JP2001249064A - Exhaust gas diluting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To substantially improve accuracy in measuring PM by forming a specific mode of exhaust gas introduction to protrude the end part of an exhaust gas introducing tube to the downstream side of an orifice and suppressing the adhesion of PM to the wall surfaces of a diluting tunnel to a minimum. SOLUTION: An orifice plate 33 in which the orifice 32 for throttling introduced air is formed and the exhaust gas introducing tube 34 for discharging exhaust gases into a tunnel 4 on the more downstream side than an air introducing part are arranged in the diluting tunnel 4 of which the upstream side an air introducing tube 5 for diluting exhaust gases is connected. The end part (a) of the exhaust gas introducing tube 34 is protruded to the downstream side of the orifice 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas diluting device in a partial dilution type gas dilution system in which a part of exhaust gas from an engine is partially diluted by a diluting gas.

[0002]

2. Description of the Related Art Fine particulate matter (P) such as soot contained in gas discharged from a diesel engine of an automobile or the like is used.
In recent years, as a gas dilution system required for measurement of articulate matter (PM), flow rate control and partial sampling of exhaust gas have been performed in place of the conventional full dilution system that collects and dilutes the entire amount of exhaust gas. A small-scale dilution system of a partial dilution system to be performed has been adopted. The gas dilution system of the partial dilution method based on the partial sampling controls the flow rate of a dilution gas (for example, air) for diluting the exhaust gas while maintaining the exhaust gas after dilution at a constant flow rate.
This is a system for controlling the flow rate of exhaust gas obtained as the difference between these flow rates.

As shown in FIGS. 6 and 7, an exhaust gas diluting device used in this system is introduced into a dilution tunnel 4 having a circular cross section to which an air introduction pipe 5 for diluting exhaust gas is connected on the upstream side. Orifice hole 3 for squeezing air
6, a circular orifice plate 33 in which the exhaust gas 2 is formed, and an exhaust gas introduction pipe 34 having a circular cross section for discharging exhaust gas into the tunnel 4 downstream of the air introduction portion are arranged concentrically.
In the exhaust gas dilution device shown in FIG.
The exhaust gas diluting device shown in FIG. 7 is configured such that the end a of the exhaust gas introduction pipe 34 is substantially flush with the downstream surface S of the orifice plate 33.が あ る Some are set so that they are flush.

According to the exhaust gas diluting device having such a configuration, the air A for dilution is restricted by the orifice hole 32,
It rapidly passes through the orifice hole 32 and diffuses at once in the tunnel 4 downstream of the orifice plate 33. On the other hand, the exhaust gas G sampled by the exhaust gas introduction pipe 34 is discharged to the central portion of the dilution air A narrowed by the orifice hole 32, and is diffused at once in the tunnel 4.
Mixed with.

[0005]

The above-mentioned PM discharged from the exhaust gas introduction pipe 34 is viscous in nature, and therefore, when not sufficiently mixed with the dilution air A, the PM 4 has a wall surface. When the wall surface W of the tunnel 4 was actually visually observed in the exhaust gas diluting device having the above-described configuration, it was confirmed that PM had adhered. This PM loss was reduced by the filter on the downstream side. There is a problem in that a variation occurs in the generation of the collected PM, which leads to a decrease in the PM measurement accuracy.

In the exhaust gas diluting device having the above structure, the present inventors have found that the mixing of the air A and the exhaust gas G is structurally insufficient, and the cause of PM on the tunnel wall W is narrowed by the orifice hole 32. It was presumed that the exhaust gas G was introduced into the dilution air A.

That is, in the exhaust gas diluting apparatus shown in FIG. 6, the exhaust gas G discharged to the center of the air A constricted by the orifice hole 32 becomes a gas flow r of extremely reduced diameter, and the exhaust gas diluting gas shown in FIG. Also in the device, the orifice hole 32
When the air A narrowed by the gas passes through the end a of the exhaust gas introduction pipe 34, the exhaust gas G acts to reduce the diameter of the exhaust gas G, so that the exhaust gas G becomes an extremely reduced gas flow r. As the air A diffuses, the air A and the exhaust gas G are mixed. In this way, the exhaust gas G is once extremely reduced in diameter and then diffused.
It was speculated that this was the cause of poor mixing.

