Method and apparatus for measuring NOx gas concentration
First Claim
1. A NOx gas concentration sensor for measuring the NOx concentration in an exhaust gas comprising NOx, O2, CO2 and H2O, comprising:
- (a) a ceramic body comprising an electrolyte having an electrically controllable conducting rate of oxygen ion;
(b) a first pair and a second pair of electrodes formed on said ceramic body;
(c) a flow channel in said ceramic body for passage of the exhaust gas;
(d) means for extracting said O2 from the exhaust gas via said ceramic body to outside the flow channel so as to form a residual gas in said flow channel;
(e) means for applying a first voltage and a second voltage across the first pair and the second pair of electrodes, respectively, said first voltage maximizing a gain by the dissociation of the NOx gas contained in said residual gas without substantial dissociation of the H2O gas contained in said residual gas and said second voltage maximizing a gain by the dissociation of the NOx gas contained in said residual gas with substantial dissociation of the H2O gas contained in said residual gas;
(f) means for measuring a first current flowing between said first pair of electrodes across which said first voltage is applied;
(g) means for measuring a second current flowing between said second pair of electrodes across which said second voltage is applied; and
(h) means for determining the NOx concentration in the exhaust, said determination of the NOx gas concentration being based on the first current being corrected by the second current.
0 Assignments
0 Petitions
Accused Products
Abstract
Method and sensor for measuring accurate measurement of NOx concentration in an exhaust gas containing O2,H2O, CO2 and NOx and a NOx gas concentration sensor. A first oxygen pump cell sufficiently pumps out oxygen in a measurement gas such as not to decompose NOx. A pair of electrodes is provided on an inner side and an outer side of a second measurement chamber into which the gas is introduced from a first measurement chamber via a diffusion resistance. A voltage is impressed across the paired electrodes for decomposing NOx in the second measurement chamber to dissociate oxygen which causes the current to flow in a second oxygen ion pump cell. The NOx gas concentration is measured for this current. The voltage impressed across the paired electrodes of the second oxygen ion pump cell is set so as not to dissociate H2O and CO2 present in the second measurement chamber.
-
Citations
40 Claims
-
1. A NOx gas concentration sensor for measuring the NOx concentration in an exhaust gas comprising NOx, O2, CO2 and H2O, comprising:
-
(a) a ceramic body comprising an electrolyte having an electrically controllable conducting rate of oxygen ion;
(b) a first pair and a second pair of electrodes formed on said ceramic body;
(c) a flow channel in said ceramic body for passage of the exhaust gas;
(d) means for extracting said O2 from the exhaust gas via said ceramic body to outside the flow channel so as to form a residual gas in said flow channel;
(e) means for applying a first voltage and a second voltage across the first pair and the second pair of electrodes, respectively, said first voltage maximizing a gain by the dissociation of the NOx gas contained in said residual gas without substantial dissociation of the H2O gas contained in said residual gas and said second voltage maximizing a gain by the dissociation of the NOx gas contained in said residual gas with substantial dissociation of the H2O gas contained in said residual gas;
(f) means for measuring a first current flowing between said first pair of electrodes across which said first voltage is applied;
(g) means for measuring a second current flowing between said second pair of electrodes across which said second voltage is applied; and
(h) means for determining the NOx concentration in the exhaust, said determination of the NOx gas concentration being based on the first current being corrected by the second current. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
wherein the third pair of electrodes has an electrode length relative to the entire length of the flow channel as follows: electrode length/entire length=¼
to ¾
.
-
-
3. The sensor as defined in claim 2, wherein the third pair of electrodes comprises a component inhibiting the NOx from dissociation.
-
4. The NOx gas concentration sensor as defined in claim 1, wherein said flow channel comprises a first flow channel in which said residual gas is formed, and a second flow channel in which NOx is dissociated, the first flow channel comprising a gas flow restrictor, the second flow channel comprising an inlet communicating to the first flow channel, and
wherein an electrode disposed in the first flow channel for extracting the O2 of the exhaust gas out of the first flow channel extends from the vicinity of the gas flow restrictor disposed in the first flow channel until at most a position closer to said gas flow restrictor than the inlet of the second flow channel. -
5. The NOx gas concentration sensor as defined in claim 1 wherein
said ceramic body is formed of plural ceramic layers laminated together; -
said flow channel including a first flow channel for forming residual gas and a second flow channel for dissociating NOx, said first and second flow channels extending along the surface of said laminated ceramic layers;
said first and second flow channels communicating with each other by a flow channel extending in the laminating direction of said ceramic layers.
-
-
6. The NOx gas concentration sensor as defined in claim 1 wherein an oxygen concentration detecting electrode for detecting the oxygen concentration in said flow channel is formed on said ceramic body facing said flow channel, and wherein an oxygen concentration for generating a reference potential versus said oxygen concentration detection electrode is formed on said ceramic body outside of said flow channel;
said oxygen concentration reference electrode being an auto-generating reference electrode across which a voltage is impressed for transporting oxygen towards said reference electrode for providing a constant oxygen concentration around said electrode.
-
7. The NOx gas concentration sensor as defined in claim 1 wherein one of the electrodes provided in said flow channel for extracting the O2 of the exhaust gas to the outside of said flow channel is sealed or covered, said one of the electrodes is provided with a gas diffision resistance.
-
8. The NOx gas concentration sensor as defined in claim 1 wherein, in one of the electrodes is provided in said, flow channel for extracting the O2 of the exhaust gas from said flow channel to the outside of said flow channel.
