Abstract:
The invention is directed to an improved mass emissions measuring system ( 15 ) for an internal combustion engine ( 17 ). In the preferred embodiment, the system is comprised of a particulate monitor ( 16 ), four sensor ( 18, 22, 23  or  29 ) which may be temporarily attached to the engine for sensing operating parameters of the engine, an engine-control interface ( 21 ), a processor ( 19 ) programmed to collect and manipulate data from the monitor and the sensors and/or engine-control interface, a display ( 20 ) for displaying the particulate emissions of the engine, an exhaust sampling system ( 31 ) which is adapted to be temporarily connected between the exhaust system of the engine and the particulate monitor, and an opacity meter ( 56  or  58 ). The particulate monitor may comprise a first photometer ( 46 ), a second photometer ( 48 ), an impactor ( 45 ) located upstream from the second photometer, whereby the impactor limits the size of particulates in the exhaust of the engine communicating with the second photometer, and a microbalance ( 59 ) adapted to measure the mass of the particulate matter in the exhaust communicating with the photometer. The system is adapted for use on-board a moving vehicle.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of vehicle emissions measuring systems and, more particularly, to an improved on-board exhaust particulate measuring system. 
     BACKGROUND ART 
     Motor vehicle emissions are the leading source of air pollution in most metropolitan areas, causing health, ecological and economical damage. As a result, considerable effort and resources are currently devoted to various emission reduction strategies, such as emission inspection programs, reformulated or alternative fuels, stricter standards for new vehicles, mass transit, improved engine control and catalyst technologies, and upgrade and repair of existing vehicles. However, in order to evaluate the impact of these reduction strategies, it is necessary to measure and collect accurate real-world emission measurements over the life of a vehicle. 
     Presently, the vast majority of emission tests are performed in a specialized laboratory, where the vehicle is driven on a dynamometer according to a prescribed driving cycle, such as I/M 240 or FTP for light and medium duty vehicles and CBD for heavy duty vehicles. 
     This approach has several significant disadvantages. First, the driving cycles do not adequately represent real-world driving conditions, which vary and are often unknown. Second, vehicles can be optimized for low emissions during the driving cycle, but do not operate optimally in actual use. Third, the testing equipment is bulky and expensive. Fourth, there are significant costs associated with testing the vehicle, such as vehicle (and/or mobile laboratory) mileage, vehicle downtime, and the test it-self, especially on heavy-duty vehicles. Fifth, individual vehicle engines have unique characteristics which effect emissions and cause variations between vehicles. Sixth, only a relatively small number of vehicles are being tested. 
     The first two disadvantages can be eliminated by using a capable testing system installed in the vehicle. Such systems can be classified into four categories: (1) laboratory-grade instruments permanently installed into dedicated instrumented vehicles (2) repair-grade gas analyzers used primarily by automotive technicians and providing only a rough estimate of mass emissions for repair purposes, (3) portable, on-board mass emissions monitoring systems, such as a system previously disclosed by the inventor, and (4) portable on-board mass emissions monitoring systems, such as the one disclosed in U.S. patent application Ser. No. 09/359,984, the aggregate disclosure of which is incorporated herein by reference. 
     Systems of the type in the first category lack the portability necessary to test a wide range of vehicles. Systems of the type in the second category are capable of only monitoring concentration of pollutants in the exhaust gas, and therefore lack the capability of accurately measuring and calculating mass emissions. 
     Systems of the type in the third category employ a five-gas analyzer drawing undiluted exhaust from the tailpipe and calculate mass exhaust flow from engine operating data obtained via a diagnostic link to the engine control unit. The system disclosed in U.S. patent application Ser. No. 09/359,984 describes two novel methods of exhaust mass flow monitoring. The first method uses an array of sensors temporarily mounted to a spark ignition engine to provide the necessary engine operating data. The second uses an inert gas injection system, where the exhaust flow is inferred from the dilution ratio from a small, known amount of inert gas injected into the exhaust system upstream from the sampling point. 
