JP2859892B2 - Engine combustion gas analysis method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for analyzing combustion gas of an engine using a quadrupole mass detector.

2. Description of the Related Art Conventionally, an engine provided with an electronic control system to perform combustion control of an air-fuel mixture or air-fuel ratio control in order to improve emission performance or fuel consumption performance has been known. In order to effectively perform such combustion control or air-fuel ratio control, it is necessary to detect the combustion gas composition or the air-fuel ratio as control information with high accuracy in real time. In the present application, the term "combustion gas" is a general term for intake and exhaust after fuel is mixed into intake air, regardless of before or after combustion.

As a gas analyzer for detecting a combustion gas composition or an air-fuel ratio in real time, for example, a gas analyzer using a quadrupole mass detector 101 is known as shown in FIG. -26660). The gas analyzer shown in FIG. 9 is for detecting the amount of hydrocarbons (air-fuel ratio) in an air-fuel mixture, and a sample gas (air-fuel mixture) extracted from an engine is mixed with air to form an oxidation catalyst. And then oxidize all the hydrocarbons in the sample gas to carbon dioxide.
Is introduced into a first decompression chamber 104 which is depressurized by the second decompression chamber 106, and further introduced into a second decompression chamber 106 of a high vacuum decompressed by a second vacuum pump 105. Is introduced into the quadrupole mass detector 101, the amount of carbon dioxide therein is detected, and the amount of hydrocarbon is calculated from the amount of carbon dioxide. Since the gas analyzer equipped with such a quadrupole mass detector 101 has a very fast detection rate of the target component amount (for example, 10 milliseconds), control information necessary for engine combustion control or air-fuel ratio control is required. Can be detected in real time.

[Problems to be Solved by the Invention] By the way, a combustion gas extraction passage communicating the combustion chamber of the engine with the gas analyzer as shown in FIG. 9 is provided, and the combustion gas in the combustion chamber is directly introduced into the gas analyzer. Then, when analyzing this in real time, the pressure (degree of vacuum) in the second decompression chamber 106 in which the quadrupole mass detector 101 is provided fluctuates with the fluctuation of the pressure in the combustion chamber.
However, since the quadrupole mass detector 101 measures the absolute amount of the target component, when the pressure in the second decompression chamber 106 changes, the detection value of the target component amount changes accordingly. . Therefore, in such a case, a pressure gauge is generally provided in the second decompression chamber 106 to detect the pressure (degree of vacuum), and the pressure is corrected based on the detected value. However, such a high-vacuum pressure gauge has a different sensitivity depending on the type of gas component. Therefore, there is a problem that the pressure correction involves a considerable error and the accuracy of the detection value of the target component amount is reduced.

The present invention has been made in view of the above-mentioned conventional problems, and directly introduces a combustion gas in a combustion chamber into a high-vacuum decompression chamber and analyzes the gas by a quadrupole mass detector. An object of the present invention is to provide an engine combustion gas analysis method capable of detecting a target component amount with high accuracy even if the pressure in the decompression chamber changes in accordance with the pressure change in the combustion chamber. And

[Means for Solving the Problems] The present inventors introduce a combustion gas directly from a combustion chamber into a decompression chamber and analyze it with a quadrupole mass detector to detect a target component amount. When the pressure in the combustion chamber changes, the pressure in the decompression chamber changes accordingly, and the ionic strength of each component detected by the quadrupole mass detector changes. And the ratio of the ion intensity of each component (ion intensity ratio) cancels out the above-mentioned change in pressure. Therefore, the ion intensity ratio is affected by the pressure change in the decompression chamber. Thought it would not be.

In order to confirm this, the combustion gas of the same composition is confined in the combustion chamber and its pressure is changed variously. Therefore, the pressure in the decompression chamber is changed and the ratio of the ion intensity of the target component to the ion intensity of the inactive component (ion intensity) As a result, it was found that the ionic strength ratio was constant even when the pressure in the combustion chamber (decompression chamber) was changed (see FIG. 3).

The amount of the inert gas component such as nitrogen contained in the mixture in the combustion chamber does not change due to the combustion of the mixture. Accordingly, if the ratio of the ion intensity of the target component to the ion intensity of the inert gas component (ion intensity ratio) is determined by the quadrupole mass detector, the target in the combustion chamber can be determined from the ion intensity ratio and the amount of intake air. It was thought that the amount of the component could be determined.