[0008]

The exhaust gas diluting apparatus of the present invention is based on the above presumption, and is provided in a dilution tunnel in which an air introducing pipe for exhaust gas dilution is connected on the upstream side. An orifice plate with an orifice hole for restricting the introduced air and an exhaust gas introduction pipe for discharging exhaust gas in a tunnel downstream of the air introduction section are provided, and the end of the exhaust gas introduction pipe is connected to the orifice hole. It is characterized in that it protrudes to the downstream side of the exhaust gas (Claim 1), and is preferably configured so that the amount of protrusion of the end of the exhaust gas introduction pipe can be adjusted (Claim 2).

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a gas dilution system. In FIG. 1, E in the figure is, for example, a diesel engine mounted on an automobile, and 1 is an exhaust pipe connected thereto.

Reference numeral 2 denotes an exhaust gas sampling pipe which is inserted and connected to the exhaust pipe 1 for sampling the exhaust gas G flowing through the exhaust pipe 1, and is connected to a dilution tunnel 4 of an exhaust gas diluting device 3 for diluting the sun ring exhaust gas G with air A. It is connected.

Reference numeral 5 denotes an inlet pipe for the dilution air A which is connected to the upstream side of the dilution tunnel 4, and is provided with a dilution gas flow control device 6 as shown in FIG.

In FIG. 2, reference numeral 7 denotes a roots blower pump provided in the flow passage 8 and capable of changing the suction capacity by, for example, controlling the number of revolutions, and is controlled by an inverter (frequency converter) 9. Reference numeral 10 denotes a Venturi flow meter as a differential pressure flow meter having high measurement accuracy, and a pressure sensor 11 for detecting a pressure of air flowing through the flow path 8 near the Venturi flow meter.
A differential pressure sensor 12 and a temperature sensor 13 are provided. Reference numeral 14 denotes a flow rate calculation unit that calculates the flow rate (actual flow rate) of the air A flowing through the flow path 8 based on the detection outputs of the sensors 10 to 13. Reference numeral 15 denotes a comparison control circuit that compares the actual flow rate of air obtained by the flow rate calculation unit with a preset flow rate and outputs a predetermined control signal to the inverter 9.

Returning to FIG. 1, reference numeral 16 denotes a gas flow path connected to the downstream side of the dilution tunnel 4 and through which the diluted sample gas S flows.
And a filter 1 for collecting PM contained in the sample gas in respective flow paths 17 and 18.
9 and 20 and control valves 21 and 22 that can change the throttle amount (pressure loss) are provided. One flow path 17 is a sample gas flow path for flowing exhaust gas for measurement, and the other flow path 18 is a non-flow path. Each of the bypass passages is configured to flow exhaust gas for measurement.

Reference numeral 23 denotes a three-way solenoid valve provided as a flow path switching means provided on the downstream side of the sample gas flow path 17 and the bypass flow path 18. The port 23a is in the sample gas flow path 17, and the port 23b is in the bypass flow path. The port 23 c is connected to a gas flow path 24 on the downstream side of the three-way solenoid valve 23.

The gas flow path 24 has a suction pump whose suction capacity can be changed by controlling the number of rotations.
For example, a roots blower pump 25 and a differential pressure flow meter with high measurement accuracy, for example, a Venturi flow meter 26 are provided in this order. 27 is a pressure sensor for detecting the pressure of the gas flowing through the gas passage 24, 28 is a differential pressure sensor, 29
Is a temperature sensor.

