A Torque Balance Method for Multi-Cylinder Gasoline Engines With Non-Uniform Cylinder-to-Cylinder Combustion Strategies

Lean burn gasoline engines have attracted more and more attentions over the past two decades. One of the main challenges in commercializing lean burn gasoline engines in the United States is lean NO_x control to meet the stringent NO_x emission regulation. Several types of lean aftertreatment systems including passive selective catalytic reduction (SCR) systems and lean NO_x traps (LNTs), have been intensively investigated to meet the NO_x emission requirements without triggering significant penalties on fuel efficiency. One of the most promising technologies to achieve this goal is non-uniform cylinder-to-cylinder combustion (NUCCC) control strategies. However, successful implementation of NUCCC strategies are challenging tasks since it may cause cylinder-to-cylinder torque imbalance and thus deterioration of drivability. The purpose of this study is to propose and evaluate a systematic method for generating the references of fuel quantity and air quantity for different cylinders to simultaneously achieve cylinder-to-cylinder torque balance and non-uniform cylinder-to-cylinder air/fuel ratio (AFR) for multi-cylinder engines in various scenarios. To validate the effectiveness of the proposed method, simulation studies were carried out using a multi-zone engine model. The simulation results show that, the proposed references, if successfully tracked, can lead to torque balance across the cylinders as well as non-uniform cylinder-to-cylinder AFR.