Abstract:
An improved instrument and method are provided for particulate characterization in combustion exhausts. An instrument for measuring particles of combustion exhausts includes a laser for producing a high intensity laser pulse. A sample cell receives a combustion exhaust input and the high intensity laser pulse. At least one detector detects a signal generated by particles in said received combustion exhaust input. The detected signal includes laser induced incandescence (LII). Signal conditioning electronics is coupled to the detector and particle data is displayed during transient operation of a combustion engine. Data related to mass concentration, number density, and particle size of particles in the received combustion exhaust input is measured and displayed.

Description:
CONTRACTUAL ORIGIN OF THE INVENTION 
     The United States Government has rights in this invention pursuant to Contract No. W-31-109-ENG-38 between the United States Government and Argonne National Laboratory. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an instrument and method for particulate characterization in combustion exhausts, and more particularly relates to a method and portable instrument based on laser induced incandescence (LII) to measure particulate content and primarily mass emissions (gms/cm 3 ) of combustion exhausts, such as from diesel engines. 
     DESCRIPTION OF THE RELATED ART 
     Particles emitted from diesel engines pose a significant health hazard to the general public because these particles are of the right size to be inhaled and deposited deep inside the lungs. An additional concern is that certain substances that condense on the surface of these particles are carcinogenic. 
     Newer particulate standards imposed by the Environmental Protection Agency (EPA) have serious implications toward the future operation of combustion equipment. Current research efforts to curtail particulate emissions are limited by the lack of proper measurement techniques. The known measurement techniques require expensive instrumentation with equally matching demands on operator skill and time. One widely accepted EPA approved technique entails the collection of particulates using a filter paper in a diluted stream of exhaust gases, which is followed by gravimetry. Alternate measurement techniques are based upon light extinction or reflection principles. Efforts to obtain quantitative measurements based upon such principles have resulted in little success. 
     Techniques used in air sampling only are effectively used for measuring particle number concentrations, N (particles/cm 3 ). However, large response-times, such as 120 seconds, preclude their use for transient evaluations. 
     Laser induced incandescence (LII), a recently developed technique facilitates real-time quantitative planar imaging of soot emissions. A doctoral thesis by Sreenath B. Gupta at Pennsylvania State University in December, 1996 entitled “CHEMICAL MECHANISTIC APPROACHES TO SOOT CONTROL IN LAMINAR DIFFUSION FLAMES” describes the use of laser induced incandescence (LII) in characterizing the soot field in flames. 
     It is an object of the invention to provide an improved instrument and method for particulate characterization in combustion exhausts. 
     It is another object of the invention to provide an improved method and instrument based on laser induced incandescence (LII) to measure particulate content and primarily mass emissions (gms/cm 3 ) of combustion exhausts. 
     It is another object of the invention to provide an improved method and instrument based on laser induced incandescence (LII) to measure particulate content and primarily mass emissions (gms/cm 3 ) of combustion exhausts during transient operation of an engine. 
     It is another object of the invention to provide such improved method and instrument for measuring particle size in nanometers and number density or number of particles per cubic centimeter and mass concentration or grams of particles per cubic centimeter (gms/cm 3 ) of combustion exhausts during transient operation of an engine. 
     It is another object of the invention to provide such instrument that is a compact and portable device and that enables fast, easy, and cost-effective characterizing of particles of combustion exhausts. 
     It is another object of the invention to provide such improved method and instrument substantially without negative effect and that overcome many of the disadvantages of prior arrangements. 
     SUMMARY OF THE INVENTION 
     In brief, an improved instrument and method are provided for particulate characterization in combustion exhausts. An instrument for measuring particles of combustion exhausts includes a laser for producing a high intensity laser pulse. A sample cell receives a combustion exhaust input and the high intensity laser pulse. At least one detector detects a signal generated by particles in said received combustion exhaust input. The detected signal includes laser induced incandescence (LII). 
     In accordance with features of the invention, signal conditioning electronics is coupled to the detector and particle data is displayed during transient operation of a combustion engine. Data related to mass concentration, number density, and particle size of particles in the received combustion exhaust input is measured and displayed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention together with the above and other objects and advantages may best be understood from the following detailed description of the preferred embodiments of the invention illustrated in the drawings, wherein: 
