JPH03131740A - Exhaust gas diverting and sampling device - Google Patents

Abstract

PURPOSE:To enable diversion at a constant ratio by arranging the throat parts of three venturi tubes which are nearly equal in contraction ratio concentrically at the same position in the flow direction of exhaust gas. CONSTITUTION:A body 1A, an intermediate annular diverting tube 3, and a center core diverting tube 5 are fixed in relative position concentrically so that their throat parts 2, 4, and 6 are at nearly the same position in the flow direction of the exhaust gas. Further, the contraction ratios of the respective venturi tubes are equalized so that the flow velocities at the fluid intakes of the body 1A, tube 3, and tube 5 are equal. Therefore, a main flow of the exhaust gas is throttled by the throat part 2 from the outermost peripheral part and recovers pressure at a pressure recovery part 14 and then the exhaust gas is throttled by the throat part of a center core part 13, mixed with part of gas recovered at a recovery part 16, and discharged from a blower. Further, the diverted gas which passes through the intermediate annular part 12 and is throttled by the throat part 4 and recovered at a recovery part 15 is passed through a vent part 9, adjusted with the main flow pressure, and admitted to a dilution tunnel. Consequently, the gas is diverted at the constant ratio.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is used to measure exhaust gas from internal combustion engines such as automobile engines. This relates to the improvement of equipment for measuring particulate matter by dividing the flow into dilution tunnels, etc., and relates to the field of pollution prevention technology caused by combustion exhaust gas.

(Prior Art) Particulate matter contained in exhaust gas from diesel engines and the like has cohesive and hygroscopic properties, and accurate measurement thereof generally requires a dilution tunnel.

However, if the exhaust gas flow rate is, for example, 10 [m3/mln 1
In a high-output engine with a power output of more than 1,000,000 yen, a large-capacity dilution tunnel is required in order to maintain the measured gas after diluting the entire amount of exhaust gas above the dew point, and such a large-capacity diluting tunnel is generally not used. This is considered extremely difficult both economically and spatially.

Therefore, various methods have been devised in which a representative sample of the exhaust gas is sampled in a divided manner instead of the entire flow rate of the exhaust gas and diluted.

Among these methods, in order to keep the ratio of the diverted exhaust gas to the total exhaust gas flow rate (i.e., the division ratio) constant, the exhaust gas is diverted and introduced into the dilution tunnel; There is a method of configuring an exhaust gas flow sampling device by providing two venturi pipes in parallel, one for bypass and one for passing the exhaust gas as it is. This exhaust gas flow sampling device is shown in FIG.

In FIG. 3, exhaust gas discharged from an engine 21 passes through a muffler 22, enters a mixing adjustment pipe 23 for stirring and mixing the exhaust gas, and from here passes through an exhaust gas flow sampling device 30, and a part of the exhaust gas is passed through a muffler 22. is diverted.

This exhaust gas branch flow sampling device 30 includes, for example, the mixing adjustment pipe 2
3, the main conduit 31A connected to the main conduit 31
The branch pipe 32A has its tip inserted into the main pipe 31A and the branch pipe 32A, and a bypass venturi 31 and a sample venturi 32 are connected to the main pipe 31A and the branch pipe 32A.

The bypass venturi 31 is connected to a discharge pipe 33A via a butterfly valve 33, and the tip of the sample venturi 32 is connected to a pipe line 33B inserted into a dilution tunnel 35, which will be described later. .

The bypass venturi 31 and the sample venturi 3
2, one suitable for each flow rate is adopted.

If the differential pressures generated by these venturis 31 and 32 are the same, then from their pipe diameters, the main pipe 31A
And the flow rate ratio of exhaust gas passing through the branch pipe line 32A is determined.

The dilution tunnel 35 is equipped with a filter 37 and a dilution tunnel inlet valve 36 on the upstream side in the air flow direction, and a positive displacement bomb (
A positive displacement pump (hereinafter referred to as FDP) 40 is provided.

The bypass venturi 31 and the sample venturi 3
The flow rate of fluid through 2 is regulated using a butterfly valve 33 and a dilution tunnel inlet valve 36.

A dilution fluid (air y) is introduced into the dilution tunnel 35 by the PDP 40 through the filter 37. The components of this dilution fluid are measured by the analyzer 38.

Further, the components of the diluted exhaust gas are measured by an analyzer 39. At this time, the measurement results of the analyzer 38 are referred to.

Generally, the method of controlling flow rate using a Venturi tube is as follows:
It has the advantage of pressure recovery when the cross section of the flow path gradually expands, resulting in less pressure loss and uniformity, but it is usually used in steady flow, and the effect of nonlinearity is ignored for pulsating flow. There are many things that cannot be done.

