Piezoelectric fuel injection: Cycle-to-cycle control of tightly spaced injections

Piezoelectric fuel injectors will require closed-loop control to realize tightly spaced injections. This paper describes an estimation algorithm for cycle-to-cycle determination of an injection flow profile for use as feedback for closed-loop control. A control design-amenable, 2-pulse approximate model is outlined to represent the dynamics of simultaneously controlling the quantity of, and realized dwell time between, injection pulses. A control law is developed to provide an overdamped response of realized dwell time to prevent pulse bleeding. Closed-loop performance is validated with the experimental data. Desired fuel quantity, and very short dwell times of 0.0002 s (two crank angle degrees at 1800 RPM), are realized with tracking error convergence time constants of approximately four engine cycles (0.27 s at 1800 RPM).