JP2945499B2 - Exhaust gas constant flow sampling method and variable venturi constant flow measurement control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for measuring exhaust gas of a fuel engine such as an automobile.

[0002]

2. Description of the Related Art As a proportional sampling device, a constant volume / volume mixing exhaust gas and clean air for dilution so that the total flow rate is always constant is used as one of the proportional sampling devices. A sampler (CVS) device is used. One of the methods is to generate a constant flow rate using a critical flow venturi known as CFV-CVS. This is U.S.A. S. Federal
Register Title 40, §86 ・
1309-84, FIG. As shown in N84-2, the technology of the gas sampling apparatus disclosed in Japanese Patent Application Publication No. 30794 (published on September 2, 1979) is used.

FIG. 2 shows this. According to this method, if the pressure and temperature immediately before the critical flow venturi are constant, when the pressure downstream of the venturi can be sufficiently reduced, the flow velocity in the slot reaches the critical velocity (the sound velocity at that temperature) and becomes constant. Is maintained.

However, when the temperature and the flow rate of the engine exhaust gas change and the temperature of the diluted exhaust gas in the critical flow venturi changes, the sound speed changes and the density also changes, so that the mass flow rate cannot always be kept constant.
In particular, when the exhaust gas purification technology advances and the pollution concentration decreases,
It is disadvantageous to increase the ratio of the dilution air, and the influence of the temperature of the exhaust gas becomes a problem. Also, it is necessary to increase the capacity of the blower for generating the critical flow, which is one problem of this method.

Furthermore, in the conventional method, since one venturi can handle only one flow rate, for example, in the case of testing a diesel engine for a large vehicle,
At the same exhaust flow rate after dilution between the idling condition where the exhaust flow rate is low and the particle concentration is relatively low, and the case where the exhaust flow rate is large and the particle concentration is relatively high under high-speed and high-load conditions, the particle concentration of the diluted exhaust sample has a large difference. This causes problems such as generation of inconvenience in collection and measurement of fine particles.

[0006]

SUMMARY OF THE INVENTION Conventional CFV-CVS
Therefore, the mass flow rate cannot always be controlled to be constant when the concentration of the diluted exhaust gas changes, and only one flow rate value can be set during measurement.
However, there is a problem that a large-capacity blower is required to generate air.

In the present invention, in order to solve these problems, the venturi tube is not limited to the critical flow, and the pressure, the pressure difference, the temperature, and the like of the slot are measured, and the flow of the slot is measured. Assuming that the road cross-sectional area is variable and known, a variable Venturi method was adopted in which the mass flow rate was constantly measured and controlled.

[0008]

SUMMARY OF THE INVENTION In accordance with this object, a method of collecting exhaust gas at a constant flow rate according to the present invention is to mix exhaust gas of a combustion engine with dilution air so that the mass flow rate after mixing becomes constant. The exhaust gas constant flow rate sampling method (CVS) for measuring the concentration of each gas component and the concentration of particulate matter in the exhaust gas or sampling at a constant flow rate to determine the emission amount of each component within a fixed time or under specific operating conditions, The present invention is characterized in that a variable venturi-type constant flow controller that automatically controls the flow cross-sectional area of the slot portion and controls the flow after mixing exhaust and air to the designated mass flow is used.

Further, the variable venturi-type constant flow rate measurement control device of the present invention includes a variable venturi-type venturi tube for defining a dilution tunnel and a gas flow rate of the dilution tunnel, and a pressure sensor for detecting a pressure at an inlet of the venturi tube. And a temperature sensor for detecting a temperature at an inlet of the Venturi tube; and a differential pressure sensor for detecting a pressure difference between a pressure at a slot of the Venturi tube and a pressure at the inlet. The slot portion is constituted by a relatively displaceable slot member and a core member, and the slot is formed by a gap between the slot outer member and the core member.
A cross-sectional area of the pressure sensor is defined, and the relative displacement is generated by a signal including a signal from the pressure sensor, the temperature sensor, and the differential pressure sensor.

[0010]

[Function] In flow measurement and flow control using a throttle,
A Venturi tube whose flow passage cross-sectional area is smoothly reduced and gently and smoothly expanded through a slot is the means with the least pressure loss. This pressure loss tends to increase as the throttle area ratio decreases, and when the throttle is throttled to a sonic speed (critical flow) with air or other gas, it enters a choke state and the flow velocity further increases. Without this, the pressure loss will increase further. Under such conditions, the pressure loss reaches 15% or more of the upstream absolute pressure. Usually called critical flow venturi, when the downstream pressure drop is sufficiently large, the flow rate can be kept constant regardless of the downstream pressure change. There is also a control device (U.S. Patent Application Publication No. 42332 in 1985), but the pressure loss is generally large.

