JPH11211631A - Apparatus for diluting sampling exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a quantity of exhaust gas to be sampled, lessen a quantity of dilution air as much as possible and make a concentration of pollution components in the diluted exhaust gas proportional to a quantity in a flow rate of the whole exhaust gas similar to a CVS(constant volume sampler) apparatus. SOLUTION: When the exhaust gas of an engine is continuously extracted with a constant mass flow rate at a temperature not lower than a dew point, mixed with N2 or pure air and diluted, an apparatus 100 controls a flow rate of the N2 or pure air to obtain a flow rate of the diluted exhaust gas proportionally to a flow rate of the whole exhaust gas, thereby making a concentration of a specific component in the diluted exhaust gas 3 proportional to a discharge quantity of the specific component in the flow rate of the whole exhaust gas. Moreover, the apparatus controls to obtain the concentration of the specific component proportional to the discharge quantity within a sampling time when the diluted exhaust gas 3 is sampled at a constant flow rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of environmental technology such as exhaust gas measurement of automobiles.

[0002]

2. Description of the Related Art In a technology for preventing air pollution caused by automobile exhaust gas, as a method of measuring the amount of polluting components,
CVS (Constant Volume Sampler) devices have been widely used worldwide since the 1970s. This is a method of diluting the entire flow rate of exhaust gas with clean air to make a constant flow rate of diluted exhaust gas, and sampling the sample gas within the operating time at a constant flow rate into a bag while preventing condensation of moisture etc. and analyzing the gas. In this device, the concentration of a specific component in the diluted exhaust gas is proportional to the emission amount.

[0003]

2. Description of the Prior Art CVS systems require a large amount of clean dilution air to dilute the total amount of exhaust gas. The whole device becomes large, the space for installation and piping, the power of a blower, etc. increase, and the cost becomes a problem. In recent years, measures have been taken to reduce exhaust gas from automobiles. In addition, measurement equipment adapted to engines with a high moisture content, such as CNG and methanol fuel, and especially for engines that emit low-concentration pollutants, have extremely high cleanliness. It is necessary to supply a large amount of dilution air, but it has become difficult to achieve this.

[0004]

In order to sample a representative sample for measuring the emission of polluting components of exhaust gas into a bag, it is necessary to dilute the exhaust gas to prevent condensation of moisture and the like as in the case of the CVS apparatus. There is. Since the amount of diluted exhaust gas is sufficient for gas analysis, etc., the amount of diluted air required to be extremely high in cleanliness by reducing the sampling amount of exhaust gas and having many difficulties in cost etc. It is an object of the present invention to make the concentration of contaminants in the diluted exhaust gas proportional to the amount in the total exhaust gas flow rate, as in the case of the CVS device, as much as possible.

[0005]

As a means for solving the above-mentioned problems, the mass flow rate of the exhaust gas to be sampled is made constant, the flow rate of the diluted air or N ₂ gas is made variable, and the flow rate of the diluted exhaust gas is changed. We chose a means to control it in inverse proportion to the exhaust gas flow rate.

[0006] Generally, the dew point of the combustion exhaust gas of petroleum-based fuel is 55 ° C to 65 ° C. However, in order to control this flow rate, it is necessary to maintain the dew point at about 80 ° C or more because a pressure change occurs. At such high temperatures, thermal mass flow controllers often have difficulty in application in terms of responsiveness and the like. In order to control the mass flow rate to be constant, it is easy to use CFV at a constant temperature and pressure. In the present invention, in consideration of such characteristics of the actual apparatus, the mass flow rate of the exhaust gas is controlled to be constant by the CFV, and the flow rate of the dilution air or N ₂ is variably controlled with a high response by a normal mass flow controller such as a thermal type. Means were adopted.

Further, the dew point of the diluted exhaust gas may cause a problem in some cases. However, in this apparatus, since the flow rate is small and the apparatus can be miniaturized, the pipe system can be easily maintained at 40 ° C. or more by a factor of 1/2. It was made possible to cope with a dilution ratio of less than about.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the flow rate of the exhaust gas actually used for the diluted exhaust gas is usually as low as 1 L / min or less. Therefore, a bypass flow is used to reduce the delay time in the exhaust gas sampling system. The temperature of the sampling system is maintained at about 110 ° C., and the exhaust gas used for dilution of about 0.4 L / min to about 3.0 L / min is extracted from a bypass flow of about 10 L / min, and constant inlet temperature and pressure conditions are obtained. Then, a constant mass flow rate is controlled by a CFV (sonic velocity nozzle) and suction is performed. This suction negative pressure is 65k in absolute pressure
The pressure is controlled to about Pa or less, and the pressure can be set to a sonic speed with a sufficient margin even with a small nozzle. Dilution air or N ₂
Is depressurized from a clean standard air generator or high-pressure cylinder capable of supplying a maximum flow rate of about 30 L / min.
As a normal temperature, put it in a thermal mass flow controller.

