Abstract:
A solid particle counting system for measuring solid particle number concentrations from engine or vehicle exhausts in real-time includes a diluter arrangement, a particle counter, and a flow splitter. The diluter arrangement mixes the dilution gas with flowing sample gases. The flow splitter receives the output flow from the diluter arrangement, provides a portion of this flow to the particle counter, and provides a by-pass flow that is received by a vacuum pump. A second flow route to the particle counter includes a valve arranged such that opening the valve during the starting of the vacuum pump reduces a pressure pulse at the particle counter caused by the starting of the vacuum pump, thereby avoiding work fluid backflow from the particle counter prior to the vacuum pump stabilizing.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to measuring solid particle number concentrations from engine or vehicle exhausts in real-time. 
     2. Background Art 
     Engine exhaust particles mainly consist of solid and volatile particles. Many studies show particles from diesel engine exhausts cause many health problems. To understand how particles impact human health, characteristics of particles from engines and vehicles should be investigated. Thus, the accurate measurement of particles emitted by modern diesel and gasoline vehicles is needed. 
     European PMP (Particle measurement programme) has recommended an approach to measure solid particle number emission from light-duty diesel vehicles. The system is shown in  FIG. 1 , and consists of a pre-classifier  10 , a hot diluter (PND 1 )  12 , an evaporation tube  14 , a cold diluter (PND 2 )  16 , and a condensation particle counter (CPC)  18 . The pre-classifier  10  is used to keep the cutoff size of particles in 2.5 to 10 μm. By running the hot diluter  12  at a high dilution air temperature, and the evaporation tube  14  heating the sample in the range of 300 to 400° C., particles formed by volatile material and sulfate are vaporized to gas phase. By following with cold dilution with the cold diluter  16 , all particles formed by volatile material and sulfate are removed. As a result, solid particles only move into the CPC  18  with the flow. The concentration of the solid particles is measured in the CPC  18 . 
     Many factors, such as dilution ratios on the hot diluter (PND 1 )  12  and cold diluter (PND 2 )  16 , solid particle penetration over the instrument, removal efficiency for volatile particles, etc., strongly influence the accuracy of the instrument. To have good accuracy on the measurement, accurate dilution ratios on the hot diluter (PND 1 )  12  and the cold diluter (PND 2 )  16 , high penetration for solid particles, and high removal efficiency for volatile particles, should be achieved on the measuring system. 
     The condensation particle counter (CPC) has been widely used to measure particle number concentration. It has fast response time and is a real-time sensor. However, the experimental setup and operation procedure and calibration to use the CPC for measuring combustion engine or vehicle exhaust aerosols are pretty complicated. The accuracy of the measured results is strongly influenced by human factors, such as, the knowledge of the operator of combustion engines and aerosol science, etc. To make the CPC more reliable for engine or vehicle exhaust aerosol measurement, it is very important to simplify the experimental setup and operation procedure. 
     Background information may be found in U.S. Pub. No. 2006/0179960. This publication describes the concept of a wide range continuous diluter. Further background information may be found in “Real-time measuring system for engine exhaust solid particle number emission—Performance and Vehicle tests,” SAE Technical Paper No. 2006-01-0865, and in “Real-time measuring system for engine exhaust solid particle number emission—Design and Performance,” SAE Technical Paper No. 2006-01-0864. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a reliable, repeatable, and easily operated instrument to measure solid particle emissions from engine or vehicle exhaust, and to use as an instrument for certification, and research and development. 
     The invention comprehends a solid particle counting system (SPCS) that in one embodiment comprises mass flow controllers, flow orifices, pressure sensors, thermocouples, ball valves, a cyclone, an evaporation tube, etc. The concept of a wide range continuous diluter is used on the hot diluter (PND 1 ) and the cold diluter (PND 2 ). These diluters give accurate and wide range dilution ratios while high solid particle penetrations are achieved. Due to real time dilution ratios available from the hot diluter (PND 1 ) and the cold diluter (PND 2 ), the instrument gives more accurate particle measurement in real time. 
     At the more detailed level, in the preferred embodiment, by turning on/off valves manually or automatically on the SPCS, the instrument can run in different modes, such as a sample mode, an idle mode, a daily calibration mode, zero and flow checks for the CPC, system zero check, and purge. 
     In accordance with one aspect of the invention, a solid particle counting system includes a diluter arrangement, a particle counter, and a flow splitter. The diluter arrangement mixes the dilution gas with flowing sample gases. The flow splitter receives the output flow from the diluter arrangement, provides a portion of this flow to the particle counter, and provides a by-pass flow that is received by a vacuum pump. A second flow route to the particle counter includes a valve arranged such that opening the valve during the starting of the vacuum pump reduces a pressure pulse at the particle counter caused by the starting of the vacuum pump, thereby avoiding work fluid backflow from the particle counter prior to the vacuum pump stabilizing. 
     Advantageously, by including the valve arranged on a second flow route to the particle counter, the pressure pulse that occurs when the vacuum pump is started can be reduced to avoid work fluid backflow from the particle counter prior to the vaccum pump stabilizing. After the vacuum pump has stabilized, the valve is closed. This valve arrangement is useful, for example, at the start of a system zero check or at the start of operating the system in the sample mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a solid particle counting system (SPCS) according to the European PMP recommended approach; 
         FIG. 2  is a flow schematic of a solid particle counting system (SPCS) according to a preferred embodiment of the invention; 
         FIG. 3  is a cross-sectional view of a flow splitter in the solid particle counting system (SPCS); 
         FIG. 4  is a schematic for the hot diluter (PND 1 ) in the solid particle counting system (SPCS); 
         FIG. 5  is a schematic for the evaporation unit in the solid particle counting system (SPCS); 
         FIG. 6  is a schematic for the cold diluter (PND 2 ) in the solid particle counting system (SPCS); and 
