Direct Digital Control of Diesel Engines

Initially, a new direct digital Diesel fuel injection system: an electronic Pump-Pipe-Valve-Injector system was introduced. A general comparison of this system with other electronic Diesel injection systems indicated that the new system can be more effective for high pressure Diesel injection and more flexible for wide engine speed range. Then, the digital injection control characteristics of this system were studied by both experiment and computer simulation. Some special digital injection control functions were obtained. In particular, it was found that transient effect of the control valve action can be used to regulate the pulsed Diesel fuel flow to achieve a low initial injection rate and high injection cut-off rate. This effect can be optimized by appropriate selection of the control valve location. Finally, a direct digital Diesel engine governing technique was investigated. The theory of discrete systems was applied to model the dynamic transfer characteristics of a Diesel engine equipped with the new injection system. A new digital Diesel idle speed governing system was designed, which adopted a cascade control structure with both the engine speed at the time of injection and the cycle average engine speed for feedback to synchronize governing action with discrete engine operation events. This system was implemented on a computer and tested on a research engine. Satisfactory governing performance was achieved, and a comparison test between the new control strategy and a conventional PID control method showed that the new system resulted in much better control performance.