(Problems to be Solved by the Invention) The above-described conventional technology had the following problems.

In other words, it is difficult to make the exhaust pressure waves and temperature conditions the same in two venturi tube passages with significantly different flow rates, so in cases such as when pulsating flow is noticeable at low speeds or during transient operating conditions where the exhaust gas flow rate changes greatly. In this case, it becomes difficult to keep the diversion ratio constant.

In addition, in the exhaust gas analyzer mentioned above, the flow rate of the exhaust gas passing through the main pipe 31A and the flow rate of the exhaust gas passing through the main pipe 31A,
The flow rate of the divided gas passing through A is not the same. That is, uniform suction is not performed at the inlet of the branch pipe 32A. As a result, when measuring particulate matter having a relatively large particle size, the splitting ratio between the particulate matter and the gas component differs.

In cases such as transient operating conditions, a split flow that can maintain the same pressure waves, temperature conditions, etc. is required, and it is also important to connect the constant velocity suction at the split point and the Venturi tube directly to the split flow section under the same conditions. becomes.

The present invention has been made to solve the above-mentioned problems, and its purpose is to always accurately maintain a constant ratio of exhaust gas not only in steady operating conditions but also in all operating conditions including transient operating conditions. An object of the present invention is to provide an exhaust gas diversion sampling device capable of dividing a flow of air and continuously collecting representative samples of particulate matter.

(Means and effects for solving the problem) In order to solve the above-mentioned problems, the present invention provides three Venturi tubes each having a different diameter and each having an approximately the same drawing ratio. The exhaust gas downstream end of the central Venturi tube (center core branch pipe) is arranged concentrically so that the throats of the Venturi tubes are at almost the same position in the flow direction of the exhaust gas. part protrudes outside an intermediate venturi pipe (intermediate annular branch pipe) disposed between the central core branch pipe and the outermost circumferential venturi pipe, and is introduced between the intermediate annular branch pipe and the center core branch pipe. The unique feature is that only the exhaust gas that has been removed is diverted.

As a result, the Venturi tubes of each flow path are directly connected to the dividing section and receive the same pressure wave, and the suction of the exhaust gas from the openings of the intermediate annular dividing tube and the central core dividing tube becomes uniform suction.

Further, the state of the flow of exhaust gas passing through each venturi pipe is approximately equal to the state of the flow of exhaust gas in the outermost venturi pipe. That is, the flow conditions (pressure, flow velocity, temperature, etc.) of the exhaust gas passing through each venturi pipe are approximately the same at each position in the exhaust gas flow direction.

Further, the branched exhaust gas pipe becomes annular and has a similar shape to the outermost venturi pipe. That is, the flow path conditions of the main flow and the branch flow can be made almost the same.

(Example) Specific examples of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 2 is a block diagram of an example of an exhaust gas analyzer employing an embodiment of the present invention, and FIG. 1 is a longitudinal sectional view showing details of the embodiment of the present invention shown in FIG. 1 and 2, the same reference numerals as in FIG. 3 represent the same or equivalent parts.

First, exhaust gas discharged from the engine 21 passes through the muffler 22 and enters the mixture adjustment pipe 23, where it is thermally insulated.
The exhaust gas is introduced into an exhaust gas diversion sampling device 1 having multiple venturi tubes and is divided. Note that the mixing adjustment tube 23 can be omitted.

This exhaust gas flow sampling device 1 is composed of three venturi pipes each having a different diameter.

That is, the exhaust gas diversion sampling device 1 includes a body IA that constitutes an outermost venturi tube by a throat portion (throttle portion) 2 and a pressure recovery portion 14, and is disposed within the body IA,
An intermediate annular branch pipe 3 that constitutes an intermediate venturi pipe by the throat part 4 and the pressure recovery part 15; and the intermediate annular branch pipe 3.
It is comprised of a central core branch pipe 5 which is disposed inside the pipe and constitutes a central Venturi pipe by a throat part 6 and a pressure recovery part 1G. The outermost Venturi tube and the intermediate Venturi tube are each arranged in an annular shape with a Venturi tube and a central Venturi tube disposed inside each of the venturi tubes.

The body IA, the intermediate annular branch pipe 3, and the center core branch pipe 5 are arranged concentrically, and their respective throat portions 2.4 and 6 are arranged at approximately the same position with respect to the exhaust gas flow direction. , their relative positions are fixed.

