An air-fuel ratio control device sets a target air-fuel ratio and performs an air-fuel ratio control based on the target air-fuel ratio for an engine of a spark ignition type. The air-fuel ratio control device includes a lean combustion determination unit that determines whether a lean combustion is performed in the engine at the target air-fuel ratio, the target air-fuel ratio being set leaner than the theoretical air-fuel ratio; a target NOx setting unit that sets a target NOx concentration according to an operation state of the engine; an acquisition unit that acquires an actual NOx concentration detected by using a NOx concentration detection unit in an exhaust passage of the engine; and a correction unit that corrects the target air-fuel ratio based on the target NOx concentration and the actual NOx concentration when determination is made that lean combustion is performed.

An engine control device is provided, which includes an ignition plug configured to ignite mixture gas inside a cylinder of the engine, an injector configured to change an air-fuel ratio inside the cylinder, a NO.sub.x sensor, and a controller including a processor. The controller performs a first control to control the ignition plug so that ignition is performed at a basic ignition timing or an ignition timing after the basic timing is corrected based on a combustion state of the mixture gas, and a second control to control the injector so that a NO.sub.x concentration approaches a given target value. When the ignition timing is corrected by the first control to a retarding side, the controller suspends a correction to a richer side even if the NO.sub.x concentration is a concentration at which the air-fuel ratio is corrected to the richer side by the second control.

Systems, apparatuses, and methods include an upstream exhaust analysis circuit structured to determine a characteristic of an exhaust gas stream entering a nitrous oxide (NOx) storage catalyst; a prediction circuit structured to predict a downstream NOx concentration of an exhaust gas stream exiting the NOx storage catalyst based on a model of a NOx storage capacity or a dynamic response of the NOx storage catalyst; a downstream exhaust analysis circuit structured to determine a downstream NOx concentration of the exhaust gas stream exiting the NOx storage catalyst; and a comparison circuit structured to compare the predicted downstream NOx concentration to the determined downstream NOx concentration, and determine a health of the NOx storage catalyst based on the comparison.

Provided is a method for diagnosing exhaust sensors, where at least one substance resulting from combustion is reduced by an additive. A first sensor intended to measure an occurrence of said substance upstream said supply of additive, and a second sensor intended to measure an occurrence of said substance downstream said supply of additive. The method comprises: determining whether the locations of said first and second sensors are reversed by: determining if a second measurement value of said second sensor exceeds a corresponding first measurement value of said first sensor at least to a first extent, and when this condition occurs, determining that the locations of said first and second sensors sensor are reversed, said measurement values are determined when a supply of additive is set to obtain at least a first reduction of said at least one substance to be reduced.

A fuel content detection system is disclosed. The fuel content detection system may include an engine control module (ECM) to receive a measurement of a parameter. The parameter may correlate with an amount of a substance in a fuel that is being consumed in an engine. The ECM may determine an estimation of the parameter based on a model. The model may use a predetermined value associated with the amount of the substance, and the engine may be configured to consume a designated type of fuel that includes an amount of the substance that corresponds to the predetermined value. The ECM may determine, based on the estimation and the measurement not being within a threshold range, that the fuel is not the designated type of fuel and perform an action associated with the engine.

Systems and apparatuses include a circuit structured to receive information indicative of a catalyst health, receive information from a sensor array indicative of a catalyst activity, determine a catalyst health management criteria has been met based on the information, determine a catalyst age based on the information indicative of the catalyst activity and the catalyst health management criteria being met, compare the determined catalyst age to a predetermined age threshold, and provide a notification when the determined catalyst age exceeds the predetermined age threshold.

A misfire detection device for an internal combustion engine includes processing circuitry. The internal combustion engine includes a selective reduction type catalyst configured to remove NOx from an exhaust gas, an addition valve arranged upstream of the catalyst to add a reducing agent into the exhaust gas, and a NOx concentration sensor arranged downstream of the catalyst to detect a downstream concentration, that is, a NOx concentration in the exhaust gas downstream of the catalyst. The processing circuitry is configured to execute an addition process adding the reducing agent into the exhaust gas with operation of the addition valve and a determination process determining that a misfire has occurred in the internal combustion engine when a detection value of the downstream concentration is decreased on condition that the addition process is being executed.

An apparatus for purifying exhaust gas includes: an engine; an exhaust gas air-fuel ratio adjustor for adjusting an air-fuel ratio of the exhaust gas; a lean NO.sub.x trap (LNT) mounted on the exhaust pipe and generating ammonia or reducing nitrogen oxides or desorbed nitrogen oxides contained in the exhaust gas using a reducing agent including carbon monoxide, hydrocarbon, or hydrogen contained in the exhaust gas; a three way catalyst (TWC) mounted on the exhaust pipe at a rear end of the LNT, and converting noxious gas in the exhaust gas into harmless components through a redox reaction; and a controller controlling the air-fuel ratio of the exhaust gas to a stoichiometric air-fuel ratio when the nitrogen oxide storage or purification performance of the LNT is in the operating period of the engine less than a predetermined level.

Various embodiments may include a method for monitoring a nitrogen oxide trap comprising: monitoring a storage capacity of the nitrogen oxide trap; deactivating nitrogen oxide trap regeneration based on the monitored storage capacity; and upon a predetermined event, reactivating nitrogen oxide trap regeneration.

A system and method to enable electronically controlled internal combustion engines to self-adjust parameters and operate properly on different fuels that have wide ranges of physical and chemical properties. Input from a sensor is utilized that gives a signal indicative of the combustion process. The ECU processes the signal and readjusts the engine operating parameters to achieve its operating goals.