Focusing on such facts and considerations, in order to achieve the above object, the present invention provides a combustion gas extraction passage for extracting combustion gas of an engine, and a vacuum exhaust means connected to the combustion gas extraction passage. A decompression chamber which is decompressed to a high vacuum, and a quadrupole mass detector disposed facing the decompression chamber, introducing combustion gas into the decompression chamber through a combustion gas extraction passage, In a combustion gas analysis method for an engine, a part of the combustion gas introduced into the decompression chamber is ionized and the ionic strength of the target component in the chamber is detected, and the amount of the target component is determined based on the ionic strength. Detects the ionic strength of the target component and the ionic strength of the inert gas component for a standard gas whose amount of the target component is known in advance, and calculates the standard ionic strength ratio from both ionic strengths Obtains the corresponding relationship between the reference ion intensity ratio and the target component amount, relative to the next actual combustion gases,
Detect the ionic strength of the target component and the ionic strength of the inert gas component, determine the ionic strength ratio from both ionic strengths, and calculate the amount of the target component in the combustion gas from the ionic strength ratio and the above correspondence. The present invention provides a method for analyzing combustion gas of an engine, characterized in that it is determined by the following method.

According to the present invention, the ratio between the ionic strength of the target component and the ionic strength of the inert gas component (ionic strength ratio) is determined, and the ionic strength ratio and the ionic strength obtained in advance with a standard gas are obtained. The target component amount is obtained from the correspondence between the ion intensity ratio and the target component amount, but the ion intensity ratio is constant regardless of the pressure in the combustion chamber or the decompression chamber. Therefore, even if the pressure in the combustion chamber, that is, the pressure in the decompression chamber, fluctuates, the target component amount in the combustion gas can be detected with high accuracy without performing pressure correction for the fluctuation.

Since pressure correction is not performed, it is not necessary to provide a pressure gauge for the decompression chamber, and the gas analyzer can be simplified.

[Examples] Examples of the present invention will be specifically described below.

<First Embodiment> As shown in Fig. 1, when an intake valve 1 is opened, an engine CE draws a mixture into a combustion chamber 4 from an intake passage 3 through an intake port 2 and mixes the mixture. The gas is compressed by the piston 5 and burned by an addition plug (not shown), and the combustion gas is discharged from the exhaust port 7 to the exhaust passage 8 when the exhaust valve 6 is opened.
To be discharged.

A combustion gas analyzer GA provided with a quadrupole mass detector 9 for detecting the amount of a target component in the combustion gas in the combustion chamber 4 is provided for the engine CE. The combustion gas analyzer GA is connected to a combustion gas extraction passage 11 that communicates with the combustion chamber 4 at an upstream end. The combustion gas extraction passage 11 has an electromagnetic on-off valve 12 that opens and closes the combustion gas at a predetermined timing. It is interposed.

The combustion gas analyzer GA includes a first decompression chamber 14 that is depressurized to a relatively low vacuum (for example, 10 ⁻² Torr) by a rotary first vacuum pump 13, a turbo molecular pump 15, and a rotary second pump. High vacuum (for example, 10 ^-5
And a second decompression chamber 17 for decompression to Torr.
The downstream end of the combustion gas extraction passage 11 passes through the end face of the first decompression chamber 14 on the engine side, and is opened into the first decompression chamber 14 slightly before the end face on the opposite side to the engine. 12
When the valve is opened, the combustion gas in the combustion chamber 4 is first introduced into the first decompression chamber 14 through the combustion gas extraction passage 11.

The second decompression chamber 17 is disposed adjacent to the end face of the first decompression chamber 14 on the side opposite to the engine, and is opposed to the downstream end of the combustion gas extraction passage 11 and the second decompression chamber 14. A communication hole 19 for communicating the two decompression chambers 14 and 17 is provided in a partition wall 18 with the communication chamber 17. The opening of the communication hole 19 on the side of the first decompression chamber 14 is passed through the communication hole 19 from the first decompression chamber 14 to the second decompression chamber 17.
An orifice 21 is provided for regulating the flow rate of the combustion gas flowing into the orifice.