Furthermore, the venturi tubes of the body IA, the intermediate annular branch pipe 3, and the central core branch pipe 5 are designed so that the flow velocity at each fluid intake port is the same. In order to make the flow velocity the same, it is necessary to make at least the same throttle ratio β2 of each venturi pipe, and to make the differential pressure generated by each venturi pipe the same. Also, if necessary, the inclination angle of each pressure recovery part (equivalent cone angle of the expansion tube)
, or the aperture cone angle, etc., may also be made the same.

Therefore, the exhaust gas flow passes from the inlet of the exhaust gas separation sampling device 1 between the exhaust gas separation sampling device 1 and the intermediate annular separation pipe 30, and the exhaust gas flow passes from the inlet of the intermediate annular separation pipe 3 to the intermediate annular separation pipe 3 and the central core separation pipe. The flow distribution state of the exhaust gas flow passing between the pipes 5 and the exhaust gas flow passing inside the center core branch pipe 5 is determined by the intermediate annular branch pipe 3 and the center core branch pipe within the body IA. The distribution state of the exhaust gas flow is almost the same as the state in which the exhaust gas flow is not arranged. That is, the pressure, flow velocity, temperature, etc. of the exhaust gas flow passing through the body IA, the intermediate annular flow branch pipe 3, and the center core flow branch pipe 5 are approximately the same at each position in the exhaust gas flow direction.

Here, the throttling ratio β2 of each venturi tube is set so that even if the exhaust gas flow reaches its maximum flow rate, it does not reach the sonic velocity at the throat portions 2.4 and 6, and the differential pressure becomes too small (
In order to prevent the error in the amount of exhaust gas to be diverted from becoming large due to the throttling effect becoming too small, it is preferable to set it within the range shown by the first equation, for example.

C1/20)<β2<(1/3)...(1
) A vent portion (bent portion) 9 is formed at the rear end of the intermediate annular branch pipe 3, and this end portion is drawn out to the outside of the body IA via the vent portion 9. Further, the discharge portion 8 of the central core branch pipe 5 passes through the vent portion 9 of the intermediate annular branch pipe 3 and is exposed within the rear end portion of the body IA.

Note that the symbols 7A and 7C are support stays for fixing the tip of the intermediate annular distribution pipe 3 and the tip of the central core distribution tube 5, and the symbols IB, IC, and 3B are for connecting the exhaust gas distribution sampling device 1. This is a flange for

Therefore, the main flow of exhaust gas passes through the outermost circumferential portion 11 and is throttled at the throat portion 2, and then recovers its pressure at the pressure recovery portion 14. Then, this main flow passes through the central core section 13 and is throttled at the throat section 6, and then is combined with a part of the exhaust gas whose pressure has been recovered at the pressure recovery section 16, passes through the exhaust duct 24, and exits from the blower 25. be discharged.

In addition, after passing through the intermediate annular portion 12 and being throttled by the throat portion 4, the branched exhaust gas whose pressure has been recovered by the pressure recovery portion 15 passes through the vent portion 9 and is brought to almost the same pressure as the output pressure of the main stream at the control valve 1o. After being adjusted, it is introduced into the dilution tunnel 19 as a sample gas.

Note that numerals 17 and 18 are pressure gauges for pressure monitoring.

The dilution tunnel 19 is generally used as a CVS (Constant Volume Sampler) device, and a filter 26 is provided at the inlet to introduce purified dilution air, and the sample is used as a reference by an analyzer 29. A portion is sampled and measured, and after the exhaust gas from the engine 21 is introduced and mixed to make a homogenized diluted sample, a portion is sampled into the exhaust gas analyzer 20 and measured.

On the other hand, most of the diluted sample gas whose temperature has been controlled through the heat exchanger 27 is sucked and discharged while being maintained at a constant flow rate by a blower equipped with a CFV (critical flow venturi) or a PDP 28. be done.

In this way, in this embodiment, three venturi tubes (body IA) each having a different diameter are formed so that their aperture ratios are approximately the same.

The intermediate annular branch pipe 3 and the central core branch pipe 5) are arranged concentrically so that the throat portions of the respective venturi pipes are located at approximately the same position with respect to the flow direction of exhaust gas. The suction of exhaust gas from the openings of the flow divider pipe 3 and the center core flow divider pipe 5 becomes uniform suction, and the flow state of the exhaust gas passing through the body IA, the intermediate annular flow flow pipe 3, and the center core flow flow pipe 5 ( (pressure, flow rate, temperature, etc.) are almost the same.

Further, a center core branch pipe 5 is disposed inside the intermediate annular branch pipe 3 serving as a branch pipe, and the exhaust gas passing through the center core branch pipe 5 is discharged to the outside of the intermediate annular branch pipe 3. Therefore, the branched exhaust gas pipe has a similar shape to the body IA through which the main flow of exhaust gas flows. That is, the flow path conditions of the main flow and the branch flow are almost the same.

