JPH04259846A - Apparatus for dynamically measuring particle density in gas flow - Google Patents

Abstract

PURPOSE: To measure particle density accurately when measurement flow changes widely without contaminating a window. CONSTITUTION: A flow, where particle density is measured, passes a measurement pipe comprising an outer pipe 1 and an inner pipe 4. An annular dead space 7 that opens to the flow to be measured is provided at the downstream side of a measurement section 8. A ring 13 that surrounds a measurement pipe 5 at the height position of the measurement section 8 includes optical windows 18 and 19. The window forms the connection members of light conductors 20 and 21. The light conductors are connected to a light source or an evaluation unit. Chambers 16 and 17 with washing air supply ports 22 and 24 are provided in front of an optical window. Air is preferably supplied to the washing air supply port by an air pump that is adjusted to a constant air flow rate so that the device achieves a positive result over a wide parameter range of gas flow.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides a measuring tube having a plurality of light beam passing ports (radiation passing ports) facing each other and arranged in a straight line, and each of the light beam passing ports extending radially outward into one chamber. According to the principle of turbidity measurement, the gas The present invention relates to a device for dynamically measuring particle density in a flow, in particular an exhaust gas flow of an internal combustion engine.

0002

BACKGROUND OF THE INVENTION Such a device, as known for example from DE 38 39 348 A1, passes transversely through a gas stream in order to generate a signal for the particle density of the gas stream. take advantage of the decrease in the intensity of the light beam. The greater the particle density in the gas stream, ie the soot density in the case of the exhaust gas of an internal combustion engine, the greater the difference in the intensity of the light beam before and after passing through the gas stream.

In an advantageous application of the invention, the particle density in the exhaust gas stream of an internal combustion engine, in particular an internal combustion engine driving a motor vehicle, is determined in all operating states of the internal combustion engine, that is to say even when running at full load. Sometimes it is necessary to ensure that the device can measure particle density with a high degree of accuracy.

Another problem in the case of devices of the type mentioned at the outset, which is closely related to the above-mentioned requirements for such devices, is that the optical window should not be contaminated by the gas flow. Federal Republic of Germany Patent Application Publication No. 38393
In the example given in publication No. 48, a chamber is provided in front of the optical window in the direction of the gas flow, ie in the direction of the interior of the measuring tube. Cleaning air is poured into this chamber. This cleaning air also reaches the interior of the measuring tube through the beam passage opening. This principle is also used in the devices described in DE 3503720 and DE 3638472. However, the gas flow flows to the venturi in the area of the measuring section, and the cleaning air is sucked into the interior of the measuring tube at negative pressure without the use of an air pump. Apart from the fact that the use of a venturi-like measuring tube gives rise to undesired flow phenomena, including backflow, under certain operating conditions of the internal combustion engine supplying the measuring gas, as has been demonstrated by experiments, this measure The disadvantage is that a sufficient cleaning air flow is never ensured over the entire operating range of the internal combustion engine. For this reason, in the device described in DE 38 39 348 A1 mentioned at the beginning, an air pump is provided for supplying air to the cleaning air supply port. However, since this air pump is operated by the exhaust pulsation of the internal combustion engine, a continuous flow of cleaning air is not available. Furthermore, there is a risk that there will not be a sufficient cleaning air flow over the entire operating range of the internal combustion engine. Furthermore, the pulsating cleaning air flow has a negative flow effect on the length of the measuring section, leading to inaccurate measurements. If, in the case of devices of the type mentioned at the outset, heating coils are used to avoid the deposition of soot particles, the contact of the soot particles with the heating coils results in a broadband spectrum due to the chemical transformation of the particles. is detected. This makes the measurements even more inaccurate.

In order to complete the presentation of the state of the art, a brief mention will be made of German Patent Application No. 1598138. This publication discloses a device based on the principle of diffuse light measurement. In this case, a nozzle-like insert is provided in the measuring tube upstream of the actual measuring section, so that a much larger flow cross-section occurs at the location of the measuring section than in front of it. A ring-shaped dead space with a cleaning air supply opening is provided between the insert and the measuring tube. This dead space opens into the interior of the measuring tube and thus into the gas stream before the measuring section. The disadvantage of this construction is that the diameter of the measurement section changes depending on the flow rate and pulsation of the gas flow to be measured. Furthermore, gas backflow due to edge vortices and differential pressure cannot be prevented. Since the cleaning air is sucked into the measuring tube by means of negative pressure, this known device likewise cannot be used in any exhaust gas backpressure that occurs during operation of the connected internal combustion engine. The use of this known device in particular upstream of the exhaust turbocharger is not possible, especially when cylinder-selective particle recognition is required.