     However, even these two systems have certain limitations. First, the sensor array employed uses an inductive pickup to measure engine rpm on spark ignition engines, and is therefore not suitable for use with compression ignition engines such as diesel engines. While mass exhaust flow can still be measured in a diesel engine using the second approach, namely, with an inert gas injector, this approach is likely to require small modifications to the vehicle, such as drilling a hole into the exhaust system. Third, these systems are not capable of accurately measuring particulate material in emissions. This is in large part because the sampling methodology does not allow for the iso-kinetic sampling of particulate matter and for the dilution of the sample necessary for an accurate particulate matter emissions measurement. 
     Finally, it is known that emissions can be sampled using a proportional sampling system, which is a sampling system in which the sampling rate is proportional to the exhaust flow. However, this type of system requires the installation of a bulky proportional sampling system to the end of the tailpipe, and thus its use and portability is limited by the design of the vehicle and its exhaust system. 
     Hence, it would be useful to provide a portable, on-board mass emissions monitoring system which could be used on heavy-duty diesel engines and would allow for on-board measurement of mass gaseous as well as particulate matter emissions. 
     DISCLOSURE OF THE INVENTION 
     With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for the purposes of illustration and not by way of limitation, the present invention provides an improved mass emissions measuring system ( 15 ) for an internal combustion engine ( 17 ), comprising a particulate monitor ( 16 ), at least one sensor ( 18 ,  22 ,  23  or  29 ) which may be temporarily attached to the engine for sensing operating parameters of the engine, and a processor ( 19 ) programmed to collect and manipulate data from the monitor and the sensor, whereby the particulate emissions of the engine may be calculated. 
     The system may further comprise a display ( 20 ) for displaying the particulate emissions of the engine, an exhaust sampling system ( 31 ) which is adapted to be temporarily connected between the exhaust system of the engine and the particulate monitor, and/or an opacity meter ( 56  or  58 ). The particulate monitor may comprise a first photometer ( 46 ), a second photometer ( 48 ), and an impactor ( 45 ) located upstream from the second photometer, whereby the impactor limits the size of particulates in the exhaust of the engine communicating with the second photometer. The system may further comprise a microbalance ( 59 ) adapted to measure the mass of the particulate matter in the exhaust communicating with the photometer. The sensor may be capable of sensing engine rpm, engine oil temperature, intake manifold pressure, or intake air temperature. The particulate monitor may be capable of measuring particulate mass, particulate surface area, particulate count, or the opacity of the emissions from the engine. The system may be adapted for use on-board a moving vehicle. The present invention also discloses a portable mass emissions measuring system for an internal combustion engine comprising a particulate monitor, an engine-control interface ( 21 ), and a processor programmed to collect and manipulate data from the monitor and the engine-control interface, whereby the particulate emissions of the engine may be calculated. 
     Accordingly, the general object of the present invention is to provide an improved mass emissions measuring system which is adapted to be used to determine real-world vehicle emissions. 
     Another object is to provide an improved emissions measuring system for determining particulate emissions of a vehicle. 
     Another object is to provide an improved emissions measuring system which is portable. 
     Another object is to provide an improved emissions measuring system which is designed for use on a wide variety of vehicles. 
     Another object is to provide an improved emissions measuring system which may be used on a vehicle without permanent modification to the vehicle. 
     Another object is to provide an improved emission measuring system which can be installed for use on a vehicle in a very short period of time. 
     Another object is to provide an improved emissions measuring system which may be used without displacing a vehicle from service. 
     Another object is to provide an improved emissions measuring system which allows for use with a large number of vehicles. 
     Another object is to provide an improved emissions measuring system which may be used to test large numbers of vehicles in a short period of time. 
     Another object is to provide an improved emissions measuring system which may be used on vehicles which do not have an engine electronic control unit. 