At approximately the center of the second decompression chamber 17 along the flow direction of the combustion gas, each component in the combustion gas is ionized, and the ionic strength of an ionic species of an arbitrary component therein can be detected. A quadrupole mass detector 9 is provided. This quadrupole mass detector 9 is an ordinary quadrupole mass detector including an ion source unit, a lens system, a quadrupole electrode, a secondary electron multiplier, and the like. Omitted. In the second decompression chamber 17, a first valve 22 and a second valve 23 are provided upstream and downstream of the quadrupole mass detector 9, respectively.

By the way, the quadrupole mass detector 9 detects the ionic strength of the ionic species of the target component and the ionic strength of the inert gas component in the combustion gas.
Each of these ion intensity detection values is stored in the control computer 24.
To calculate the ratio of the ionic strength of the target component to the ionic strength of the inert gas component (the ionic strength ratio), and calculate the amount of the target component in the combustion gas with high accuracy based on the ionic strength ratio. It has become.

Hereinafter, a method of detecting the target component in the combustion gas by the control computer 24 will be described with reference to the flowchart shown in FIG.

In step S1, a standard gas whose target component amount is known is introduced into the second decompression chamber 17. The standard gas may be prepared, for example, by mixing a target component gas whose mass has been measured in advance and air. The standard gas may be directly introduced into the combustion gas analyzer GA without passing through the combustion chamber 4.

In step S2, the ionic strength of the inert gas component and the ionic strength of the target component gas in the standard gas are measured. Nitrogen or argon may be selected as the inert gas component. As in the case of a general quadrupole mass detector, the ion intensity is detected by ionizing a standard gas in an ion source, and converging each of these ions with a lens system to form an ion beam. A component other than the component to be detected is introduced into the quadrupole electrode, and only the ion beam of the component to be detected is introduced into the secondary electrode multiplier and the current value (ion intensity) is detected. Done.

In step S3, for the reference gas, a ratio (reference ion intensity ratio) between the ion intensity of the target component gas and the ion intensity of the inert gas component is calculated, and the ratio between the reference ion intensity ratio and the target component amount in the standard gas is calculated. The correspondence between them is stored in a memory in the control computer 24.

In step S4, the electromagnetic on-off valve 12 is opened at a predetermined timing according to a signal from the control computer 24, and a sample gas (combustion gas) is introduced from the combustion chamber 4 into the combustion gas analyzer GA. This sample gas is first introduced into the first decompression chamber 14, the flow rate is adjusted by the orifice 21,
After that, a part thereof is introduced into the quadrupole mass detector 9.

In step S5, the ionic strength of the inert gas component and the ionic strength of the target component gas in the sample gas are detected. The method for detecting the ionic strength is the same as that for the standard gas described above.

In step S6, for the combustion gas (sample gas), a ratio (ion intensity ratio) between the ion intensity of the target component gas and the ion intensity of the inert gas component is calculated, and the ion intensity ratio and the standard stored in the memory are calculated. The target component amount in the combustion gas is calculated from the correspondence between the reference ion intensity ratio for the gas and the target component amount. In this case, as described above, since the ion intensity ratio is not affected by the pressure in the combustion chamber 4 (in the second decompression chamber 17), the detected value of the target component gas amount is also in the combustion chamber 4 (in the second decompression chamber 17). ) Is no longer affected by the pressure.

The results of measuring the ion intensity ratio between the target component gas (CO ₂ ) and the inert gas component (N ₂ ) for the sample gas having the same composition by varying the pressure in the combustion chamber 4 variously are shown in FIG. It is shown in FIG. As is clear from FIG. 3, the ion intensity ratio is constant even when the pressure in the combustion chamber 4 changes. Therefore, even if the pressure in the combustion chamber 4 (in the second decompression chamber 17) fluctuates, the target component gas amount in the combustion gas can always be measured with high accuracy regardless of the fluctuation.

In step S7, it is determined whether or not to continue the analysis of the combustion gas. If the analysis is to be continued (YES), steps S4 to S4 are performed.
Step S7 is repeatedly executed.

