A numerical 1D-3D investigation on different LPG injection strategies and engine concepts

An innovative concept for the use of Liquefied Petroleum Gas (LPG) in a modern turbocharged s.i. engine has been investigated by means of both 1D and 3D numerical simulations. Direct Injection of liquid fuel and Port Fuel Injection of both liquid and gaseous fuel were analyzed and compared with a Gasoline Direct Injection concept, that was assumed as a reference. In particular the use of large valve overlaps to achieve a “scavenging” effect in order to improve the engine low end torque and its implications in case of LPG injection were deeply investigated, pointing out the main issues and highlighting the potential of DI LPG. While a significant performance decrease (up to 15% bmep decrease in the worst case) was found for PFI LPG, LPG DI showed a limited performance decrease (about 3%) that could be fully compensated thanks to its higher octane quality that allowed boost and/or spark advance increase. Finally, the 3D simulations allowed a better understanding of the charge formation process in case of LPG direct injection, highlighting significant benefits in terms of the charge homogeneity, oil dilution and smoke emissions in comparison with gasoline direct injection.