Control of Fuel Injection Rate for Marine Diesel Engines Using a Direct Drive Volume Control System

A direct drive volume control (DDVC) is applied to fuel injection control for marine diesel engine. The DDVC consists of an AC servomotor, a fixed-displacement hydraulic pump, and a hydraulic cylinder. The hydraulic cylinder pushes a plunger pump and fuel is pressurized. When the fuel pressure becomes greater than injection pressure, fuel is injected to a combustion chamber. A brief introduction of the DDVC is described first in this paper referring to conventional fuel injection systems including a cam mechanism and a common rail system. A mathematical model of the DDVC for simulation is summarized. Experiments of fuel injection shows the control function of the DDVC fuel injection system. The topic of this paper is feedback control of the quantity of fuel injection (fuel mass per injection) of the DDVC. The feedback control system is simulated using the above mathematical model. Fuel injection is stopped by switching a drive signal of the AC servomotor and retracting a piston of the hydraulic cylinder. The timing to stop injection is adjusted based on crank angle. An algorithm of updating the crank angle to stop injection is proposed so that the quantity of fuel injection follows the target value. Simulation study shows that the update algorithm works successfully.