Knock, Auto-Ignition and Pre-Ignition Tendency of Fuels for Advanced Combustion Engines (FACE) with Ethanol Blends and Similar RON

Researchers have known about a higher pre-ignition frequency of alcohol fuels for several decades now. Several studies, assessing the effect of ethanol addition on stochastic pre-ignition, have shown contradicting observations. Researchers at FEV observed an increase in pre-ignition frequency with an increase in ethanol concentration, however the pre-ignition events at high ethanol content did not lead to super-knock. Most of the studies have used varying ethanol fraction in a common base-fuel, thereby varying the auto-ignition tendency of the blend. In the current study, the effect of ethanol addition on FACE (Fuels for Advanced Combustion Engines) gasolines is assessed. Five different FACE gasolines (FACE A, C, I, J and G) were used for the study. Ignition delay time of varying ethanol fractions in FACE gasolines was measured in an Ignition Quality Tester (IQT), following ASTM 6890. The measurements showed that 13% ethanol (v/v) is needed for FACE A and C, while 27% ethanol (v/v) is needed for FACE I and J to match the ignition delay time of FACE G fuel. The five blends were tested in a Co-operative Fuel Research (CFR) engine in Homogeneous Charge Compression Ignition (HCCI) and Spark Ignition (SI) combustion mode. The experiments showed similar auto-ignition and knocking tendency for the five blends. After that, the pre-ignition tendency of the blends was assessed in a supercharged AVL engine. In general, increasing ethanol content led to higher pre-ignition frequency. Moreover, the effect of ethanol on increasing pre-ignition frequency was dependent on the base-fuel into which ethanol was added. For the same ethanol fraction added, base-fuels with higher aromatic content showed higher pre-ignition frequency.