         FIG. 7  is a schematic for an alternative embodiment of a flow splitter in the solid particle counting system (SPCS). 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 2-6  illustrate the preferred embodiment of a solid particle counting system (SPCS) made in accordance with the invention. It is to be appreciated that those skilled in the art may implement various aspects of the system in other ways and that the following description is intended to be exemplary and not intended to be limiting. Specifically, the following description relates to the preferred embodiment illustrated in  FIGS. 2-6 , and other embodiments of the invention may be implemented in other ways. 
     In the following description of the preferred embodiment, the work principle of the instrument is explained in three aspects, general description, detail components, and functions. To understand how the SPCS works, the three sections should be considered together. 
     General Description 
     With reference to  FIG. 2 , the solid particle counting system (SPCS) in the preferred embodiment is generally indicated at  30 . The SPCS sample inlet is indicated at  32 . SPCS  30  includes various components, generally described below. 
     Ball valves, V 1 , V 2 , V 4 , V 6 , and V 7 , are normally-closed valves. These valves can be operated manually or automatically, for example, air or electrically actuated. Ball valves V 3  and V 5  are normally-open valves. In the same way as the other ball valves, these valves can be operated manually or automatically. There are no flow restrictions while ball valves are opened. Thus, the ball valves do not result in particle losses while particles move through them. A solenoid valve SV is a normally-open valve. The solenoid valve SV is closed when the solenoid is energized. By opening or closing valves, the SPCS  30  can be operated for different functions. 
     A first orifice flow meter  40  is composed of thermocouples TC 1  and TC 2 , ball valves V 1  and V 2 , orifices  01  and  02 , absolute pressure transducer P 1 , and differential pressure transducer ΔP 1 . Thermocouples TC 1  and TC 2  measure flow temperatures upstream of ball valves V 1  and V 2 , respectively. The absolute pressure transducer, P 1 , measures the absolute pressure in the flow. The differential pressure transducer, ΔP 1 , measures the pressure difference over orifice O 1  or O 2 . For example, ΔP 1  measures pressure difference over orifice O 1  when ball valve V 1  is open and ball valve V 2  is closed; ΔP 1  measures pressure difference over orifice O 2  when ball valve V 2  is open and ball valve V 1  is closed. The status of V 1  and V 2  is determined by the status of the instrument. Orifice flow meter  40  is calibrated by a precise flow meter. The volume flow through O 1  or O 2  is a function of the pressure difference over O 1  and O 2 . The mass flow rate can be calculated from the flow temperature and absolute pressure. Two calibration curves which are in polynomial equations are established for O 1  and O 2 , respectively. When O 1  is picked up, the calibration curve for O 1  is used to calculate the flow. In opposite, the calibration curve for O 2  is used to calculate the flow when O 2  is picked up. 
     A second orifice flow meter  42  is composed of a thermocouple TC 3 , an absolute pressure transducer P 2 , a differential pressure transducer ΔP 2 , and an orifice O 3 . The calibration procedure of orifice flow meter  42  is as same as above. To minimize the heat transfer between the flow meter  42  and ambient, it is insulated. As a result, particle losses due to thermophoresis are minimized. 
     A cyclone (CL), ball valves V 1  and V 2 , orifices O 1  and O 2 , thermocouples TC 1  and TC 2 , and a part of by-pass  44  are installed in a heat enclosure  46 . The heat enclosure  46  is heated by a heater and the temperature is controlled at constant temperature, 47° C., by a temperature controller. The status of V 1  and V 2  (open or closed) is determined by the status of the instrument. Since the heat enclosure  46  is controlled at a constant temperature, the flow through orifice O 1  or orifice O 2  is maintained at the constant temperature as well. As a result, the fluctuation of the flow through orifice flow meter  40  due to temperature variations is minimized. 
     Thermocouple TC 5  measures the sample temperature (near sample inlet  32 ), and thermocouple TC 4  measures the temperature of the flow which moves into the CPC  48 . Both temperatures are monitored carefully during the test. 
     The compressed air chamber  50  is the source of the compressed air supply for the instrument. Compressed air chamber  50  supplies particle free compressed air for mass flow controllers  52 ,  54 ,  56 ,  58  and ball valve V 7 . A regulator  60  is installed upstream of the chamber  50 , and controls compressed air pressure at a desired value. A high efficiency particle air filter (HEPA)  62  removes particles from the compressed air. As a result, the compressed air in the chamber  50  is particle free. 
     Vacuum chamber  70  is the source of vacuum, and is connected to a vacuum pump  72 . Chamber  70  draws flow from critical orifices CO 1 , CO 2 , and CO 3 . Those critical orifices control flow through each flow route as constant. Alternatively, the critical orifices can be replaced by mass flow controllers. The advantage of the critical orifice for the flow control is that the cost of the critical orifice is much less than that of the mass flow controller. However, the critical orifice requires much stronger vacuum pump and the volume flow is fixed as well. For the mass flow controller, it provides a wide flow range, and a much smaller vacuum pump can be used with it to maintain the same level of flow as a critical orifice. 
     All tubings and fittings which contact to aerosol flow are made by stainless-steel. The stainless-steel material has good electrical conductivity and chemical resistance, and can minimize particle losses by electrostatic. In  FIG. 2 , tubings and fittings for flow routes, sample inlet  32 →sample probe SP→transfer line TL→cyclone CL→ball valve V 2  (V 1 )→orifice O 2  (O 1 )→Mixer  80 →orifice O 3 →evaporation unit  82 →Mixer  84 →ball valve V 4 →CPC  48 , and Calibration port  76 →ball valve V 6 →CPC  48 , are stainless-steel. 
     Since a high temperature aerosol moves into orifice O 2  (O 1 )→Mixer  80 →orifice O 3 →evaporation unit  82 →Mixer  84 , tubings and fittings are well insulated to minimize heat transfer. As a result, particle losses are minimized as well. 
