Patent Publication Number: US-2019187025-A1

Title: Exhaust gas analysis system and exhaust gas analysis method

Description:
TECHNICAL FIELD 
     The present invention relates to an exhaust gas analysis system and exhaust gas analysis method for analyzing exhaust gas of an internal combustion engine. 
     BACKGROUND ART 
     In the past, as an exhaust gas analysis system for analyzing particulate matter contained in exhaust gas, as disclosed in Patent Literature 1, there has been one including a soot measuring system for measuring soot and an SOF measuring system for measuring a soluble organic fraction (SOF). 
     The soot measuring system uses a diffusion charger sensor (DCS) for measuring soot, and is configured to heat sampled exhaust gas to volatilize SOF and then guide the resulting exhaust gas to the DCS through a pipe. 
     However, in the above-described configuration, the exhaust gas is cooled in the pipe to the DCS and in the DCS and thereby the SOF contained in the exhaust gas is condensed, thus failing to accurately analyze soot. 
     In addition, in the above-described configuration, the SOF measuring system and the soot measuring system are both included in order to measure SOF and soot, thus causing the problem that the system becomes large-scale and expensive. 
     CITATION LIST 
     Patent Literatures 
     Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2006-153716 
     SUMMARY OF INVENTION 
     Technical Problem 
     Therefore, the present invention has been made in order to solve the above-described problems at once, and a main object thereof is to make it possible to accurately measure various particulate matter contained in exhaust gas without making a system large-scale or expensive. 
     Solution to Problem 
     That is, an exhaust gas analysis system according to the present invention is one including: an exhaust gas flow path through which exhaust gas of an internal combustion engine is introduced; a branch flow path that branches from the exhaust gas flow path; a first analyzer that is provided downstream of a branch point of the branch flow path in the exhaust gas flow path and measures particulate matter contained in the exhaust gas; a second analyzer that is provided in the branch flow path and measures the particulate matter contained in the exhaust gas; and a temperature control mechanism that controls temperature of the first analyzer to a temperature higher than a temperature of the second analyzer. 
     In such an exhaust gas analysis system, since the temperature control mechanism controls the first analyzer to a high temperature, the exhaust gas guided to the first analyzer is not cooled, and a volatile component such as SOF contained in the exhaust gas is not condensed but remains vaporized, thus making it possible to accurately analyze a nonvolatile component such as soot using the first analyzer. In addition, as an embodiment for controlling the temperature of the first analyzer, the first analyzer may be directly heated to control the temperature, or a pipe connected to the first analyzer may be heated to thereby control the temperature. 
     Further, by keeping the second analyzer at a lower temperature, the particulate matter containing the volatile component and the nonvolatile component can be analyzed using the second analyzer, and therefore by comparing an analysis result by the first analyzer and an analysis result by the second analyzer, the volatile component contained in the exhaust gas can be analyzer. As a result, without including both the soot measurement system and the SOF measurement system as in the conventional case, both the nonvolatile component and the volatile component can be analyzed, and therefore without making the system large-scale or expensive, the particulate matter contained in the exhaust gas can be accurately analyzed. 
     In order to equalize analysis conditions of the respective analyzers to compare the analysis result by the first analyzer and the analysis result by the second analyzer, it is preferable that the first analyzer and the second analyzer are ones using mutually the same analysis principle. 
     As the respective analyzers, arranging ones using the same analysis principle as described above makes it possible to accurately analyze the volatile component by comparing the analysis results by the respective analyzers. 
     In order to know the concentration or the like of the volatile component of the particulate matter, it is preferable that the exhaust gas analysis system further includes an information processor that acquires an output from the first analyzer and an output from the second analyzer, and by comparing the analysis results by the respective analyzers, calculates the concentration of particulate matter consisting of the volatile component contained in the exhaust gas or a value related to the concentration. 
     In order to know the concentration or the like of the volatile component in real time, it is preferable that the first analyzer is one that analyzes the exhaust gas flowing through the exhaust gas flow path in real time, and the second analyzer is one that analyzes the exhaust gas flowing through the branch flow path in real time. 
     Meanwhile, in recent years, there has been an increasing demand to measure the total amount of particulate matter including not only soot and SOF but also a sulfur component called sulfate. However, the above-described conventional configuration can measure only SOF and soot, but cannot measure the total amount of particulate matter. 
     Accordingly, in order to measure the total amount of the particulate matter contained in the exhaust gas, it is preferable that the first analyzer and the second analyzer are ones that measure the particulate matter with use of a diffusion charger method. 
