Modeling and Simulation of Airflow Dynamics in a Dynamic Skip Fire Engine 2015-01-1717
Dynamic skip fire is a control method for internal combustion engines in which engine cylinders are selectively fired or skipped to meet driver torque demand. In this type of engine operation, fueling, and possibly intake and exhaust valves of each cylinder are actuated on an individual firing opportunity basis. The ability to operate each cylinder at or near its best thermal efficiency, and to achieve flexible control of acoustic and vibrational excitations has been described in previous publications.
Due to intermittent induction and exhaust events, air induction and torque production in a DSF engine can vary more than conventional engines on a cycle-to-cycle basis. This paper describes engine thermofluid modeling for this type of operation for purposes of air flow and torque prediction. Development of a one-dimensional model of medium complexity is described, along with solutions for practical issues encountered with the standard configuration of one-dimensional simulation packages such as GT-SUITE.
Airflow dynamic and thermodynamic simulation results for skip fire engine operation are presented and compared with experimental data under several different firing sequences. The dependence of air charge and net indicated mean effective pressure on skip fire sequence is illustrated.
Finally, a method of air estimation compensation is described via characterization of each induction event by skip history, both of the particular cylinder as well as previous cylinders in the firing order.