     Another object is to provide an improved emissions measuring system which has improved accuracy in measuring particulates. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a complete schematic of the emissions measuring system. 
     FIG. 2 is a partial schematic of the emissions measuring system, showing the sensor array temporarily mounted to the engine and the engine control unit and interface. 
     FIG. 3 is a partial schematic of the emissions measuring system, showing the sampling system. 
     FIG. 4 is a partial schematic of the emissions measuring system, showing the particulate monitoring system. 
     FIG. 5 is a schematic of the particulate monitor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, debris, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof, (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or access of rotation, as appropriate. 
     Referring now to the drawings and, more particularly, to FIG. 1 thereof, this invention provides an improved portable particulate emissions measuring system, of which the presently preferred embodiment is generally indicated at  15 . The system is shown as broadly including a particulate monitor  16 , four engine sensors  18 ,  22 ,  23  and  29 , a sensor data acquisition interface  27 , an engine control interface  21 , and a processor  19 . 
     Processor  19 , particulate monitor  16 , data acquisition interface  27 , and engine control unit interface  21  are enclosed in a single aluminum housing  37 , which is vented for heat dispersion and adapted for placement on the seat, on the floor, or on any other suitable horizontal surface inside the vehicle. 
     As shown in FIG. 2, in engines which are not computer controlled or for which the computer does not provide the necessary data, engine rpm, intake manifold pressure, engine oil temperature, and intake air temperature are measured using engine rpm sensor  18 , intake manifold pressure sensor  22 , oil temperature sensor  29 , and intake air temperature sensor  23 . Sensors  18 ,  22 ,  29 , and  23  are adapted to be temporarily mounted to the engine during testing. Data acquisition interface  27  is a conventional A/D converter which converts analog input from the sensors to digital output. In the preferred embodiment, engine rpm sensor  18  is a phototachometer. The phototachometer includes a reflective surface which is temporarily affixed to the crankshaft or other rotating part of the engine. A light source and a light detector are then positioned such that each time the rotating part completes a full turn, the light hits and is reflected from the reflective surface on the rotating engine part and is detected by the detector. 
     It is contemplated that alternative rpm sensors may be used. For example, engine rpm sensor  18  may be a Hall effect sensor, which employs a magnetic strip temporarily attached to the crankshaft or other rotating part of the engine and a detector. The detector is arranged such that it provides a signal each time the magnetic strip on the rotating part of the engine completes a full turn. Alternatively, engine rpm sensor  18  may be a vibrational detector, which senses engine vibrations. This signal may then be converted electronically to an rpm reading. 
     Manifold pressure sensor  22  is a manifold absolute pressure transducer which is connected to the intake air manifold of the engine and senses the manifold absolute pressure in the manifold. On turbocharged engines, pressure sensor  22  is placed downstream of the turbocharger. 
     Intake air temperature sensor  23  is connected in a similar position to manifold pressure sensor  22 . Intake air temperature sensor  23  is a conventional temperature measuring device which is capable of sensing intake air temperature. 
     Intake oil temperature sensor  29  is a conventional dipstick temperature probe which is inserted in place of the oil dipstick. 
     As also shown in FIG. 2, in computer controlled engines where engine data can be obtained by an engine diagnostic link, intake air flow or fuel flow is computed from the engine data obtained by engine control interface  21 . Because modern computer-controlled engines provide operating data such as vehicle speed, engine rpm, intake air and coolant temperature, intake air pressure, intake air mass flow, throttle position and engine load to an engine control unit  30 , this information can be fed to processor  19  by engine control interface  21 . The Pro-Link 9000 scan tool with heavy-duty cartridge manufactured by Microprocessor Systems Inc. of Sterling Heights, Mich. may be employed in the preferred embodiment. 