On the other hand, the total flow rate of the exhaust gas is measured by another exhaust gas flow meter, and the signal is used for a control circuit. The total mass flow rate of the exhaust gas is X, a constant exhaust gas mass flow rate to be used for diluting and c _i, as the mass flow rate d _a of dilution air to be controlled, when the relationship between the dilution ratio r with constant A in equation It looks like this:

D _a = (A / X) −c _i , r = c _i /
(D .. + c _i ) _i = 1, 2,... The mass flow controller controls the dilution air flow rate according to the signal X so that d _a in this equation is satisfied.

Since the diluted exhaust gas flow rate varies inversely with the total mass flow of the exhaust gas, the concentration of a particular component therein is proportional to the emission value of that component. Therefore, if a sample is sampled at a constant flow rate from the diluted exhaust gas of this system and collected in a bag, a sample representative of the amount discharged during the operation time can be obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the apparatus explanatory diagram of FIG. An exhaust gas 1 is extracted at a substantially constant flow rate from an exhaust sampling probe 21 inserted into a tail pipe 51 at the end of an exhaust pipe system of the engine, and is extracted at a rate of about 10 L / min through a sampling system 22 maintained at about 110 ° C. A flow rate of the exhaust gas sample is introduced into the apparatus 100 through the gas connector 23. After passing through the high temperature filter 24,
Exhaust gas 2 used for dilution at a constant flow rate is divided in an exhaust gas distributor 25, and the remaining gas is supplied to a buffer tank 2.
6 and a bypass pump 27, a flow control valve 28, and an exhaust discharge duct that is guided to the outside of the apparatus from the exhaust discharge connector 30 via a flow monitor 29 and that does not affect the exhaust sampling probe on the downstream side of the engine exhaust system. It is returned to 32. In this way, the delay in the exhaust sampling system can be made within approximately 0.2%. The exhaust gas 2 used for dilution passes through the three-way solenoid valve 10, is accurately temperature-controlled to about 100 ° C., and enters either the CFV 11 or 11 ′ which joins at the junction 37. Here, since the flow rate at the throat cross-sectional area of the venturi not more than about pressure ratio 0.7 there is a pressure on the downstream side is determined, it is readily automatically controlled to a constant mass flow rate c ₁ or c _2. The clean air or N ₂ used for dilution is supplied from the outside of the present apparatus 100. For example, as shown in the figure, the gas is connected to the gas connector 4-43 while the pressure is kept constant from the cylinder 41 by the pressure reducing valve 42 and monitored by the pressure gauge 45. Introduced into the device 100 from
The flow rate is controlled by the mass flow controller 20 via the solenoid valve 44 and the three-way solenoid valve 46, and supplied as dilution air.
This flow rate is controlled with good responsiveness to the flow rate value da in response to a signal from the control circuit 50 by a thermal mass flow controller 20 operating at a temperature close to room temperature.

The exhaust gas and the clean dilution air are mixed in the mixing section 12.
Are mixed under a constant pressure condition to become 3 with diluted exhaust gas. This pressure is controlled by a relief valve 36 attached to the inlet side buffer tank 35 of the suction pump 38 connected at the dilution exhaust gas diverting section 13, but the absolute pressure 65
It is kept at about kPa and discharged from the exhaust discharge connector 34. A part of the diluted exhaust gas is controlled by a flow control valve 16 and monitored by a flow meter 17 while being suctioned at a constant flow rate by a bag sampling pump 14 and sent to a bag 6 or the like via a three-way solenoid valve 18 to be pumped. It is collected to form a sample 5 for gas analysis.

In many cases, a plurality of bags 6 are mounted, and each branch pipe is provided with a solenoid valve 9 for switching and used.
A detachable connector-8 is provided. Further, a pressure switch 7 is arranged and designed in the pipeline to secure the bag 6.

A discharge pump 47 and solenoid valves 48 and 49 are provided for discharging the sample gas from the bag. As a result, the sample gas is sent from the analysis gas connector-33 to a gas analyzer (not shown). The switching of each solenoid valve introduces sample gas and introduces / discharges purge air for cleaning the bag.

The control circuit 50 has a signal X of the total exhaust gas flow rate.
Is set, the exhaust gas flow rate c ₁ or c ₂ used for dilution set by the CFV 11 or CFV 11 ′ is set, and a constant A related to the dilution ratio is set. Control circuit 5
From 0, when the total exhaust gas flow rate is larger than a certain value, CF
A set signal of V11 (for example, 3 L / min) is issued,
When the value is smaller than a certain value, the CFV 11 '(for example, 0.4L
/ Min) set signal to together with is transmitted to the solenoid valve 10, an instruction signal flow d _a mass flow controller 20 is transmitted is calculated by the following equation.

[0017] _{d a = (A / X)} -c i (i is 1 or by selection of CFV in 2) tau as a delay time from the signal of the time X is input to the signal d _a is transmitted _{Be prepared} to set _L. This τ _L is defined as a function of X, and corrects the delay time of the exhaust gas from the tail pipe based on the dead volume of the exhaust system of the engine and the delay time of the exhaust gas sampling system of the present apparatus, and is usually 1 second. Within hours.

