FR2945349A1 - Method for determining spatial distribution of e.g. temperature gradient, in exhaust gas of combustion chamber, involves determining spatial distribution of thermodynamic parameter in semi-transparent medium - Google Patents

Abstract

The method involves emitting a ray through a semi-transparent medium, and receiving retrodiffused ray by the medium. A retrodiffusion of the received ray is measured, and another ray emitted by the medium is received. A luminance of the received ray is measured based on wave length. A spatial distribution of a thermodynamic parameter in a semi-transparent medium is determined from the measured luminance, measured retrodiffusion, radiation transfer theoretical equation, and retrodiffusion theoretical equation. An independent claim is also included for a system for determining a spatial distribution of a thermodynamic parameter in a semi-transparent medium comprising an emitter.

Description

Method and system for determining the spatial distribution of a thermodynamic parameter of a semi-transparent medium

The invention relates to the analysis of the properties of an exhaust gas of a combustion chamber. Such analyzes are carried out in particular to improve the combustion of engines and to reduce the release of non-atmospheric components in order to improve the stealth of air-land vehicles.

In particular, the present invention relates to a method and a system for determining the spatial distribution of a thermodynamic parameter in a semi-transparent medium and in particular an exhaust gas of a combustion chamber.

When developing aerobic thrusters, ramjets or detonation rocket engines, it is useful to know instantaneous maps of the concentration and temperature of flue gas components. The evolution of these maps makes it possible to know the progress of the combustion, the efficiency of the latter, and to understand the operation of the engine thus facilitating its adjustment.

To draw up such mappings, it is known to use suction probes which make it possible to determine the local concentration and temperature of the components.

However, these probes disrupt subsonic or supersonic flows. They do not withstand temperatures above 2,000 ° C and their slow response time is not suitable for pulsed measurements.

To establish these maps, it is also known to determine the concentration of a gas by a so-called Rayleigh scattering method.

However, this method requires knowing the local pressure of the component in the gas and this information is difficult to access.

The object of the invention is in particular to propose a method and a system for determining the spatial distribution of a thermodynamic parameter of a semi-transparent medium. The knowledge of this distribution allows in particular a better analysis of the performance of an engine and a setting at least faster thereof.

For this purpose, the subject of the invention is a method for determining the spatial distribution of at least one thermodynamic parameter in a semi-transparent medium, the method comprising the following steps: emission of a first radiation through the medium semi-transparent, by an emitter; receiving the first radiation backscattered by the semitransparent medium; measuring the backscattering of the radiation received as a function of the time and the wavelength of the radiation received; characterized in that it further comprises the following steps: - receiving a second radiation emitted by the semi-transparent medium; measuring the luminance of the second radiation received as a function of its wavelength; determining the spatial distribution of at least one thermodynamic parameter of the semi-transparent medium from said measured luminance, said measured backscattering, the theoretical radiative transfer equation and the theoretical backscattering equation.

According to particular embodiments, the method comprises one or more of the following characteristics: the thermodynamic parameter is the temperature of the semi-transparent medium; the thermodynamic parameter is the concentration of a component of the semi-transparent medium; the first emitted radiation belongs to the spectral range between 100 micrometers and 200 nanometers; 3

the first emitted radiation belongs to the spectral range between 0.4 micrometer and 5 micrometers; the first emitted radiation is pulsed at a frequency of between 1 Hertz and 500 Megahertz; the first radiation belongs to a frequency range different from the frequency range of the second radiation; the determination step is carried out on the basis of an inversion method of the theoretical radiative transfer equation and the theoretical retro-diffusion equation; the semi-transparent medium is an exhaust gas from a combustion chamber.

The invention also relates to a system for determining the spatial distribution of at least one thermodynamic parameter of the semi-transparent medium of a combustion chamber, the system comprising: a transmitter capable of emitting a first radiation through the semitransparent medium; a receiver capable of receiving the first retro-reflected radiation by the semi-transparent medium, said receiver being able to measure the backscattering of the first radiation received as a function of its wavelength and of the time; characterized in that the receiver is adapted to receive a second radiation emitted by the semi-transparent medium, said receiver being able to measure the luminance of the second radiation received as a function of its wavelength; and in that the system further comprises a calculation unit capable of determining the spatial distribution of at least one thermodynamic parameter of the semi-transparent medium from said measured luminance, of said measured backscatter, of the theoretical transfer equation radiative and the theoretical equation of retro diffusion.