     Flow splitters, FS 1 , FS 2 , and FS 3 , are designed to minimize large size particle over sampled due to main flow direction change.  FIG. 3  shows the schematic for this design in the preferred embodiment. The flow splitter consists of a ½″ stainless-steel union Tee  110 , a ½″ to ¼ bore through reducer  112 , a flow inlet  114 , a flow outlet  116 , and a by-pass  118 . For the flow inlet  114  and by-pass  118 , they are ½″ stainless-steel tubings. For the flow outlet  116 , it is a ¼″ stainless-steel tubing. The ¼″ stainless-steel tubing extends into the union Tee  110  through the bore through reducer  112 . The length of the ¼″ stainless-steel tubing exceeding ( 120 ) the left-side wall of the union Tee  110  is 0.1969″ or 5 mm. The aerosol flow moves into the splitter from the flow inlet  114 . A large fraction of flow leaves the splitter from the by-pass  118 . A small fraction of flow moves into other devices through the flow outlet  116 . Since the flow outlet  116  takes sample from the location up-stream of the by-pass  118 , it avoids over sampling large size particles due to the main stream direction changed at the by-pass  118 . 
       FIG. 7  shows the schematic for the flow splitters, FS 1 , FS 2 , and FS 3 , in an alternative embodiment. Flow splitter  200  includes a flow inlet  202 , a flow outlet  204 , and a by-pass  206 . A plate  208  is installed in flow splitter  200  at a location upstream of by-pass  206 . The plate  208  composes a guiding element that guides particles from the sampling location to the sample outlet  204 . Tube  210  extends into the flow splitter  200  toward plate  208 . 
     In more detail, flow splitters FS 1 , FS 2 , and FS 3  include a guiding element that guides particles from the sampling location to the sample outlet. The sampling location is located upstream of the by-pass. By sampling upstream of the by-pass, an accurate, representative sample is taken, and oversampling large size particles is avoided. That is, the main stream direction change at the by-pass, if the guiding element were omitted, could result in large size particles being over-represented in the sample flow because such particles with larger inertial force would not be as responsive to the main flow direction change as smaller particles. 
     In the  FIG. 3  embodiment, the guiding element is achieved by the extension of flow outlet tubing  116  to the sampling location upstream of by-pass  118 , thereby sampling the flow prior to the main stream direction change. In the  FIG. 7  embodiment, plate  208  is installed upstream of by-pass outlet  206  to guide particles from the sampling location to sample outlet  204 . That is, plate  208  assures that large particles are not over-sampled. 
     Detail Components 
       FIG. 1  illustrates the SPCS, according to the European PMP recommended approach, in block diagram form composed of the sample inlet, pre-classifier  10 , hot diluter (PND 1 )  12 , evaporation unit (EU)  14 , cold diluter (PND 2 )  16 , and CPC  18 . These components are implemented in the SPCS  30  of  FIG. 2 , according to the preferred embodiment of the invention, as described in detail below. 
     a. Sample Inlet 
     The sample inlet consists of sample probe SP, transfer line TL, and thermocouple TC 5 . The sample probe receives a diluted diesel aerosol from a constant volume sampler (CVS) or a partial flow diluter. The aerosol moves in the transfer line to a pre-classifier. TC 5  measures the temperature of the aerosol. 
     b. Pre-classifier 
     The pre-classifier consists of stainless-steel cyclone CL, flow splitter FS 1 , by-pass  44 , and critical orifice CO 1  (or a mass flow controller). The cyclone gives a particle cutoff size between 2.5 and 10 μm which depends on the flow rate of by-pass  44 . By using a different size critical orifice CO 1  or setting different flow on the mass flow controller, different cutoff size on particles can be obtained. 
     The flow splitter, FS 1 , which is described above, is connected to the cyclone CL. There are two outlets on the flow splitter. One is connected to by-pass  44 , and the other is connected to the inlet of orifice flow meter  40 . A big fraction of the flow moves out through by-pass  44  while a small fraction of the aerosol flows into orifice flow meter  40 . The residence time of aerosol in the transfer line TL and sample probe SP is minimized due to the large by-pass flow (by-pass flow  44 ). As a result, particle losses by diffusion are minimized in the transfer line TL and the sample probe SP. Since the aerosol into orifice flow meter  40  is taken upstream of the by-pass  44 , this minimizes the probability of large size particles being over sampled, due to 90 degree turning of the flow direction. 
     The pre-classifier except CO 1  (or mass flow controller (MFC)) is installed in the heat enclosure  46 . The temperature of the heat enclosure  46  is maintained at a constant, such as, 47° C. The flow in the pre-classifier maintains at a constant temperature. As a result, the aerosol with a constant temperature is supplied to orifice flow meter  40 . This design avoids the fluctuation of test results due to temperature variations from test to test. 
     c. Hot Diluter (PND 1 ) 
     With reference to  FIGS. 2 and 4 , the hot diluter (PND 1 ) consists of orifice flow meter  40 , mass flow controllers MFC  52  and MFC  54 , heated tube  86 , Mixer  80 , by-pass  88 , critical orifice CO 2  (or mass flow controller), flow splitter FS 2 , temperature controllers  130  and  132 , and a PID loop (summer  134 , PID  136 ). 
     Orifice flow meter  40  measures an aerosol mass flow rate in real-time. The mass flow controller (MFC)  52  controls the dilution air flow. MFC  52  receives the particle free dilution air from the compressed air chamber  50 . The heated tube  86  heats the dilution air temperature in the range of 150 to 190° C. The temperature of the dilution air is controlled by temperature controller  130 . Mixer  80  is wrapped with a heating tape, and the temperature is controlled by temperature controller  132 . The aerosol temperature in the mixer is controlled as same as that of the dilution air. The aerosol flow and the dilution air flow are mixed in the mixer  80  uniformly. Equation 1 shows the calculation of the dilution ratio on the PND 1 . Based on equation 1, the dilution ratio on the PND 1  can be adjusted by either adjusting dilution air flow or sample flow or both. By adjusting flow setting manually or automatically on MFC  52 , the dilution air flow can be changed. The sample flow can be adjusted by changing the flow rate (make up air) on MFC  54 . For example, by increasing the flow rate on MFC  54 , the flow rate of the sample flow can be decreased. By decreasing the flow rate on MFC  54 , the flow rate of the sample flow can be increased. The air flow on MFC  54  is supplied by the compressed air chamber. According to equation 1, 
                     DR     PND   ⁢           ⁢   1       =         Q     air   ⁢           ⁢   1         Q     s   ⁢           ⁢   1         +   1             (   1   )               
where DR PND1  is the dilution ratio on the PND 1 , Q air1  is the flow rate of the dilution air at the standard or a reference condition, Q s1  is the aerosol flow rate at the standard or a reference condition, Q s1  is measured by orifice flow meter  40 .
 
