlled environment such as attached to the stack of a power station, or funnel of a ship or a less controlled environment provided at the road side for determining the exhaust gas emissions of passing vehicles remotely.
• the present invention also provides a method for analysing the constituents of a plume comprising: determining the optical absorbance of a first constituent of the plume along a path through the plume and, dete ⁇ nining the spatial variation in mass of a second constituent over at least one dimension within said plume, and determine the total mass of said first constituent of said plume by relating the extent of said plume sample as determined by the optical absorbance determining step to the total spatial extent of the plume as determined by the spatial variation determining step.
• the present invention also provides a method for measuring the constituents of a plume comprising: determining the ratio of concentrations of a first and a second constituent of the plume along a path through the plume and, determining the spatial variation in concentration of the second constituent over at least one dimension within the plume, and thereby to dete ⁇ nining the concentration of the first constituent in the plume.
• Figure 1 is a perspective view of a first apparatus for analysing an exhaust plume of a moving motor vehicle
• Figure 2 is a perspective view of a second apparatus for analysing an exhaust plume of a moving motor vehicle.
• a motor vehicle 10 (which may be a car, van truck or bus) travelling in the direction 11 along a road 12.
• Motor vehicle 10 includes an exhaust pipe 13 emitting a plume 14 of exhaust gas.
• the apparatus of the invention comprises a source 15 of electromagnetic radiation at one side of the road 12, and a detector 16 at the opposite side of the road 12.
• the detector 16 includes two detection means, an optical absorbance determining apparatus comprising a first detection means 17 for detecting electromagnetic radiation along a defined path 20 in the form of a collimated beam 25 of electromagnetic radiation which passes through the exhaust plume, and a spatial variation determining apparatus comprising a second detecting means 18 which detects electromagnetic radiation from a two dimensional plane indicated at 21, the two dimensional plane including the path 20.
• the outputs of the first and second detector means 17, 18 are passed as digital signals to a memory store 22 at the roadside where the signals may be recorded onto a memory medium 23 such as a magnetic disc, or a CD, or a zip disc or any equivalent means; the memory medium 23 may be removed periodically for analysis in a computer 24 remote from the detectors.
• the digital signals may be passed by a cable 26 or transmitted by a radio microwave or infra-red link 27 direct to computer 24.
• the detection means 17 and 18 may be in the form of PbSe (Lead Selenide) temperature stabilised infrared detectors from CalSensors (part BXT2-17T) and the source 15 may be a TomaTech CS-IR21-V small area infrared source.
• a chopper may be used so that the beam is modulated.
• the second detector mean 18 comprises a "camera” comprising a two dimensional array of pyroelectric sensors, which is tuned using optical filter techniques in such a way as to visualise the exhaust plume as it is generated, i.e. as a vehicle passes the camera.
• the detector means 18 comprises an infrared camera operating in the 2 - 15 ⁇ m region which can be used to acquire an image, which defines the spatial location of the exhaust plume.
• the image intensities depend on how the camera 18 and illumination source 15 are deployed, and may result from (a) the specific absorption of electromagnetic radiation by constituents in the exhaust gas, (b) the re-emission of radiation absorbed by the constituents of the gas, or (c) the higher temperature of the exhaust gases compared to the surrounding air.
• the image obtained using the device is processed to give direct information about the spatial characteristics of the plume.
• the intensity of the image results from absorbance of the radiation from the source 15 by the exhaust gas plume which is located between the source 15 and the detector/camera 18.
• the exhaust gas absorbs some light from the source 15 and the detector 18 only detects re-emitted absorbed light.
• the detection means 17, 18, may operate continuously or may be pulsed or chopped electronically or by providing a physical chopper to interrupt the beam as is already known so as to provide a series of readings over a course of time. Operation of the detection means 17, 18 may be initiated by detection of the passage of the motor vehicle 10. A succession of output signals from the two detection means the 17, 18 is taken and passed to the computer 24 either directly by the cable 26 or radio, microwave or infra-red link 27 or by means of the intermediary of the memory medium 23.
