Apparatus for measuring combustible-gas concentration, system for measuring combustible-gas concentration, system for treating exhaust gas, method for measuring combustible-gas concentration, and method for deriving constant

A method for measuring combustible-gas concentration serving as a carbon-equivalent concentration of a combustible gas in a target gas with a sensor element including a mixed potential cell that includes a solid electrolyte body, a detection electrode arranged on the solid electrolyte body, and a reference electrode arranged on the solid electrolyte body, the method comprising:

• an electromotive force acquisition step of acquiring information about an electromotive force of the mixed potential cell while the detection electrode is exposed to the target gas;
• an oxygen concentration acquisition step of acquiring information about oxygen concentration in the target gas;
• and
• a combustible gas concentration derivation step of determining the combustible-gas concentration in the target gas based on the acquired information about the electromotive force, the acquired information about the oxygen concentration, and a relationship represented by formula (1):
• EMF=α loga(pTHC)−β logb(pO2)+B (1)
• (where
• EMF:
• the electromotive force of the mixed potential cell,
• α, β, B:
• constants,
• a and b:
• any base (provided that a≠1, a>0, b≠1, and b>0),
• pTHC:
• the combustible-gas concentration in the target gas, and
• pO2:
• the oxygen concentration in the target gas).

A method for deriving a constant in a relational formula used to measure combustible-gas concentration serving as carbon-equivalent concentration of a combustible gas in a target gas with a sensor element including a mixed potential cell that includes a solid electrolyte body, a detection electrode arranged on the solid electrolyte body, and a reference electrode arranged on the solid electrolyte body, the method comprising:

• (a) a step of multiple times of executing electromotive force measurement processing that measures an electromotive force of the mixed potential cell in a state in which the detection electrode is exposed to the target gas while at least one of oxygen concentration and the carbon-equivalent concentration of at least one combustible gas of one or more combustible gases in the target gas is changed, a gas containing oxygen and the one or more combustible gases being used as the target gas;
• and
• (b) a step of deriving constants α, β, and B in formula (1) from results of the electromotive force measurement processing executed multiple times:
• EMF=α loga(pTHC)−β logb(pO2)+B (1)
• (where
• EMF:
• the electromotive force of the mixed potential cell,
• α, β, and B:
• constants,
• a and b:
• any base (provided that a≠1, a>0, b≠1, and b>0),
• pTHC:
• the combustible-gas concentration in the target gas, and
• pO2:
• the oxygen concentration in the target gas).