Exhaust gas analyzer for diesel engines
BACKGROUND OF THE INVENTION 
     This invention relates generally to exhaust gas analyzer apparatus preferably for diesel engines, of the type having an inlet connectable to the exhaust of a test engine and including filter means between the exhaust and the gas analyzer device. More particularly, the invention provides improved filter means in the form of an electrostatic separator for assuring delivery of particulate free exhaust gas to said gas analyzer device. 
     Accurate analysis of exhaust gases from an internal combustion engine, particularly diesel engines, is made difficult due to fine particulate matter such as soot carried by said gases. Such particulate matter quickly fouls the analyzer device. Where the gas analyzer operates on the infra-red absorption principle, the presence of such particulate matter in the gases delivered to the analyzer is of considerable disadvantage. 
     It is known that to counter such problem, filter means can be placed between the analyzer and the source of the exhaust gases. Since the particulate matter is of fine particle size, the filter medium used must also be fine so as to collect the small soot particles, for example. Accordingly, the filter medium soon becomes clogged, often blocked as to require frequent cleaning and/or replacement. 
     Thus, a need arises to provide means for removing the fine particulate matter from the exhaust gases prior to delivery to the gas analyzer device, whereby to obviate the disadvantages encountered in use of known devices, and which enables continuous operation of the gas analyzer without requiring change in the filter. 
     In addition, such filter means must be relatively simple in construction so as to enable inexpensive production and facile and rapid servicing. The particulate removal capacity of such filter device should be substantial so that continuous runs are possible without requiring change of filter or interruption for cleaning, if cleaning is possible. 
     Another difficulty encountered in the testing of exhaust gases involve the presence of water vapor or particles (droplets) carried by such gases. It would be highly desirable if the filter means employed would include means for separating such water vapor and/or particles from said gases before they reach the gas analyzer device. It would be advantageous also if the filter means could be provided with means for removing the separated particulate matter without dismantling the filter from the test line. 
     SUMMARY OF THE INVENTION 
     There is provided for use in exhaust gas analyzer apparatus, particularly for use in analyzing diesel engines, where a filter is interposed between the source of the exhaust gases and a gas analyzing device. The filter comprises an electrostatic separator formed of an ionization electrode and two sets of collector electrodes downstream of said ionization electrode, the sets of collector electrodes being maintained at different electrical potentials, one set relative the other set, said ionization electrode being arranged transverse the direction of flow of the exhaust gases and the collector electrodes arranged parallel the flow of said gases. Means also are provided for cooling the exhaust gases received from the source and for separating water vapor and/or droplets therefrom prior to entry of the gases into the filter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic flow diagram of the exhaust gas analyzer apparatus embodying the invention; 
     FIG. 2 is a sectional view of the electrostatic filter employed in the apparatus represented in FIG. 1 and viewed looking downward toward the top; and 
     FIG. 3 is a sectional view taken along lines 3--3 of FIG. 2 and viewed in the direction of the arrows, the inlet and outlet portions thereof being deleted. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     The exhaust gas analyzer as defined in the invention consists of a connection pipe 1 which is fastened in the usual manner on the exhaust 2 of the vehicle whose exhaust gases are supposed to be analyzed. The connection pipe 1 is connected to a heat exchanger coil 3, in which the hot exhaust gases are cooled and are directed into a condenser 4 in which the water present in the exhaust gases is removed. The condenser 4 is coupled to an electrostatic separator 5. 
     Referring to FIGS. 2 and 3, it can be seen that electrostatic separator 5 has an ionization electrode 6, a collector electrode 7 connected therewith and grounded collector electrodes 8. The ionization electrode 6 and the collector electrode 7 connected therewith can be connected electrically with the positive pole 9 of a high voltage power source 10 which, for example is capable of supplying a voltage of 10 kV and whose negative connection 11 is grounded. Particulate matter such as soot particles are present in the exhaust gases, particularly gases discharged as exhaust from diesel engines. These soot particles are provided with a positive charge by means of the ionization electrode 6 and, when passing the positive electrode 7, are repulsed by the latter. Grounded electrodes 8 are negative and thus accumulation of the positively charged soot particles takes place on said electrodes 8. 
     The exhaust gases, which are cleaned in this manner, are connected with a suction pump 17 by way of a two-way valve 13 defining a branch, one leg 14&#39; of which is coupled to a compressed air source 14, the other leg 15 of the branch being coupled to a paper filter 16. Conduit 18 then couples the output of pump 17 to a conventional exhaust gas analyzer 19 having an indicating instrument 20. Preferably the analyzer 19 operates on infra red absorption. 
     In operation, the suction pump 17 is activated. The exhaust gases are led by means of pump 17 to the analyzer 19 by way of the heat exchanger coil 3, the condenser 4, the electrostatic separator 5 and the two-way valve 13 and the paper filter 16 which functions as a secondary filter. This occurs when the two-way valve 13 is positioned as indicated by a solid line 21. When the two-way valve 13 is operated to the position illustrated by broken line 22, the compressed air source 14, such as a pressure pump, is operated to force surrounding air through the electrostatic filter 5, the condenser 4 and back through heat exchanger coil 3. Not only the electrostatic separator 5 is cleaned but the water which had collected in condenser 4 is led away. Nothing needs to be dismantled. 
     FIGS. 2 and 3 illustrate the construction of the electrostatic separator 5 in greater detail. Separator 5 includes housing 25 having an inlet 26 and an outlet 27. Housing 25 has a base plate 28 which is grounded, and is connected to negative pole 11 of the voltage source 10. The base plate 28 carries vertically oriented spaced upright parallel electrodes 8 collectively functioning as a grounded collector electrode. Between each electrode 8 is an electrode 7, collectively functioning as a collector electrode. Electrodes 7 are likewise parallel arranged and are connected to the high voltage and also are connected to the ionization electrode wire 6. Electrodes 7 are connected to the upper wall 30 removably coupled to housing 25 by way of insulation elements 29. When the upper wall 30 is removed from housing 25, the collector electrodes 7 are separated from electrodes 8 to facilitate servicing and possibly additional cleaning of the separator 5. 
     The electrode 6 is disposed transverse the direction of flow of the exhaust gases indicated by arrow 32 while electrodes 7 and 8 are arranged in parallel array and parallel to the direction of flow of said gases. The electrodes 7 are connected with the positive pole of the high voltage source 10 via connector 31. Source 10 provides a voltage of approximately 10 kV referring to the negative pole. 
     Because electrodes 8 are grounded relative to electrodes 7 which in turn are coupled to electrode wire 6, said electrodes 7 and 8 are maintained at different relative potential. The electrostatic separator 5 not only enables a thorough cleaning of the exhaust gases of particulate matter and moisture but improves the reliability of the analysis.