     FIG. 1 is a block diagram representation of a portable instrument based on laser induced incandescence (LII) to measure particulate content and primarily mass emissions (gms/cm 3 ) of combustion exhausts, such as from diesel engines in accordance with the preferred embodiment; 
     FIG. 2 is a diagrammatic top view of the portable instrument of FIG. 1 in accordance with the preferred embodiment; and 
     FIG. 3 is a diagrammatic front view of the portable instrument of FIG. 1 in accordance with the preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Having reference now to the drawings, in FIG. 1 there is shown a block diagram representation of a portable instrument in accordance with the preferred embodiment based on laser induced incandescence (LII) to measure particulate content and primarily mass emissions (gms/cm 3 ) of combustion exhausts, such as from diesel engines, generally designated by the reference number  100 . LII portable combustion exhaust measurement instrument  100  includes a laser  102  producing a high intensity laser beam pulse. The laser beam pulse is coupled through a plurality of optical elements  104  and applied to a sample cell  106 . The sample cell  106  receives an exhaust input. Laser induced incandescence (LII) is used to measure particulate content and primarily mass emissions (gms/cm 3 ) of the combustion exhaust applied to the sample cell  106 . A beam trap  108  is coupled to the sample cell  106 . 
     In accordance with features of the preferred embodiment, with the laser induced incandescence (LII) technique, a high-energy laser pulse heats the tiny particles in combustion exhausts. Upon heating, the particles emit light, which, when collected appropriately, indicates particulate content and primarily mass emissions (gms/cm 3 ) of combustion exhausts. LII portable combustion exhaust measurement instrument  100  measures mean particle size in nanometers, number density or number of particles per cubic centimeter, and the mass concentration or grams per cubic centimeter. LII portable combustion exhaust measurement instrument  100  enables characterizing particles in a fast, easy, and cost-effective way. LII portable combustion exhaust measurement instrument  100  is used in real time, that is during transient operation of an engine. LII portable combustion exhaust measurement instrument  100  is a compact and portable instrument. 
     LII portable combustion exhaust measurement instrument  100  includes a plurality of detectors  110  coupled to the sample cell  106 , such as a pair of photo-multiplier tube (PMT) detectors PMT 1 , PMT 2   110 . PMT detectors  110  detect a signal generated by particles in the combustion exhaust. 
     Signal conditioning electronics  112  is coupled to the detectors  110  to characterize, in real time during transient operation of an engine, particulate emissions in the combustion exhaust, such as of diesel engines. Signal conditioning electronics  112  includes a pair of peak detectors  114  respectively coupled to the PMT detectors  110  and providing a peak detected signal to a respective calibration multiplier  116 . One of the calibration multipliers  116  provides a calibrated signal to a display  120  for displaying mass concentration (gms/cc) measured values in real time during transient operation of an engine. The calibration multipliers  116  are coupled by an arithmetic operator block  118  to display  120  for displaying number density (#/cc) and particle diameter (nm) measured values in real time during transient operation of an engine. 
     In the LII portable combustion exhaust measurement instrument  100 , the combustion exhaust stream is partially sampled by a vacuum generated by a dilution tunnel  122 . In this tunnel  122  the exhaust sample stream is diluted using filtered air in a predetermined ratio. The diluted sample stream is then passed through the sample cell  106 , to be finally exhausted out of the instrument  100 . The high intensity emission from a pulsed laser  102  is expanded as a vertical sheet and focused onto the center of the sample cell  106  using multiple optical elements  104 . The laser beam is finally terminated using the beam trap  108 . Upon the incidence of the laser pulse, the particles in the combustion exhaust within sample cell  106  are heated to their sublimation temperature and emit thermal radiation as they cool down. This laser induced incandescence (LII) emission when appropriately collected by detectors  110  is directly proportional to the local mass concentration (gms/cc). This signal is focused using a train of optical elements including a first spherical lens S 1 , a second spherical lens S 2  and an aperture with a blue interference filter F 1  as shown in FIG. 2, onto a PMT 1  detector  110 . Similarly, the Rayleigh scattering signal is focused onto a second PMT 2  detector  110 . This signal is focused onto PMT 2  detector  110  using a second set of optical elements including a first spherical lens S 3 , a second spherical lens S 4  and an aperture with a green filter F 2 . 
     Signal conditioning electronics  112  is coupled to the PMT 1 , PMT 2  detectors  110  reflect the following relations: 
     
