Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N1/00—Sampling; Preparing specimens for investigation
  • G01N1/02—Devices for withdrawing samples
  • G01N1/22—Devices for withdrawing samples in the gaseous state
  • G01N1/2202—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N1/00—Sampling; Preparing specimens for investigation
  • G01N1/02—Devices for withdrawing samples
  • G01N1/22—Devices for withdrawing samples in the gaseous state
  • G01N1/2247—Sampling from a flowing stream of gas
  • G01N1/2252—Sampling from a flowing stream of gas in a vehicle exhaust
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N1/00—Sampling; Preparing specimens for investigation
  • G01N1/02—Devices for withdrawing samples
  • G01N1/22—Devices for withdrawing samples in the gaseous state
  • G01N1/2247—Sampling from a flowing stream of gas
  • G01N2001/2264—Sampling from a flowing stream of gas with dilution

Definitions

• the present invention pertains to a fluid dilution sampling apparatus for either proportional sampling or fixed dilution sampling of a fluid.
• the invention is useful with any source, but has particular application to exhaust analysis. While the invention is illustrated for engine exhaust emission analysis and, in particular, to measuring the mass of particulate matter in the engine exhaust, it may also be used for exhaust analysis for boilers, industrial stacks, and the like.
• Partial exhaust dilution sampling has been considered as the basis of measuring particulates from this new transient engine test.
• Partial exhaust dilution systems work by sampling part of the engine exhaust gas-flow, keeping a constant split ratio (the ratio of exhaust total flow to sampled flow). This is carried out by mixing the sample gas with dilution air inside a small dilution chamber and then the diluted exhaust gas passes through filters where the particulate material is deposited.
• the control of the dilution air requires fast response to control inputs.
• the first factor can be corrected by using a predictive control method.
• a first approach replaced the traditional vortex blower rotation control method (used on full flow dilution systems) with a flow control method that used a piezo-valve to control the flow rate of compressed air used for dilution.
• This approach came from a design for a hot-wire type mass-flow controller that uses a piezo control valve. Such devices are in common use, although their accuracy and response speed are not satisfactory for use in this application.
• a second approach combines a piezo-valve with a venturi flowmeter.
• CFO critical flow orifice
• the present invention provides a fast dilution sampling control system which can be used as either a proportional sampling system or a fixed dilution system and method for exhaust analysis that overcomes the difficulties set forth above.
• a dilution apparatus for sampling of a source gas emitted from a source includes a flowmeter, a mixing chamber, a first flow control and a processing unit.
• the flowmeter is adapted to measuring a parameter that is indicative of the flow rate of the source gas.
• the mixing chamber is adapted to mixing a portion of the source gas with a dilution gas, thereby generating a diluted sample.
• the first flow control is adapted to at least partially controlling the flow rate of the portion of the source gas.
• the first flow control includes a first parallel array of solenoid valves, each defining a flow restriction.
• the processing unit is responsive to an output of the flowmeter. The processing unit controls the sampling ratio of the source gas by activating the combination of the solenoid valves of the first parallel array as a function of the flow rate of the source gas.
• the dilution apparatus may further include a second flow control.
• the second flow control is adapted to at least partially controlling the flow rate of the diluted sample.
• the second flow control includes a second parallel array of solenoid valves, each defining a flow restriction.
• the processing unit controls the flow rate of the diluted sample from the mixing chamber at least in part by activating a combination of the solenoid valves of the second parallel array as a function of the flow rate of the source gas.
• the processing unit may control the flow rate of the sample from the mixing chamber at a generally constant flow rate.
• the flow restriction may be a flow orifice, a critical flow orifice and/or a needle valve. At least some of the solenoid valves have different flow restrictions than others of the solenoid valves.
• the apparatus may include one or more particulate analyzers for analyzing the diluted sample for particulate mass.
• the particulate analyzer may include a particulate filter, wherein the diluted sample is conveyed through the particulate filter for trapping of the particulate matter present in the diluted sample.
• the particulate filter may be weighed for the determination of the mass of the particulate matter trapped in the particulate filter.
• the apparatus may include a calibration flowmeter to balance the airflow of the first control with the flow rate of the diluted sample produced with the second flow control.
• the apparatus may be adapted for use with an exhaust producing apparatus, such as an engine exhaust.