The control circuit 50 calculates and displays the dilution ratio r according to the following equation: r = C _i / (d _a + c _i ) The dew point of the diluted exhaust gas and the temperature up to the bag inlet can be considered. It is like that. Normally, the pipe system is 40 when r ≦ 1/2.
Keep it above the dew point above ℃.

The diluted exhaust gas is partially or possibly entirely sucked by the suction pump 38. The negative suction pressure is controlled to a constant pressure by a relief valve 36 mounted on a buffer tank 35 arranged on the inlet side of the suction pump 38, and is monitored by a pressure gauge 19. The supply of the diluted exhaust gas sample 4 to the bag 6 is set to a required flow rate by the sampling pump 14, the flow control valve 16 and the flow meter 17, and the three-way solenoid valve 18 is switched to perform the bag sampling for a necessary time. It is desirable to select a buffer tank 15 attached to the inlet / outlet of the sampling pump 14 that has a substantial delay in gas flow.

[0020]

According to the present invention, it is possible to obtain a diluted exhaust gas sample having a concentration proportional to the emission amount of a specific component of the exhaust gas of an engine by using a very small amount of clean diluent gas by an extremely small apparatus. Compared to the conventional CVS apparatus which requires a diluting gas corresponding to the total exhaust gas flow rate, a bag sample required for gas analysis can be obtained with approximately 1/1000 of the diluting gas. The cleanliness of the gas used for dilution is important especially when applied to an engine with advanced exhaust gas measures.However, in the apparatus of the present invention, since the dilution gas has a small flow rate, a high-purity cylinder gas or a highly clean gas is used. A gas containing no water from the gas purification device can be used, and highly reliable measurement can be performed without being affected by the background concentration.

Since the temperature of the pipeline system can be easily raised in relation to the dew point of the diluted exhaust gas, the dilution ratio can be reduced. Further, since the apparatus can be downsized as a whole, the degree of freedom in the space in the measurement chamber is increased, and the cost for exhaust gas sampling can be significantly reduced.

[Brief description of the drawings]

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

[Explanation of symbols]

1 Sample exhaust gas introduced into the apparatus 2 Sample exhaust gas used for dilution 3 Dilution exhaust gas 4 Diluted exhaust gas sample collected in a bag 5 Diluted exhaust gas sample collected in a bag 6, 6 ', 6 Bag 7 Pressure Switch 8, 8-, 8 Connector 9, 9 ', 9 Solenoid valve 10 High-temperature three-way solenoid valve 11 CFV (critical flow venturi) 11' CFV 12 Exhaust gas / diluent gas mixing unit 13 Diluted exhaust gas distribution unit 41 Pure Air cylinder 14 Sampling pump 42 Pressure reducing valve 15 Buffer tank 43 Gas connector 16 Flow control valve 44 Solenoid valve 17 Flow meter 45 Pressure gauge 18 Three-way solenoid valve 46 Three-way solenoid valve 19 Pressure gauge 47 Discharge pump 20 Mass flow controller 48 Solenoid valve 21 Sampling Probe 49 Solenoid Valve 22 Sampling System 50 Control Circuit 23 Connector 51 Tail pipe 24 High temperature filter 100 Exhaust gas dilution sampling 25 Divider device 26 Buffer tank 27 Bypass pump 28 Flow control valve 29 Flow monitor 30 Exhaust exhaust connector 31 Sampling probe holder 32 Exhaust exhaust duct 33 Analytical gas connector 34 Exhaust exhaust connector 35 buffer tank 36 relief valve 37 junction 38 suction pump

Claims (2)

[Claims] 1. A method of continuously extracting an exhaust gas of an engine at a temperature equal to or higher than a dew point at a constant mass flow rate and diluting the mixed gas with N ₂ or pure air to dilute the exhaust gas in proportion to the total exhaust gas flow rate. Exhaust in which the flow rate of N ₂ or pure air is controlled so that the gas flow rate is reached, so that the concentration of a specific component in the diluted exhaust gas is proportional to the emission amount of the specific component in the total exhaust gas flow rate What is claimed is: 1. A gas dilution sampling apparatus, further comprising: sampling a diluted exhaust gas at a constant flow rate to obtain a concentration of a specific component in proportion to an emission amount during the sampling time. 2. The exhaust gas dilution sampling apparatus according to claim 1, wherein when the exhaust gas of the engine is continuously extracted at a constant mass flow rate, the flow rate of the exhaust gas to be sampled is set within the range of the total exhaust gas flow rate or the engine speed. The concentration of a specific component in the diluted exhaust gas is adjusted to the total exhaust gas flow while appropriately switching the range in which the diluted exhaust gas flow is changed by gradually switching to two or more flow setting values according to the range. An exhaust gas dilution sampling device that is proportional to the amount of emission of a specific component in the exhaust gas.