According to particular embodiments, the determination system comprises one or more of the following characteristics: the transmitter is a white laser; the transmitter comprises discrete laser diodes; the receiver comprises a monochromator and a camera; the receiver comprises an oscilloscope.

The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the drawings, in which: FIG. 1 is a schematic view of the determination system according to the invention; in a combustion chamber open to the outside; FIG. 2 is a diagram of the steps of the determination method according to the invention; FIG. 3 is a curve representative of the backscattering measured by the receiver of the determination system according to the invention; FIG. 4 is a curve representative of the luminance measured by the receiver of the determination system according to the invention; and FIG. 5 is a schematic view of the determination system according to the invention in a closed combustion chamber.

The method and the determination system according to the invention can be implemented in a semi-transparent medium such as in an exhaust gas or in glass. The knowledge of thermodynamic parameters such as temperature gradients and concentrations of the constituents of the glass during shaping and cooling thereof is industrially demanded. Only the example of implementation of the method and the determination system in an exhaust gas of a combustion chamber has been described below.

Such a combustion chamber may be open to the outside such as the chamber of a propellant, a turbo reactor or a ramjet. Such a combustion chamber may also be closed such as the chamber of a cyclic engine, a detonation engine, a power plant or a boiler.

FIG. 1 represents the determination system 2 according to the invention implemented in an open combustion chamber on the outside.

This determination system 2 comprises a transmitter 4 capable of emitting a first radiation through an aggregate or an exhaust gas flow 6 of a combustion chamber (not shown), for example of a motor, a mirror 8 and a semi-reflecting plate 10 adapted to reflect the backscattered radiation by the components of the exhaust gas 6, and a receiver 12 adapted to receive the reflected radiation.

The transmitter 4 is able to emit the first radiation along an X axis in the near infrared and the visible light. In particular, the first radiation belongs to the spectral range between 100 micrometers and 200 nanometers, and preferably between 0.4 micrometer and 2.5 micrometers.

The transmitter 4 is capable of transmitting pulses of a duration of between 10 femto-seconds and 5 picoseconds, and preferably equal to 5 picoseconds, at a frequency of between 1 Hz and 500 MHz and, preferably at a frequency equal to 80 megahertz.

In practice, the transmitter 4 is constituted, for example, by a white laser or by pico laser diodes. The mirror 8 has a concave face and an orifice 14 able to allow the passage of the first radiation coming from the emitter 4.

The semi-reflecting plate 10 reflects a portion of the first radiation 25 from the first mirror 8 to the detector 12.

The detector 12 comprises a dispersive system such as a network monochromator 16, an array of detectors such as photomultipliers (not shown) and a CCD camera 18. The detector 12 is able to measure the backscattering R2 ,, (t ) back-reflected radiation from the exhaust gas components as a function of its wavelength. An example of a curve representative of the backscattering R2 ,, (t) is shown in FIG.

The determination system 2 according to the invention further comprises a Fourier transform spectrometer 24 capable of measuring the luminance La, of a second radiation emitted by the exhaust gas 6 outside the emission periods of the emitter 4.

For this purpose, the spectrometer 24 is synchronized to the transmitter 4.

In a variant, the transmitter 4 is able to transmit a single pulse. In this case, the first radiation belongs to wavelength ranges that are smaller than the wavelength ranges of the second radiation, that is to say wavelength ranges of between 200 nanometers and 1000 nanometers. .

Alternatively, the Fourier transform spectrometer 24 is replaced by a grating spectrometer.

Alternatively, the CCD camera 18 is replaced by a slot scanning camera (called STREAK). These cameras make it possible to analyze spectra with temporal resolutions in pico-seconds. They are used here to determine the quantitative distribution of a component of an exhaust gas of a detonation engine or a cyclic engine.

Alternatively, the CCD camera 18 is replaced by a 20 Gigahertz oscilloscope.

The determination system 2 according to the invention further comprises a calculation unit 20 connected to the detector 12, and a memory 22 contained in the calculation unit 20.