     Using the diffusion charger method as described above makes it possible for the second analyzer to measure the total particulate matter including not only soot and SOF but also a sulfur component called sulfate. 
     As a specific embodiment, it is preferable that the first analyzer measures the nonvolatile component of the particulate matter, and the second analyzer measures the nonvolatile component and the volatile component of the particulate matter. 
     In such a configuration, the volatile component contained in the exhaust gas can be analyzed by comparing the analysis result by the first analyzer and the analysis result by the second analyzer. 
     More specific embodiments include one in which the first analyzer measures particulate matter including at least soot, and the second analyzer measures particulate matter including at least soot, SOF, and sulfate. 
     It is preferable that the exhaust gas analysis system includes a volatile component calculation part that calculates the concentration of particulate matter including at least the SOF and the sulfate by, from the concentration of the particulate matter including at least the soot, the SOF, and the sulfate, which is obtained by the second analyzer, subtracting the concentration of the particulate matter including at least the soot, which obtained by the first analyzer. 
     Such a configuration makes it possible to know the concentration of the volatile component including at least the SOF and the sulfate of the particulate matter. 
     When heating the exhaust gas flow path to the first analyzer, the volume flow rate of the heated exhaust gas increases to increase flow speed, and therefore the exhaust gas subjected to the branching at the branch point reaches the first analyzer before reaching the second analyzer. As a result, the analysis result by the first analyzer and the analysis result by the second analyzer are not synchronized, and comparing these analysis results in an unsynchronized state causes a reduction in analysis accuracy. 
     Accordingly, it is preferable that a pipe forming the exhaust gas flow path from the branch point to the first analyzer is longer or larger in diameter than a pipe forming the branch flow path from the branch point to the second analyzer. 
     In such a configuration, the exhaust gas subjected to the branching at the branch point reaches the first analyzer and the second analyzer at almost the same time, and therefore the analysis result by the first analyzer and the analysis result by the second analyzer can be synchronized. 
     In order to ensure the analysis accuracy of the nonvolatile component by the first analyzer, it is preferable that the temperature of the first analyzer, which results from the control by the temperature control mechanism, is equal to or higher than the evaporating temperature of the volatile component contained in the exhaust gas. 
     In order to prevent the condensation of moisture contained in the exhaust gas in the exhaust gas flow path to ensure the analysis accuracy, it is preferable that a diluter is provided on the upper stream side than the branch point in the exhaust gas flow path. 
     Also, an exhaust gas analysis method according to the present invention is one using an exhaust gas analysis system including an exhaust gas flow path through which exhaust gas of an internal combustion engine is introduced; a branch flow path that branches from the exhaust gas flow path; a first analyzer that is provided downstream of a branch point of the branch flow path in the exhaust gas flow path and measures particulate matter contained in the exhaust gas; and a second analyzer that is provided in the branch flow path and measures the particulate matter contained in the exhaust gas. In addition, the exhaust gas analysis method controls the temperature of the first analyzer to a temperature higher than the temperature of the second analyzer. 
     Such an exhaust gas analysis method makes it possible to obtain the same working effect as that of the above-described exhaust gas analysis system. 
     Advantageous Effects of Invention 
     According to the present invention configured as described above, it is possible to accurately analyze various particulate matter contained in exhaust gas without making a system large-scale or expensive. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram illustrating the configuration of an exhaust gas analysis system in the present embodiment; 
         FIG. 2  is a schematic diagram illustrating the configuration of a first analyzer and a second analyzer in the present embodiment; and 
         FIG. 3  is a functional block diagram illustrating functions of an information processor in the present embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, one embodiment of the exhaust gas analysis system according to the present invention will be described with reference to the drawings. 
     An exhaust gas analysis system  100  of the present embodiment is one that analyzes components contained in exhaust gas discharged from an unillustrated internal combustion engine, and here used to measure particulate matter (PM) in the exhaust gas. 
     Specifically, the exhaust gas analysis system  100  includes: an exhaust gas flow path L 1  through which sampled exhaust gas is introduced; a temperature control mechanism  10  that controls the temperature of the exhaust gas flow path L 1 ; and a first analyzer  20   a  that is provided in the exhaust gas flow path L 1  and measures the particulate matter contained in the exhaust gas. 
