The pollutant emission of an internal combustion engine can be effectively reduced by the catalytic retreatment of the exhaust gas with the aid of an exhaust gas catalytic converter. To reduce the particle emission occurring, for example, during the combustion of diesel fuel, particle filters are employed which usually follow one or more exhaust gas catalytic converters. The particles retained from the exhaust gas by the particle filter, that is to say collected in the filter, are primarily soot particles. Regular cleaning or regeneration of the particle filter is necessary, depending on the soot particle load of the particle filter and the accompanying increase in the exhaust gas backpressure. This cleaning or regeneration is achieved by oxidation, that is to say the burning of the soot particles in the particle filter, with the result that the proper functioning of the particle filter is maintained while the internal combustion engine is in operation.
According to stage 6 of the European exhaust gas standard (Euro-6), stringent particle emission limit values also have to be adhered to in future for gasoline engines with direct injection. Gasoline engines, unlike diesel engines, typically are operated at or near stoichiometry. Therefore, during normal engine operation, there may not be a sufficient amount of oxygen in the exhaust to allow regeneration of the particulate filter.
An exhaust gas purification system for an internal combustion engine is known from European patent specification EP 1 970 547 B1. The exhaust gas purification system is employed in a motorcycle in order to purify the exhaust gas from the internal combustion engine by three catalytic converters connected in series in an exhaust line. It is proposed to provide, at least between the second and third catalytic converter, a secondary air introduction line for introducing secondary air into the exhaust line, in order to assist the oxidation of CO and HC in the third catalytic converter. The secondary air is supplied to the exhaust line by an air filter via a flutter valve.
The inventors have recognized herein an issue with the above approach. During typical engine operation, particularly when the particle filter has a high soot load causing increased back pressure, the exhaust pressure tends to be higher than the pressure of the secondary air, which typically is at ambient air pressure. Thus, an insufficient amount of oxygen may be provided to regenerate the filter.
An exhaust system for an internal combustion engine is provided. In one embodiment, the system comprises an exhaust tract which is connectable to an outlet side of the internal combustion engine, at least one catalytic converter arranged in the exhaust tract downstream of the engine, a particle filter downstream of the at least one catalytic converter, and a secondary-air inlet port provided in the exhaust tract upstream of the particle filter for introducing compressed secondary air into the exhaust tract via at least one flutter valve.
In this way, additional oxygen may be provided to the filter, even in low load conditions. Thus, the functioning of a particle filter of an exhaust system for an internal combustion engine may be improved at low outlay over the entire or over the largest possible operating or load range of the internal combustion engine.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.