• the temporal characteristics of its spatial extent can also be determined.
• a more precise profile of plume characteristics is determined by using a combination of spatial or spatio-temporal characteristics with mathematical models (based on computational fluid dynamics techniques - CFD) in the computer 24. Selecting an arrangement in which the intensity variations in the image are due to differing amounts of optical absorption by a constituent such as carbon dioxide means that the image generated is actually a map of concentration of this constituent in various parts of the plume and surrounding space. If the actual concentration of the imaged constituent is known for just one point in the image, the concentration at all other points in the image can be calculated using the relative image intensities.
• the addition of the second detector means 18 overcomes the first limitation and associated sources of error, and substantially overcomes the second limitation by relating the dynamics of the gas in the sampling region of the first means to the dynamics of the plume as a whole.
• the detector 16 uses a beam 25 of electromagnetic radiation with much smaller cross-sectional area than the plume dimensions, for example a collimated beam, passing through the plume 14 and recording the optical absorbance at specific wavelengths due to the presence of each constituent of interest, the detector 16 provides a signal which is proportional to the number of molecules of the constituent of interest located in the beam 25. If such a measurement is made either before the vehicle 10 passes the detector 16 or a sufficiently long time afterwards, a measure of background optical absorbance can be made and by subtraction, optical absorbance proportional to the number of molecules emitted into the beam path by the vehicle 10 can be measured. In practical applications, attenuation of the beam 25 by scattering or masking effects due to dust, smoke, suspended particulates etc. affects the measured optical absorption and it is necessary to compensate for this by making further measurements in a region of the electromagnetic spectrum which is not absorbed by the constituent of interest. Such measurements then provide a baseline for offsetting these effects.
• a term ⁇ v / / can be defined - this is the same as the effective cross sectional area of the beam.
• a term ⁇ n x m can be defined - this is the total mass of the constituent of interest in the sampled beam, where m is the molecular mass of the absorbing constituent.
• A ⁇ ⁇ / m ⁇ ⁇ is a significant value since it represents mass emitted into the beam path in the distance the vehicle travelled while crossing the beam path, which is linearly related to mass emitted into the beam path per kilometre travelled.
• ⁇ is determined by calibration of the instrumentation
• m is a constant for the absorbing gas species
• ⁇ is a known design parameter
• ⁇ can be directly measured by the application of the above equation to optical absorbance measurements made by the first detection means 16.
• ⁇ is a direct measure of mass emission, but only in the region of space sampled by the first detection means 16 (ie the beam 25). In order to measure the total mass emission, it is necessary to relate the mass measured in this region to the mass emitted into the regions of the plume 14 which are outside the beam path 25. This is the purpose of the second detection means 18.
• This spatial distribution information is used to form a ratio ct2/ai which relates the amount of exhaust emitted gas in a transverse section 21 through the whole of the plume 14 to the amount of exhaust gas in a region of this transverse section corresponding to the beam path 20.
• the second detection means 18 of Figure 1 which provides information regarding the spatial extent of the plume 14, is replaced by a plurality of pairs of illuminated sources and detectors arranged on each side of the path of the vehicle 10.
• Support 28 mounts six illumination sources 31-36 and support 30 mounts six detectors 37-42.
• Each illumination source/sensor pair (illumination source 31-36 sensor 37-42) are arranged opposite one another so that light from the relevant illumination source 31- 36 passes horizontally along a respective path 43-48 to the sensor 37-42.
• the plane 21 provided in the embodiment of Figure 1 by the camera 18 is provided by the spaced paths 43-48.

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• 2000
  • 2000-06-19 GB GB0015015A patent/GB0015015D0/en not_active Ceased
• 2001
  • 2001-06-18 EP EP01943608A patent/EP1292821A1/de not_active Withdrawn
  • 2001-06-18 WO PCT/GB2001/002663 patent/WO2001098758A1/en not_active Ceased
  • 2001-06-18 AU AU2001266145A patent/AU2001266145A1/en not_active Abandoned

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