Reference numeral 30 denotes an inverter (frequency converter) for controlling the Roots blower pump 25, and reference numeral 31 denotes a flow control unit for controlling the entire apparatus. The flow control unit 31 outputs a command to the control valves 21 and 22 and the inverter 30, and outputs a command to the sensors 27 to 29.
Is input.

In the gas sample system, the comparison control circuit 1 in the dilution gas flow control device 6 is used.
A command value is output from the inverter 5 to the inverter 9, and the roots blower pump 7 provided in the flow path 8 is controlled based on the command value, whereby a predetermined flow rate of dilution air is supplied to the dilution tunnel 4. A command value output by a PID controller (not shown) provided in the flow control unit 31 is output to the inverter 30, and the Roots blower pump 25 is controlled based on the command value output from the inverter 30 based on the command value. As a result, the sample gas flow rate S flowing through the gas flow paths 16, 18, and 24 is controlled so as to be always a predetermined flow rate.
The sampling flow rate of the exhaust gas is controlled.

FIG. 3 shows an exhaust gas diluting device 3.
In the figure, reference numeral 4 denotes a dilution tunnel described above, which has a circular cross section, and an air introduction pipe 5 for exhaust gas dilution is connected to the upstream side. Inside the dilution tunnel 4, an orifice plate 33 having a circular cross section in which an orifice hole 32 is formed at the center for narrowing the introduced air, and a circular orifice plate for discharging the exhaust gas G into the tunnel downstream of the air introduction part. Exhaust gas introduction pipe 3
4 are arranged concentrically.

The exhaust gas introduction pipe 34 is moved, for example, by a screw-type expansion / contraction means 35 for moving the pipe 34 in the axial direction.
This exhaust gas introduction pipe 3 is connected to the exhaust gas collection pipe 2 and forms an annular air flow path R between the orifice hole 32 and the exhaust gas introduction pipe 34 as shown in FIG.
4 has an end a protruding downstream of the orifice hole 32.

According to the exhaust gas diluting device 3 having the above-described structure, the end a of the exhaust gas introducing pipe 34 is made to protrude downstream from the surface S on the downstream side of the orifice plate 33, as shown in FIG. The air A throttled by the orifice hole 32 and passing through the air flow path R first diffuses at a stroke to the wall surface W side of the dilution tunnel 4, and the air A reaches the end a of the exhaust gas introduction pipe 34, It functions to reduce the diameter of the exhaust gas G discharged from the introduction pipe 34.

However, at the time of the action of the diameter reduction, the air A has diffused to the wall surface W side of the dilution tunnel 4 at a stretch, and the air flow velocity has been extremely reduced. The exhaust gas G discharged to the gas flow r becomes a gas flow r having a small degree of diameter reduction.

The protrusion amount t of the end a of the exhaust gas introduction pipe is
For example, from 1 mm to 10 mm by the screw type expansion / contraction means 35
Is adjustable over a range of

Here, in order to compare the present invention with a conventional example, an exhaust gas dilution apparatus shown in FIG.
Of the orifice hole 32 is about 1 mm, the diameter L of the mixed dilution up to the end of the tunnel is about 600 mm, and the inside diameter d of the orifice hole 32 is about 1 mm.
6 mm, the outer diameter D1 of the exhaust gas introduction pipe 34 was about 13 mm, the inner diameter d1 was about 11 mm, and the length L1 of the end a from the orifice plate 33 to the upstream side was about 2 mm.
As the exhaust gas diluting device shown in FIG. 7, of the exhaust gas diluting device shown in FIG.
I prepared something that was the same.

The exhaust gas diluting device 3 according to the configuration of the present invention is the same in dimensions as the exhaust gas diluting device shown in FIG. 7, but the exhaust gas introducing pipe 34 is passed through the orifice hole 32 and An end a is protruded to the downstream side of the orifice hole.
The air A of 30 l / min is supplied, and the exhaust gas G of about 5 l / min is supplied from the exhaust gas introduction pipe 34, and the protruding amount t of the end a of the exhaust gas introduction pipe 34 is adjusted in positions of 1 mm in a range of 10 mm. However, when the amount of PM collected by the filter 10 was examined, the amount of PM collected significantly increased as compared with the conventional configuration. It is considered that this is because in the exhaust gas dilution device 3 according to the configuration of the present invention, the adhesion of PM to the wall surface W was significantly reduced.

