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In previous work, several significant improvements in the measurement of distillation curves for complex fluids were introduced. The modifications to the classical measurement provide for (1) temperature and volume measurements of low uncertainty, (2) temperature control based upon fluid behavior with a model predictive temperature controller, and, most important, (3) a composition-explicit data channel in addition to the temperature-volume relationship that usually comprises the measurement. This latter modification was achieved with a new sampling approach that allows precise qualitative as well as quantitative analyses of each fraction, during the measurement of the distillation curve. In this paper, we utilize the composition-explicit information to characterize distillate cuts in terms of available energy content. This is critical information in the study of real fuels. The measure we use for the fluid energy content is the composite enthalpy of combustion for each component selected for identification in each distillate fraction. As a test system, we present the distillation cuts of two prepared mixtures of n-decane + n-tetradecane. Then, as a further illustration of the approach, we present an analysis of distillate fractions of a 91 antiknock index (AI) gasoline and a 91 AI gasoline with 15% methanol (vol/vol) added.
In previous work, several significant improvements in the measurement of distillation curves for complex fluids were introduced. The modifications to the classical measurement provide for (1) temperature and volume measurements of low uncertainty, (2) temperature control based upon fluid behavior with a model predictive temperature controller, and, most important, (3) a composition-explicit data channel in addition to the temperature-volume relationship that usually comprises the measurement. This latter modification was achieved with a new sampling approach that allows precise qualitative as well as quantitative analyses of each fraction, during the measurement of the distillation curve. In this paper, we utilize the composition-explicit information to characterize distillate cuts in terms of available energy content. This is critical information in the study of real fuels. The measure we use for the fluid energy content is the composite enthalpy of combustion for each component selected for identification in each distillate fraction. As a test system, we present the distillation cuts of two prepared mixtures of n-decane + n-tetradecane. Then, as a further illustration of the approach, we present an analysis of distillate fractions of a 91 antiknock index (AI) gasoline and a 91 AI gasoline with 15% methanol (vol/vol) added.
The distillation (or boiling) curve of a complex fluid is a critically important indicator of the bulk behavior or response of the fluid. For this reason, the distillation curve, usually presented graphically as the boiling temperature against the volume fraction distilled, is often cited as a primary design and testing criterion for liquid fuels, lubricants, and other important industrial fluids. While the distillation curve gives a direct measure of fluid volatility fraction by fraction, the information the curve contains can be taken much further; there are numerous engineering and application-specific parameters that can be correlated to the distillation curve. When applied to liquid motor fuels, for example, one can estimate engine starting ability, drivability, fuel system icing and vapor lock, the fuel injector schedule, and fuel autoignition, etc. It can be used in environmental applications as a guide for blending virgin stock with reclaimed oil, guiding the formulation of product that will be suitable in various applications. Moreover, the distillation curve can be related to mutagenicity and the composition of the pollutant suite. It is therefore desirable to enhance or extend the usual approach to distillation curve measurement to allow optimal information content. In this paper, we present several modifications to the measurement of distillation curves that provide (1) temperature and volume measurement(s) of low uncertainty and, most important, (2) a composition-explicit data channel in addition to the usual temperature-volume relationship. This latter modification is achieved with a new sampling approach that allows precise qualitative as well as quantitative analyses of each fraction, on the fly. The analysis is done by gas chromatography coupled with specific or universal detectors. This second modification is the most significant change, since it is composition that is the most important underlying parameter that governs curve shape.
In previous work, several significant improvements in the measurement of distillation curves for complex fluids were introduced. The modifications to the classical measurement provide for (1) temperature and volume measurements of low uncertainty, (2) temperature control based upon fluid behavior, and, most important, (3) a composition-explicit data channel in addition to the usual temperature-volume relationship. This latter modification is achieved with a new sampling approach that allows precise qualitative as well as quantitative analyses of each fraction, on the fly. Moreover, as part of the improved approach, the distillation temperature is measured in two locations. The temperature is measured in the usual location, at the bottom of the takeoff in the distillation head, but it is also measured directly in the fluid. The measurement in the fluid is a valid equilibrium thermodynamic state point that can be theoretically explained and modeled. The usual temperature measurement location (in the head) provides a temperature that is not a thermodynamic state point for a variety of reasons but which is comparable to historical measurements made for many decades. We also use a modification of the Sidney Young equation (to correct the temperatures to standard atmospheric pressure) in which explicit account is taken of the average length of the carbon chains of the fluid. In this paper, we have applied the advanced approach to samples of 91 AI gasoline and to mixtures of this gasoline with methanol (10 and 15%, vol/vol) as examples of oxygenates. On the individual fractions, we have done chemical analysis by gas chromatography (using flame ionization detection and mass spectrometry). For the methanol blends, the approach allows characterization of the azeotropic inflections in terms of fraction composition and energy content.
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