Octane Numbers of Ethanol− and Methanol−Gasoline Blends Estimated from Molar Concentrations

Energy & Fuels (Impact Factor: 2.79). 11/2010; 24(12). DOI: 10.1021/ef101125c


When expressed using volumetric concentrations (as is industry practice), the addition of relatively small amounts of ethanol or methanol (e.g., 10% by volume) to gasoline appears to result in disproportionately large, nonlinear increases in research octane number (RON) and motor octane number (MON). As a result, volumetric “blending octane numbers” are of limited value for estimating the octane number of alcohol−gasoline blends because they vary with alcohol content and base gasoline composition. We show that RON and MON increases with alcohol content are approximately linear when expressed using molar concentrations. Moreover, molar-based blending octane numbers are effectively equal to the octane numbers of the pure alcohols for most base gasolines. A limited dependence on gasoline composition was observed, namely, greater-than-predicted octane numbers for ethanol−gasoline blends with unusually high isoparaffin content. We suggest that octane numbers of methanol−gasoline and ethanol−gasoline blends can be estimated conveniently and more accurately from their molar composition by linear interpolation between the octane numbers of the base gasoline and the pure alcohol.

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    • "[9;10]). Previous work on blending ethanol to gasoline blendstocks shows an approximately linear relationship of RON with ethanol mole fractions [11]. However, more recent piece of work suggests introducing a scaling parameter (2 nd -order dependence with respect to ethanol mole fraction) to yield more accurate prediction results [7;12]. "

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    • "compression ratio). Table 3 reports the compression ratios used in all the operative conditions tested, while the characteristics of the gasoline [30] [38] [39] and propane [34] [40] used in the tests are resumed in Table 4. Fig. 1. Experimental system layout. "
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    ABSTRACT: Gaseous fuels, such as Liquefied Petroleum Gas (LPG) and Natural Gas (NG), thanks to their excellent mixing capabilities and high knocking resistance, allow complete and cleaner combustion than gasoline in Spark Ignition (SI) engines, resulting in lower pollutant emissions, above all if particulate matter is considered. In previous works [1, 2] the authors proved how the simultaneous combustion of gasoline and gaseous fuel (NG or LPG) may strongly reduce both fuel consumption and pollutant emissions with respect to pure gasoline operation without a significant power loss. These very encouraging results were obtained thanks to the strong knock resistance increase obtained adding gaseous fuel to gasoline, which allowed the use of stoichiometric mixtures and better spark advances, even at full load. The introduction of such a kind of combustion in series production engines would however require the use of properly calibrated simulation models, capable to adequately predict the performance and efficiency of engines fuelled by gaseous fuel-gasoline mixtures; in particular, specific combustion models are needed, together with reliable knock onset prediction sub-model. The total absence of such sub-models in the scientific literature induced the authors to investigate the knocking resistance of gasoline-propane mixtures and calibrate a proper knock onset prediction sub-model to be implemented in the zero dimensional thermodynamic models usually employed for engine performance optimization. To this purpose several light knocking in-cylinder pressure cycles have been recorded on a CFR engine, fuelled by gasoline, propane and their mixtures, varying the most important knock-related parameters: compression ratio, spark advance, inlet mixture temperature and fuel mixture composition. The collected data have been used to calibrate two different models, compared in terms of knock onset prediction accuracy: the Knock Integral model (KI) and the Ignition Delay model (ID). Both models revealed a good reliability in predicting the onset of knocking phenomena, with maximum errors around 4 crank angle degrees. The Knock Integral model showed a slightly higher accuracy, which, together with its lower computational effort, makes it preferable for the implementation in the commonly employed thermodynamic engine models.
    Full-text · Article · Jan 2015 · Journal- Energy Institute
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    • "Questions have been raised as to whether the RON and MON methods are appropriate for rating fuel blends with high ethanol content. Originally developed for rating gasoline, use of the standard CFR engine may be problematic for fuels with drastically different properties [21] [22]. The major hardware limitation is the fuel metering jet and the air–fuel mixture heater. "
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    ABSTRACT: This paper reports the Research (RON) and Motor (MON) Octane Numbers of ethanol blended with production gasoline, four gasoline surrogates, n-heptane, isooctane and toluene. The ethanol concentration was varied from zero to 100%, resulting in a clear picture of the variations of the RONs and MONs in all cases. Of initial interest are the RONs and MONs of ethanol blended with an Australian production gasoline and with several US production gasolines. The observed differences then prompt a systematic study of the variation in the RONs and MONs of ethanol blended with four gasoline surrogates, as well as with n-heptane, isooctane and toluene. Both n-heptane, isooctane and their Primary Reference Fuels (PRFs) are shown to blend synergistically with ethanol, whilst toluene blends antagonistically. Consistent with these trends, a progressive increase in the toluene content in Toluene Reference Fuels (TRFs) of a constant RON results in increasingly linear ethanol/TRF blending. Together, these results show that the antagonism of ethanol’s blending with toluene acts against its synergism with isooctane and n-heptane, and more broadly suggest that the antagonism of ethanol’s blending with aromatics may act against its synergism with paraffins. If correct, this explains trends observed both in the literature and in this study, and has implications for fuel design.
    Full-text · Article · Jan 2014 · Fuel
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