The reason for this is not clear at the moment, and the elucidation is urgently needed.
The exhaust gas G is diffused into the air A without extremely reducing the diameter of the exhaust gas G by adopting a unique form of introducing the exhaust gas into the downstream side of the orifice hole 32.
It is presumed that the mixing of the gas and the exhaust gas G became good.

In the above embodiment, the orifice hole 32
The inner peripheral surface is formed in a substantially semicircular cross-sectional shape,
As shown in FIG. 5 (A), a simple orifice hole 3
2, or as shown in FIGS. 5 (B) and 5 (C), or as a tapered orifice hole 32 having a tapered opening or a tapered hole as shown in FIG. 5 (D), or as shown in FIG. It may be 32.

Although the end a of the exhaust gas introducing pipe 34 is a simple cut-off end face, as shown in FIG. 5A, a substantially semi-circular chamfered end a or FIG. As shown in (1), the end may be at the end a of the tapered surface that expands.

Further, as shown in FIG. 5C, the end b of the exhaust gas introduction pipe 34 may be enlarged in a trumpet shape. Conversely, as shown in FIG. The end b of the orifice 34 may be narrowed and the inner peripheral surface of the orifice hole 32 and the exhaust gas introduction pipe 34 may be reduced.
It is needless to say that the shape of the end a can be arbitrarily combined.

[0029]

As described above, according to the exhaust gas diluting device according to the first aspect, a unique exhaust gas introduction mode is adopted in which the end of the exhaust gas introduction pipe projects to the downstream side of the orifice hole. Good mixing of the air and exhaust gas in the dilution tunnel is achieved, which makes it possible to minimize the adhesion of PM to the wall of the tunnel, that is, the PM loss, and furthermore, to capture the PM by a downstream filter. Since the variation in the generation of collected PM is extremely small, there is an effect that the measurement accuracy of PM can be greatly improved.

Then, by adjusting the flow rate of the dilution air,
When the measurement is performed by changing the dilution ratio of the sample exhaust gas, the protrusion amount of the end portion of the exhaust gas introduction pipe can be adjusted as described in claim 2, and the protrusion amount can be set to the optimum protrusion amount according to the dilution ratio. is there.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a gas dilution system.

FIG. 2 is a configuration diagram of a dilution gas flow control device.

FIG. 3 is a sectional view of an exhaust gas dilution device.

FIG. 4 is an explanatory diagram showing a flow state of air and exhaust gas.

FIGS. 5A to 5D are cross-sectional views showing an inner surface shape of an orifice hole and an end shape of an exhaust gas introduction pipe according to another embodiment.

FIG. 6 is a cross-sectional view showing a conventional exhaust gas dilution device.

FIG. 7 is a cross-sectional view showing a conventional exhaust gas dilution device according to another embodiment.

[Explanation of symbols]

4 ... dilution tunnel, 5 ... air introduction pipe, 32 ... orifice hole, 33 ... orifice plate, 34 ... exhaust gas introduction pipe, a ... end.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 3G004 AA01 BA00 DA21 3G091 AA18 BA31

Claims (2)

[Claims] 1. An orifice plate having an orifice hole for restricting introduced air in a dilution tunnel to which an air introduction pipe for exhaust gas dilution is connected on the upstream side, and in a tunnel downstream of an air introduction section. An exhaust gas introduction pipe for discharging exhaust gas, and an end of the exhaust gas introduction pipe protruding downstream of the orifice hole. 2. The exhaust gas diluting apparatus according to claim 1, wherein the amount of protrusion of the exhaust gas introduction pipe end is adjustable.