     Processor  19  is programmed to use data from engine control unit  30  to compute intake air mass flow. As mentioned above, in most modem engines, intake air mass flow and/or fuel flow can be obtained from engine electronic control unit  30  using engine control interface  21 . On throttled (such as gasoline powered) engines, the intake air flow (MF i ) is usually determined by the formula:            MF   i                [     mol        /        s     ]     =       (               (     Adjusted                   MAP        [   kPa   ]         )                 (     Engine                   displacement        [   liters   ]         )          (     engine                   speed        [   rpm   ]         )               30        (     engine                 cycle     )           8.314        (       Intake                 air                   temp   .     [     deg   .              C   .     ]         +   273     )         )        VEF                            
     MAP is the manifold absolute pressure and the engine cycle will be either 2 or 4. VEF is the volumetric efficiency multiplier, denoting an overall engine volumetric efficiency at full throttle. A value of 0.95 is used as a default for modem engines.          Adjusted                 MAP     =       Measured                 MAP     -       Atmospheric                 pressure       Engine                 compression                 ratio                                
     If the intake air temperature is not available, it is approximated by the arithmetic average of oil temperature and ambient air temperature. Some engines report intake air mass flow directly in grams per second. 
     On naturally aspirated diesel engines, atmospheric pressure is used instead of Measured MAP. On turbocharged engines, Measured MAP can be substituted with the sum of the atmospheric pressure and turbo boost, where turbo boost is the difference between the intake manifold pressure and atmospheric pressure. 
     Fuel flow can be obtained either directly as a mass or volume per unit of time (such as on some heavy-duty diesel engines), or calculated from a formula:        FuelFlow   =       (     Injector                 displacement     )          (     number                 of                 cylinders     )          (       Engine                 rpm       30        (     engine                 cycles     )         )                              
     Injector displacement is the amount of fuel injected by one injector during one engine cycle. Injector displacement is directly proportional to the injector pulse width, reported by many newer engines. The proportion constant may be obtained from the vehicle manufacturer or determined. 
     As shown in FIG. 1, sensors  18 ,  22 ,  23  and  29 , engine control interface  27  and particulate monitor  16  are connected to processor  19  via a serial (RS-232) port. An Axiom P-1000 panel PC may be used in the preferred embodiment. The present system uses software to simultaneously receive both sets of data. The data is parsed, a system time stamp and the most recent tag is added to each complete record, and each record is stored in computer memory. 
     Particulate monitor  16  is designed to provide qualitative and/or quantitative particulate matter emissions measurements. Particulate monitor  16  operates in conjunction with exhaust sampling system  31 . As shown in FIGS. 3 and 4, exhaust sampling system  31  includes sampling probe  32 , alternate sampling probe  33 , sampling line  34 , dilution system  35 , and zero air intake  36 . In the preferred embodiment, a sample of raw undiluted vehicle exhaust is collected through a 12 inch sampling probe  32  inserted into the tailpipe and secured by a clamp. Alternatively, sampling probe  33  may be inserted into a temporary sampling port drilled into the exhaust pipe  41 . The sample is drawn perpendicular to the laminar flow of exhaust at a rate of 0.1-0.2 liters per second, depending on the configuration of the monitoring system. 
     An isokinetic sampling system, in which the samples are drawn in the same direction and at the same speed as that of the laminar exhaust flow, is not necessary in this invention, as diesel exhaust particles are sufficiently small (&lt;1 μm in diameter) to obtain a representative sample without isokinetic sampling. The sample is drawn perpendicular to the laminar flow of exhaust, with the purpose of excluding relatively large (greater than 1 μm in diameter) road dust and engine wear particles. 
     An electrically conductive sample line  34  is used to prevent the electrostatic deposit of particles in the sampling system. The sample line is not heated. While use of an unheated line is likely to cause condensation in the line, thereby possibly reducing the accuracy of the measurement, the power consumption of the heated line would necessitate the use of an external power source, such as a battery, and reduce the portability of the system. 
