Liquefied Petroleum Gas direct injection (LPG DI) is believed to be the key enabler for the adaption of modern downsized gasoline engines to the usage of LPG, since LPG DI avoids the significant low end torque drop, which goes along with the application of conventional LPG port fuel injection systems to downsized gasoline DI engines, and provides higher combustion efficiencies. However, especially the high vapor pressure of C3 hydrocarbons can result in hot fuel handling issues as evaporation or even in reaching the supercritical state of LPG upstream or inside the high pressure pump (HPP). This is particularly critical under hot soak conditions. As a result of a rapid fuel density drop close to the supercritical point, the HPP is not able to keep the rail pressure constant and the engine stalls. Thus, in order to enable wider use of LPG and to assist the process of standardization, a limitation for maximum content of C3 fuel components - as propane and propene - is required as a key enabler for LPG DI applications. In order to determine a maximum C3 limit, hot idle investigations were performed on a modern turbocharged 4-cylinder direct injection spark ignition (DI SI) engine operated in a climate cham. Furthermore, stationary idle tests were carried out on a single cylinder engine with four different LPG fuels, all in accordance with EN 589. The experimental investigations indicate a maximum content of 70 % (m/m) C3 fuel components as an upper limit for an LPG DI injection concept, when a HPP, which is based on state-of-the-art HPP technology for gasoline engines, is used. For a maximum propane content of 70 % (m/m), pump functionality can be maintained with a fuel pressure of approximately 45 bar upstream the HPP at fuel temperatures of about 110 °C during hot idle. For lower pressures upstream the HPP, cooling measures need to be implemented.