The memory 22 stores the theoretical radiative transfer equation [1] and the theoretical backscattering equation [2] mentioned below. La = [T (x), Ci (x), P (x)] x Ci (x) XT (x), Ct (x), P (x)] xCi (x) dx L ~ i (T (x) )) dx [1] In which: e1 i [T (x), C ~ (x), P (x)] = emissivity of the exhaust gas i; T (x) = temperature of the exhaust gas;

C ~ (x) = concentration of the component in the exhaust gas i; x = location along the X axis of the exhaust gas component;

p (x) = pressure of the exhaust gas; L9 (T (x)) = luminance of a black body at temperature T R (t = 2x = Io (2) / 32, i [T (x), Ci (x)] x C. (x) - 210 E2a [T (x), Ci (x), P (x)} xCi (x) dx v [2] Wherein:

e2 i [T (x), C ~ (x), P (x)] = emissivity of the exhaust gas i; T (x) = temperature of the exhaust gas;

C ~ (x) = concentration of the component in the exhaust gas; x = location of the component along the X axis;

A = value of x at the end of the exhaust gas aggregate;

p (x) = pressure of the exhaust gas; / 3, = backscattering coefficient of the exhaust gas i; 1 (~,) = intensity of the transmitter 4 at the wavelength X; v = speed of light in the gas; t = 2x / v is the return time of the signal reflected at abscissa x. The coefficient (3) is derived from a database such as HITRAN, which coefficient 3 depends on the component to be analyzed in the exhaust gas The calculation unit 20 is able to implement the determination method described. below and illustrated in Figure 2.

The determination method according to the invention starts with a step 10 for emitting a first radiation by the emitter 4.

During a step 32, the first radiation is backscattered by the components of the exhaust gas 6.

During a step 34, the mirror 8 and then the blade 10 reflect the first radiation backscattered by the exhaust gas components.

During a step 36, the detector 12 receives a portion of the first radiation reflected by the mirror 8 and the blade 10. During a step 38, the camera 18 measures the backscattering R2 (t) of this part of the first radiation as a function of its wavelength and time. In particular, the camera 18 captures M x L discrete backscatter measurements

Kik comprising measurements made at different times and at different wavelengths. The M x L measurements are introduced into the backscattering equation [2] to obtain M x L equations with 2x unknowns. The 2x unknowns are the temperature at x locations and the concentration at x locations. A place x of the exhaust gas 6 is determined from the instant t of reception of the first radiation and of the following formula:

In a step 39, a radiation called second radiation is emitted by the exhaust gas 6. This emission comes from the clean thermal emission of the exhaust gas.

During a step 40, the spectrometer 24 measures the luminance La, of the second radiation emitted by the exhaust gas 6 as a function of its wavelength. In particular, the spectrometer 24 measures N distinct luminance values La corresponding each to a given wavelength. The N discrete values of luminance La are introduced into the radiative transfer equation [1] to obtain N equations with 2x unknowns, the 2x unknowns being the temperature at x places and the concentration at x places.

During a step 42, the computing unit 20 determines the spatial distribution of at least one thermodynamic parameter of the exhaust gas 6 by inverting the system of equations comprising N radiative transfer equations and MxL backscattering equations.

This inversion is achieved by the minimization of a residual function also called cost function, mentioned below. J = N + MxL) 2 F = E (s J ù SJCalculated J = 1 Where: - Sj is either a luminance measurement L? K or a backscattering measurement Rak; - SJCalculated is a value chosen a priori for it is close to an expected value of luminance La or an expected backscattering value R ak; - N is the number of luminance measurements emitted by the exhaust gas; - M x L is the number of measurements of backscattering by the exhaust gas.25

This function F is minimized by an algorithm, for example based on the so-called conjugate gradient method associated with the calculation of the adjoint state.