On the other hand, many blowers generally have a characteristic that the flow rate is small at a large suction negative pressure and the flow rate is large at a small suction negative pressure. That is, when sucking with a blower of a fixed capacity, the front venturi tube may have a small pressure loss with a small throttle area ratio when the flow rate is small, but may have a large pressure loss with a small throttle area ratio when the flow rate is large. Small ones are suitable. Furthermore, when the temperature and pressure of the gas flowing into the venturi tube change, in order to keep the mass flow constant, it is necessary to adjust the throttle area ratio corresponding to the change in the temperature and pressure conditions. In the present invention, the exhaust gas constant flow rate sampling device (CVS) is not limited to the critical flow, but employs a means utilizing a venturi tube having a variable flow path cross-sectional area, and the above-described dilution exhaust gas collecting device (CVS) is used. The problem was solved by constantly measuring and controlling the mass flow rate in response to changes in temperature and pressure, changing the set flow rate as necessary, and reducing the pressure loss.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a specific embodiment of the present invention will be described with reference to FIG. In the figure, reference numeral 1 denotes an exhaust gas constant flow sampling device. The exhaust gas constant flow sampling device 1 mixes and dilutes the exhaust gas with clean air to maintain a constant mass flow rate, while collecting a constant flow rate for a bag sample, continuous gas analysis, and particle measurement. Things. The exhaust gas constant flow sampling apparatus 1 includes a dilution tunnel 10, and a filter 14 is provided at an external air inlet 51 on the upstream side of the dilution tunnel 10 to introduce clean air and to sample the gas sample at a constant flow rate. Check the background concentration. The exhaust gas of the engine 3 is entirely introduced into the dilution air flow from the exhaust introduction pipe 13 and, if necessary, mixed with the mixing orifice 1.
Exhaust gas and dilution air are mixed through 2 and flow in the dilution tunnel 10 as a constant mass flow rate. A constant flow rate of analysis gas is collected from the heated sample line 35 to the carbon-hydrogen analyzer HFID 36, and continuous analysis of other gases is performed. For this purpose, a constant flow rate of the analysis gas is sampled from the sample line 37, and the sample gas for the bag sample is supplied at a constant flow rate under a predetermined condition of each mode operation.
Is collected through the valve 39. Further, a measurement system in which a temperature-controlled filter 41 and a backup filter 42 and a mass flow controller 43, a sampling pump 44, and a gas meter 45 are connected to the dilution tunnel 10 for measuring particulate matter is mounted.

In the dilution tunnel 10, a constant flow rate measurement control device 2 is disposed upstream of the blower 15 to control the gas mixed with the exhaust gas of the dilution tunnel and the dilution air to a constant mass. The constant flow rate measurement control device 2 includes a Venturi tube 50 having a variable slot cross-sectional area. The venturi tube 50 has a slot outer periphery 21 which is a slot outer member constituting the slot portion 53 and a movable body 2 which is a core member.
The movable body 22 is axially displaceable relative to the outer periphery 21 of the slot. Slot outer circumference 2
Both the movable body 1 and the movable body 22 have a slope whose diameter changes depending on the position in the axial direction, and the cross-sectional area of the slot 53 is determined by the gap between the outer periphery 21 of the slot and the movable body 22. . The pressure P ₀ and temperature T ₀ at the inlet of the venturi tube are detected by the absolute pressure sensor 25 and the temperature sensor 28 and the slot 53
The pressure difference between the pressure P ₁ and the inlet pressure P ₀ is
The movable body 22 is moved in the axial direction by the servo motor 23 based on these detection signals.
2 is position-controlled. The cross sectional area of the slot 53 formed by the movable body 22 whose position is controlled by the gap with the outer periphery 21 of the slot is a function of the moving distance x of the movable body 22 and includes the signal of the Venturi tube 50 including its signal. Signals indicating the inlet and absolute pressure at which the mass flow rate can be calculated, the temperature, the throttle ratio of the Venturi tube, and the differential pressure between the inlet and the slot are input to the calculation circuit 26. The calculation circuit 26 can use a gas constant, an inlet cross-sectional area, a flow coefficient as required, and the like, and the flow rate is immediately calculated according to an input signal.

The specified value of the mass flow rate is arbitrarily specified in the control circuit 27, is compared with the calculated flow rate, and a servo output corresponding to the difference is supplied to the servo motor 23, and the movable body The cross-sectional area of the slot 53 is controlled by changing the moving distance x of the slot 22. With this control circuit 27, the constant flow rate measurement control layer 2 using the variable venturi method always automatically flows into the constant flow rate measurement control apparatus 2 from the dilution tunnel 10 to the designated mass flow rate regardless of changes in the inlet temperature and pressure. The flow rate of the mixed gas can be controlled. Therefore, the flow rate of the exhaust gas constant flow rate sampling device 1 is controlled to the designated mass flow rate within the range of the suction capacity of the blower 15, and the flow rate measurement value can be displayed / recorded as needed.

