Knock, auto-ignition and pre-ignition tendency of FACE fuel and ethanol blends with similar RON. 2020-01-0613
Researchers have known about a higher pre-ignition frequency of alcohol fuels for several decades now. Several studies have been conducted recently to assess the effect of ethanol addition on stochastic pre-ignition and shown contradicting observations. Researchers at FEV observed an increase in pre-ignition frequency with increase in ethanol, 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 fixed base-fuel, which changes the auto-ignition tendency of the blend. In the current study, the effect of ethanol addition on FACE (Fuels for Advanced Combustion Engines) fuels is assessed. Five different FACE fuels (FACE A, C, I, J and G) were used for the study. An Ignition Delay Test was conducted in IQT (Ignition Quality Tester), according to ASTM 6890, which showed that, 13% ethanol (v/v) needs to be added to FACE A and C, while 27% ethanol (v/v) needs to be added to 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. Thereafter, the blends were tested for pre-ignition, 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.
Eshan Singh, Robert Dibble
King Abdullah University of Science & Technology