A study on the injection characteristics of a liquid-phase liquefied petroleum gas injector for air-fuel ratio control

Liquefied petroleum gas (LPG) is widely used as a gaseous fuel in spark ignition engines because of its considerable advantages over gasoline. However, the LPG engine suffers a torque loss because the vapour-phase LPG displaces a larger volume of air than do gasoline droplets. In order to improve engine power as well as fuel consumption and air-fuel ratio control, considerable research has been devoted to improving the LPG injection system. In the liquid-phase LPG injection systems, the injection rate of an injector is affected by the fuel temperature, injection pressure, and driving voltage. When injection conditions change, the air-fuel ratio should be accurately controlled in order to reduce exhaust emissions. In this study, correction factors for the fuel injection rate are developed on the basis of fuel temperature, injection pressure, and injector driving voltage. A compensation method to control the amount of injected fuel is proposed for a liquid-phase LPG injection control system. The experimental results show that the liquid-phase LPG injection system works well over the entire range of engine speeds and load conditions, and the air-fuel ratio can be accurately controlled by using the proposed compensation algorithm.