DEVELOPMENT OF A LIQUID-PHASE LPG DELIVERY SYSTEM FOR DIRECT INJECTION, SPARK-IGNITED ENGINES

Liquefied petroleum gas (LPG) is a promising diesel fuel alternative for heavy-duty vehicle applications due to its CO2 reduction potential, high knock resistance, easy liquefication capability, and lower fuel cost. Direct injection (DI) of liquid-phase LPG has emerged as a promising technology in sparkignited (SI) engines due to the benefits from the in-cylinder charge cooling effect in comparison to external mixture formation systems. But this DI LPG technology requires a fuel delivery system that can supply the desired amount of LPG fuel in the liquid state at high pressure. This work first describes the design and component integration of an LPG fuel system that delivers fuel from the tank to the injector in the liquid state at around 172 bar, mainly focusing on thermal management aspects to avoid multi-phase behavior within the system. A detailed description of the injector developmental work, from reverse engineering of stock injectors to manufacturing a prototype LPG direct injector, is also presented, including nozzle modifications to accommodate a high LPG flow rate for heavy-duty applications. A one-dimensional (1D) flow model of the fuel delivery system is developed using the MATLAB/Simulink software platform to guide the selection and sizing of components and characterize the prototype injector. Bench testing of the fuel delivery system is performed with the unmodified stock and prototype LPG injectors using a Viscor calibration fluid and LPG to study the effect of fuel pressure and current profiles on the injected fuel quantity. The simulation models are shown to be capable of predicting the experimental results. Durability tests are also performed to understand the failure modes of different components in the fuel delivery system.