     In the preferred embodiment, the exhaust remains undiluted and the measuring instruments are adapted to operate with undiluted exhaust. However, the invention does provide for the inclusion of a dilution system  35  when such dilution is necessary. When exhaust dilution is necessary, the sample is routed through metric dilution system  35 . Dilution system  35  mixes the exhaust with filtered and particulate-free zero air at a predetermined dilution ratio. Zero air is provided through zero air intake  36 . A suitable miniature dilution system is the MD19-1E, available from EcoChem Analytics of West Hills, Calif. The dilution system is positioned upstream of the instruments requiring a diluted sample. 
     As shown in FIG. 5, particulate monitor  16  includes a sample input line  38 , a condensate bowl  39 , a condensate outlet  40 , condensate filter  41 , sample heater  42 , sample pump  43 , first impactor  44 , second impactor  45 , first photometer  46 , second photometer  48 , particulate filter  49 , air drier  50 , control box  51 , particulate filters  52 , critical orifices  53 , and a number of check valves, severally indicated at  54 . 
     Sample input line  38  connects with sampling line  34 . As shown, particulate monitor  16  draws the sample from sampling system  31  through sampling input line  38  and into condensate bowl  39 . Condensate bowl  39  has an inlet at the top and two outlets, top and bottom. Condensate bowl  39  operates much like condensate bowls found in compressed air systems and is used to collect condensed vapors at the bottom of the bowl. 
     From condensation bowl  39 , a mixture of condensate and sample is drawn at a rate of approximately a quarter of the total sample flow through condensate outlet  40 , through condensate filter  41 , and into the wet side  43   a  of sample pump  43 , where it is expelled from the system. Condensate filter  41  is a disposable particulate filter, such as an automotive fuel filter, which operates to prevent the accumulation of particulate matter in sample pump  43 . 
     Condensate-free sample exhaust is drawn from condensate bowl  39  at a rate of approximately three quarters of the total sample flow through sample heater  42 . Sample heater  42  raises the temperature of the sample, which reduces the relative humidity of the sample and prevents condensation from forming. Sample heater  42  consists of loops of the sampling line elongated around a heated bulb. 
     After being heated, the sample flow is divided, with one portion of the sample passing through first impactor  44  and the other portion passing through second impactor  45 . First and second impactors  44  and  45  are designed to trap particles larger than a predetermined diameter, thereby limiting the size of the particles entering photometers  46  and  48 , respectively. Impactor  44  has a large cut-off diameter (0.5-1.0 μm) and impactor  45  has a smaller cut-off diameter (0.2-0.5 μm). 
     As shown in FIG. 5, first impactor  44  and second impactor  45  are positioned upstream of first photometer  46  and second photometer  48 , respectively. Photometers  46  and  48  are light scattering measurement devices. Each light scattering device consists of an enclosure which houses a laser light source pointed into the flow of the sample and a light detector mounted at an angle to the laser beam. The detector measures the intensity of the light scattered by particles within the sample. Photometer  46  has a low intensity laser (5 mW) and is intended to be used downstream from impactor  44 . Alternatively, photometer  46  may be used without an upstream impactor. Photometer  46  measures the overall light-scattering ability of the sample, which is primarily determined by the light scattering caused by the larger particles in the sample. Photometer  48  has a high-intensity light source (15 mW) and is intended to be used downstream from impactor  45 . Photometer  48  measures the light scattering caused by the smaller particles in the sample. 
     To protect the optics of the photometer, and to prevent deposition of particulate matter within the photometer, a sheath of air is drawn into the photometer enclosure along with the sample such that the sample is contained and surrounded by a cylinder of air. This air is ambient air, drawn through sample dryer  50  and a HEPA particulate filter  49 . Dryer  50  and filter  49  assure that the sheath of air is particle-free and has low relative humidity. The intensity of the light sources and the detector signal are analyzed by control unit  51 , which provides voltage signals to processor  19 . 
