Abstract:
The invention relates to an CO 2  tracing method for measuring a raw exhaust gas ( 3 ) flow rate at exit from an internal combustion engine ( 1 A) for a motor vehicle ( 1 ). The inventive CO 2  tracing method for measuring raw exhaust gas flow rate at exit from an internal combustion engine for a motor vehicle consists, prior to starting the motor vehicle internal combustion engine, in injecting a known flow rate of a gas CO 2  and N 2  mixture into a metering line ( 20 ) in such a way that a raw CO 2  analyser ( 22 ) and a diluted CO 2  analyser ( 24 ) are triggered.

Description:
[0001]    The present invention relates in general to the measurement of the flow rate of exhaust gas output by an internal combustion engine of a motor vehicle. 
         [0002]    It relates more particularly to a CO 2  tracing method for measuring the flow rate of the raw exhaust gas output by an internal combustion engine of a motor vehicle and a measurement installation for implementing the CO 2  tracing method of measurement. 
         [0003]    The invention is particularly advantageously applicable for determining, second by second, the masses of the polluting constituents in the exhaust gas, the measurement of the exhaust gas flow rate being an intermediate step. 
       TECHNOLOGICAL BACKGROUND 
       [0004]    To measure by CO 2  tracing the masses of the polluting constituents of the raw exhaust gas output by an internal combustion engine of a motor vehicle, two types of analysis may be carried out. 
         [0005]    It is possible to carry out an overall analysis of the concentrations of the polluting constituents of the raw exhaust gas output by an engine. In this case, the analysis carried out is an analysis using a sampling bag, carried out over the entire duration of the measurement cycle. The mass of each of the polluting constituents emitted over the entire measurement cycle is thus obtained. 
         [0006]    When it is desired to analyze the masses of the polluting constituents of the exhaust gas second by second, in order to make adjustments to the engine, an analysis referred to as “modal” analysis is carried out. 
         [0007]    By determining the flow rate of the raw exhaust gas second by second output by the engine second by second, it is possible to determine the masses of the polluting constituents of the exhaust gas second by second. 
         [0008]    The two types of measurement—measurement by overall analysis and measurement by modal analysis—are usually combined and the results obtained are correlated. 
         [0009]    Currently, one such CO 2  tracing method for measuring the flow rate of the raw exhaust gas output by an internal combustion engine of a motor vehicle comprises the following steps:
       a flow of raw exhaust gas output by an exhaust line of an internal combustion engine is received in a measurement line;   the raw CO 2  content in the flow of raw exhaust gas flowing through the measurement line is measured using a raw CO 2  analyzer;   a flow of fresh dilution air is injected into said flow of raw exhaust gas flowing through the measurement line in order to obtain a flow of diluted exhaust gas;   the diluted CO 2  content in said flow of diluted exhaust gas is measured using a diluted CO 2  analyzer;   the flow rate of said diluted exhaust gas is measured;   the dilution factor corresponding to the ratio of the measured raw CO 2  content to the measured diluted CO 2  content is calculated; and       
 