According to the exhaust gas constant flow sampling device, the mixed gas of the exhaust gas and the dilution air keeps a constant mass flow without causing condensation, so that, for example, the CO concentration in the gas can be controlled. Proportional to the mass emission under the conditions, and if the gas is collected in a bag at a constant flow rate during a certain operating condition, the CO concentration therein is proportional to the total emission during the operating condition It is characterized by. In addition, it is used as a device that can easily obtain an emission value with respect to a product of a traveling distance and an output-time, for example, under the operating conditions, irrespective of changes in the size of the engine and the exhaust flow rate. However, this is based on the premise that the mass flow rate of the mixed gas of the exhaust gas and the dilution air, that is, the gas flowing inside the dilution tunnel 10 is constant and known. However, even if the exhaust gas flow rate is much smaller than the dilution air flow rate, if the exhaust gas temperature changes greatly or the exhaust gas flow rate changes, the dilution tunnel 10
Gas temperature is affected. Therefore, normal CFV-CV
In S, the sound speed changes depending on the gas temperature in the dilution tunnel. Since the sound velocity a is obtained by the following equation 1, the flow velocity increases as the temperature increases, and the density decreases in proportion to T as the temperature increases, and the mass flow rate decreases. The pressure does not usually change much, but the temperature changes, which must be taken into account. In many cases, a method of adjusting the temperature using a heat exchanger or the like is employed, but it is difficult to maintain a sufficiently constant mass flow rate. In particular, when the ratio of the flow rate of the exhaust gas to the flow rate of the dilution air is increased, or when the high-load operation condition is continued for 3 minutes or more and the thermal condition is greatly affected, the mass flow rate is changed by the temperature change of the mixed gas. Changes cannot be ignored.

[0015]

(Equation 1)

According to the present apparatus, even if the condition of the exhaust gas changes greatly, the mass flow rate can always be measured by the variable venturi-type constant flow rate measurement control device and automatically controlled to a specified constant value. The mass flow can be kept constant even when the gas temperature changes. Even where it is inappropriate to place a heat exchanger in the sample gas path, such as in the case of particulate matter measurements in diesel engine exhaust,
Accurately control the mass flow rate.

Further, according to the present apparatus, when the condition such as the exhaust gas flow rate is greatly changed and it is desired to change the flow rate of the dilution to change the flow rate of the mixed gas, the operation can be performed only by changing the designated flow rate value. Can be easily changed.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing an exhaust gas constant flow rate sampling device of the present invention.

FIG. 2 is a configuration explanatory view showing a conventional exhaust gas constant flow rate sampling device.

[Description of sign]

 DESCRIPTION OF SYMBOLS 1 Exhaust gas constant flow sampling device 2 Constant flow measurement control device 3 Engine 12 Mixing orifice 13 Exhaust introduction pipe 15 Blower 21 Slot outer periphery 22 Movable body 23 Servo motor 26 Calculation circuit 27 Control circuit 35 Heating sample line 36 Hydrocarbon analyzer 37 Sample line 38 Sample line 39 Valve 41 Filter 42 Backup filter 43 Mass flow controller 44 Sampling pump 45 Gas meter 50 Venturi pipe 51 External air intake 52 Gap 53 Slot part

Claims (2)

(57) [Claims] An exhaust gas of a combustion engine is mixed with dilution air to measure a gas component concentration and a particulate matter concentration in the exhaust gas such that a mass flow rate after mixing is constant, or a constant flow rate is sampled. The exhaust gas constant flow rate sampling method (C
VS), a variable venturi constant flow controller that automatically controls the flow cross-sectional area of the slot and controls the flow after mixing exhaust and air to the specified mass flow is used. Exhaust gas constant flow sampling method. 2. A variable venturi type venturi tube for defining a dilution tunnel and a gas flow rate of the dilution tunnel, a pressure sensor for detecting a pressure at an inlet of the venturi tube,
A temperature sensor for detecting a temperature at an inlet of the Venturi pipe; and a differential pressure sensor for detecting a pressure difference between a pressure at a slot of the Venturi pipe and a pressure at the inlet. The slot is constituted by a relatively displaceable slot member and a core member, and a cross-sectional area between the slot outer member and the core member defines a cross-sectional area of the slot portion. A variable venturi-type constant flow measurement control device, wherein the relative displacement is generated by a signal including a signal from a sensor, the temperature sensor, and the differential pressure sensor.