The present invention can be applied not only to the analysis of the combustion gas in the combustion chamber 4 as in the first embodiment, but also to the analysis of the exhaust gas in the exhaust passage or the analysis of the air-fuel mixture in the intake passage. .

Second Embodiment The present invention is also applied to real-time measurement of the air-fuel ratio (A / F). Hereinafter, a second embodiment in which the present invention is applied to the measurement of the air-fuel ratio (A / F) will be described.

FIG. 4 shows an air-fuel ratio detecting apparatus FA for detecting an air-fuel ratio (A / F) of an air-fuel mixture provided with a quadrupole mass detector 9. The configuration of each part is the combustion shown in FIG. Since the gas analyzer is almost the same as the gas analyzer, members having the same structure and function are denoted by the same reference numerals as those in FIG. 1 and their description is omitted.

Generally, when the air-fuel ratio is calculated by analyzing the air-fuel mixture using a quadrupole mass detector, one of the constituents of all kinds of hydrocarbons and air that originally constitute the fuel (air-fuel mixture) Although the content of (e.g., oxygen) should be detected, the amount of hydrocarbons that make up the fuel is so diverse that it takes too long to detect all types of hydrocarbons, and real-time detection Becomes virtually impossible.

Therefore, in the gas analyzer for air-fuel ratio measurement provided with the quadrupole mass detector 101 shown in FIG. 9, all hydrocarbons in the sample gas are converted into carbon dioxide by a converter 102 using an oxygen catalyst. The amount of carbon dioxide in the sample gas is measured, and the total amount of hydrocarbons is calculated from the amount of carbon dioxide. However, in this method, it takes a little time to oxidize hydrocarbons and convert them to carbon dioxide, so that there is a problem that responsiveness is deteriorated.

Further, as shown in FIG. 10, the activity of the oxidation catalyst in converter 102 decreases unless the sample gas temperature is maintained at 300 ° C. or higher. For this reason, the converter 102 must be provided with a sample gas heating device, and there is a problem that the structure of the gas analyzer becomes complicated.

The present applicant has in hydrocarbons contained in the sample gas, to select several representative components (e.g., C ₅ -C ₈ components), by measuring the ionic strength only these representative components thereof Measure the content, based on the general correlation between the representative component amount and the total hydrocarbon amount, to propose a gas analysis method to calculate the total hydrocarbon amount in the sample gas (See JP-A-63-262561). However, according to this analysis method, a phenomenon occurs in which the calculated air-fuel ratio (A / F) slightly deviates from the actual air-fuel ratio (A / F) in the high rotation range of the engine.

Then, the inventors of the present application conducted detailed studies on the cause, and obtained the following conclusions.

Although the high rpm the temperature of the mixture increases, the temperature of the mixture is increased, subject to measurement representative component (e.g., C ₅ -C ₈ component) hydrocarbon low molecular weight that do not qualify for measurement (e.g., C ₄ component) is thermally decomposed. In FIG.
C when normal gasoline is changed from normal temperature to 350 ° C
₄ -C ₈ shows a characteristic of a component change of. As is apparent from FIG. 5, above approximately 180 ° C., particularly the C _{7 to} C ₈ components are thermally decomposed, and thus have not been conventionally measured.
It can be seen that C ₄ components has increased significantly.

6 and 7 show mass spectra obtained by actually analyzing a gas mixture at 50 ° C. and 250 ° C. with the quadrupole mass detector 9. From FIG. 6 and FIG. 7, at 250 ° C.,
While the ion species of the decomposition component (charge ratio m / e = 41) and the like are detected, the representative ion species of the fuel (charge ratio m / e = 91,105) decreases. The mass fragments having a charge ratio m / e = 28 and a charge ratio m / e = 32 respectively represent nitrogen ions and oxygen ions due to the intake air.

However, even if a certain component in the total hydrocarbon is thermally decomposed, only the type of the hydrocarbon changes, but the total hydrocarbon amount (mass) does not change. Therefore, the ratio (correlation) between the representative component amount and the total hydrocarbon amount becomes smaller than the ratio between the representative component amount of the fuel before cracking and the preceding hydrocarbon amount.