         [0016]    the flow rate of the raw exhaust gas output by the internal combustion engine of the motor vehicle is deduced from the measurement of the flow rate of diluted exhaust gas and from the dilution factor. 
         [0017]    In such a measurement method, it is necessary for the raw CO 2  analyzer and the diluted CO 2  analyzer to be provided with a priming time of a few seconds in order to be able to carry out the measurement of the CO 2  content present in the flow of raw exhaust gas or the flow of diluted exhaust gas. 
         [0018]    Upon starting up the internal combustion engine of the motor vehicle, a first flow of raw exhaust gas is emitted into the exhaust line. This flow of raw exhaust gas is collected downstream of the exhaust line by the measurement line. The flow then reaches the raw CO 2  analyzer and then, after dilution, it reaches the diluted CO 2  analyzer. 
         [0019]    When the flow of raw or diluted exhaust gas reaches the raw CO 2  analyzer and the diluted CO 2  analyzer, these are primed by the CO 2  contained in the flow of raw or diluted exhaust gas. 
         [0020]    However, during this priming phase, the raw CO 2  analyzer and the diluted CO 2  analyzer do not have the time to calculate the corresponding amount of raw and diluted CO 2  contained in the flow of raw or diluted exhaust gas. 
         [0021]    Thus, using this method it is not possible to know the raw exhaust gas dilution factor during the engine startup phase. As a result, it is not possible by calculation to obtain the flow rate of the raw exhaust gas from the flow rate of the diluted exhaust gas, the value of which is known. 
         [0022]    Likewise, during the phases when the injection of fuel into the internal combustion engine is cut off, the raw CO 2  analyzer and the diluted CO 2  analyzer become unprimed, as they no longer measure the CO 2  content. 
         [0023]    Here again, it is not possible to calculate the raw exhaust gas dilution factor corresponding to these fuel injection cut-off phases. 
         [0024]    Nor is it possible, by not having the raw exhaust gas flow rate to calculate the masses of the polluting constituents during these engine start up and fuel injection cut-off phases. 
         [0025]    However, it is particularly advantageous to know the masses of the polluting constituents emitted during the engine start up phase and the fuel injection cut-off phases, as it is during these phases that there is peak emission of hydrocarbons, carbon oxides and nitrogen oxides, these being the greatest pollutant emitters. 
       SUBJECT OF THE INVENTION 
       [0026]    To remedy the aforementioned drawbacks of the prior art, the present invention provides a CO 2  tracing method for measuring the flow rate of the raw exhaust gas output by an internal combustion engine of a motor vehicle, by which it is possible to measure the flow rate of the raw exhaust gas output by the internal combustion engine during the engine startup phase and the phases when the injection of fuel into the engine is cut off. 
         [0027]    For this purpose, the invention provides a CO 2  tracing method for measuring the flow rate of the raw exhaust gas output by an internal combustion engine of a motor vehicle, which comprises the following steps:
       a flow of raw exhaust gas output by an exhaust line of an internal combustion engine is received in a measurement line;   the raw CO 2  content in the flow of raw exhaust gas flowing through the measurement line is measured using a raw CO 2  analyzer;   a flow of fresh dilution air is injected into said flow of raw exhaust gas flowing through the measurement line in order to obtain a flow of diluted exhaust gas;   the diluted CO 2  content in said flow of diluted exhaust gas is measured using a diluted CO 2  analyzer;   the flow rate of the diluted exhaust gas is measured;   the dilution factor corresponding to the ratio of the measured raw CO 2  content to the measured diluted CO 2  content is calculated; and   the flow rate of the raw exhaust gas output by the internal combustion engine of the motor vehicle is deduced from the measurement of the flow rate of diluted exhaust gas and from the dilution factor, in which provision is made, before the internal combustion engine is started, for a known flow of a CO 2 /N 2  gas mixture to be injected into the measurement line so as to prime the raw CO 2  analyzer and the diluted CO 2  analyzer.       
 
         [0035]    Thus, thanks to the prior priming of the raw CO 2  analyzer and the diluted CO 2  analyzer, it is possible to measure the flow rate of the raw exhaust gas output by the internal combustion engine during the engine startup phase and the phases when the injection of fuel into the engine is cut off. 
         [0036]    When the raw exhaust gas is output and reaches the point where the CO 2 /N 2  gas mixture is injected, the meeting of the raw exhaust gas with this CO 2 /N 2  gas mixture creates a gas mixture flow. Thereafter, the injection of the flow of fresh dilution air into the gas mixture flow creates a diluted gas mixture flow. 
         [0037]    According to one advantageous feature of the method according to the invention, the known flow of CO 2 /N 2  gas mixture is injected until the flow of the diluted gas mixture reaches the diluted CO 2  analyzer. 
         [0038]    According to another advantageous feature of the method according to the invention, said known flow of CO 2 /N 2  gas mixture is injected during the phases when the injection of fuel into the internal combustion engine is cut off. 
         [0039]    According to another advantageous feature of the method according to the invention, the known flow of CO 2 /N 2  gas mixture is injected throughout the duration of the process of measuring the flow rate of the raw exhaust gas. 
         [0040]    According to another advantageous feature of the method according to the invention, upstream of the injection of the known flow of CO 2 /N 2  gas mixture, the polluting constituents of the raw exhaust gas are analyzed before and after passing through a catalytic converter upon exiting the internal combustion engine. 
         [0041]    According to another advantageous feature of the method according to the invention, before the flow rate of said diluted gas mixture is measured, a portion of the volume of the diluted gas mixture is taken off into a sampling bag in order to carry out an overall analysis, at the end of the measurement cycle, of the polluting constituents of the diluted gas mixture. 
         [0042]    According to another advantageous feature of the method according to the invention, during the step of injecting the flow of fresh dilution air into the gas mixture flow, a portion of the volume of fresh dilution air is collected in a sampling bag. 
         [0043]    According to another advantageous feature of the method according to the invention, to calculate the flow rate of the raw exhaust gas output by the internal combustion engine, the volume of diluted gas mixture taken off into the corresponding sampling bag and the volume of the raw exhaust gas taken off by the analyzers for analyzing the polluting constituents of the raw exhaust gas and the raw CO 2  analyzer are taken into account. 
         [0044]    The invention also relates to a measurement installation for implementing the CO 2  tracing method of measurement, which comprises:
       a measurement line suitable for being connected to an outlet of an exhaust line of an internal combustion engine;   a raw CO 2  analyzer positioned on the measurement line in order to measure the raw CO 2  content in the flow of raw exhaust gas coming from said exhaust line;   means for injecting fresh dilution air into the measurement line downstream of the raw CO 2  analyzer;   a diluted CO 2  analyzer, positioned on the measurement line, for measuring the diluted CO 2  content in the flow of diluted gas mixture;   means for measuring the flow rate of the diluted gas mixture; and   means for determining the flow rate of the raw exhaust gas from the measurement of the flow rate of the diluted gas mixture, from the raw CO 2  content and from the diluted CO 2  content,
 