[0006]

SUMMARY OF THE INVENTION The object of the invention is to improve a device of the type mentioned at the outset, while maintaining its advantages, as follows. i.e. without the risk of dirty windows.
The object of the present invention is to improve the particle density to be able to be measured with high accuracy over a wide range of changes in the measurement flow.

[0007]

The solution according to the invention to this problem is such that the measuring tube is divided into two parts while maintaining a constant flow cross-sectional area over its entire length and forming at least one dead space by means of an outer pipe and an inner pipe. It is constructed in a heavy-walled manner in that this dead space opens into the gas stream downstream of the measuring section formed between the optical windows. Advantageous embodiments of the invention are set out in claims 2 to 8.

By using a double-walled measuring tube with a constant flow cross-section for the flow of the measuring gas over its entire length, undesirable flow phenomena such as backflow can be avoided in the device supplying the gas to be measured, especially in the avoided over the entire operating range of internal combustion engines. Since the cleaning air is introduced into the gas stream in the flow direction in front of the measuring section, the cleaning air does not have an adverse effect on the measurement. Furthermore, in a preferred embodiment of the invention, an air pump (e.g. Ro
mega 080 type 84) is used. As a result, a sufficient amount of cleaning air is supplied to clean the optical window, independent of the respective gas backpressure in the measuring tube. This can be omitted if, according to another embodiment of the invention, at least one other cleaning air flow is introduced into the dead space upstream of the measurement section. This cleaning air flow entrains the cleaning air exiting the dead space through a beam passage opening extending between the chamber and the dead space, so that no cleaning air flows through the beam passage opening of the inner tube.

The present invention can advantageously measure particle density in the exhaust gas of a supercharged internal combustion engine. This is because, as mentioned above, the high exhaust backpressure generated in the measuring tube has no practical effect on the cleaning air flow.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the invention of a device for dynamically measuring particle density in an exhaust gas stream will now be described with reference to the figures.

As shown in FIG. 1, an outer tube 1 and both tube portions 2
, 3 is attached or bolted to an exhaust pipe 6 of an internal combustion engine (not shown) via a flange joint. Exhaust gas flow is indicated by arrows. The outer tube 1 and the inner tube 4 form an annular dead space 7. This dead space opens at its downstream end between the two inner tube sections 2, 3 into the exhaust gas flow. Figure 1
Since the entire tube system shown in FIG. 1 has a constant internal diameter over its entire length, no effect on the exhaust gas flow due to sudden changes in diameter occurs, especially in the measurement section 8. The inlet of the dead space 7 to the exhaust gas flow is configured as follows. That is,
The downstream section 3 of the inner tube 4 has a conical widening which surrounds the downstream end of the tube section 2 at a distance.

The measurement section 8 is the light beam passage opening 9, 10 of the inner tube 4.
and the positions of the light beam passage ports 11 and 12 of the outer tube 1. All the ray apertures are diametrically opposed. 13 designates a ring surrounding the measuring tube 5 in the area of the measuring section 8. This ring is provided with passages 14, 15 located in line with the beam passage openings 9-12. The radially outer chambers 16, 17 are connected to this passage. The chamber itself has an optical window 18,1 on the outside.
9. In this embodiment, ordinary light guides 20, 21 extend from this window. The light guide 20 extends to the light source, and the light guide 21 extends to the light receiver and the light converter. This light receiver and light converter are part of the evaluation device. Such an evaluation device is known, for example, in a modified embodiment from German Patent Application No. 3,503,720 mentioned above. In this case, the adjustment serves to ensure a constant light intensity at the transmitter. Since such evaluation and adjustment devices are state of the art, they will not be described further here.

Measurement using the above device is carried out as follows. That is, the exhaust gas flows through the measuring tube 1 and the light beam passes through the light guide 20, the window 16, the channel 14 and the light beam passage openings 12, 9.
The light is transmitted to the measurement section 8 through the . The light beam passes through the light beam passage port 10.
, 11 and a channel 15 and is finally led via a light guide 21 to an evaluation device. The greater the particle density in the exhaust gas stream, the greater the difference between the emitted and received light intensities. This difference serves to generate a signal of the respective particle density.

Optical window 1 defining chambers 16, 17
In order to avoid the deposition of particles on the surfaces of 8,19, several measures have been taken in the device according to the invention.

