An Evaporative and Engine-Cycle Model for Fuel Octane Sensitivity Prediction

Improving the use of liquid biofuels in internal combustion engines

“…The motor octane numbers (MONs) of these fuels are proportionally less high and thus their sensitivity (RON-MON) is very high relative to gasoline; nevertheless, these fuels would not be considered as having a low MON relative to most gasoline sold throughout the world. Moran and Taylor ( 1995 ) posited that, because the intake manifold temperature is not controlled during the RON test, the high heat of vaporization of the low-carbon number alcohols would cause a physical cooling effect which would have a direct bearing on the knock-limited compression ratio. In contrast, the MON test uses a heater to try to control the intake manifold temperature to 149 o C, which is well above the respective boiling points of these alcohols and is thus not affected by this physical cooling effect.…”

A CFD Study of Fuel Evaporation and Related Thermo-fluid Dynamics in the Inlet Manifold, Port and Cylinder of the CFR Octane Engine

“…Opinions differ widely when it comes to an explanation for high values of OS. Some studies [7,8] attribute OS entirely to evaporative cooling effects associated with different classes of fuels (e.g. paraffins, olefins, aromatics and alcohols).…”

“…This also results in the assumption that all the air and fuel is fully and uniformly mixed. Since liquid fuel distributions cannot be accounted for, all the liquid fuel is assumed to form part of the wall film or is fully evaporated [7,20].…”

“…Others have concluded that the difference in test conditions gives rise to evaporative cooling effects in the RON test which explains the better anti-knock measurement (higher RON value). This evaporative cooling hypothesis was studied in a masters thesis by Moran [8] at the University of Cape Town (UCT) and later followed up with research work in the industry with Taylor [7]. Combining physical and chemical effects would be the best way to study knock in SI engines, and this was done in the work by Stauch and Maas [38].…”

“…In a later paper by the same author [7], an additional model was created to investigate the unburnt gas temperature in the cylinder under RON conditions. One of the focuses of this study was liquid fuel entering the cylinder and its effect on unburnt gas temperatures.…”