Abstract:
A system and method is disclosed for measuring mass of hydrocarbons from point source contributions to overall hydrocarbon emissions from an automotive vehicle at rest.

Description:
BACKGROUND OF INVENTION 
     The present invention relates generally to a system and method for determining the hydrocarbon emission from point sources located within an automotive vehicle. 
     It is known to those skilled in the art that an automotive vehicle at rest releases hydrocarbons to the atmosphere which may be fuel, lubricant, or polymer based, the latter emanating from plastic components. The mass of hydrocarbons emanating from a vehicle at rest is typically determined by placing the vehicle in a test facility and performing a Sealed Housing for Evaporative Determination (SHED) test procedure, in which gases within the test facility are drawn into a flame ionization detector (FID) periodically over a 72-hour test period. Based on the concentration of hydrocarbons detected by the FID and the SHED volume, the mass of hydrocarbons emitted by the vehicle can be determined. 
     The inventors of the present invention have recognized a need to measure the mass of hydrocarbons emanating from discrete portions of a vehicle. Stringent emission regulations, which limit hydrocarbon emission, necessitate the capability to precisely measure all hydrocarbon sources. For example, hydrocarbons may be emitted from the vehicle through the vehicle&#39;s air induction system (AIS). Hence, it is desirable to measure the mass of hydrocarbon material emanating from the AIS to substantially ensure that the vehicle is in compliance with these emission regulations, to allow diagnostic tests to be conducted, and to allow various designs to be evaluated. 
     It has previously been attempted to measure point source or subassembly emissions by forcibly drawing out hydrocarbon material from the subassembly. These have been found to provide a false indication of the amount of hydrocarbons. Furthermore, these prior methods to measure subassembly emission of hydrocarbons: are complex, are costly, and require a relatively extensive amount of modification to the vehicle. Such methods may also interfere with the normal operation of the vehicle, eg., testing other than SHED testing. 
     The inventors of the present invention have determined a method and apparatus for determining point source hydrocarbon emissions without intrusion upon the normal operation of the vehicle or the results of the SHED test. 
     SUMMARY OF INVENTION 
     Disadvantages of prior art systems are overcome by a system for measuring an amount of material emitted from a portion of a vehicle, which includes: a collection fixture coupled to the portion of the vehicle, a sampling tube fitted to the collection fixture; a pump coupled to the sampling tube for drawing gases near the portion of the vehicle to which the collection fixture is coupled and an analyzer for receiving the gases and for producing a concentration signal proportional to the concentration of the material pumped through the analyzer. 
     The present invention further provides a method for measuring a flow rate of hydrocarbons emitted from a portion of a vehicle wherein a pump draws gases from the portion of the vehicle. In the method an indication of a flow rate of the gases and an indication of hydrocarbon concentration of the gases are provided. Based on the flow rate and concentration, a flow rate of hydrocarbons emitted from the portion of the vehicle can be determined. 
     A primary advantage of the present invention is that this method and apparatus permits an accurate determination of the role of a vehicle subassembly or point source in contributing to the overall vehicle hydrocarbon emissions. 
     A further advantage is that the present invention does not impair the measurement accuracy of the vehicle&#39;s total hydrocarbon emission in the SHED test. 
     Yet another advantage is that the intrusion upon the vehicle and the modifications required are minimal. For example, to make such a measurement on the AIS, a tube is inserted into an air intake conduit. The tube may be left in place and still allow the vehicle to be normally operated or tested for other purposes. 
     Another advantage of the present invention is that the point source or subassembly of the vehicle that is being tested need not be removed from the vehicle to determine the hydrocarbon emission from the point source during the SHED test. Furthermore, a special test facility is not required to perform point source or subassembly measurements as the SHED test facility may be used for this purpose. Additionally, the point source hydrocarbons may be measured concurrently with the total vehicle hydrocarbon measurements; thus, efficiently employing a SHED test facility. 
     A further advantage is that the measuring apparatus is not complicated or expensive. 
    
