Methods and systems for estimating a composition of flow through a scavenge exhaust gas recirculation system of a split exhaust engine system

A system for an engine, comprising:

• a plurality of cylinders, each including an intake valve, a scavenge exhaust valve, and a blowdown exhaust valve;
• an intake manifold coupled to the intake valve of each cylinder;
• a scavenge manifold coupled to the scavenge exhaust valve of each cylinder and an intake passage, upstream of a compressor, via a scavenge exhaust gas recirculation passage;
• a blowdown manifold coupled to the blowdown exhaust valve of each cylinder and an exhaust passage including a turbine;
• and
• a controller with computer readable instructions stored on non-transitory memory that when executed during engine operation, cause the controller to:
• determine a total flow of gases through the scavenge exhaust gas recirculation passage, from the scavenge manifold to the intake manifold, upstream of the compressor, based on a valve opening overlap area between the scavenge exhaust valve and intake valve;
• determine a total flow of burnt gases, a total flow of fresh air, and a total flow of fuel through the scavenge exhaust gas recirculation passage based on the determined total flow of gases and an amount of valve opening overlap between the scavenge exhaust valve and intake valve;
• and
• adjust an operating parameter of the engine based on the determined total flow of burnt gases, determined total flow of fresh air, and determined total flow of fuel.