On the effect of a rail pressure error state observer in reducing fuel injection cycle-to-cycle variation in an opposed-piston compression ignition engine

The fuel injection cycle-to-cycle variation characteristic in an opposed-piston compression ignition engine was investigated experimentally. Based on the optimal Proportion Integration Differentiation (PID) method, a new control method was proposed by utilizing a rail pressure error state observer (OBS) before feedback. Compared with the conventional filtering treatment method, the OBS method was developed to simultaneously account for the flow mass changing and the dynamics of a common rail system, rather than representing the rail pressure state as an average value over a period time. The OBS method was subsequently implemented in the control system to investigate the injection pressure oscillation characteristic and cycle-to-cycle variation of injected fuel quantity. The results show that the present OBS method substantially reduces the injection pressure oscillation, improves response characteristics of the control system, and produces qualitatively satisfactory fuel injection cycle-to-cycle variation in the opposed-piston compression ignition (OPCI) engine.