       
         Mass concentration,  M  (gms/cc) =calibration factor×signal from  PMT   1   
       
     
     
       
         Volumetric cross section,  Qvv =calibration factor×signal from  PMT   2   
       
     
     
       
         Mean particle size,  D  (nm) =function 1 ( M,Qvv ) 
       
     
     
       
         Number Density,  N  (number of particles/cm 3 )=function 2 ( M,Qvv ) 
       
     
     Respective signals from each PMT detectors PMT 1 , PMT 2   110  are passed to a set of signal processing electronics  112 . The peaks of the signals are detected by the peak detection circuitry  114 , and then are further multiplied by calibration factors by the calibration multiplier circuitry  116 . The resulting signals are further processed by an arithmetic operator  118  to obtain mean particle diameter (nm) and number density (number of particles/cm3). However, the processed signal from PMT 1   110  directly results in mass concentration (gms/cc) and is routed to the numeric display  120 . 
     In accordance with features of the preferred embodiment, LII portable combustion exhaust measurement instrument  100  provides data on the three parameters that are essential for understanding diesel exhausts; the mass concentration, number density, and mean size of the particles. LII portable combustion exhaust measurement instrument  100  by providing effective real time measurements can enable development of technologies to reduce particulate emissions. Certain transient phases of engine operation result in increased emission of particles, for example, an engine accelerating from idle. Because conventional instruments cannot measure particles during transient operation, engine designers are unable to fine-tune the engine parameters to reduce the emission of particles during transient operation. LII portable combustion exhaust measurement instrument  100  with its ability to collect information during transient operations can assist engine designers to design a cleaner-burning engine. 
     Referring also to FIGS. 2 and 3, more details of optical elements  104  and signal focusing and filtering of the signal generated by the particles of the LII portable combustion exhaust measurement instrument  100  are shown. LII portable combustion exhaust measurement instrument  100  has a two layer construction. A top layer includes the laser  102 , optical elements  104 , the sample cell  106 , detectors  110  and the signal conditioning electronics  112 . A lower layer includes a dilution tunnel  122  shown in dotted line to dilute the exhaust sample using air. LII portable combustion exhaust measurement instrument  100  includes a housing  124  that contains the two layer construction. The display  120  is carried by the housing  124  for viewing measured results by the user. 
     As shown in FIG. 2, optical elements  104  includes a pair of elements E 1 , E 1  for turning the laser beam through 90 degrees twice to pass through a plurality of cylindrical lenses C 1 , C 2  and C 3 . The resulting laser beam passes through the sample cell  106 . The beam trap  108  captures the laser beam from the sample cell  106 . The signal generated by the particles is focused by two spherical lenses S 1  and S 2  onto the aperture/blue filter F 1 . This focused signal is filtered by a blue interference filter F 1  before being detected by the PMTI detector  110 . The Rayleigh scattering signal is similarly focused onto PMT 2  detector  110  by two spherical lenses S 3  and S 4  onto the aperture/green filter F 2 . 
     While the present invention has been described with reference to the details of the embodiments of the invention shown in the drawing, these details are not intended to limit the scope of the invention as claimed in the appended claims.