FIG. 5 represents the determination system 2 according to the invention implemented in a closed combustion chamber. In this case, the first radiation is reflected by the bottom 50 so that the theoretical radiative transfer equation [1] is modified by the addition of a term proportional to the emissivity of the bottom wall 50 of the chamber. combustion. Thus, in this case, the memory 22 has the following formula: L2 (t) = f e2 i [T (x), Ci (x), P (x)] x Ci (x) x e_50 Ea [T (x) ), Ct (x), P (x)] x C t (x) dx L02 (T (x)) dx + [1e-2a [T (x), Ci (x), P (x)] dx] xSfond xL0, (T (x)) [3]

In which: e2 [T (x), Ci (x), P (x)] = emissivity of the exhaust gas i; T (x) = temperature of the exhaust gas i; C ~ (x) = concentration of the component in the exhaust gas i; x = location of the component along the X axis;

A = value of x at the end of the exhaust gas; p (x) = pressure of the exhaust gas i;

 bottom = emissivity of the bottom wall 50 of the combustion chamber; L °, (T (x)) = luminance of a black body. In a closed combustion chamber, the computing unit 20 is able to implement the determination method illustrated in FIG. 2 using this new formula during step 42.

Claims (1)

CLAIMS1.- A method for determining the spatial distribution of at least one thermodynamic parameter in a semi-transparent medium (6), the method comprising the following steps: - emission (30) of a first radiation through the semi-transparent medium transparent (6), by an emitter (4); - receiving (36) the first backscattered radiation by the semi-transparent medium (6); measuring (38) the retro-diffusion (R2 (t)) of the radiation received as a function of the time and the wavelength of the radiation received; characterized in that it further comprises the following steps: - reception (38) of a second radiation emitted by the semi-transparent medium (6); measuring (40) the luminance (La) of the second radiation received as a function of its wavelength; determining (42) the spatial distribution of at least one thermodynamic parameter of the semi-transparent medium (6) from said measured luminance (La), said measured backscattering (R2, (t)), the equation radiative transfer theory and the theoretical retro-diffusion equation. 2. The determination method according to claim 1, wherein the thermodynamic parameter is the temperature (T (x)) of the semi-transparent medium (6). 3. A method of determination according to any one of claims 1 and 2, wherein the thermodynamic parameter is the concentration (c; (x)) of a component of the semi-transparent medium (6). 4. A method of determination according to any one of claims 1 to 3, wherein the first emitted radiation belongs to the spectral range between 100 micrometers and 200 nanometers. 5. A determination method according to claim 4, wherein the first emitted radiation belongs to the spectral range between 0.4 micrometer and 5 micrometers. 6. A method of determination according to any one of claims 1 to 5, wherein the first emitted radiation is pulsed at a frequency between 1 Hertz and 500 Megahertz. 7. A method of determination according to any one of claims 1 to 5, wherein the first radiation belongs to a frequency range different from the frequency range of the second radiation. 8. A method of determination according to any one of claims 1 to 7, wherein the determining step (42) is carried out from a method of inversion of the theoretical equation of radiative transfer and theoretical equation of retro diffusion. 9. A determination method according to any one of claims 1 to 8, wherein the semi-transparent medium (6) is an exhaust gas of a combustion chamber. 20 10. System (2) for determining the spatial distribution of at least one thermodynamic parameter of the semi-transparent medium (6) of a combustion chamber, the system comprising: a transmitter (4) capable of emitting a first radiation through the semi-transparent medium (6); a receiver (12, 24) capable of receiving the first retro-reflected radiation by the semi-transparent medium (6), said receiver (12, 24) being able to measure the backscattering (R2 (t)) of the first radiation received according to its wavelength and time; Characterized in that the receiver (12, 24) is adapted to receive a second radiation emitted by the semi-transparent medium (6), said receiver (12, 24) being able to measure the luminance (La) of the second radiation received according to its wavelength; and in that the system (2) further comprises a computing unit (20, 22) capable of determining the spatial distribution of at least one thermodynamic parameter of the semi-transparent medium (6) from said measured luminance (Lx ), said measured backscattering (R2, (t)), the theoretical radiative transfer equation and the theoretical backscattering equation. 11. System (2) according to claim 10, wherein the emitter (4) is a white laser. 12. System (2) according to claim 10, wherein the transmitter (4) comprises discrete laser diodes. 13. System (2) according to any one of claims 10 to 12, wherein the receiver (12, 24) comprises a monochromator (16) and a camera (18). 14. System (2) according to any one of claims 10 to 13, wherein the receiver (12, 24) comprises an oscilloscope.