Therefore, the particulate matter contained in the exhaust gas is divided at a constant ratio similar to that of the gas components, and the influence of the pulsation of the exhaust pressure wave is absorbed into each body IA.

Since the intermediate annular distribution tube 3 and the central core distribution tube 5 can be made to have substantially the same distribution, the distribution ratio can be kept approximately constant even in a transient operating state.

Now, in an exhaust gas analyzer using a dilution tunnel, the flow rate of exhaust gas diverted from the intermediate annular flow branch pipe 3 is usually 1 of the total flow rate of exhaust gas discharged from the engine 21.
It is set within the range of /10 to 1/40. Therefore, the inner diameter of the opening of the intermediate annular branch pipe 3 is the same as that of the body IA.
It is preferable to set the diameter within a range of about 1/3 to about 1/6 of the inner diameter of the opening.

In addition, in FIG. 1, the discharge part 8 of the central core branch pipe 5
passes through the vent portion 9 of the intermediate annular flow branch pipe 3 to the body I.
The exhaust gas exposed in A and passed through the center core distribution pipe 5 is configured to merge with the main stream of exhaust gas passed through the body IA, but the present invention is particularly limited to this. This is not the case, and the exhaust gas that has passed through the central core branch pipe 5 may be prevented from being discharged into the intermediate annular branch pipe 3. Therefore, the ejection part 8 is, for example, the body I
It is also possible to protrude to the outside of the center core flow pipe A so that the exhaust gas that has passed through the center core branch pipe 5 does not merge with the main flow of the exhaust gas that has passed through the body IA.

Furthermore, in the above description, the intermediate annular branch pipe 3
A vent part 9 is formed at the rear end, and the end part is
Although it has been described that the pipe is drawn out to the outside of the body IA through the vent portion 9, the present invention is not limited to this. It goes without saying that the rear end of the intermediate annular flow branch pipe 3 may be bent to allow the rear end of the intermediate annular flow branch pipe 3 to be drawn out of the body IA.

(Effects of the Invention) As is clear from the above description, according to the present invention, the following effects are achieved.

In other words, the flow conditions (pressure, flow velocity, temperature, etc.) of the exhaust gas passing through each of the Venturi tubes of the body IA, the intermediate annular distribution tube 3, and the central core distribution tube 5 are approximately the same at each position in the exhaust gas flow direction. Furthermore, since the flow path conditions of the main stream and the branch flow are almost the same, the branch flow ratio can always be kept almost constant even in a transient operating state where the exhaust pulsation is large and the flow rate, temperature, pressure, etc. vary greatly.

In addition, since the suction of exhaust gas from the openings of the intermediate annular diverter pipe 3 and the center core diverter pipe 5 is a uniform suction, particulate matter is likely to be biased and the flow line may be different from that of the exhaust gas flow. Even when sampling a sample containing a certain component, gas components and particulate matter components are divided at a constant ratio proportional to the cross-sectional area of the diverter tube.

Furthermore, since it has a relatively simple structure, the exhaust gas flow sampling device can be made smaller and lighter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of an embodiment of the present invention. FIG. 2 is a block diagram of an example of an exhaust gas analyzer employing an embodiment of the present invention. FIG. 3 is a block diagram of an example of a conventional exhaust gas analyzer.

Claims (1)

[Claims] (1) An exhaust gas flow sampling device that continuously introduces exhaust gas from an internal combustion engine by partially flowing the exhaust gas at a fixed ratio, has a body connected to an exhaust gas passage connected to the internal combustion engine, and whose inner wall is formed in the shape of a venturi tube. , comprising: an intermediate annular branch pipe disposed within the body and having an inner wall formed in the shape of a Venturi pipe; and a central core branch pipe disposed within the intermediate annular branch pipe and having an inner wall formed in the shape of a Venturi pipe; Venturi tubes in each flow path formed by walls of the body, the intermediate annular distribution tube, and the central core distribution tube are formed so that their aperture ratios are approximately the same; The center core diverter tube is configured such that each diverter, venturi throat, and pressure recovery section are concentric, and each diverter, venturi throat, and pressure recovery section is arranged such that the flow of exhaust gas passes through them. They are placed at almost the same position with respect to the direction, and the conditions of flow velocity, temperature, and pressure in the branch part of each annular flow path and the Venturi pipe are kept the same, especially under conditions with pressure waves and flow rate changes. An exhaust gas diversion sampling device characterized in that it is always possible to divide the flow in proportion to the cross-sectional area of the flow path at the diversion point.