• the processing unit may control the flow rate of the dilution apparatus to provide proportional sampling or fixed dilution sampling.
• a method for diluting a source gas emitted from the source includes sampling the source gas to provide a portion of the source gas and measuring a parameter indicative of the flow rate of the source gas.
• a dilution gas is provided at a flow rate.
• the portion of the source gas is mixed with the dilution gas, thereby generating a diluted sample.
• the flow rate of the portion of the source gas is at least partially controlled with the first parallel array of solenoid valves, each defining a flow restriction.
• the sampling ratio of the source gas is controlled by activating a combination of the solenoid valves of the first array as a function of the flow rate of the source gas.
• the method may further include controlling the flow rate of the diluted sample with a second parallel array of solenoid valves, each defining a flow restriction.
• the flow rate of the diluted sample may be controlled by activating a combination of the solenoid valves of the second parallel array as a function of the flow rate of the source gas.
• the diluted sample flow rate may be controlled at a generally constant flow rate.
• At least one particulate analyzer may be provided and a portion of the diluted sample provided to the particulate analyzer to analyze the mass of the particulate matter of the diluted sample.
• the mass of the particulate matter contents present in the source gas may be determined from the mass of the particulate matter of the diluted sample, the flow rate of the diluted sample and the flow rate of the source gas.
• the at least one particulate analyzer may measure light-scattering and/or electrical charge.
• the at least one particulate analyzer may measure the mass of particulate matter trapped at a substrate placed in a stream of the diluted sample.
• the substrate may oscillate at a frequency related to the mass of the particulate matter collected from the diluted sample or may oscillate at an amplitude related to the mass of the particulate matter and the diluted sample.
• the method may be used to measure particulate matter in an exhaust, such as an engine exhaust.
• the sampling may be proportional sampling or fixed dilution sampling.
• Fig. 1 is a side elevation of an engine exhaust analyzer, according to the invention.
• Fig. 2 is a block diagram of the exhaust analyzer in Fig. 1;
• Fig. 3 is a schematic diagram illustrating operation of a flow control unit, according to the invention.
• Fig. 4 is a block diagram of the flow control unit in Fig. 3.
• Fig. 5 is a schematic diagram of a mixing chamber, illustrating operation thereof. DESCRIPTION OF THE PREFERRED EMBODIMENT
• an engine exhaust analyzer 10 for measuring the mass of particulate matter in the exhaust of an engine includes a sample probe 12 for sampling exhaust gas from a tailpipe 14 and a flowmeter 16 for measuring the flow rate of the exhaust gas (Figs. 1 and 2).
• Analyzer 10 further includes a mixing chamber 18 that mixes exhaust gas from sample probe 12 with a dilution gas from a flow control unit 20.
• a second particulate analyzer 28 may also be provided to analyze particulate matter from discharge 24. It should be understood that only one particulate analyzer or more than two particulate analyzers can be used.
• flowmeter 16 is an EFM exhaust flowmeter that is commercially available from Sensors, Inc. of Ann Arbor, Michigan.
• Analyzer 10 may include a fitting, such as an elbow 13, that allows mixing chamber 18 to be positioned close to probe 12. This may eliminate the need for a heated line between probe 12 and chamber 18.
• a processing unit 26 retrieves the flow rate of the exhaust gas from flowmeter 16 and controls the flow rate of dilution gas, such as air, from flow control unit 20.
• Flow control unit 20 is made up of at least one parallel array of solenoid valves 30 (Figs. 3 and 4). Each of the solenoid valves 30 defines a flow restriction.
• Each of the solenoid valves has a solenoid actuator 32 and an associated flow orifice 34.
• Each flow orifice is made up of a flow restriction that may operate as a critical flow orifice (critical flow orifice) or may be a non-critical flow orifice or a needle valve.
• flow orifices are different from other flow orifices and, in the illustrative embodiment, each flow orifice is different from the other flow orifices 34.
• a particular actuator 32 is actuated by processing unit 26
• dilution gas from a compressed air manifold 36 is supplied through one or more of the flow orifices 34 in parallel, thereby producing a controlled flow of dilution gas.
• flow control unit 20 is made up of a first dilution flow control 20a and a second dilution flow control 20b. Outlets of flow orifices of first dilution flow control 20a are collected at first diluted sample output 21a.