characterized in that it includes upstream of tile raw CO 2  analyzer, means for injecting a known flow of a CO 2 /N 2  gas mixture into the measurement line so as to prime the raw CO 2  analyzer and the diluted CO 2  analyzer.
       
 
         [0051]    Other nonlimiting and advantageous features of the installation for measuring the flow rate of the raw exhaust gas according to the invention are the following:
       it includes analyzers for analyzing the polluting constituents of the raw exhaust gas and the means for injecting the flow of CO 2 /N 2  gas mixture are placed downstream of the analyzers for analyzing the polluting constituents of the raw exhaust gas;   it includes at least one sampling bag suitable for taking off a portion of the volume of the diluted gas mixture;   it includes, upstream of the means for injecting fresh dilution air, at least one sampling bag suitable for taking off a portion of the volume of fresh dilution air;   it includes rollers placed beneath the driven wheels of a motor vehicle driven by an internal combustion engine that are suitable for driving said motor vehicle; and   it includes means for receiving an internal combustion engine of a motor vehicle connected to the exhaust line.       
 
     
    
     
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
         [0057]    The following description with regard to the appended drawings, given by way of nonlimiting examples, will make it clearly understood what the invention consists of and how it can be realized. 
           [0000]    In the appended drawings: 
           [0058]      FIG. 1  is an overall view of the measurement installation according to a first embodiment in accordance with the invention; and 
           [0059]      FIG. 2  is an overall view of the measurement installation according to a second embodiment in accordance with the invention. 
       
    
    
