Effects of LPG Fuel Formulations on Knock and Pre-Ignition Behavior of a DI SI Engine 2015-01-1947

Due to their CO₂ reduction potential and their high knock resistance gaseous fuels present a promising alternative for modern highly boosted spark ignition engines. Especially the direct injection of LPG reveals significant advantages. Previous studies have already shown the highest thermodynamic potential for the LPG direct injection concept and its advantages in comparison to external mixture formation systems. In the performed research study a comparison of different LPG fuels in direct injection mode shows that LPG fuels have better auto-ignition behavior than gasoline. A correlation between auto-ignition behavior and the calculated motor octane number could not be found. However, a significantly higher correlation of R² = 0.88 - 0.99 for CR13 could be seen when using the methane number. One major challenge in order to implement the LPG direct injection concept is to ensure the liquid state of the fuel under all engine operating conditions. Especially at hot soak conditions, the critical point can be exceeded and the supercritical state can be reached. In this context SI combustion anomalies for LPG depending on the gas mixture components are largely unexplored. Therefore the study also focuses on investigations of the pre-ignition behavior of different LPG fuel formulations in liquid and supercritical state.