    
     The above advantages and other advantages, objects, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings. 
     BRIEF DESCRIPTION OF DRAWINGS 
     The advantages described herein will be more fully understood by reading an example of an embodiment in which the invention is used to advantage, referred to herein as the Detailed Description, with reference to the drawings wherein: 
     FIG. 1 is a schematic of the SHED test facility in which the vehicle is contained and the associated hardware to ascertain hydrocarbon emissions from one of the vehicle&#39;s subassemblies, according to an aspect of the present invention; 
     FIG. 2 is a schematic of the test setup employed to verify the method described herein; and 
     FIG. 3 is a graph of pentane concentration detected over time at a particular location in the test setup. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, the SHED test facility  40  contains vehicle  10 . Vehicle  10  is equipped with engine  12 , an inline 3-cylinder in the present example. During the SHED test, the engine is not operating. However, to understand the relationship of vehicle  10  hardware, the components will be discussed in relation to an operating vehicle. Engine  12  inducts air from the atmosphere through bell mouth  20  into air filter assembly  18  and into intake manifold  14 . Engine  12  exhausts combusted gases through exhaust manifold  16  and discharges the gases to the atmosphere through exhaust pipe  38 . Engine  12  receives fuel from fuel tank  26  through fuel lines, fuel rail  32 , and injectors  34 . FIG. 1 indicates injectors  34  supplying fuel to engine  12  directly, i.e., a direct injection engine. The present invention applies as well to port injection configurations in which injectors  34  supply fuel into intake manifold  14 . 
     Vehicle  10  is fueled through filler cap  28  and fuel flows into fuel tank  26 . Fuel tank  26  is coupled to a carbon canister  30  which receives vapors emanating from fuel tank  26 . Fuel tank  26  emits vapors, typically, during fuel filling when vaporized fuel above the liquid fuel is displaced and also due to temperature changes affecting the vapor pressure in fuel tank  26 . These hydrocarbon vapors exiting fuel tank  26  are conducted into carbon canister  30 . Typically carbon canister  30  stores hydrocarbon vapors for a period and is subsequently purged of hydrocarbon vapors. During the purge portion of the cycle, valve  36  is opened. A depressed pressure in intake manifold  14  causes fresh air to be drawn through carbon canister  30 , so as to strip off stored hydrocarbon vapors. This gaseous mixture is inducted into intake manifold  14  and combusted in engine  12 . 
     The method and system of the present invention may be used to measure various point sources. By way of example, the configuration shown in FIG. 1 may be used to isolate hydrocarbons from the air induction system (AIS). The AIS includes elements  14 ,  18 , and  20  of FIG.  1 . 
     In FIG. 1, tube  22  is inserted into bell mouth  20 . The interface between tube  22  and bell mouth  20  is well sealed so that the gases collected are from the AIS. Tube  22  provides a location proximate to the AIS for tube  42  to be coupled. Sampled gases are pulled into pump  44  via tube  42 . The volume of extracted gases is measured in flow meter  46 , and the gases are then directed into flame ionization detector (FID)  48 . Within FID  48 , a fraction of the flow passes through chamber  52  which contains a hydrogen-air flame. The hydrocarbons in the extracted gases are combusted and become ionized. By measuring ionization level, FID  48  provides a measure of the amount of hydrocarbons fed to it. Within FID  48 , the majority of the extracted gases, however, bypass chamber  52  and are exhausted from FID  48  unreacted. The gases exhausted from FID  48  are discharged back into SHED test facility  40  so that the hydrocarbons, less the fraction consumed in chamber  52 , extracted by pump  44  are returned to SHED test facility  40  to ensure the integrity of the test. 
     A second measurement system (not shown), which includes elements analogous to  42 ,  44 ,  46 ,  48 ,  50 ,  52 , and  54 , is used to measure the concentration of the hydrocarbon material within SHED test facility  40 , i.e., the background or total vehicle concentration. In this way, the hydrocarbons emanating solely from the AIS can be accurately determined. The second measurement system need only be operated periodically to determine the background hydrocarbon concentration. 
     The mass emission rate of hydrocarbons from the AIS is computed by computer  54  of FIG. 1 as: 
     
       
           m =( C   ps   −C   bkg )* Q*P*MW /( R*T ) 
       