     The relationship between the light scattering caused by particles in the sample and particulate mass emissions is highly dependent on the particle size distribution of the sample. For example, the particle size distribution of emissions from a diesel engine is dependent on the engine design, age, mechanical condition, operating conditions, and fuel characteristics, and is often difficult to predict. However, the simultaneous use of two photometers allows for a qualitative determination of the particle size distribution, which, in turn, allows for a more accurate quantitative determination of particulate mass emissions. 
     The sample is drawn from photometers  46  and  48  through particulate filters  52 , critical orifices  53 , check valves  54  and into dry side  43   b  of pump  43 . The sample is then exhausted from monitor  16 . Filters  52  are commercially available automotive filters and prevent the accumulation of particulate matter within the sampling pump. Orifices  53  provide a maximum limit to the flow rate and prevent the flow from becoming turbulent as it passes through photometers  46  and  48 . Check valves  54  prevent back-flow. 
     In the preferred embodiment, suitable photometers  46  and  48 , control unit  51 , and critical orifices  53  may be adopted from the 8100 series particle filter tester manufactured by TSI, Inc. of St. Paul, Minn. Examples of suitable impactors  44  and  45 , and dryer  50  are also manufactured by TSI, Inc. The sample pump manufactured by Hargraves Technology Corporation of Mooresville, N.C., is an example of a suitable pump  43  in the preferred embodiment. 
     It should be noted that the relationship between the response of the light scattering monitors and the total particulate mass is dependent on the properties (such as size, distribution or chemical composition) of the measured exhaust, and can be extremely difficult to describe mathematically. Rather, this relationship should be determined by comparing the instrument response to the emission rates obtained using (1) the traditional test methods, and/or (2) using high quality laboratory grade instruments. This comparison should be done on a variety of diesel engines. In a preferred embodiment, the processor  19  uses a knowledge based expert system to determine total particulate mass from the readings of first and second photometers  46  and  48 . 
     As shown in FIG. 4, in the preferred embodiment, a partial flow opacity meter  56  may be added to particulate monitor  16 . Opacity meter  56  measures the extinction of light passing through the sample. The LCS-2000 opacity meter provided by Sensors, Inc. of Saline, Mich., is an example of a suitable partial flow monitor. In an alternative embodiment, a full flow opacity meter  58  may be used. Opacity meter  58  consists of a light source, a detector, and a mounting system which allows the light sensor and detector to be mounted on the end of the tailpipe of a vehicle. A control unit provides the opacity readings to processor  19 . An example of a suitable full-flow opacity meter is Wager Model 6500 provided by Robert H. Wager Co., Inc., of Rural Hall, N.C. 
     The function of opacity meter  56  is to complement the light scattering readings in order to improve the accuracy of the system. However, it is contemplated that in some cases opacity readings alone will be sufficient to provide a qualitative, and to some extent quantitative, particulate mass emission measurements. An emission inspection test, the goal of which is to simply identify vehicles with extremely high emissions, is an example of such a case. 
     The simultaneous use and output from light scattering photometers  46  and  48  and opacity meter  56  or  58  may be used to qualitatively differentiate between elemental carbon particles (soot) and organic carbon (condensed organic compounds), based on the large difference in the light absorption capabilities between the elemental and organic carbon particles. 
     In the preferred embodiment, particulate monitor  16  may also include the addition of a tapered element oscillating microbalance  59 . A suitable oscillating microbalance  59  is the TEOM diesel particulate monitor provided by Rupprecht &amp; Patashnick Co., Inc. of Albany, N.Y. This device directly measures total particulate mass by depositing particulates on a filter which is attached to an oscillating element. The total filter mass is determined from the frequency of the natural oscillation of the element. With the addition of microbalance  59 , the conversion factor between light scattering and particulate mass may be more accurately determined by comparing the particulate mass measurements derived from the photometer readings, including indicated particle size distribution, with the particle mass emissions from microbalance  59 . This conversion factor may then be applied to the real-time emissions data obtained from particulate monitor  16  to determine a more accurate measurement of particulate mass emissions. 
