A apparatus 70 for measuring combustible-gas concentration includes an electromotive force acquisition section 75 configured to acquire information about an electromotive force of a mixed potential cell 55 while a detection electrode 51 is exposed to a target gas, an oxygen concentration acquisition section 76 configured to acquire information about oxygen concentration p.sub.O2 in the target gas, and a control section 72. The control section 72 derives combustible-gas concentration p.sub.THC in the target gas from the acquired information about the electromotive force EMF, the acquired information about the oxygen concentration p.sub.O2, and the relationship represented by formula (1):

EMF= log.sub.a(p.sub.THC) log.sub.b(p.sub.O2)+B(1)

where , , and B each represent a constant, and a and b each represent any base (provided that a1, a>0, b1, and b>0).

A method for diagnosing the degree of deterioration of a catalyst disposed in an exhaust path of an internal combustion engine and oxidizes or adsorbs a target gas, including at least one of a hydrocarbon gas and a carbon monoxide gas, in an exhaust gas from the internal combustion engine, is adapted to determine whether deterioration exceeding an acceptable level of a catalyst occurs or not by comparing, at any timing when the internal combustion engine is in a state of a steady operation, the concentration of a target gas detected downstream from the catalyst in the exhaust path with a threshold value of the concentration of a target gas corresponding to the temperature of a catalyst at the timing which is previously defined according to an allowable range of an index value representing the degree of oxidation or adsorption at the catalyst corresponding to the temperature of a catalyst at the timing.

In a gas sensor determining a NOx concentration in a measurement gas based on a pump current flowing between a NOx measurement electrode and an outer pump electrode, the outer pump electrode has catalytic activity inactivated for HC and CO, so that a sensor element further includes a HC sensor part having a mixed potential cell constituted by the outer pump electrode, a reference electrode, and a solid electrolyte between these electrodes, and a HC mode for determining a HC concentration in the measurement gas based on a potential difference between the outer pump electrode and the reference electrode when the sensor element is heated to a temperature which is 400 C. or higher and 650 C. or lower and a NOx mode for determining a NOx concentration in the measurement gas based on the pump current can selectively be performed based on the temperature of the sensor element.

A system for diagnosing the degree of deterioration of a catalyst disposed in an exhaust path of an internal combustion engine and oxidizes or adsorbs a target gas in an exhaust gas, includes a temperature sensor measuring a temperature of the exhaust gas at the upstream from a catalyst in an exhaust path and a gas sensor detecting a target gas at the downstream of the exhaust path and outputting an output value in accordance with a concentration of the target gas, wherein a control element is configured to diagnose the degree of deterioration in the catalyst, based on at least the output value in the gas sensor, the temperature of the catalyst identified based on a measurement value in the temperature sensor, and the threshold value at the temperature of the catalyst.

An exhaust emission control system of an engine is provided including a NO.sub.x catalyst for oxidizing HC and storing NO.sub.x within exhaust gas when an air-fuel ratio of the exhaust gas is lean, and reducing the NO.sub.x when the air-fuel ratio is approximately stoichiometric or rich. The system includes a SCR catalyst for purifying NO.sub.x by causing a reaction with NH.sub.3, a urea injector, a fuel injection controlling module, and a processor configured to execute a NO.sub.x reduction controlling module for performing a NO.sub.x reduction control to enrich the air-fuel ratio to reach a target ratio. When the urea injection is determined to be abnormal, the NO.sub.x reduction controlling module performs a NH.sub.3-supplied NO.sub.x reduction control in a state where a larger amount of unburned fuel than the amount of unburned fuel in the exhaust passage in the NO.sub.x reduction control is supplied to the exhaust passage.

A method and device for controlling emissions of VOC's comprises transporting VOC's to an engine and transporting the exhaust from the engine into a manifold. Supplemental air is transporting into the manifold and heat is transferred from the exhaust to the supplemental air within the manifold. The supplemental air is mixed with the exhaust and the mixture is transferred to a pollution abatement device.

In order to provide an exhaust gas measuring system capable of more accurately correcting errors in measurement results caused by response delays of exhaust gas measuring devices, and the like, the exhaust gas measuring system is adapted to include: a sampling pipe adapted to, from a lead-out port, lead out exhaust gas introduced from an introduction port; one or more types of exhaust gas measuring devices that are connected to the lead-out port and measure predetermined physical quantities related to the exhaust gas flowing through the sampling pipe; a correction device adapted to correct measurement results by the exhaust gas measuring devices; and a pressure sensor adapted to measure the pressure inside the sampling pipe, in which the correction device corrects errors in the measurement results, which are caused by response delays, with the measured pressure by the pressure sensor as a parameter.

In an internal combustion engine, a hydrocarbon feed valve (15), NO.sub.x storage catalyst (13), particulate filter (14), and electric resistance type sensor (29) are arranged in an engine exhaust passage in this order from an upstream side. The electric resistance type sensor (29) generates an output value corresponding to the amounts of deposition of particulate matter and hydrocarbons which are contained in the exhaust gas and deposited at the sensor part thereof. From the change of the output value of the electric resistance type sensor (29), it is judged if the hydrocarbons have slipped through the NO.sub.x storage catalyst (13) and if the particulate matter has slipped through the particulate filter (14).

An exhaust system comprises an engine, a three-way catalytic converter including a first catalyst and a second catalyst, a tailpipe adjacent to the three-way catalytic converter, a first oxygen sensor disposed between the engine and the catalytic converter, a nitrogen oxides (NOx) sensor disposed in the three-way catalytic converter, and an engine control module (ECM) configured to obtain first oxygen sensor data from the first oxygen sensor, second oxygen sensor data from the NOx sensor, and NOx sensor data from the NOx sensor, the ECM being configured to perform catalyst health diagnostic operations and adjust one or more characteristics of the exhaust system based on at least the first oxygen sensor data, the second oxygen sensor data, and the NOx sensor data.

An exhaust system comprises an engine, a three-way catalytic converter including a first catalyst and a second catalyst, a tailpipe adjacent to the three-way catalytic converter, a first oxygen sensor disposed between the engine and the catalytic converter, a nitrogen oxides (NOx) sensor disposed in the three-way catalytic converter, and an engine control module (ECM) configured to obtain first oxygen sensor data from the first oxygen sensor, second oxygen sensor data from the NOx sensor, and NOx sensor data from the NOx sensor, the ECM being configured to perform catalyst health diagnostic operations and adjust one or more characteristics of the exhaust system based on at least the first oxygen sensor data, the second oxygen sensor data, and the NOx sensor data.