Method and system for particulate filter regeneration

A method for a vehicle engine, comprising:

• responsive to a particulate filter load higher than threshold at an exhaust particulate filter as determined via a controller;
• operating a turbocharger using electric assist with a waste-gate valve fully open via the controller, the electric assist adjusted based on torque demand;
• and
• operating the engine with a first number of cylinders combusting lean, a second number of cylinders combusting rich, and spark timing retard while maintaining an exhaust air-fuel ratio at stoichiometry via the controller;
• wherein each of a degree of leanness and richness and the spark timing retard is adjusted based on exhaust temperature as determined via the controller.

A vehicle system, comprising:

• an engine;
• a turbocharger including an intake compressor coupled to an exhaust turbine via a shaft, and an electric motor;
• a waste-gate valve coupled in a bypass around the exhaust turbine;
• an exhaust passage including a particulate filter and an exhaust catalyst, the exhaust catalyst coupled downstream of the particulate filter;
• an exhaust aft pump for flowing aft into the exhaust passage, upstream of the particulate filter;
• an exhaust fuel injector for injecting fuel into the exhaust passage, downstream of the particulate filter and upstream of the exhaust catalyst;
• and
• a controller with computer-readable instructions stored on non-transitory memory for:
• operating in a first mode to heat the particulate filter via the controller, the operating in the first mode including operating the turbocharger via the electric motor with the waste-gate valve open, operating the engine with cylinder-to-cylinder air-fuel imbalance;
• wherein the cylinder-to-cylinder air-fuel imbalance is adjusted to provide stoichiometric exhaust air-fuel ratio as determined via the controller;
• and
• responsive to a temperature of the particulate filter exceeding a threshold, transitioning to operating in a second mode via the controller to regenerate the particulate filter, operating in the second mode including operating the engine loner than stoichiometry while injecting fuel into the exhaust passage via the exhaust fuel injector;
• wherein the exhaust fuel injection is adjusted based on a degree of leanness of engine operation as determined via the controller.