     This invention contemplates that a number of alternatives and/or additions to the particulate monitor  16  disclosed in the preferred embodiment may be used. For example, a condensation particulate counter (CPC) of the type provided by TSI, Inc. may be used to measure particulate count. A photoelectric aerosol sensor, such as the PAS-2000 available from EcoChem Analytics, may be used to measure the concentrations of particle-bound aromatic hydrocarbons. An aerodynamic time-of-flight particle sizer, available from TSI, Inc., may be used to obtain a particle size distribution. Also, an oscillating microbalance diesel particulate monitor such as the TEOM manufactured by Rupprecht &amp; Patashnick Co. may be used to provide total particulate mass. A photo-acoustic particulate detector, an X-ray diffraction detector, an electrostatic impactor, and other similar devices may be used as part of the particulate monitor  16  for monitoring different properties of the particulate matter in the subject exhaust. 
     The readings from particulate monitor  16  are transmitted to processor  19 , where they are converted into particulate count, surface area, or particle mass per second units. Given a known sampling rate, readings given per second are converted into count, surface area or particle mass per volume of sample. Conversion factors, derived from manufacturer or scientific literature, may be used to convert the reading of the monitor into the desired parameters. 
     While in the preferred embodiment one of the above approaches is used to determine particulate concentrations, in an alternative embodiment several of the monitors of the same or different type may be used in series if the monitor does not collect or alter the particles. These different types of monitors may be used in series with filters, impactors or other devices which limit the maximum diameter of the passing particles placed upstream of each monitor, with the purpose of limiting the maximum particle diameter flowing through the monitor. 
     Processor  19  is programmed to synchronize the data received. For example, sensors  18 ,  22 ,  23  and  29 , and particulate monitor  16  produce data with a certain delay (or response time), at a certain rate, and with gaps. Both the delay and the rate can be obtained from the instrument manufacturer and/or obtained experimentally. The gaps are caused by equipment malfunction or by events such as periodic zeroing of particulate monitor  16 . 
     On each set of data, the delay is subtracted from the time stamp. Linear interpolation is then used to generate one record every second (or other set time interval). Small gaps (usually less than 3 seconds) in the data are filled using the linear interpolation. If a large gap exists, the data is marked as “missing”. All data is then combined into one set, which includes vehicle speed and engine operating parameters, such as intake/fuel/exhaust flow, exhaust concentrations of gaseous pollutants and particulate matter in the exhaust. 
     To obtain mass emissions data, the sample to be analyzed must be drawn from a known flow of gas. Traditionally, dilution tunnels and constant volume samplers were used for this purpose. In the preferred embodiment, the system samples undiluted exhaust and measures the exhaust flow in real-time. To calculate exhaust flow, either intake mass air flow or fuel flow must be known. Also, vehicle speed is necessary for distance and real-time fuel economy (mpg) and emissions (grams/mile, grams/gallon) calculations. Additional data, such as engine temperature, throttle position, or air conditioning operation are useful in correlating emission data to particular operating conditions. 
     Particulate count, particulate surface area and particulate mass emissions per second are calculated using the following formula. 
     
       
         i E( PM   x )[ Us   −1   ]=C ( PM   x )[ U volume −1   ]*EF [Volume  S   −1   ]*DR ( PM   x ) 
       
     
     U is the desired particulate mass (“PM”) units (i e., particulate count, particulate surface area, or mass units). E(PM x ) is the emissions value for particles of a diameter smaller than X. C(PM x ) is the relative concentration of the particles in the sample. EF is the exhaust flow at the time corresponding to C(PM x ). DR(PM x ) is the corresponding dilution ratio (DR=1 for undiluted exhaust). 
     The present invention contemplates that many other changes and modifications may be made. The particular materials of which the various body parts and component parts are formed are not deemed critical and may be readily varied. 
     Therefore, while the presently-preferred form of the emissions measuring system has been shown and described, and several modifications discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.