     The inlet of the flow splitter FS 2  is connected to the outlet of the mixer  80 . The mixture of the dilution air and the aerosol flow moves through the splitter FS 2 . A big fraction of the mixture moves into the vacuum chamber through by-pass  88  and critical orifice CO 2  or mass flow controller. A small fraction of flow moves into orifice flow meter  42  through the other outlet of the flow splitter. The unique design of the flow splitter minimizes the probability of the large size particles being over sampled due to flow direction change at the inlet of by-pass  88 . 
     Two flow orifices, O 1  and O 2 , are enclosed in orifice flow meter  40 . To minimize particle losses caused by particle diffusion, the residence time of aerosol in the flow meter is reduced by shorting the tubing length and using right inside diameter stainless-steel tubing. Each orifice covers a range of aerosol sample flow. For example, based on the desired dilution ratio, the sample flow can be calculated from equation 1 while the dilution air flow is set at the desired value. If the sample flow rate is falling into the flow range covered by O 1 , the calibration curve for O 1  is used. Thus, ball valve V 1  is open and ball valve V 2  is closed manually or automatically. In other cases, O 2  is picked up, and ball valve V 2  is open and ball valve V 1  is closed manually or automatically. Since multiple orifices (could be over two orifices) are enclosed in orifice flow meter  40 , PND 1  provides a wide dilution ratio range. 
     Orifice flow meter  40  is installed in the heat enclosure  46 . As mentioned above, the heat enclosure  46  is controlled at a constant temperature. Thus, the aerosol temperature in the orifice flow meter is constant as well. As a result, it minimizes the flow variation caused by temperature and gets rid of particle concentration variation by temperature as well. This design gives an advantage on the repeatability of the instrument. 
     To ensure accurate dilution ratios are obtained during engine or vehicle tests from PND 1 , a PID loop (summer  134 , PID  136 ) is integrated in the system to keep the aerosol flow at constant by adjusting the flow on MFC  54 . For example, when the sample flow is higher than a set point, the PID loop drives MFC  54  to increase the flow. When the sample flow is lower than a set point, the PID loop drives MFC  54  to decrease the flow. As a result, the dilution ratio on the PND 1  is kept at constant. Thus, the accurate result can be obtained from the instrument while the flow conditions such as temperature and pressure are fluctuated in the sample inlet.  FIG. 4  shows the schematic for this control. 
     The orifice flow meter  40  measures the aerosol flow accurately and does not result in particle losses. Therefore, PND 1  provides real-time accurate dilution ratio and gives high penetration to particles. 
     d. Evaporation Unit (EU) 
       FIG. 5  shows the schematic of the evaporation unit  82 . The evaporation unit  82  includes insulation and heating tape  140 , stainless-steel tubing  142 , and temperature controller  144 . 
     A heating tape is wrapped on the stainless-steel tubing  142  to ensure uniform wall temperature over the length. Temperature controller  144  controls the wall temperature in the range of 300 to 400° C. A thermocouple  146  measures wall temperature, and sends a signal to the temperature controller  144 . To minimize the heat transfer between the EU  82  and the ambient air, the EU  82  is insulated well. 
     While aerosol moves through the EU  82 , volatile particles are vaporized to gas phase. Solid particles in the aerosol flow through the EU  82  without particle losses. Then, following a cold dilution from the cold diluter (PND 2 ), the aerosol temperature is decreased below 35° C., and volatile particles are removed from the aerosol. 
     f. Cold Diluter (PND 2 ) 
     The cold diluter consists of orifice flow meter  42 , mass flow controllers MFC  56  and MFC  58 , mixer  84 , flow splitter FS 3 , by-pass  150 , and critical orifice CO 3  (or a mass flow controller). 
     Orifice flow meter  42  is insulated and installed upstream of the evaporation unit  82 . Orifice flow meter  42  measures aerosol flow into the PND 2  and the evaporation unit  82 . By installing orifice flow meter  42  upstream of the evaporation unit  82 , it minimizes the flow measurement errors caused by high temperature aerosol since the temperature upstream of the EU  82  is much lower than that of the downstream of the EU  82 . The flow measurement errors caused by the high temperature may include the flow variation due to the shape and the size of the stainless-steel orifice changed under high temperatures. Thus, by installing orifice flow meter  42  upstream of the EU  82 , more accurate and consistent flow measurement is obtained. 
     The dilution air temperature on the cold diluter is the same as that in the ambient air. The flow rate of the dilution air is controlled by a mass flow controller, MFC  56 . As same as PND 1 , the dilution ratio on the PND 2  is controlled by adjusting either dilution air flow from MFC  56  or make up air flow from MFC  58 . For example, at a constant dilution air flow, the aerosol flow through orifice flow meter  42  is increased while the make up air flow from MFC  58  is decreased. In other words, the aerosol flow through orifice flow meter  42  is decreased while the make up air flow from MFC  58  is increased. As a result, dilution ratios on the PND 2  are adjusted. Equation 2 shows the dilution ratio from the PND 2 , and equation 3 presents total dilution ratio calculation for the instrument. 
                     DR     PND   ⁢           ⁢   2       =         Q     air   ⁢           ⁢   2         Q     s   ⁢           ⁢   2         +   1             (   2   )                 DR=DR   PND1   ×DR   PND2   (3) 
     where DR PND2  is the dilution ratio on the cold diluter (PND 2 ), Q air2  is the dilution air flow rate on the PND 2  at the standard or reference conditions, Q s2  is the aerosol flow moving through orifice flow meter  42 , DR is the total dilution ratio on the SPCS. 
     The flow splitter, FS 3 , is connected to Mixer  84  at one side. Mixer  84  is well insulated to minimize the heat transfer between the mixer and ambient air. Dilution air controlled by MFC  56  and aerosol flow measured by orifice flow meter  42  are mixed uniformly in Mixer  84 . One outlet of the flow splitter FS 3  is connected to by-pass  150 . A big fraction of the mixture moves through it. The flow through by-pass  150  is controlled by critical orifice CO 3 . CO 3  could be replaced by a mass flow controller. The other outlet of the flow splitter FS 3  is connected to the inlet of the CPC  48  through a ball valve, V 4 . A small fraction of the aerosol flows through it. Since it takes sample upstream of by-pass  150 , it avoids large size particles being over sampled due to the direction change of the main stream of the aerosol flow. 
     To have a constant dilution ratio from PND 2 , a PID loop (summer  170 , PID  172 ) is integrated in the PND 2  to ensure the dilution ratio running at the desired set point, as illustrated in  FIG. 6 . 
     g. Condensation Particle Counter (CPC) 
     The condensation particle counter (CPC)  48  is a particle sensor to measure particle number concentrations. CPC  48  is a real-time instrument. Many companies manufacture a suitable CPC. 
     For some CPC, there is no internal vacuum pump. To draw a sample into the instrument, an external pump is required. Vacuum pump  180  (Vacuum pump I) in  FIG. 2  is prepared for a CPC without an internal pump. For a CPC with an internal pump, vacuum pump  180  can be removed. 
     A thermocouple, TC 4 , measures the aerosol temperature into the CPC  48 . This temperature is monitored during the test. CPC  48  provides a well-defined (for example, constant) instrument flow. 
     Functions 
     When the SPCS  30  main power is turned on, SPCS  30  needs to be warmed up for about 15 minutes. During the warm-up, the CPC  48  is warmed up and all heated parts are controlled to set points. If the CPC  48  has an internal vacuum pump, vacuum pump  180  can be removed from the system. If CPC  48  does not have an internal vacuum pump, vacuum pump  180  is used to draw the aerosol through the CPC  48 . At this circumstance, vacuum pump  180  is on as well for the warm-up. 
     a. Idle Mode 
     After the main power on the CPC  48  is on and warmed for about 15 minutes, the SPCS  30  enters the idle mode. 
     At the idle mode, no ball valves are energized or manually turned on/off. They stay at their original statuses. A flow moves from: HEPA  182 →flow meter (FM)  184 →ball valve V 5 →CPC  48 . 
     HEPA  182  is a high efficiency particle filter. HEPA  182  provides a flow inlet, and removes particles from the inlet flow. Then the particle free flow moves into flow meter (FM)  184 . After that, the flow moves through ball valve V 5 . V 5  is a normally-open ball valve. Finally, the flow moves into the CPC  48 . HEPA  182  protects the CPC  48  from contamination in the idle mode. Table 1 shows the status of valves and vacuum pumps for the idle mode. 
                                                                                                                 TABLE 1                   Status of valves and vacuum pump for the idle mode                                                Vacuum   Vacuum           V1   V2   V3   V4   V5   V6   V7   SV   pump I   pump                        Idle mode                                   X                   X - For valves, it means the valve is energized or off the original status. For pumps, it means the pump is on.            
b. CPC Zero and Flow Check
 