       [0060]      FIGS. 1 and 2  show two embodiments of a measurement installation  10 ;  10 A for implementing, a CO 2  tracing method for measuring the flow rate of the raw exhaust gas  3  output by an internal combustion engine  1 A of a motor vehicle  1 . 
         [0061]    This measurement installation  10 ;  10 A comprises a measurement line  20  suitable for being connected to an outlet of an exhaust line  2  of an internal combustion engine  1 A, which here includes a catalytic converter  5 . 
         [0062]    A raw CO 2  analyzer  22  is provided on the measurement line  20  in order to measure the raw CO 2  content in the flow of gas flowing in the measurement line  20  from said exhaust line  2 . 
         [0063]    Furthermore, downstream of the raw CO 2  analyzer  22 , means  23  for injecting fresh dilution air  23 A into the measurement line  20  are provided. 
         [0064]    After said injection means  23 , a diluted CO 2  analyzer  24  is positioned on the measurement line  20  in order to measure the diluted CO 2  content in the flow of gas flowing in the measurement line  20 . 
         [0065]    At the end of the measurement installation  10 ;  10 A and before venting to atmosphere  4 , means  25 ,  27  for measuring the flow rate of the gas flowing in the measurement line  20  are provided. 
         [0066]    These means consist here of a sonic throat  25  and of pressure and temperature measurement means  27  upstream of the sonic throat  25   
         [0067]    Furthermore, means (not shown here) are used to determine by calculation the flow rate of the raw exhaust gas  3  from the measurement of the flow of gas flowing in the measurement line  20 , from the raw CO 2  content and from the diluted CO 2  content. 
         [0068]    Advantageously, according to the invention, the measurement installation includes, upstream of the raw CO 2  analyzer, means  30  for injecting a known flow of a CO 2 /N 2  gas mixture  30 A into the measurement line  20  so as to prime the raw CO 2  analyzer  22  and the diluted CO 2  analyzer  24  before the engine  1 A is started up. 
         [0069]    When the raw exhaust gas  3  is output and reaches the point where the CO 2 /N 2  gas mixture is injected, the meeting of the raw exhaust gas  3 , with this CO 2 /N 2  gas mixture  30 A creates a gas mixture flow  33 . Thereafter, the injection of the flow of fresh dilution air  23 A into the gas mixture flow  33  creates a diluted gas mixture flow  56 . 
         [0070]    Said injection means  30  are sufficiently precise for the flow rate of the CO 2 /N 2  mixture injected into the measurement line to be known with certainty and so that it can be subsequently subtracted from the flow rate of the raw exhaust gas calculated from the dilution factor. 
         [0071]    In addition, these injection means  30  must be mounted sufficiently upstream of the raw CO 2  analyzer so as to obtain, after the engine  1 A has been started up, a homogeneous flow of gas mixture  33 . 
         [0072]    Finally, these injection means  30  must be insensitive to the pressure fluctuations in the exhaust line  2 . 
         [0073]    For calculating the concentrations of the polluting constituents, the measurement installation  10 ;  10 A includes analyzers  21  for analyzing the polluting constituents of the raw exhaust gas  3  placed on either side of a catalytic converter  5 , and the means  30  for injecting the flow of CO 2 /N 2  gas mixture  30 A are placed downstream of these polluting-constituent analyzers  21 . 
         [0074]    Furthermore, according to the typical case shown, the measurement installation  10 ;  10 A includes a sampling bag  26  suitable for taking off a portion of the volume of the diluted gas mixture  56  and, upstream of the means  23  for injecting fresh dilution air  23 A, at least one sampling bag  28  suitable for taking off a portion of the volume of fresh dilution air  23 A. 
         [0075]    According to the embodiment of the invention shown in  FIG. 1 , the measurement installation  10  includes rollers  11  placed beneath the driven wheels  7  of a motor vehicle  1  powered by an internal combustion engine  1 A that are suitable for driving said motor vehicle  1 , the nondriven wheels of the motor vehicle being moreover blocked in order to avoid entertainment of the vehicle. 
         [0076]    According to the embodiment of the invention shown in  FIG. 2 , the measurement installation  10 A includes means for receiving an internal combustion engine  1 A connected to the exhaust line  2 . 
         [0077]    The two embodiments of the installation according to the invention shown in  FIGS. 1 and 2  are advantageously used for implementing a CO 2  tracing method for measuring the flow rate of the raw exhaust gas  3  output by an internal combustion engine  1 A of a motor vehicle  1 . 
         [0078]    According to this method, before the internal combustion engine  1 A of the motor vehicle  1  is started up, a known flow of a CO 2 /N 2  gas mixture  30 A is injected into the measurement line  20  so as to prime the raw CO 2  analyzer  22  and the diluted CO 2  analyzer  24 . 
         [0079]    The CO 2  is mixed with N 2  so as not to saturate the raw CO 2  analyzer and the diluted CO 2  analyzer  24 . 
         [0080]    Next, the engine  1 A is started up so as to receive in the measurement line  20  a flow of raw exhaust gas  3  output by the exhaust line  2  of the internal combustion engine  1 A after said raw exhaust gas  3  has passed through the catalytic converter  5 . 