     
     where m is the mass emission flow rate of hydrocarbons, C is the concentration (unitless, eg., ppm), Q is the volumetric flow rate, P is the pressure in the SHED test facility  40 , MW is the molecular weight, R is the universal gas constant, and T is the temperature in the SHED test facility  40 . MW refers to the molecular weight of hydrocarbons; however, since the hydrocarbons are a mixture of species, it is difficult to find a number to characterize the mixture. It is common practice to characterize the hydrocarbons in terms of a single hydrocarbon species. As an example, the calibration gas used in FID  48  may be propane, C 3 H 8 , in which case, MW is  44 . The subscripts, ps and bkg, in the above equation, refer respectively to the point source concentration measured via the test configuration shown in FIG.  1  and to the background reading which is measured by an alternate set of measuring hardware as discussed above. In the embodiment shown in FIG. 1, FID  48  receives a signal of flow rate from flow meter  46 . FID  48  transmits both flow rate and concentration signals to computer  54 . Alternatively, the flow rate signal from flow meter  46  could be transmitted to computer  54  directly. Pressure and temperature are determined via temperature sensor  60  and pressure sensor  62  within SHED test facility  40 . 
     The total mass of hydrocarbons emitted from the point source may be determined by calculating the mass flow rate of hydrocarbons, using the equation above, over a short time period, for example 10 seconds and then multiplying the flow rate by the sample period. 
     The result is the mass of hydrocarbons emitted during that time period. The total mass of hydrocarbons can be determined by summing the mass results from all of the individual time periods for the duration of the SHED test. 
     Those skilled in the art will recognize that FID  48  is one type of analyzer that could be used to determine HC concentration. Other analyzers, such as thermal conductivity sensors, non-dispersive infrared detectors, or others could be used in place of FID  48  To maintain the integrity of the SHED test, the present invention should not substantially affect the SHED procedure. As mentioned above, the gases that are extracted from SHED test facility  40  into chamber  52  of FID  48  are returned to SHED test facility  40  without the fraction of hydrocarbons going through the burner or chamber  52 . The fraction of hydrocarbons consumed in chamber  52  can be computed as: 
     
       
         
           f=b*Q*d*t/V 
         
       
     
     where f is the fraction of total SHED hydrocarbons consumed, b is the fraction of the gases fed to FID  48  which enter chamber  52 , Q is pump  44  flow rate, d is the duty cycle of pump  44  (eg., d=1.0 if pump  44  is employed continuously), t is the time since the initiation of the test, and V is the volume of SHED test facility  40 . The value of f should be maintained less than about 0.01 (or 1%) to ensure SHED test integrity. An example of typical numbers: FID draws 5% of the flow into chamber  52  (b=0.05); the flowrate is 6.4 ft 3 /hr; the duty cycle is 100% (d=1.0); the time of the test is 72 hours; and the volume of SHED test facility is 2500 ft 3 . The resulting f=0.009 is within the required value for f. 
     To determine whether the point source test procedure, disclosed herein, interferes with the natural vaporization processes, a test assembly was constructed and is shown in FIG.  2 . 
     Vessel  62  is a surrogate point source, i.e., it may simulate intake manifold  14  or other point sources. At the bottom of vessel  62  is a small cup  64  into which a few milliliters of a hydrocarbon may be placed. Surrogate point source  62  is connected to a surrogate air filter assembly  66 . These are connected to the test apparatus that were previously shown and discussed in regards to FIG.  1 : pump  44 , flow meter  46 , and FID  48 . Hydrocarbon sensors  70 ,  72 , and  74  are installed near the surrogate point source  62 , the surrogate air filter assembly  66 , and bell mouth  22 , respectively. Hydrocarbon sensors  70 ,  72 , and  74  may be thermal conductivity type sensors. The tests were conducted by placing several milliliters of pentane into cup  64  within vessel  62 . Pentane was chosen because it is a very volatile hydrocarbon. The test was conducted twice, once with pump  44  drawing gases through tube  42  and once without pump  44  operating, using an identical volume of pentane for both runs. Referring to FIG. 3, hydrocarbon sensor  74  gave similar results regardless of whether pump  44  was operating or not. That means that operation of the sampling apparatus (elements  44 ,  46 , and  48 ) has neglible impact on the amount of hydrocarbons at location  74 . Although not shown herein, hydrocarbon sensors  70  and  72  also were found to detect substantially identical hydrocarbon levels over the duration of the test with pump  44  operating or not. 
     The present invention has been described in regards to measuring a particular point source, namely, the AIS. However, other point sources may also be measured by the invention described herein. For example, shrouds or other collection fixtures could be constructed to measure other point sources, including but not limited to: fuel rail  32  and fuel injectors  34 , fuel filler cap  28 , and carbon canister  14 . 
     While several modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize alternative designs and embodiments for practicing the invention. The above-described embodiments are intended to be illustrative of the invention, which may be modified within the scope of the following claims.