Identification and Robust Control of LPG Fuel Supply System 2009-01-1025
This paper proposes a new returnless LPG fuel supply system designed to increase the efficiency of current LPG engines. With a conventional engine fuel supply system, the fuel pump is driven at a certain speed to pressurize the fuel to an excessive level, and excess fuel that is discharged from the fuel pump but not injected from the injector is returned to the fuel tank via a pressure regulator and a return line. This arrangement keeps the pressure in the fuel supply line at a constant level. Accordingly, during engine idling, fuel cut-off or other times when very little or no fuel is injected from the injector, nearly all the fuel discharged from the fuel pump is returned to the fuel tank via the pressure regulator and return line. Therefore, the energy (electric power) applied to drive the fuel pump is wastefully consumed. Moreover, returning a large amount of excess fuel to the fuel tank can raise the fuel temperature in the tank, causing the fuel to evaporate. To avoid that problem, it is necessary to raise the pressure in the tank to an excessive level, especially when using fuel that evaporates easily. In addition, if the fuel pressure could be controlled at a lower pump speed, it would cause less component wear and have a good effect on equipment durability compared with the situation where the fuel pump is operated at high speed all the time. As a solution to this issue, this paper proposes a returnless fuel supply control system that does not use a pressure regulator or a return line. This system maintains a constant pressure in the fuel supply line by controlling the fuel pump so that it supplies only the quantity of fuel needed to meet the injection quantity that the engine demands from the injector. The modeling of the fuel supply system is described first along with the system identification based on the use of a genetic algorithm (GA). The system was configured by designing a robust sliding mode controller in relation to the identified nonlinear system. Simulations and experiments conducted with the control system showed that it provides excellent control performance as planned, with good agreement seen between the simulation and experimental data. That agreement confirmed the validity of the modeling method. The results also verified that this fuel supply control system saves needless energy consumption, especially under conditions of low engine output such as when idling. As a result, it works to improve the efficiency of the overall engine system.