     The CPC zero is defined as the verification of the measured particle concentration by the CPC  48  while particle free gas is sent into the CPC  48 . The reading should be zero if there is no leak on the CPC  48 . The flow check is defined as the verification of the aerosol flow of the CPC  48 . 
     European PMP recommends that the CPC  48  should have a zero check prior to each day test. The aerosol flow into the CPC  48  (CPC flow check) should be verified as well. The flow rate can be off a few percents from the manufacturer&#39;s flow specification. 
     Those two functions have been combined as one function on the SPCS  30 . The flow route is the same as that of the idle mode. Thus, the flow direction is: HEPA  182 →FM  184 →ball valve V 5 →CPC  48 . No ball valves are energized or turned on/off manually. This function, which combines the CPC zero and the CPC flow check, makes CPC zero and flow check more efficient. 
     There is no difference for the flow route between the idle mode and CPC zero and flow check. The main difference between the two modes is the data acquisition if the SPCS  30  has a data acquisition system. When the SPCS  30  runs at CPC zero and flow check, the concentrations measured by the CPC  48  and the CPC inlet flow measured by the flow meter (FM)  184  are recorded by the data acquisition system. If there is not a data acquisition system on the SPCS  30 , the concentrations and flows may be recorded manually. At the idle mode, the above actions are not necessary. Table 2 shows the status of valves and vacuum pumps at this mode. 
                                                                                                                 TABLE 2                   Status of valves and vacuum pumps for the CPC zero and flow check                                                Vacuum   Vacuum           V1   V2   V3   V4   V5   V6   V7   SV   pump I   pump                        Idle mode                                   X                   X - For valves, it means the valve is energized or off the original status. For pumps, it means the pump is on.            
c. System Zero Check
 