For this reason, in the conventional calculation method, the total hydrocarbon amount is calculated to be lower by an amount corresponding to the representative component amount reduced by the thermal decomposition, and the air-fuel ratio (A / F) calculated based on this is reduced. It shifts to leaner than it really is.

Such Focusing on the fact, in the second embodiment, in the air-fuel ratio detecting device FA (quadrupole mass detector 9), conventional representative components (e.g., C ₅ -C ₈ component) ionic species ( For example, the charge ratio
In addition to the m / e = 56,78,91,105), these cracking components (e.g., ion species of C ₄ component) (e.g., charge ratio m / e = 41)
As for, the ionic strength is detected, and the total hydrocarbon amount is calculated based on the correlation between the amounts of these components (for example, C _{4 to} C ₈ components) and the total hydrocarbon amount. The amount of air is nitrogen (charge ratio m / e = 28) or oxygen (charge ratio m / e =
The air-fuel ratio (A / F) is calculated by detecting the ionic strength in 32), and from the total hydrocarbon amount and the air amount.

As shown in FIG. 8, in the detection method including the decomposition component (straight line H ₁ ) according to the second embodiment, 100% of the total hydrocarbon amount can be detected regardless of the combustion chamber temperature. In the conventional detection method (curve H ₂ ), the detection rate of the total hydrocarbon amount decreases as the combustion chamber temperature increases. Therefore, with the conventional detection method, the air-fuel ratio (A
/ F) is 18.3 (actually A / F = 14.7), which is shifted to the lean side.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of an engine and a combustion gas analyzer according to a first embodiment of the present invention. FIG. 2 is a flowchart showing a combustion gas analysis method by the combustion gas analyzer shown in FIG. FIG. 3 is a diagram showing characteristics of the ion intensity ratio with respect to the pressure in the combustion chamber in the first embodiment. FIG. 4 is a system configuration diagram of an air-fuel ratio detection device showing a second embodiment of the present invention. FIG. 5 is a graph showing characteristics of a change in a hydrocarbon component in an air-fuel mixture depending on a temperature in a combustion chamber. FIG. 6 and FIG. 7 are diagrams showing examples of mass spectra of the air-fuel mixture at 50 ° C. and 250 ° C., respectively. FIG. 8 is a diagram showing characteristics of the total hydrocarbon amount detection rate by the hydrocarbon detection method of the second embodiment and the total hydrocarbon amount detection rate by the conventional detection method with respect to the combustion chamber temperature. FIG. 9 is a system configuration diagram of a conventional gas analyzer for measuring an air-fuel ratio provided with a quadrupole mass detector. FIG. 10 is a graph showing the characteristics of the oxidation rate of hydrocarbons of the oxidation catalyst of the converter of the gas analyzer shown in FIG. 9 with respect to gas temperature. CE ... engine, GA ... combustion gas analyzer, FA ... air-fuel ratio detector, 4 ... combustion chamber, 9 ... quadrupole mass detector,
11: combustion gas extraction passage, 12: solenoid on-off valve, 13: first vacuum pump, 14: first decompression chamber, 15: turbo molecular pump, 16: second vacuum pump, 17 ... 2 decompression chambers, 24 ...
... Control computer.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 27/62-27/70 H01J 49/00-49/48

Claims (1)

(57) [Claims] 1. A combustion gas extraction passage for extracting combustion gas from an engine, a decompression chamber connected to the combustion gas extraction passage and decompressed to a high vacuum by a vacuum exhaust means, and facing the decompression chamber. And a mass detector to be arranged,
The combustion gas is introduced into the decompression chamber through the combustion gas extraction passage,
Engine combustion gas analysis in which a part of the combustion gas introduced into the decompression chamber is ionized by the mass detector, the ionic strength of the target component in the chamber is detected, and the amount of the target component is determined based on the ionic strength. The method comprises the steps of:
Detect the ionic strength of the target component and the ionic strength of the inert gas component, determine the reference ion intensity ratio from both of these ion intensities, determine the correspondence between the reference ion intensity ratio and the target component amount, and then The ionic strength of the target component and the ionic strength of the inert gas component are detected for the combustion gas, and the ionic strength ratio is calculated from both ionic strengths. A combustion gas analysis method for an engine, wherein the target component amount is calculated and obtained.