Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1999-05-17
2001-08-07
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S338500, C250S341300
Reexamination Certificate
active
06271522
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to processes for the quantitative analysis of gas volumes, more specifically random exhaust gases from combustion systems, such as jet engines, their combustion chambers and other gas turbines, as well as from incineration plants, chemical facilities, power plant furnaces, or landfills. The invention also relates to systems for performing these processes, and to modeling processes and evaluation processes.
REVIEW OF RELATED TECHNOLOGY
Nowadays the characteristics of industrial incineration plants or combustion systems, which include aircraft turbines and similar combustion systems, are determined by (among other factors) two essential requirements: the maximization of the energetic effectiveness of the combustion (an economic requirement) and the minimization of undesirable components in the exhaust gas (an ecological requirement). Ecological aspects also determine, among other things, the interest in the quantitative composition of exhaust gases that occur in natural fires. The fact that combustion processes, as a rule, do not proceed in a spatially homogeneous form, and that the degree of effectiveness of combustion and the composition of the exhaust gases are impacted by inhomogeneities, make a spatially resolved analysis of the combustion and exhaust gas desirable.
The operational part of gas analysis is currently performed by sampling. This encompasses both static collection processes, such as the collection of individual samples, for example by means of evacuated collection containers, and also dynamic collection processes, e.g., continuous sampling, for example by means of extraction systems. A continuous, spatially resolved exhaust gas analysis for the usually large exhaust streams from the systems in question is not possible with these methods, or else is possible only with technically highly complex and/or time-consuming processes.
There furthermore is no a priori guarantee that the sample does not undergo any changes during the time between collection and analysis, for example due to temperature changes and/or chemical reactions. The analysis, as a rule, requires different methods for the different components of the exhaust gas and is frequently time-consuming. The probes used in the sampling process may cause undesired reactions with the combustion process, possibly even jeopardizing the operation of the system, for example, in the case of combustion chambers or jet turbine engines.
In recent times, the suitability of non-intrusive infrared-spectrometric processes for emission analysis has been studied within the context of research projects. These optical processes do detect several components of the exhaust gas simultaneously. However, the information along an optical beam line is integrated over the volume scanned. These processes therefore do not permit a spatial resolution, as is required particularly for the analysis of exhaust gases from gas turbines under development; instead they offer only one dimensional detection of the exhaust gases.
The following are shortcomings of the methods currently used for exhaust gas analysis:
1. Processes in which samples are collected are slow; they require a separate analysis instrument for each component of the exhaust gas; they involve the risk that samples may become corrupted; if they permit a high spatial resolution they are technically highly involved and/or require considerable amounts of time; and they may cause problems in the combustion process.
2. Non-intrusive infrared spectrometric methods permit only a one-dimensional detection of the exhaust gases and yield the concentrations of the exhaust gas components in the volume of the covered beam of rays only as a mean value. Particularly for the development of combustion chambers and turbines of jet engines, however, it is necessary to know the spatially resolved distribution of the temperature and concentration of the exhaust gas constituents, in order to be able to make any statements regarding the effectiveness and the emission indices (quantity of exhaust gas relative to the burnt amount of fuel). A knowledge of the spatial distribution could also be used to derive characteristics of and, hence, development criteria for the combustion chamber.
3. The spatial resolution of the measurement, which is required for the precise quantitative determination of quantities of exhaust gas from industrial or natural combustion processes, is not possible in a non-intrusive manner and often cannot be justified because of the required expenditures.
Essential elements of the evaluation comprise a modeling of the infrared radiation received by a detector by solving the radiation transport equation and fit the model to the measured by parameter estimation methods.
In a forward model of radiation transport, the radiance (intensity) I(v, s) of wave-number v which is received by a detector at a location s is obtained with the integral form of the radiative transfer equation:
I
(
v
,
s
)
=
I
(
v
,
s
0
)
𝒯
(
v
;
s
,
s
0
)
+
∫
s
0
s
ⅆ
s
′
B
(
v
,
T
(
s
′
)
)
∂
𝒯
(
v
;
s
,
s
′
)
∂
s
′
(
1
)
wherein s′ denotes the distance from the observer along the line of sight (see FIG.
1
); B denotes the Planck function at the temperature T, and I(v, so) denotes a source term. The monochromatic transmission &tgr;(v; s,s′) describes the attenuation of the radiation between two locations s
0
and s
1
and is defined by:
𝒯
(
v
;
s
0
,
s
1
)
=
exp
(
-
∫
s
0
s
1
k
(
v
,
s
′
)
n
(
s
′
)
ⅆ
s
′
)
,
(
2
)
wherein k(v;s)=k (v,p(s),T(s)) is the pressure-dependent and temperature-dependent absorption coefficient, and n(s) is the molecular particle density. In inhomogeneous media these values are spatially dependent. In the common radiative transfer models, the path integration of equations (1) and (2) are performed via the so-called Curtis-Godson approximation in such a way that the inhomogeneous medium is replaced by a series of homogenous layers with constant temperature and molecule concentrations, for example the mean values within these layers, and summed over these layers.
In the general case with a number of absorbing molecules, k(v;s′)n(s′) must be generalized via a sum over all species
&Sgr;
g
k
g
(v;s′)n
g
(s′)
The radiation received by a spectrometer must, of course, be calculated via convolution of the monochromatic spectrum (equation (1) or (2)) with the instrumental line shape function.
The shortcoming of this modeling of the measured spectrum, as it is used in the customary evaluation processes, is that the finite aperture and the finite field of view (FOV) of real spectrometers are not taken into consideration. Furthermore, the Curtis-Godson approximation, which is “commonly” used for radiative transfer calculations, should not be used here since least squares methods, as will be explained later, generally require a considerably greater number of iteration steps than solving the integrals with standard quadrature methods.
The equations (1) and (2) are (generally non-linear) integral equations of the general form g(v)=∫Y[v,f (s)]ds, which are converted into a linear equation system for the inversion, i.e., the determination of the unknown “source function” f (e.g., the temperature or gas concentration profile) via linearization—which leads to the Fredholm integral equation of the first type, g(v)=∫K(v,s)f(s)ds, and—discretization. As a general rule, a spectrum is known only for a finite number of discrete spectral elements v
i
, i=1, . . .,m. In the customary evaluation processes the unknown temperature and/or gas concentration profiles are described only through their mean values, i.e., constant profiles are assumed within the exhaust stream, for example a one-layer model of the gas volume or a three-layer model when foreground and background are taken int
Haschberger Peter
Lindermeir Erwin
Schimpp Birger
Schreier Franz
Tank Volker
Browdy & Neimark
Deutsches Zentrum fur Luft-und Raumfahrt e.V.
Gabor Otilia
Hannaher Constantine
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