The invention reduces exhaust emission by quickly supplying CO2 into a cylinder, and restraining a delay in EGR, when an EGR request occurs. An engine 10 includes an upstream EGR passage 34, a middle EGR passage 36, a downstream EGR passage 38, a bypass passage 40, an EGR valve 42, a changeover valve 44, an EGR cooler 46, a CO2 adsorbent 48. When an EGR request does not occur, the ECU 70 keeps a temperature of the CO2 adsorbent 48 in a release temperature region by the heater 50, and opens the EGR valve 42 by a valve opening set time period t so that a gas in the middle EGR passage 36 is replaced with CO2 released from the CO2 adsorbent. When an EGR request occurs, CO2 accumulated in the middle EGR passage 36 can be quickly supplied into a cylinder, without releasing CO2 from the CO2 adsorbent 48.

An engine system includes main exhaust ports fluidly communicating with each combustion chamber. An exhaust variable valve lift apparatus controls an operation of a main exhaust valve which closes or opens each main exhaust port. A main exhaust manifold is connected with the main exhaust ports. Scavenge exhaust ports fluidly communicate with each combustion chamber. A variable scavenge apparatus controls an operation of a scavenge valve which closes and opens each scavenge exhaust port. A scavenge manifold is connected with the scavenge exhaust ports. A controller is configured to control operations of the exhaust variable valve lift apparatus and the variable scavenge apparatus according to a vehicle operation state.

An engine system includes main exhaust ports fluidly communicating with each combustion chamber. An exhaust variable valve lift apparatus controls an operation of a main exhaust valve which closes or opens each main exhaust port. A main exhaust manifold is connected with the main exhaust ports. Scavenge exhaust ports fluidly communicate with each combustion chamber. A variable scavenge apparatus controls an operation of a scavenge valve which closes and opens each scavenge exhaust port. A scavenge manifold is connected with the scavenge exhaust ports. A controller is configured to control operations of the exhaust variable valve lift apparatus and the variable scavenge apparatus according to a vehicle operation state.

Methods and systems are provided for an exhaust bypass valve and a heat exchanger upstream of a three-way valve. In one example, a method may include flowing exhaust gas through one or more of an exhaust passage, bypass passage, recirculating passage, and EGR passage based on positions of a three-way valve and a bypass valve.

Methods and systems are provided for an exhaust bypass valve and a heat exchanger upstream of a three-way valve. In one example, a method may include flowing exhaust gas through one or more of an exhaust passage, bypass passage, recirculating passage, and EGR passage based on positions of a three-way valve and a bypass valve.

Methods and systems are provided for an engine including a humidity sensor. Degradation of the humidity sensor may be determined based on a change in intake air relative humidity as compared to a change in intake air temperature or pressure, under selected conditions. An amount of exhaust gas recirculated to an engine intake is adjusted differently based on whether the humidity sensor is degraded or functional.

Methods and systems are provided for an engine including a humidity sensor. Degradation of the humidity sensor may be determined based on a change in intake air relative humidity as compared to a change in intake air temperature or pressure, under selected conditions. An amount of exhaust gas recirculated to an engine intake is adjusted differently based on whether the humidity sensor is degraded or functional.

The instant invention is based on techniques for using non-thermal plasma reactors in both the main exhaust pipe and in the exhaust gas recirculation feed pipe to reduce particulate matter sufficiently to meet EPA limits for PM and enhanced exhaust gas recirculation to meet NOx limits. More specifically, it is based upon the use of a non-thermal plasma device in which a high voltage charge in the plasma reactor causes extremely rapid oxidation of soot particles in the exhaust stream of an engine and further chemical reactions that aid in the reduction of NOx. The primary benefit of this technology is that it can be calibrated to optimize both soot and NOx reduction.

The instant invention is based on techniques for using non-thermal plasma reactors in both the main exhaust pipe and in the exhaust gas recirculation feed pipe to reduce particulate matter sufficiently to meet EPA limits for PM and enhanced exhaust gas recirculation to meet NOx limits. More specifically, it is based upon the use of a non-thermal plasma device in which a high voltage charge in the plasma reactor causes extremely rapid oxidation of soot particles in the exhaust stream of an engine and further chemical reactions that aid in the reduction of NOx. The primary benefit of this technology is that it can be calibrated to optimize both soot and NOx reduction.

An exhaust gas recirculation system for a multi-cylinder engine is provided, which includes an exhaust manifold connected to a cylinder head, a catalyst connected to a downstream end of the exhaust manifold in terms of an exhaust gas flow, an EGR gas outlet provided downstream of the catalyst, an in-head EGR passage penetrating the cylinder head, and an EGR pipe extending from the EGR gas outlet and directly connected to an inlet of the in-head EGR passage to lead EGR gas thereto. The catalyst is disposed so that the exhaust gas flows therein from a first side to a second side in an engine cylinder lined-up direction. The EGR gas outlet is located on the second side with respect to the center of the engine in the cylinder lined-up direction, and the inlet of the in-head EGR passage is located in the first side with respect to the engine center.