The autoignition behavior of 21 surrogate gasoline fuels formulated with n-heptane, isooctane, methylcyclohexane, toluene, and 1-hexene using an augmented simplex-lattice mixture design was studied in an Ignition Quality Tester (IQT) and in a single-cylinder engine operating under homogeneous charge compression ignition (HCCI) conditions. The measured ignition delays were highly correlated to fuel composition, while the observed correlation between ignition delay and research (RON) and motor (MON) octane numbers was poor. The statistical modeling using canonical Scheffé polynomials indicated strong effects from n-heptane (autoignition enhancer), toluene, and isooctane (autoignition inhibitors), while methylcyclohexane and 1-hexene showed minor effects, acting essentially as inactive components in this system. The analysis of global burning rates showed that there was a limited correlation between burning rate and ignition delay, which suggests the possibility to control ignition delay and burning rate independently by manipulating the fuel chemistry. The measured ignition delays were also well correlated with the combustion phasing observed in the HCCImeasured as crank angle for 50% heat release (CA50).

The performance of paraffin inhibitors from several chemical families was evaluated using two model waxy oils in bench-top tests such as cloud point and pour point, and in small-scale deposition rigs using a cold finger and a flow loop. In addition, rheological characterization of the inhibited systems was conducted to provide additional insights into the function of the paraffin inhibitors. Similarities and differences in the response of the model oils to the paraffin inhibitors are discussed along with the correlations between the results from bench-top tests and the observed wax deposit inhibition performance.The model waxy-oils were formulated using blends of commercially available waxes dissolved in a paraffinic solvent or a mixture of paraffinic and aromatic solvents. The wax blends were chosen to represent a broad range of carbon number distributions including one highly polydisperse distribution with an extended distribution of high carbon number waxes exceeding C50. Candidate paraffin inhibitors were initially evaluated for their impact on cloud point and pour point in these model oils. Subsequent testing of the inhibited systems included rheological characterization over a range of temperatures, cold finger deposition tests and flow loop deposition tests in a pipe-in-pipe geometry. All results are compared to the baseline results for the uninhibited model waxy oils.While changes in cloud point and pour point gave a good indication that a particular paraffin inhibitor was impacting the wax crystallization process, this did not guarantee a significant reduction in deposits of the inhibited system. Moreover, the experimental conditions used in the small-scale deposition tests also affected the observed performance of paraffin inhibitors, indicating that temperature gradients (i.e., oil temperature and coolant temperature) must be optimized to achieve the highest discriminating power. This study highlights the degree of correlation and the areas of departure between bench-top test results and the main objectives of deposit reduction, and yield stress reduction in flowing systems. It also discusses the advantages and risks of using only the bench-top test results for the selection of paraffin inhibitors.

This paper presents the results from the studies of the combustion performance of surrogate gasoline fuels in a Ricardo Hydra single-cylinder engine under homogeneous charge compression ignition (HCCI) conditions. The studies at fixed engine speed, intake air temperature, and intake manifold pressure (900 rpm, 200 °C, and 1.8 bar, respectively) demonstrated that fuel chemistry, i.e., the chemical nature of the components and their concentration in the mixture, was strongly correlated to selected parameters of HCCI performance, such as thermal efficiency (η f ), combustion phasing (CA50), and maximum pressure rise rate (MPRR). Using a multivariate optimization method based on desirability functions, it was determined that optimal HCCI combustion performance would be obtained with mixtures rich in isooctane, methylcyclohexane, and toluene (about 30 vol % each), with minimal content of n-heptane and 1-hexene (<10%).

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In this paper, we explore the correlations between the effectiveness of several wax inhibitors and physico-chemical properties of crude oils. First, the effects of the type of fluid was studied by dissolving refined paraffin waxes in non-waxy crude oils-here termed ЉdoctoredЉ crude oils-of different properties and comparing the wax appearance temperature and pour point of the doctored crude oils to those determined for a model waxy fluid used in previous studies [1]. After treating the doctored crude oils with wax inhibitors, the ability of the chemicals to depress pour point was examined. Even though the paraffin waxes in these fluids were exactly the same, marked differences in the effectiveness of the chemicals were observed. The doctored condensate was very responsive to the inhibitors in a similar manner to that observed for the model waxy fluid, while doctored crude oils from the Middle East showed a significantly reduced response to most inhibitors. The results are discussed in terms of the differences in solubility of the paraffin waxes, and the chemical composition of the crude oils.Secondly, the influence of a wide range of crude oil properties on the effectiveness of wax inhibitors was investigated by treating seven (7) crude oils of different geographical origin with five (5) wax inhibitors and evaluating their performance to reduce wax deposits in a cold finger experiments. Distinct crude oil behaviors were observed in terms of their responsiveness to the wax inhibitors. Some crude oils were equally responsive to wax inhibitors, while others showed moderate response, and one was not responsive at all. The results are clear examples of the crude oil ЉspecificityЉ, and demonstrate the risks of using model waxy fluids, or even different crude oils, to extrapolate the performance of wax inhibitors. Additives that worked well in model fluids might not work at all in real crude oils.Lastly, physical properties of crude oils and molecular characteristics derived from high-temperature gas chromatography (HTGC) were used to seek a correlation to wax inhibition performance using chemometrics tools, specifically, principal component analysis (PCA). Preliminary results from the PCA approach indicate that several crude oil properties affect inhibition efficiency. The analysis suggests that the efficiency of the inhibitors studied here increases for crude oils with lower wax appearance temperature, lower pour point and lower carbon number distribution. It could also be inferred that inhibition efficiency was improved in crude oils containing higher amounts of asphaltenes but low wax content.