Optics: measuring and testing – For light transmission or absorption – Of fluent material
Reexamination Certificate
2000-11-24
2003-05-27
Anderson, Bruce (Department: 2881)
Optics: measuring and testing
For light transmission or absorption
Of fluent material
C356S409000, C356S419000
Reexamination Certificate
active
06570655
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for measuring the opacity in gases, especially in exhaust gases or in the atmosphere, at or near the maximum of eye sensitivity in the green wavelength range with a central wavelength range between 550 and 570 nm, as well as a device for measuring the opacity in gases, especially in exhaust gases or in the atmosphere, which device is equipped with an optical filter arrangement for the visible green spectral range at or near the maximum of eye sensitivity within a wavelength range from 550 to 570 nm in the beam path in front of at least one optical detector, and which is connectable with or is provided with an evaluating electronic system.
In opacity meters, at present, according to law or standards, measuring is done with a wavelength in the “green spectral range”, at a peak wavelength of 550 to 570 nm and with a cutoff of less than 4% of the peak-value sensitivity of the peak wavelength for transmissions below 420 nm and above 680 nm. The opacity is defined there as measurement of the “clouding in the visible spectral range of the human eye sensitivity”. The measurement in this spectral range of the “eye sensitivity” is knowingly so chosen that thereby the clouding of the atmosphere or “smog formation”, caused by emissions should be checked. Alternatively, very often also the “k-value” in this spectral range is used as measure for the clouding, in which case the two values are reconvertible into one another by the Lambert Beer law:
100-opacity=100*EXP(-k*L), with L=measuring cell length, or measuring path length.
Mainly the “black” soot particles are/were caught by the opacity measurement and at present, in the legislation and the legally prescribed tests, it is assumed that the clouding or the k-value in the green spectral range is caused only by soot particles. In the opacity meters in use at present, with the measurement of the opacity in the “visible spectral range” at only one defined wavelength, it is not possible to distinguish whether the measurement value “opacity” or k-value (in m
−1
) is really caused by soot, or not also by other exhaust gas components.
In motors, however, in reality there can occur also potential exhaust gas components (for example some nitrogen compounds, especially NO
2
) which likewise absorb in this spectral range, and that can bring about a clouding. These additional components are wrongly included as “soot” in measurements made with the conventional opacity meter systems. In motor designs which were used in earlier years the dominant constituent causing the opacity really was the soot emission; this, however, is no longer valid for the present and future generations of motors.
In modem motor designs, for example those with CRT (Continuous Regenerating Type) exhaust gas treatment, soot particles are largely catalytically oxidized; on the other hand, however, a part of the NO concentrations present in the exhaust gas is transformed into NO
2
by these catalytic processes. NO
2
, however, is a gas component which is likewise absorbed in the green opacity meter spectral range, and is concurrently measured as “soot”. On the other hand, “white”, nonabsorbing particles can also occur (for example sulfates with agglomerated water or also other particle-form reacting products such as condensing hydrocarbons), which by weakening of the light in consequence of a light scattering can likewise have an effect on the measuring.
Likewise with the measuring apparatuses which measure in the middle IR-range, such a discrimination cannot be carried out, especially not for sulfates and for NO
2
. It is not possible to measure NO
2
in motor exhaust gases by means of IR absorption through cross-sensitivity with the steam that is present in the exhaust gas, and neither can the water be removed for this measurement by means of a gas cooling, since NO
2
that is soluble in water is simultaneously removed along with it. The measurement of the NO
2
concentration can occur at present only by chemo-luminescnce detectors (CLD), and there, however, also only indirectly by means of a difference measurement (NO
x
−NO=NO
2
).
For similar reasons sulfate particles in the IR range likewise cannot be measured; especially a direct measurement of the opacity constituent resulting from the light scattering of the sulfate particles is not possible in the visible spectral range. The same holds also for the opacity caused by non-absorbing but condensed, and therewith likewise light-scattering, HC particle constituents.
All concepts in effect at present in the IR range for the total particle measurement are based on measurements of the HC total concentrations (as gas or as gas+particles) and on back-reckoning models (thus also are the examples in EP 0 094 374 and EP 0 123 458). Some of the concepts at present on hand for the HC particle calculation are based on complicated measurements at different temperatures, on the filtering of the gas, on measurement of the “gaseous ” HC concentration present, and on a back calculation of the particle constituents, as represented in EP 0 616 205.
A direct measurement of the “clouding” by the light scattering, which is still definitive for the visible green spectral range is, for physical reasons, not possible in the IR range, since through the proportionality of the effect to the 4th power of the ratio of light wave length to particle size, factually no light scattering for particles from motor exhaust gases is present in the IR range.
A back calculation such as theoretically might be possible at least in measurements of the total absorption spectra of the exhaust gas in IR (NIR to FIR),with rapid and high-resolving FTIR systems which, however, are extremely costly and expensive, even for NO
2
, ultimately fails on the fact that the momentary dynamic relations, which occur in the free acceleration and that certainly definitively influence the momentary particle composition, cannot be recalculated from the data obtained. The same holds also for measurements with laser diodes, such as are described, say, in EP 0 920 285, in which there, too, only soot and HC are measured.
Because of the great differences among the “middle IR” wavelength ranges, all of the present-day methods are completely incapable to describe, or can describe only very incompletely, the conditions present in the visible spectral range. In DE 25 57 268 there is described a process for extinction measurement which can be used, for example, for the determination of the smoke density in smokestacks, but also for the measurement of the dust concentration in work-places, of the emission in the lime works environment, as well as for the determination of the visibility range in fog on highways and at airports. There, by extinction measurements at two different wavelengths, a distinction can be made possible between absorbing and non-absorbing particles, primarily between soot or aerosol particles and vapor-form water. It is not determined, however, in what manner and to what extent an opacity in a certain wavelength range affects the value for the opacity in another wavelength range.
SUMMARY OF THE INVENTION
The problem of the present invention, therefore, was to find a process which in a simple manner, and avoiding the above-described disadvantages of the state of the art, makes it possible separately to determine the components which are responsible for the clouding in the visible wavelength range and which, for the measurement of opacity on the basis of soot particles, permits a correction by consideration of further components having an effect in the visible range. A further problem was a device for the execution of the process.
For the solution of the above problem the process mentioned at the outset is characterized in that the opacity, additionally, is also measured in at least one second wavelength range which is located in the spectral range between 200 nm to 2&mgr;, and which at best slightly overlaps the first wavelength range. The invention is based on the principle that it
Schiefer Erich
Schindler Wolfgang
Anderson Bruce
AVL List GmbH
Hashmi Zia R.
Sonnenschein Nath & Rosenthal
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