     The exhaust gas flow path L 1  is configured to sample the total amount of the exhaust gas discharged from the internal combustion engine and also mix the sampled exhaust gas with diluent gas to produce diluted exhaust gas, and the exhaust gas flow path L 1  is provided with a diluter referred to as a so-called full tunnel. In addition, the exhaust gas flow path L 1  may be one using a so-called micro tunnel that is configured to sample part of the exhaust gas discharged from the internal combustion engine and dilute the sampled exhaust gas. 
     In the present embodiment, the exhaust gas flow path L 1  is provided with multiple diluters  30 , and specifically, a first diluter  30   a  and a second diluter  30   b  provided on the downstream side of the first diluter  30   a  are arranged in series. In addition, the number of diluters provided in the exhaust gas flow path L 1  may be one. 
     The temperature control mechanism  10  is one that heats the downstream side of the second diluter  30   b  in the exhaust gas flow path L 1 , and specifically, a heater or the like that controls the temperature of a pipe forming the exhaust gas flow path L 1  or the temperature of the exhaust gas flowing through the pipe to a predetermined set temperature (e.g., 191° C.) equal to or higher than the evaporating temperatures of volatile components contained in the exhaust gas. 
     The first analyzer  20   a  is one that measures nonvolatile components including, for example, soot of the particulate matter contained in the exhaust gas, and here analyzes the nonvolatile components in the exhaust gas flowing through the exhaust gas flow path L 1  in real time. Specifically, as illustrated in  FIG. 2 , the first analyzer  20   a  is one that can analyze the nonvolatile components, which is referred to as a diffusion charger sensor (hereinafter described as DCS) using a diffusion charger method, and here an analyzer for calculating the mass concentration of the particulate matter. 
     Describing in more detail, the DCS as the first analyzer  20   a  is configured to charge the surfaces of introduced particles by corona discharge and thereby allow a current detection part  21  to detect current whose magnitude corresponds to the total particle length per unit volume. In addition, by preliminarily obtaining correlation data indicating the relationship between the total particle length and mass, the mass concentration of the particulate matter can be continuously calculated on the basis of the correlation data and the output (specifically, a current value detected by the current detection part  21 ) of the first analyzer  20   a.    
     Further, the exhaust gas analysis system  100  of the present embodiment is configured to allow the above-described temperature control mechanism  10  to control the temperature of the first analyzer  20   a  to a temperature higher than the temperature of the below-described second analyzer. Specifically, the temperature control mechanism  10  is one that heats the first analyzer  20   a  to a predetermined set temperature equal to or higher than the evaporating temperatures of the volatile components contained in the exhaust gas, and here heats the first analyzer  20   a  to the same set temperature (e.g., 191° C.) as that of the exhaust gas flow path L 1 . 
     In addition, a temperature control mechanism for controlling the temperature of the exhaust gas flow path L 1  and a temperature control mechanism for controlling the temperature of the first analyzer  20   a  may be different, and the controlled temperature of the exhaust gas flow path L 1  and the controlled temperature of the first analyzer  20   a  may be mutually different temperatures. 
     As illustrated in  FIG. 1 , the exhaust gas analysis system  100  of the present embodiment further includes: a branch flow path L 2  branching from the exhaust gas flow path L 1 ; the second analyzer  20   b  that is provided in the branch flow path L 2  and measures the particulate matter contained in the exhaust gas; and an information processor  40  that acquires outputs from the first analyzer  20   a  and second analyzer  20   b.    
     The branch flow path L 2  branches from downstream of the second diluter  30   b  in the exhaust gas flow path L 1  and from upstream of an area whose temperature is controlled by the temperature control mechanism  10  in the exhaust gas flow path L 1 , and here is kept at a temperature (e.g., room temperature) lower than the evaporating temperatures of the volatile components contained in the exhaust gas without being subjected to temperature control. In the present embodiment, the diameter of the pipe forming the exhaust gas flow path L 1  from the branch point X to the first analyzer  20   a  is made larger than the diameter of a pipe forming the branch flow path L 2  from the branch point X to the second analyzer  20   b . In addition, more specific embodiments include a configuration in which for example, when the mass flow rate of the exhaust gas flowing into the first analyzer  20   a  is equal to the mass flow rate of the exhaust gas flowing into the second analyzer  20   b , the volume of the exhaust gas flow path L 1  from the branch point X to the first analyzer  20   a  and the volume of the branch flow path L 2  from the branch point X to the second analyzer  20   b  are proportional to the absolute temperatures of the respective flow paths L 1  and L 2 . 