     The system zero check is defined as the verification of the measured particle concentration while the particle free gas enters from the inlet of the SPCS  30 . If there is no leakage in the SPCS  30 , the reading of the CPC  48  should be zero. If the reading of the CPC  48  is not zero and larger than a critical value, serious leaks may be in the system. Thus, the instrument should be served to remove leaks. Based on the PMP recommendation, this critical value is 10 particles/cc. 
     When this mode is running, the vacuum pump  72  which is connected to the vacuum chamber  70  is turned on. When the vacuum pump  72  is turned on, a big pressure pulse is generated. As a result, the pressure at the inlet of the CPC  48  may be lower than that specified by the CPC manufacturer. If this happens, the work fluid in the CPC  48  may be sucked out from the CPC inlet, and enter some components in the SPCS  30 , such as ball valve V 4 , flow splitter FS 3 , Mixer  84 , etc. To avoid this issue, a solenoid valve (SV) and a ball valve V 3  are installed. 
     Before the start of this mode, dilution air flows and dilution ratios on the hot diluter (PND 1 ) and the cold diluter (PND 2 ) should be set at some values. Once this mode is run, the two PID loops, one for PND 1 , and the other for PND 2 , drive MFC  54  and MFC  56  to run dilution ratios on PND 1  and PND 2  to desired values, respectively. 
     At the start of this mode, the vacuum pump  72  is turned on. There are two major flow routes ending at the CPC  48 . One is solenoid valve SV→ball valve V 3 →ball valve V 4 →CPC  48 , and the other one is compressed air chamber  50 →ball valve V 7 →cyclone CL→ball valve V 2  (V 1 )→orifice O 2  (O 1 )→Mixer  80 →orifice O 3 →evaporation unit (EU)  82 →Mixer  84 →ball valve V 4 →CPC  48 . 
     The solenoid valve SV and ball valve V 3  are normally open valves. Due to this flow route, it minimizes the pressure pulse caused by the starting of the vacuum pump  72  to the CPC  48 . The SV keeps open for 5 to 30 seconds, and the open time can be decided by the operator or integrated in the control software. After the vacuum pump  72  is stabilized, the SV is energized and is closed. Thus, the flow route, solenoid valve SV→ball valve V 3 →ball valve V 4 →CPC  48 , is turned off. Ball valve V 3  can be turned off or kept on. The purpose to install ball valve V 3  upstream of the solenoid valve SV is to shut off this flow route once the solenoid valve SV is failed or a leakage is detected on the solenoid valve SV. With this design (flow route SV→V 3 →V 4 →CPC), the issue of the CPC work fluid moving out from the inlet of the CPC  48  is solved. 
     After the flow route SV→V 3 →V 4 →CPC is turned off, there is only one flow route to the CPC  48 . It is: compressed air chamber  50 →ball valve V 7 →cyclone CL→ball valve V 2  (V 1 )→orifice O 2  (O 1 )→Mixer  80 →orifice O 3 →evaporation unit (EU)  82 →Mixer  84 →ball valve V 4 →CPC  48 . As mentioned above, the compressed air in the compressed air chamber  50  is particle free. When this mode is running, the particle free compressed air moves through ball valve V 7  into the cyclone (CL). To ensure only particle free compressed air into orifice flow meter  40 , equation 4 should be satisfied; otherwise, aerosol with particles may move into the system from the sample probe (SP). By adjusting the compressed air pressure from the regulator  60 , equation 4 can be satisfied easily.
 
