Knock and Pre-Ignition Limits on Utilization of Ethanol in Octane–on–Demand Concept
Octane-on-Demand (OoD) is a viable technology for reducing global greenhouse emissions from automobiles. The concept utilizes a low-octane fuel for most operating conditions. Previous research has focused on the minimum ethanol content required for achieving a specific load at a given speed as the low-octane fuel becomes knock limited as the load increases. However, it is also widely known that ethanol has a high tendency to pre-ignite, attributed by few to its high laminar flame speed and surface ignition tendency. Moreover, ethanol has a lower calorific value, requiring a larger fuel mass to be injected to achieve similar power. A larger fuel mass increases the oil dilution by the liquid fuel, creating precursors for pre-ignition. Hence the limits on ethanol addition owing to pre-ignition also needs consideration before the technology can be implemented.