• Outlets of second dilution flow control 20b are collected at second diluted sample output 21b. Outputs 21a, 21b are supplied to mixing chamber 18.
• Each flow control unit 20a, 20b includes one or more electrical connectors 38 for electrical interconnection with a control unit of processing unit 26.
• the dilution flow is controlled by flow control unit 20 using a pair of multi-bit parallel solenoid arrays.
• Each array is made up of a plurality of solenoids 30, each associated with a critical flow orifice 34 (or critical adjustable needle valve) to provide precise and repeatable flow characteristics.
• This system may be operated at 10-20 Hz, thereby providing approximately 50 ms to 100 ms adjustment of the dilution flow. Slower or faster control is also possible.
• a positive feedback loop with exhaust flowmeter 16 is used to meet proportional sampling requirements.
• a flow input signal that is proportional to exhaust flow such as a fuel flow signal, a combustion air flow signal, or the like, may be used.
• first dilution flow control 20a is included in first dilution flow control 20a and a portion is included in a second dilution flow control 20b.
• First dilution flow control 20a is controlled to provide the correct dilution ration to obtain a certain proportion of the exhaust flow. This is accomplished by a venturi 40 in mixing chamber 40.
• Venturi 40 in the illustrative embodiment, includes a laminar flow capillary 42, a secondary transport capillary 44 and a flow restriction 46.
• processing unit 26 determines a change in exhaust gas flow rate, it selects particular solenoids 30 to activate in the first flow control 20a. This changes the flow of dilution air at 21a, which causes a change in vacuum at venturi 40.
• Second dilution flow control 20b provides a make up flow of dilution gas in order to maintain total sample flow rate from mixing chamber 18 at a near constant flow rate.
• processing unit 26 determines a change in exhaust gas flow rate, it determines an additional amount of dilution air required to bring the flow rate at discharge 24 to a particular level.
• Operation of apparatus 10 includes obtaining a particulate sample over a given sample period and measuring mass of the sample. Because flow control 20 is able to maintain a generally constant sampling, or dilution, ratio at a generally constant flow rate, it is not necessary to consider in the calculations the amount of dilution air used.
• Mixing chamber 18, in the illustrated embodiment, includes a flowmeter (not shown), such as an internal flowmeter, for direct measurement of sample flow rate. The flowmeter associated with mixing chamber 18 provides an input to processing unit 26 representative of actual sample flow. Processing unit 26 uses this sample flow signal to monitor system performance, not to operate flow control 20.
• critical orifice(s) used for each "bit" control are illustrated below for a range of flow rates (10-bit system illustrated). Other values may be used. For a 12-bit system with a filter flow rate of 30 LPM, the smallest orifice diameter would be 28 um (70 cc/min). In applications where orifice diameter is small, the flow orifice may be replaced with a critical flow needle valve, for example.
• the system may be calibrated for flow over the complete range of operation, such as by using a calibration flowmeter 27.
• the flow characteristics for each orifice are measured and used to generate a "look-up" table correlating the actual flow rate to a binary array (bit control number).
• This calibration is then checked by measuring the sample flow rate over the appropriate range using the Filter Mass Flowmeter as a reference flowmeter.
• particulate analyzer 22 may utilize known particulate analysis techniques.
• known particulate analyzers utilize various techniques, such as light-scattering principles electrical charge generated by the particulate matters as well as a particulate filter for trapping the particulate matter present in the exhaust gas.
• particulate analyzer 28 is a gravimetric meter and utilizes a mass flow controller 29 to draw a controlled amount of flow needed for the particulate analyzer.
• other known particulate analyzers may be used.
• the present invention provides a very fast dilution flow control system that is capable of exceptional accuracy, as required for the application.
• An orifice flow balancing system may be used to auto-calibrate or balance the dilution airflow rate and filter flow.

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• 2005
  • 2005-07-21 EP EP20050777246 patent/EP1779084A4/en not_active Withdrawn
  • 2005-07-21 JP JP2007522760A patent/JP4815438B2/ja not_active Expired - Fee Related
  • 2005-07-21 US US11/883,465 patent/US7798020B2/en not_active Expired - Fee Related
  • 2005-07-21 WO PCT/US2005/025903 patent/WO2006012433A2/en not_active Ceased

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