 Q   V7   ≧Q   bypassI   +Q   s1   (4)
 
where Q V7  is the flow rate of the particle free compressed air through V 7 , Q bypassI  is the flow through critical orifice CO 1  (or mass flow controller), Q s1  is the sample flow into orifice flow meter  40 .
 
     If there are no particles detected by the CPC  48 , it means there is no leak in the system. If the number concentration on the CPC  48  is higher than the CPC noise level, some leaks are in the system. They should be removed before vehicle or engine tests are run. 
     In summary, table 3 presents the status of ball valves and vacuum pumps. If the column is empty, valves stay at the original status. 
                                                                                                                 TABLE 3                   Status of valves and vacuum pump                                                Vacuum   Vacuum           V1   V2   V3   V4   V5   V6   V7   SV   pump I   pump                        Start of   X           X   X       X       X   X       the       mode       After 5   X           X   X       X   X   X   X       to 30       seconds       (Option       I)       After 5   X       X   X   X       X   X   X   X       to 30       seconds       (Option       II)               X - For valves, it means the valve is energized or off the original status. For pumps, it means the pump is on.            
d. Daily Calibration for the CPC
 
     The daily calibration for the CPC  48  is defined as the verification of the CPC linearity. European PMP recommends it should be done prior to the daily test. 
     Before this mode is run, an external unit which is able to provide constant particle concentrations from 0 to 100% of the maximum concentration is connected to the calibration port  76 . 
     When this mode is run, the flow route is: Calibration port  76 →ball valve V 6 →CPC  48 . Table 4 shows the summary for valve status. 
                                                                                                                 TABLE 4                   Status of valves and vacuum pump for the daily calibration for the CPC                                                Vacuum   Vacuum           V1   V2   V3   V4   V5   V6   V7   SV   pump I   pump                        Daily                   X   X           X           calibration       for the       CPC               X - For valves, it means the valve is energized or off the original status. For pumps, it means the pump is on.            
e. Sample Mode
 
