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Knocking combustion is a major obstacle towards engine downsizing and boosting—popular techniques towards meeting the increasingly stringent emission standards of SI engines. The commercially available gasoline is a mixture of many chemical compounds like paraffins, isoparaffins, olefins and aromatics⁠. Therefore, the modeling of its combustion process is a difficult task. Additionally, the blends of certain compounds exhibit non-linear behavior in comparison to the pure components in terms of knock resistance. These facts require further analysis from the perspective of combustion chemistry. The present work analyses the effects of blending ethanol to FACE-C gasoline. A range of pressures, temperatures, and equivalence ratios has been considered for this purpose. The open source softwares Cantera version 2.4.0 and OpenSMOKE++ Suite have been used for the simulations.

Gasoline blending is known to be complicated, because individual gasoline fractions with different octane numbers, Research Octane Number (RON) or Motor Octane Number (MON) do not always blend linearly. Instead, they may blend non-linearly, in a synergistic or antagonistic manner. Even though RON and MON are regulated properties, linear and non-linear octane blending is not a broadly understood topic. The target in the developing process of a modern SI engine is to have 100% combustion efficiency which would lead to the reduction of hydrocarbon and carbon monoxide emissions. Therefore, the properties of gasoline, especially RON and MON, need to be optimized to ensure proper ignition in the engine and prevent harmful autoignition reactions. There are hundreds of hydrocarbons in gasoline which have different octane numbers (ON). The explanations for these variations are the structural differences in hydrocarbon molecules that influence on their reactivity.

In this study, fuel octane number boosters such as toluene, ethanol, methanol, 2-methylfuran (MF), and 2,5-dimethylfuran (DMF) are blended with primary reference fuels (PRFs) in a cooperative fuel research (CFR) engine at research octane number (RON) relevant conditions. In addition to RON determination, engine operation is characterized by measuring (i) cylinder, intake and exhaust pressure, (ii) averaged intake and exhaust temperature, and (iii) air-fuel-ratio. For known fuel blends, the measured RON corresponds well with existing literature. The addition of MF in PRF yields a significant increase in RON and blending octane numbers (indicating booster impact) up to 216. Cylinder pressure fluctuations, the classical definition of knock intensity, are however not consistent, deviating between PRFs and all boosted blends at higher RON values. Moreover, some fuel blends exhibit scarcely any knocking behavior in the test conditions.