     The second analyzer  20   b  is one that measures the total particulate matter by measuring the nonvolatile components and volatile components of the particulate matter contained in the exhaust gas, and here analyzes the total particulate matter in the exhaust gas flowing through the branch flow path L 2  in real time. The nonvolatile components include at least the soot as described above, and the volatile components include at least a soluble organic fraction (SOF) and sulfur components (sulfates). The second analyzer  20   b  is one based on the same analysis principle as the first analyzer  20   a , and here a DCS. The second analyzer  20   b  is kept at a temperature (e.g., room temperature) lower than the evaporating temperatures of the volatile components contained in the exhaust gas. 
     The information processor  40  is a computer including a CPU, a memory, an A/D converter, and the like. In addition, as illustrated in  FIG. 3 , the information processor  40  is configured so that the CPU and peripheral devices cooperate in accordance with a program stored in a predetermined area of the memory, and thereby the information processor  40  fulfills functions as a nonvolatile component calculation part  41 , total particulate matter calculation part  42 , and volatile component calculation part  43 . 
     The nonvolatile component calculation part  41  is one that acquires the output from the first analyzer  20   a  to calculate the mass concentration of the nonvolatile components, and here continuously calculates the mass concentration of the nonvolatile components including at least the soot of the particulate matter. 
     The total particulate matter calculation part  42  is one that acquires the output from the second analyzer  20   b  to calculate the mass concentration of the total particulate matter contained in the exhaust gas, and here continuously calculates the mass concentration of the particulate matter including at least the soot, the SOF, and the sulfates. 
     The volatile component calculation part  43  is one that calculates the mass concentration of the volatile components on the basis of the results of the calculations by the nonvolatile component calculation part  41  and the total particulate matter calculation part  42 . Specifically, the volatile component calculation part  43  continuously calculates the mass concentration of the volatile components including at least the SOF and the sulfates in real time by subtracting the mass concentration calculated by the nonvolatile component calculation part  41  from the mass concentration calculated by the total particulate matter calculation part  42 . 
     In the exhaust gas analysis system  100  according to the present embodiment configured as described above, since the temperature control mechanism  10  controls the temperature of the first analyzer  20   a  to the temperature equal to or higher than the evaporating temperatures of the volatile components, the volatile components contained in the exhaust gas guided to the first analyzer  20   a  is not condensed but remains vaporized. This makes it possible to accurately calculate the mass concentration of the nonvolatile components including, for example, the soot and the like using the first analyzer  20   a.    
     Further, since the branch flow path L 2  and the second analyzer  20   b  are kept at the predetermined temperature lower than the evaporating temperatures of the volatile components, the mass concentration of the total particulate matter including at least the soot, the SOF, and the sulfates using the second analyzer  20   b . As a result, the volatile components contained in the exhaust gas can be analyzed by comparing the calculation result by the first analyzer  20   a  and the calculation result by the second analyzer  20   b . Accordingly, without including an analyzer for measuring soot and an analyzer for measuring SOF, the nonvolatile components and the volatile components can be both analyzed, and without making a system large-scale or expensive, the particulate matter contained in the exhaust gas can be accurately analyzed. 
     In addition, by analyzing both of the nonvolatile components and the volatile components as described above, from the result of analyzing the nonvolatile components, for example, the uniformity of fuel injection can be evaluated, and from the result of analyzing the volatile components, for example, the degree of incomplete combustion can be evaluated. 
     Also, since the diameter of the pipe forming the exhaust gas flow path L 1  from the branch point X to the first analyzer  20   a  is made larger than the diameter of the pipe forming the branch flow path L 2  from the branch point X to the second analyzer  20   b , the exhaust gas subjected to the branching at the branch point X can be made to reach the first analyzer  20   a  and the second analyzer  20   b  at substantially the same time, and therefore the analysis result by the first analyzer  20   a  and the analysis result by the second analyzer  20   b  can be synchronized. This makes it possible to measure the mass concentrations or the like of the nonvolatile components, volatile components, and total particulate matter in real time. 
     Further, since the diluters are provided in the exhaust gas flow path L 1 , moisture contained in the exhaust gas can be prevented from being condensed in the exhaust gas flow path L 1 , and therefore analysis accuracy can be ensured. 
     Note that the present invention is not limited to the above-described embodiment. 
     For example, as an embodiment for synchronizing the analysis result by the first analyzer  20   a  and the analysis result by the second analyzer  20   b , the pipe forming the exhaust gas flow path L 1  from the branch point X to the first analyzer  20   a  may be made longer than the pipe forming the branch flow path L 2  from the branch point X to the second analyzer  20   b.    
