Closed-Loop Diesel Combustion Control Leveraging Ignition Assist

Diesel engines equipped with ignition assisting actuators may improve combustion in aerial powertrains operating at low temperatures and with fuels of varying ignition behavior. Fuel injection timing can be aided by the additional energy from ignition assist (IA) devices such as glow plugs. This work presents a closed-loop control scheme that coordinates start of injection (SOI) and IA power to regulate both mean and cycle-to-cycle variability (CV) in diesel combustion phasing. Engine experiments at a chilled condition demonstrated the IA's slow dynamics, high sensitivity to engine thermal state, and large nonlinearities in control authority that justify its limited use as a secondary actuator. A low-order model informed by experiments facilitated closed-loop system simulation. Control of mean combustion phasing was achieved using a PI controller for SOI. Reduction and control of CV within acceptable bounds was achieved with mean Kalman filtering of feedback, adaptation of mean phasing using windowed variance estimation from feedback, and conditional IA activation driven by saturation of the mean phasing or SOI values. Simulation results show the controller can track a desired mean setpoint of the start of combustion within 4-6 engine cycles without amplifying closed-loop CV, and can conditionally actuate IA while coordinating with SOI to manage unplanned disturbances in system CV behavior.