         [0081]    At the point of injection of the CO 2 /N 2  gas mixture  30 A, the meeting of the raw exhaust gas  3  with this CO 2 /N 2  gas mixture  30 A creates a gas mixture flow  33 . 
         [0082]    When this gas mixture  33  reaches the raw CO 2  analyzer  22 , the latter measures the raw CO 2  content in the flow of this gas mixture  33  flowing through the measurement line  20 . 
         [0083]    After the content of raw CO 2  in the gas mixture flow  33  has been measured, a flow of fresh dilution air  23 A is injected into the gas mixture flow  33  to reduce the deleterious effect of water on the measurements carried out on the gas mixture  33  during the overall analysis, at the end of the measurement cycle, of the polluting constituents of the diluted gas mixture. This injection of fresh dilution air  23 A into the flow of gas mixture  33  creates a flow of diluted gas mixture  56 . 
         [0084]    The flow of fresh dilution air  23 A is adapted to the driving cycle studied, consisting of slowing-down phases, steady-speed phases and acceleration phases. 
         [0085]    Diluted CO 2  content in said flow of diluted gas mixture  56  is then measured using a diluted CO 2  analyzer  24 . 
         [0086]    Next, the flow rate of said diluted gas mixture  56  is determined by measuring, thanks to the measurement means  25 ,  27 , the temperature and pressure upstream of the sonic throat  27 , the characteristics of which are known. 
         [0087]    Finally, the dilution factor corresponding to the ratio of the measured raw CO 2  content to the measured diluted CO 2  content is calculated. 
         [0088]    It is then possible for the flow rate of the raw exhaust gas  3  output by the internal combustion engine  1 A to be deduced from the measurement of the flow rate of the diluted gas mixture  56  and from the dilution factor. 
         [0089]    It should be pointed out that the known flow of CO 2 /N 2  gas mixture  30 A is injected at least until the flow of diluted gas mixture  56  reaches the diluted CO 2  analyzer  24 . 
         [0090]    Thereafter, said known flow of CO 2 /N 2  gas mixture  30 A is injected on detecting cut-offs in the injection of fuel into the internal combustion engine  1 A. 
         [0091]    This injection of CO 2 /N 2  gas mixture  30 A during phases when the injection of fuel into the engine  1 A is Cut off avoids having an indeterminate form of the dilution factor during the fuel injection cut-off phases and ensures continuity in the measurement of the flow rate of the raw exhaust gas  56  output by the engine  1 A. 
         [0092]    To simplify the calculations, the CO 2 /N 2  gas mixture  30 A may be injected throughout the duration of the process of measuring the flow rate of raw exhaust gas  3 . 
         [0093]    The polluting-constituent analyzers  21  give the concentrations of the principal polluting constituents, which here are mainly carbon oxides, hydrocarbons, nitrogen oxides and carbon dioxide. 
         [0094]    The polluting constituents of the raw exhaust gas  3  are analyzed upstream of the injection of the known flow of CO 2 /N 2  gas mixture  30 A before and after passing through the catalytic converter  5  at the output of the internal combustion engine  1 A. 
         [0095]    Since the raw and diluted CO 2  analyzers  22 ,  24  are primed, masses of the various polluting constituents of the raw exhaust gas  3  can be calculated second by second. 
         [0096]    Furthermore, according to this method, before the flow rate of said diluted gas mixture  56  is measured, a portion of the volume of the diluted gas mixture  56  is taken off into a sampling bag  26  in order to carry out an overall analysis at the end of the measurement of the polluting constituents of the diluted gas mixture  56 . 
         [0097]    Likewise, during injection of the flow of fresh dilution air  23 A into said flow of raw exhaust gas  3 , a portion of the volume of fresh dilution air  23 A is recovered in a sampling bag  28  for the overall calculation of the masses of the polluting constituents over the cycle from the measured concentrations of these polluting constituents in the sampling bags. 
         [0098]    It should also be pointed out that, for calculating the flow rate of the raw exhaust gas  3  output by the internal combustion engine  1 A, the volume of diluted gas mixture  56  taken off into the corresponding sampling bag  26  and the volume of the raw exhaust gas  3 ,  33  taken off by the analyzers  21  for analyzing the polluting constituents of the raw exhaust gas and the raw CO 2  analyzer  22  are taken into account. 
         [0099]    Thanks to the raw CO 2  analyzer  22  and the diluted CO 2  analyzer  24  being primed according to the invention, it is possible to measure the flow rate of the raw exhaust gas  3  output by the internal combustion engine  1 A during the startup phase of the engine  1 A and during the phases when the injection of fuel into the engine  1 A is cut off. 
         [0100]    Thus, knowing the flow rate of the raw exhaust gas  3 , the concentration of all the polluting constituents of the raw exhaust gas  3 , their density, and the flow rate of the injected CO 2 /N 2  mixture, it is then possible to calculate the mass of the polluting constituents of the exhaust gas second by second, in particular during the startup and fuel injection cut-off phases. 
         [0101]    The present invention is in no way limited to the embodiments described and shown, rather a person skilled in the art will be capable of providing any variant thereof consistent with its purview.