×

Device for measuring concentration of nitrogen oxide in combustion gas

  • US 5,034,112 A
  • Filed: 05/16/1989
  • Issued: 07/23/1991
  • Est. Priority Date: 05/19/1988
  • Status: Expired due to Term
First Claim
Patent Images

1. A device for measuring the concentration of a nitrogen oxide in a combustion gas, comprising:

  • an electrochemical cell which comprises a member of an oxygen ion conductive solid electrolyte and first and second electrodes attached to the solid electrolyte member;

    a diffusion rate determining means for diffusing a fraction of the combustion gas, with a predetermined resistance to the gas diffusion, into a space in which the first electrode of the electrochemical cell is exposed;

    a catalyst which is provided in or in the vicinity of the first electrode of said cell and which decomposes the nitrogen oxide only when the partial pressure of oxygen coexisting with the nitrogen oxide is lower than a predetermined level;

    means for supplying a variable DC current to said electrochemical cell to flow in the solid electrolyte between the first and second electrodes to thereby cause migration of oxygen ions in a predetermined direction through the solid electrolyte between the first and second electrodes for adjusting the partial pressure of oxygen in the vicinity of the first electrode of said cell;

    means for detecting the partial pressure of oxygen in the vicinity of the first electrode of said cell;

    a discriminating means for deciding whether the detected partial pressure of oxygen is lower than said predetermined level or not;

    a first current measuring means for measuring the current supplied to said electrochemical cell when it is decided that the detected partial pressure of oxygen is not lower than said predetermined level;

    a second current measuring means for measuring the current supplied to said electrochemical cell when it is decided that the detected partial pressure of oxygen is lower than said predetermined level; and

    means for computing the concentration of the nitrogen oxide in the combustion gas by using the two current values measured by the first and second current measuring means, respectively, the relationship between the concentration of oxygen in said gas and the current measured by the first current measuring means, and the relationship between said concentration of oxygen and the current measured by said second current measuring means, according to the following equation;

    
    
    space="preserve" listing-type="equation">X.sub.NO =[(I.sub.P(B) -α

    .sub.(B))-(γ

    .sub.O(B) /γ

    .sub.O(A))×

    (I.sub.P(A) -α

    .sub.(A))]/η

    .sub.NO ·

    γ

    .sub.O(B) where XNO is the concentration of the nitrogen oxide, IP(A) is the current measured by the first current measuring means, IP(B) is the current measured by the second current measuring means, α

    .sub.(A) is a current measured by the first current measuring means when the device is operated in a reference gas containing neither oxygen nor the nitrogen oxide, α

    .sub.(B) is a current measured by the second current measuring means when the device is operated in said reference gas, γ

    O(A) is a predetermined coefficient indicating the ratio of the current measured by the first current measuring means to the concentration of oxygen in the combustion gas, γ

    O(B) is a predetermined coefficient indicating the ratio of the current measured by the second current measuring means to the concentration of oxygen in the combustion gas, and η

    NO is a constant.

View all claims
  • 1 Assignment
Timeline View
Assignment View
    ×
    ×