Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2001-07-16
2003-07-15
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S339010, C250S458100
Reexamination Certificate
active
06593573
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to apparatus for monitoring the distribution and mixing of chemical species in a region of space such as a vessel or a free space such as a space containing an engine exhaust plume.
The spatial and temporal distribution and mixing of chemical species can be a critical determinant of the performance of chemical reactors. For example, the combustion chamber of an internal combustion engine is a chemical reactor in which the spatial and temporal variation of the air-fuel ratio prior to ignition bas a significant influence on both fuel efficiency and emissions performance. Various attempts have been made to analyse the spatial variation of the air-fuel ratio within internal combustion engines. Typically the cylinders and/or pistons of internal combustion engines have been provided with windows through which it has been possible to take graphs using high-speed camera equipment so as to image variations in the air-fuel ratio. It is known for example to introduce a fluorescent dopant into fuel introduced into the cylinder so as to provide a visual indication of fuel distribution within the air-fuel mixture.
A wide range of tomography modalities have been developed which encompass the classes of hard-field, soft-field and emission techniques. Each of these classes has various strengths and weaknesses. In particular, all of the classes require an inversion calculation to reconstruct the distribution of a parameter of interest. The stimulation process for fluorescence tomography has a hard-field nature in that the only material which can be stimulated to fluoresce is that lying on the geometrical path of input radiation, whilst detection of the isotropically emitted fluorescence clearly has an emission nature.
Work has been conducted in the case of X-ray fluorescence as described by Cesareo R., and Mascarenhas S. (1989), A new tomographic device based on the detection of fluorescent X-rays, Nucl. Instr. Meth. A277, 669-672. This paper points out that collimation of both the stimulation beam and detector acceptance results in an unambiguous determination of the spatial region referred to as the “space-point” from which detected fluorescence photons were emitted. In the described X-ray fluorescence case however the material under study strongly attenuated both the stimulation beam and the fluorescence photons and this required an additional complexity in image reconstruction by de-convoluting the attenuation. Thus this earlier work appeared to indicate that using collimated stimulation beams and detector fields of view did not avoid the need for computationally intensive image reconstruction techniques.
The technique of planar laser-induced fluorescence (PLIF) has been the most successful to date in providing information on the mixing and combustion processes in internal combustion engines. To implement this technique, large glass inserts are placed between the cylinder head and the engine block. The laser emission is formed into a sheet, passing through the cylinder head and exciting fluorescence. The fluorescence is observed in the orthogonal direction through an elongated piston with a central glass window and a mirror, typically by a CCD camera However, PLIF systems can only produce a low number of frames per cycle because of the comparatively low frequency of the light samples, determined by the low repetition rate (10-100 Hz) of the laser sources.
The known systems require extensive optical access which in ton requires substantial modifications to an internal combustion engine the performance of which is to be assessed, The provision of relatively large optical windows in a cylinder wall for example can significantly affect engine performance as compared with an engine in which no such optical windows are provided. Furthermore, the temporal resolution of such known techniques is limited to a few Hertz due to the pulsed laser sources used. These techniques are not suitable for application to routine engine operations.
It is known that air containing hydrocarbons absorbs laser radiation to a greater extent than air fee of hydrocarbons if the laser radiation is at a frequency which excites vibrational/rotational transitions in hydrocarbon molecules. In particular, the presence of CH
3
, CH
2
and CH groups in molecules in an air/hydrocarbon mixture results in a greater absorption due to various vibrational transitions and their overtones and combinations than is the case with air not containing such molecules.
SUMMARY OF THE INVENTION
It is an object of the present invention to exploit the specific absorption of radiation to monitor spatial and temporal variations in the air-fuel ratio within for example an internal combustion engine.
It is a firer object of the present invention to provide an improved apparatus for monitoring the spatial distribution within a vessel of a chemical species without requiring the use of computationally intensive techniques to produce a representation of the distribution.
According to the present invention, there is provided an apparatus for monitoring the distribution within a defined space of a chemical species, wherein a plurality of radiation sources and radiation detectors are distributed around the perimeter of the space, the radiation sources being distributed to emit beams of radiation across the interior of the space, the wavelength of the radiation being selected such that an interaction occurs between the radiation and the chemical species which can be detected by the detectors, and means being provided for deriving a representation of the distribution of the chemical species within the space from the detected interactions.
In one embodiment of the present invention a plurality of radiation sources and radiation detectors are distributed around the perimeter of the space such that radiation from each source is directed along a predetermined path towards at least one detector, the sources emit radiation at a wavelength selected to excite vibrational and/or rotational traditions in at least one of the chemical species such that radiation is absorbed to a greater degree by the said at least one species than by at least one other species, absorption of the radiation occurring along each of the predetermined paths is monitored to provide a measure of the path integral of the concentration of the said at least one species along each path, and a representation of the distribution of the concentration of the said at least one species within the space is derived from the measured path integrals of concentration.
The radiation sources and detectors may be arranged in pairs such that each detector receives radiation via a respective path from a respective source. Alternatively, at least one source may be arranged to direct radiation in a beam defining respective predetermined paths to each of a plurality of detectors, each detector having a collimated field of view which includes only the respective predetermined path.
In the case of the application of the invention to monitoring the spatial variation of air-fuel ratios within internal combustion engines, the specific if weak absorption of electromagnetic radiation in the near infra-red region of the electromagnetic spectrum (1 &mgr;m to 2.5 &mgr;m) may be exploited to distinguish between absorption resulting from overtones and combinations of various hydrocarbon vibrational and/or rotational transitions, particularly such transitions arising with CH
3
, CH
2
and CH groups in molecules. A suitable wavelength for use in the apparatus of the first embodiment of the present invention is 1700 nm (−15, +50 nm), as hydrocarbons exhibit weak absorption at this wavelength. Thus in contrast to prior art techniques, which rely upon the addition of fluorescent dopants to the fuel, the first aspect of the present invention uses the inherent absorption properties of hydrocarbon systems to derive data described in the spatial variation of the air-fuel ratio without in any way modifying the chemical constituents by for example adding dopants to the fu
Carey Stephen John
Hindle Francis Peter
McCann Hugh
Ozanian Krikor Bertch
Hannaher Constantine
Moran Timothy
The University of Manchester Institute of Science and Technology
Woodard, Emhardt, Naughton Moriarty & McNett LLP
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