Robust Common-Rail Pressure Control for a Diesel-Dual-Fuel Engine Using QFT-Based Controller

Despite promising future, the diesel-dual-fuel engine, with diesel as pilot and natural gas as main, abounds with challenges from high NOx emission and knock especially at high speed and low load. To cope with these challenges, variation of common-rail pressure provides another desirable degree of freedom. Nevertheless, crippling with complicated dynamics, pressure wave inside the transporting rail, disturbance from varying of injections, engine speed variation, and actuator limitation, common-rail pressure control has relied on the simple PID to deliver only marginally satisfactory result. Some attempts to achieve better control have resulted in either too complicated or not too robust control system. We devise a controller from the quantitative feedback theory. Besides being able to quantitatively enforce specifications such as tracking, plant input and output disturbance rejections, and stability margin, the controller is designed from a simple model, whose parameters are allowed to be uncertain, hence robustness. The resulting controller has low order and is readily implementable. Experiment with a common-rail system in a Ricardo Hydra engine, modified to run dual fuel, shows the controller’s effectiveness over the PID.