Effect of Liquefied-Gas Fluid Properties in a High-Pressure Fuel Pump

Paper considers the effects of fluid properties of liquified gases during high pressure pumping, at ranges from 200 to 1500 bar. In particular, the paper examines the effects of compressibility on the pumping and resulting loading torque characteristics. Experimental tests and simulated performance based on a 1-D model of the pump are compared for D2 and DME on a high-pressure fuel pump, piston style, featuring two plunger-barrels. Each of the pump’s plunger-barrel is inlet metered electronically, allowing the pump to run at a variable displacement and with the flexibility to deactivate one or both plungers fully. Tests were conducted at speeds of 500 to 1500 rpm, and to pressures of 1500 bar, a range of pressure nor seeing before with liquified fluids such as DME. The model captures the response of the inlet metering valve and output valve lifts across speed and loads. The output check valve is subject to the pressure pulsations and shows the importance to optimize its time response to stabilize it and thus provide optimal pumping. The model also captures the torque response, with contributions arising from the pressure loading, spring return force, and acceleration. Torque depends on the volume pumped, which conversely is dependent on pressure and compressibility. The volumetric efficiency is reduced as pressure increases, but the mechanical efficiency of output pressure-work over input torque remains high, between 80-90% in most of the pump operating conditions. Experimental torque measurements show close alignment with the simulations at elevated pump speeds and pressures but differences are noted at lower speeds. The deviations appear to arise from the outlet check valve stability and at the lower pump speeds.