-
9. The sensor as defined in claim 1 wherein the voltage is applied to an extent that does not substantially dissociate H2O and CO2 in the residual gas below about 450 mV at about 700°
- C.
-
10. The sensor as defined in claim 1 wherein said extrating oxygen is carried out without substantial decomposition of NOx in the exhaust gas.
-
11. The sensor as defined in claim 1, wherein the voltage applied across the electrodes is about 450±
- 50 mV.
-
12. The sensor as defined in claim 1, wherein the voltage applied across the electrode is about 450 mV.
-
13. The sensor as defined in claim 1, wherein the NOx gas contained in the residual gas includes NO.
-
14. A method for measuring a NOx gas concentration, comprising:
-
providing an apparatus having a first measurement chamber into which an exhaust gas comprising O2, H2O, CO2 and NOx is introduced via a first diffusion resistance;
measuring an oxygen partial pressure in the exhaust gas in said first measurement chamber with an oxygen partial pressure detection electrode;
pumping out a portion of said O2 in said exhaust gas from said first measurement chamber to form a residual gas in said first measurement chamber, said pumping being carried out with a first oxygen ion pump cell, based on a potential of said oxygen partial pressure detection electrode, to an extent such that said pumping substantially does not decompose NOx in the exhaust gas;
introducing the residual gas into a second measurement chamber from said first measurement chamber via a second diffusion resistance;
measuring a first current and a second current flowing through a second oxygen ion pump cell and a third oxygen ion pump cell, respectively; and
determining the NOx concentration in the exhaust gas based on the first current being corrected by the second current. - View Dependent Claims (15, 16, 17, 18)
-
-
19. A NOx gas concentration sensor, comprising:
-
a first measurement chamber into which an exhaust gas comprising O2, H2O, CO2 and NOx is introduced via a first diffusion resistance;
an oxygen partial pressure detection electrode for measuring the oxygen partial pressure in the exhaust gas in said first measurement chamber;
a first oxygen ion pump cell for pumping out said O2 in said exhaust gas in said first measurement chamber therefrom, based on a potential of said oxygen partial pressure detection electrode, to a sufficient extent such as not to substantially decompose NOx in the exhaust gas and form a residual gas in the first measurement chamber;
a second measurement chamber into which the residual gas is introduced from said first measurement chamber via a second diffusion resistance;
a second oxygen ion pump cell having first paired electrodes on inner and outer sides of said second measurement chamber and a first current flowing through said second oxygen ion pump cell, said first current being caused under a first voltage impressed across the first paired electrodes of said second oxygen ion pump cell;
a third oxygen ion pump cell having second paired electrodes on the inner and outer sides of a third measurement chamber and a second current flowing through said third oxygen ion pump cell, said second current being caused on impression of a second voltage across said second paired electrodes;
the first voltage is set at a value that substantially prevents dissociation of H2O present in said second measurement chamber, the second voltage is set at a value that substantially allows dissociation of H2O present in said third measurement chamber, and means for determining the NOx concentration based on the first current being corrected by the second current. - View Dependent Claims (20, 21)
-
-
22. An NOx gas concentration sensor comprising:
-
a first measurement chamber into which an gas comprising O2, H2O, CO2 and NOx is introduced via a first diffusion resistance;
an oxygen partial pressure detection electrode for measuring the oxygen partial pressure in the exhaust gas in said first measurement chamber;
a first oxygen ion pump cell for pumping out the oxygen in said exhaust gas in said first measurement chamber therefrom, based on a potential of said oxygen partial pressure detection electrode, under the condition that does not allow substantial decomposition of NO in the first measurement chamber;
a second measurement chamber into which a gas is introduced from said first measurement chamber via a second diffusion resistance;
a second oxygen ion pump cell having first paired electrodes on inner and outer sides of said second measurement chamber, wherein said second oxygen ion pump cell flows a current caused by oxygen dissociated on decomposition of NOx in said second measurement chamber on application of a voltage across said first paired electrodes, said current having a first current under a first voltage;
a third oxygen ion pump cell having second paired electrodes on the inner and outer sides of a third measurement chamber and a second current flowing through said third oxygen ion pump cell, said second current being caused on impression of a second voltage across said second paired electrodes; and
means for determining the NOx gas concentration based on the first current being corrected by the second current. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30)
-
-
31. A method for determining a NOx concentration in an exhaust gas comprising O2, H2O, CO2 and NOx employing an electrically controlled electrochemical cell comprising at least a first oxygen ion conductive solid electrolyte body and a second oxygen ion conductive solid electrolyte body, said method comprising:
-
(1) flowing the exhaust gas through a flow channel formed in the first oxygen ion conductive solid electrolyte body and the second oxygen ion conductive solid electrolyte body, (2) forming a residual gas that has a different NO concentration than that of the exhaust gas at a high temperature while the exhaust gas travels through the flow channel, (3) contacting said residual gas with a first catalytic electrode to which a first dc voltage that does not substantially dissociate H2O and CO2 but dissociates NO is applied to produce a first current, (4) contacting said residual gas with a second catalytic electrode to which a second dc voltage that does substantially dissociate H2O and NO is applied to produce a second current, (5) determining the NOx concentration in the exhaust gas based on the current flowing through the electrolyte body, and based on the first current being corrected by the second current, and (6) applying the dc voltage across the catalytic electrode and an electrode that is formed outside of the electrolyte body in the range of about dc 450±
50 mV and a maximum gain of NOx detection is obtained, said maximum gain of NOx being determined by a current gain of NOx at a given voltage applied as said dc voltage.- View Dependent Claims (32, 33, 34, 35, 36, 37, 38, 39, 40)
-
Specification