     Also, the present invention may be adapted to make the exhaust gas subjected to the branching at the branch point X reach the first analyzer  20   a  and the second analyzer  20   b  at substantially the same time by providing the exhaust gas flow path L 1  from the branch point X to the first analyzer  20   a  and the branch flow path L 2  from the branch point X to the second analyzer  20   b  respectively with, for example, critical flow venturis, mass flow controllers, or the like to appropriately control the flow rate of the exhaust gas flowing into the first analyzer  20   a  and the flow rate of the exhaust gas flowing into the second analyzer  20   b.    
     Further, when the exhaust gas subjected to the branching at the branch point X does not reach the first analyzer  20   a  and the second analyzer  20   b  at the same time, the volatile component calculation part  43  may be configured to calculate the mass concentration of the volatile components by, for example, from the mass concentration calculated by the total particulate matter calculation part  42 , subtracting the mass concentration calculated by the nonvolatile component calculation part  41  a predetermined time before the time of the calculation by the total particulate matter calculation part  42 . 
     The temperature control mechanism  10  in the above-described embodiment is one that directly heats the first analyzer  20   a . However, the temperature control mechanism  10  may be configured to, without directly heating the first analyzer  20   a , heat the downstream side of the branch point X in the exhaust gas flow path L 1  connected to the first analyzer  20   a , and use the resulting heat to control the temperature of the first analyzer. 
     Also, in the above-described embodiment, the second analyzer  20   b  is kept at room temperature, but may be heated or cooled to a temperature as long as the temperature is lower than the evaporating temperatures of the volatile components as measurement targets. 
     The first analyzer  20   a  and the second analyzer  20   b  are not limited to ones for calculating the mass concentration of the particulate matter, but may be ones for calculating a value related to the concentration of the particulate matter, such as the number (PN), mass, or number concentration of the particulate matter. 
     Without the need to include the functions as the nonvolatile component calculation part  41  and the total particulate matter calculation part  42  in the information processor, the first analyzer  20   a  may include the nonvolatile component calculation part  41  and the second analyzer  20   b  may include the total particulate matter calculation part  42 . 
     Meanwhile, when the current detection part  21  of the first analyzer  20   a  includes an amplifier for amplifying an electrical signal, such as a preamplifier, and the amplifier is heated, noise occurs. 
     Accordingly, embodiments for solving such a problem include one in which the preamplifier is separated from the main body of the current detection part  21  to the extent that heat is not transferred to the preamplifier. However, when the separation distance between the preamplifier and the main body is long, a lead for connecting them also requires long length, and consequently noise is likely to occur on the lead. Therefore, as another embodiment, it is conceivable to use cooling means adapted to cool the preamplifier or the lead connecting between the preamplifier and the main body, such as a fan or a heat dissipation member. 
     Also, as still another embodiment, it is conceivable to arrange the preamplifier together with the current detection part  21  in a place not heated by the temperature control mechanism  10 . 
     In addition, in each of the above-described embodiments, it is not necessarily required to entirely prevent heat from being transferred to the preamplifier. Some heat may be transferred as long as analysis accuracy can be ensured. Also, when desiring to control the preamplifier to a predetermined temperature, the preamplifier may be controlled to the predetermined temperature by changing the air volume of the above-described fan, the calorific value of the temperature control mechanism  10 , or the like. 
     The first analyzer  20   a  or the second analyzer  20   b  is not limited to the DCS but only has to be one that can analyze the nonvolatile components of the particulate matter contained in the exhaust gas, and as such an analyzer, a condensed particle counter (CPC), an electrical low pressure impactor (ELPI), a scanning mobility particle sizer (SMPS), or the like can be cited. 
     The exhaust gas analysis system according to the present invention can be equipped in a vehicle running on a road, and in doing so, particulate matter consisting of nonvolatile components, particulate matter consisting of volatile components, and the total particulate matter contained in exhaust gas discharged from an internal combustion engine can be measured, for example, in real time during an actual on-road run. 
     Besides, it should be appreciated that the present invention is not limited to the above-described embodiment, but can be variously modified without departing from the scope thereof. 
     REFERENCE SIGNS LIST 
     
         
           100 : Exhaust gas analysis system 
         L 1 : Exhaust gas flow path 
         L 2 : Branch flow path 
           10 : Temperature control mechanism 
           20   a : First analyzer 
           20   b : Second analyzer 
           40 : Information processor