     The sample mode is defined as the SPCS  30  is taking sample from sample inlet  32 . Aerosol moves into the system from the sample probe SP. All temperatures, number concentrations, flows etc. are recorded manually or by a data acquisition system. 
     As same as the mode called “system zero check”, when this mode is running, the vacuum pump  72  which is connected to the vacuum chamber  70  is turned on. When the vacuum pump  72  is turned on, the big pressure pulse is generated. As a result, the pressure at the inlet of the CPC  48  may be lower than that specified by the CPC manufacturer. If it happens, the work fluid in the CPC  48  may be sucked out from the CPC inlet, and enters some components in the SPCS  30 , such as ball valve V 4 , flow splitter FS 3 , Mixer  84 , etc. To resolve this issue, the solenoid valve SV and ball valve V 3  are utilized. 
     Before the start of this mode, the system should be warmed up. Temperatures on evaporation unit  82 , mixer  80 , PND 1  dilution air and heat enclosure  46  should achieve set points. Dilution air flows and dilution ratios on the hot diluter (PND 1 ) and the cold diluter (PND 2 ) should be set at some values. When this mode is run, the two PID loops, one for PND 1 , and the other for PND 2 , drive MFC  54  and MFC  56  to run dilution ratios on PND 1  and PND 2  to desired values, respectively. 
     At the start of this mode, the vacuum pump  72  is turned on. There are two flow routes in the SPCS  30  to the CPC  48 . One is solenoid valve SV→ball valve V 3 →ball valve V 4 →CPC  48 , and the other is Sample inlet  32 →sample probe SP→transfer line TL→cyclone CL→ball valve V 2  (V 1 )→orifice O 2  (O 1 )→Mixer  80 →orifice O 3 →evaporation unit  82 →Mixer  84 →ball valve V 4 →CPC  48 . Based on the desired dilution ratio, orifice O 1  or O 2  is determined. If the orifice O 1  is picked up, ball valve V 1  is open and ball valve V 2  is closed. In opposite, if the orifice O 2  is picked up, ball valve V 2  is open and ball valve V 1  is closed. 
     The solenoid valve SV and ball valve V 3  are normal open valves. Due to this flow route, it minimizes the pressure pulse caused by the starting of the vacuum pump  72  to the CPC  48 . The solenoid valve SV keeps open for 5 to 30 seconds, and the open time can be decided by the operator or integrated in the control software. After the vacuum pump  72  is stabilized, the solenoid valve SV is energized and is closed. Thus, the flow route, solenoid valve SV→ball valve V 3 →ball valve V 4 →CPC  48 , is turned off. Ball valve V 3  can be turned off or kept on. The purpose to install ball valve V 3  upstream of the solenoid valve SV is to shut off this flow route while the solenoid valve SV is failed or leakage is detected on the solenoid valve SV. With this design (flow route SV→V 3 →V 4 →CPC), the issue of the CPC work fluid moving out from the inlet of the CPC is solved. 
     After the flow route SV→V 3 →V 4 →CPC  48  is turned off, there is only one flow route to the CPC  48 . It is: Sample inlet  32 →sample probe SP→transfer line TL→cyclone CL→ball valve V 2  (V 1 )→orifice O 2  (O 1 )→Mixer  80 →orifice O 3 →evaporation unit  82 →Mixer  84 →ball valve V 4 →CPC  48 . During the sample mode, the dilution ratio on the system can be adjusted by changing dilution air flows on PND 1  and PND 2  and changing make up air flows on MFC  54  and MFC  58 . Table 5 shows the summary of the status of valves and pumps. 
                                                                                                                 TABLE 5                   Status of valves and vacuum pumps for the sample mode                                                Vacuum   Vacuum           V1   V2   V3   V4   V5   V6   V7   SV   pump I   pump                        Start of   X           X   X               X   X       the       mode       (Option       I)       Start of       X       X   X               X   X       the       mode       (Option       II)       After 5   X           X   X           X   X   X       to 30       seconds       (Option       I)       After 5       X       X   X           X   X   X       to 30       seconds       (Option       II)               X - For valves, it means the valve is energized or off the original status. For pumps, it means the pump is on.       Option I - Based on the dilution ratio, orifice O1 is chosen.       Option II - Based on the dilution ratio, orifice O2 is chosen.            
f. Purge Mode
 
     The purge is defined as an approach to clean the SPCS  30  by overflow. It is a simple and effective method to keep the whole system out of particle contamination, especially for orifice flow meters  40  and  42 . This mode is recommended to run periodically. 
     Before this mode is running, flows on mass flow controllers, MFC  52 , MFC  54 , MFC  56 , and MFC  58 , are set to some values. To have reverse flow on orifice flow meters  40  and  42 , equations 5 and 6 should be satisfied. To avoid pressure transducers (P 1 , P 2 , ΔP 1 , and ΔP 2 ) being damaged by reverse flow, the left sides of equations 5 and 6 should be larger than the right hand sides slightly.
 
 Q   air1   +Q   makeup1   &gt;Q   bypassII   +Q   s2   (5)
 
 Q   air2   +Q   makeup2   &gt;Q   bypassIII   (6)
 
where Q air1  is the dilution air flow on MFC  52 , Q makeup1  is the makeup air on MFC  54 , Q bypassII  is the bypass flow on by-pass  88 , Q s2  is the aerosol flow into orifice flow meter  42 , Q air2  is the flow on MFC  56 , Q makeup2  is the make up air on MFC  58 , and Q bypassIII  is the bypass flow on by-pass  150 .
 
     When this mode is running, ball valve V 4  keeps its original status. Thus, it is closed and no flow is moving through the CPC  48 . Therefore, the pressure pulse caused by the start of the vacuum pump  72  does not influence the CPC  48 . As a result, it is not necessary for solenoid valve SV to have a delay action. To purge orifice flow meter  40  completely, both ball valves V 1  and V 2  are picked up in this mode. Table 6 shows the status for valves and vacuum pumps. 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Status of valves and vacuum pump for the purge mode 
               
             
          
           
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Vacuum 
                 Vacuum 
               
               
                   
                 V1 
                 V2 
                 V3 
                 V4 
                 V5 
                 V6 
                 V7 
                 SV 
                 pump I 
                 pump 
               
               
                   
                   
               
             
          
           
               
                 Purge 
                 X 
                 X 
                   
                   
                   
                   
                   
                 X 
                 X 
                 X 
               
               
                   
               
               
                 X - For valves, it means the valve is energized or off the original status. For pumps, it means the pump is on. 
               
             
          
         
       
     
     Except flow routes upstream of ball valve V 4 , there is the other flow route in the SPCS  30 : HEPA  182  FM  184 →ball valve V 5 →CPC  48 . This flow loop keeps the CPC  48  running normally. 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.