There are two secondary air supply ports leading to the chamber 16.
It is located at 2. This secondary air supply port is
A cleaning air flow is oriented in the chambers 16, 17 approximately along the surface of the window 18 or 19. The cleaning air also reaches the dead space 7 through channels 14, 15. The cleaning air reaches the exhaust gas stream from the downstream end of this dead space. That is, the exhaust gas flow is reached at a relatively remote location from the measuring section 8. Other means to keep the optical windows 18, 19 clean are the flow passage openings 9/
12 and/or channels 14, 15 are designed with a small diameter so that they simultaneously have a throttling function. However, this not only makes it more difficult for the particles to enter the chambers 16, 17, but also prevents scattered light from reaching the receiver and making the measurements inaccurate. in this case,
An air pump is used to supply air to the secondary air supply ports 22, 23. This pump is regulated with a constant air flow, that is to say independent of the exhaust backpressure in the measuring tube 4. This ensures that in all operating modes of the internal combustion engine and thus in all exhaust gas backpressures in the measuring tube 4, there is a sufficient cleaning air flow to avoid fouling.

As clearly shown in FIG.
10 directly faces the cleaning air passages 14 and 15,
A small amount of the cleaning air stream passes through the passage openings 9, 10 into the exhaust gas stream. To avoid this, and to ensure a strong flow of cleaning air, a dead space 7, as shown at 24, is provided.
An additional cleaning air supply opening is provided leading to. This cleaning air supply runs parallel to the axis 25 of the device. The cleaning air supply opening can be formed by holes at 24 locations in combination with the flow guide member (guide plate in the dead space 7). The flow cross-sectional area of this hole is larger than the cross-sectional area of the adjacent beam passage opening 14 (the ratio of the cross-sectional areas is approximately 3:1). In any case, the additional cleaning air stream prevents cleaning air from entering the exhaust gas stream through the beam passage openings 9,10.

[0017] Instead of one dead space, a plurality of dead spaces arranged in the circumferential direction can be provided.

In order to prevent temperature changes from affecting the measurement accuracy, a cooling medium passage 26 is provided in the ring 13 that extends in the circumferential direction. This cooling medium channel prevents heat buildup in the area of the ring 13 in particular.

[0019] The invention provides a device of the type mentioned at the outset, which makes it possible to obtain high measurement accuracy over a large range of flow parameters of the stream to be measured with simple means.

[0020]

As explained above, the device according to the invention makes it possible to measure particle density with high accuracy over a wide range of changes in the measured flow without the risk of contaminating the window.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an embodiment of the invention.

2 is a cross-sectional view of an embodiment of the invention along line II-II in FIG. 1; FIG.

[Explanation of symbols]

1 Outer tube 4 Inner tube 5 Measurement tube 7 Dead space 8 Measurement section 16, 17 Chamber 18, 19 Window

Claims (8)

[Claims] Claim: 1. A measuring tube is provided with a plurality of light beam passage ports facing each other and arranged in a straight line, each of the light beam passage holes opening radially outward into a chamber, which chamber receives the measurement light beam. or to drive the particle density in a gas stream, in particular an exhaust gas stream of an internal combustion engine, by the principle of turbidity measurement, defined by an optical window for outflow and equipped with a pump-operated cleaning air supply. In a device for measuring the temperature of a meter, the measuring tube (5) maintains a constant flow cross-sectional area over its entire length and forms at least one dead space (7) by the outer tube (1) and the inner tube (4). Device characterized in that it is designed as a heavy wall and that this dead space opens into the gas stream downstream of the measuring section (8) formed between the optical windows (18, 19). 2. Device according to claim 1, characterized in that an air pump regulated at a constant air flow rate supplies air to the cleaning air supply openings (22, 23). [Claim 3] Light beam passage ports (9, 10, 11, 12,
3. Device according to claim 1, characterized in that 14, 15) have such a small cross-sectional area that they act as a diaphragm. 4. Upstream of the measurement section (8), in the longitudinal plane containing the measurement section, at least one other cleaning air supply opening (24) opens into the dead space (7), and from the cleaning air supply opening The cleaning air flow generated in the dead space (7) is arranged so that the cleaning air exiting from the beam passage opening (14, 15) extending between the at least one chamber (16, 17) and the dead space (7) is transferred to the measuring section (8). 4. Device according to claim 1, characterized in that it is entrained in a transverse direction relative to the object. 5. At least one chamber (16,1
5. Device according to claim 1, characterized in that in the area of 7) a cooling medium channel (26) is provided. 6. Chamber (16, 17), window (18,
19) and possibly cleaning air supply ports (22, 2
6. Device according to claim 1, characterized in that 3) is provided in a ring (13) surrounding the measuring tube (5). 7. At the point of opening of the dead space (7) to the gas flow, the inner tube (4) is divided into two tube sections (2, 3), the enlargement of the downstream tube section (3) being , surrounding the end region of the other tube section (2) at a distance. 8. Device according to claim 1, characterized in that the optical window (18, 19) is part of a light guiding device.