Paul M. Rawson

FTIR analysis and monitoring of synthetic aviation engine oils

Synthetic turbine oils from military aircraft engines were analysed for antioxidant content and total acid number using infrared (IR) spectroscopy. Two-dimensional IR correlation analysis was employed to investigate and interpret observed trends in the spectra, as acid was formed and antioxidant species were depleted in the oils, as a function of aging and engine wear. Principal components and partial least squares algorithms were used and compared for the development of calibration and prediction models. Transmission IR spectrometry is demonstrated to be effective for the analysis and monitoring of synthetic aviation turbine engine oils and shown to provide rapid and accurate information as compared with traditional analytical techniques and methods.

Multidimensional gas chromatography of oxidative degradation products in algae-derived fuel oil samples using narrow heartcuts and rapid cycle times

To characterize a fuels thermal and storage stability an understanding of the process of oxidation and oxidation pathways is essential. Oxidation pathways commence with hydroperoxides which quickly decompose to form a range of alcohols, acids and other oxygen-containing species. In the presence of significant levels of hydrocarbon-based matrix, analysis of these heteroatomic species is difficult. Applying multidimensional gas chromatography with very narrow heart-cut windows (0.20 min) minimizes the number of compounds transferred to the second dimension (2D) column during each heart-cut. Successive heart-cuts every 2.00 min are taken throughout the analytical run, since each heart-cut has a maximum retention on 2D of <2.00 min on the fast elution 2D column. Subsequent analyses involve incrementing or offsetting the heart-cut windows by 0.20 min, so after 10 analyses, a complete coverage of the sample components can be obtained. On the polar 1D and non-polar 2D phase column arrangement, non-polar matrix compounds elute last on the 2D column, and this determines the largest (2t)R; i.e., (2t)R < P(M) to ensure retained components on 2D will not overlap with subsequent heart-cuts. Heartcutting is supported by cryotrapping at the start of the 2D column in order to provide significantly better resolution. Good quality MS library match data generally demonstrate the high resolution separation of oxygenates achieved. Whilst 1D GC-MS was unsuccessful in identifying any of the oxygen-containing compounds reported here, good correlation of MS data (with average MS library similarity data) for acids (903), alcohols (909), ketones (941) and aldehydes (938) in the sample is obtained. The method requires ten sequential runs, and this can be accomplished automatically once the events table is set up. However if fewer target compounds are to be transferred, a reduced number of sequential runs can be implemented.

Continuum in MDGC Technology: From Classical Multidimensional to Comprehensive Two-Dimensional Gas Chromatography

Recent advances in multidimensional gas chromatography (MDGC) comprise methods such as multiple heart-cut (H/C) analysis and comprehensive two-dimensional gas chromatography (GC × GC); however, clear approaches to evaluate the MDGC results, choice of the most appropriate method, and optimized separation remain of concern. In order to track the capability of these analytical techniques and select an effective experimental approach, a fundamental approach was developed utilizing a time summation model incorporating temperature-dependent linear solvation energy relationship (LSER). The approach allows prediction of optimized analyte distribution in the 2D space for various MDGC approaches employing different experimental variables such as column lengths, temperature programs, and stationary phase combinations in order to evaluate separation performance (apparent (1)D, (2)D, total number of separated peaks, and orthogonality) for simulated MDGC results. The methodology applied LSER to generate results for nonpolar-polar and polar-nonpolar 2D column configurations for separation of 678 compounds in an oxidized kerosene-based jet fuel sample. Three-dimensional plots were generated in order to illustrate the dependency of separation performance on (2)D column length and number of injections for different stationary phase combinations. With a given limit of analysis time, a MDGC approach to obtain an optimized total separated peak number for a particular column set was proposed depending on (1)D and (2)D analyte peak distribution. This study introduces fundamental concepts and establishes approaches to design effective GC × GC or multiple H/C systems for different column combinations, to provide the best overall separation outcomes with the highest separated peak number and/or orthogonality.

Quantification of trace fatty acid methyl esters in diesel fuel by using multidimensional gas chromatography with electron and chemical ionization mass spectrometry.

Measurement of contamination of marine and naval diesel fuels (arising from product mixing or adulteration) with biodiesel or fatty acid methyl esters can be problematic, especially at very low levels. A suitable solution for this task for trace amounts of individual fatty acid methyl esters with resolution and quantification can be achieved by using a multidimensional gas chromatographic approach with electron and chemical ionization mass spectrometric detection. A unique column set comprising a 100 m methyl-siloxane nonpolar first dimension column and high-temperature ionic liquid column in the second dimension enabled identification of individual fatty acid methyl esters at below the lowest concentrations required to be reported in a diesel fuel matrix. Detection limits for individual fatty acid methyl esters compounds ranged from 0.5 to 5.0 mg/L, with excellent linearity up to 5000 mg/L and repeatability of the method from 1.3 to 3.2%. The method was applied to the analysis of diesel fuel samples with suspected biodiesel contamination. Contamination at 568 mg/L was calculated for an unknown sample and interpretation of the results permitted the determination of a likely source of the contamination.

Derived Cetane Number, Distillation and Ignition Delay Properties of Diesel and Jet Fuels Containing Blended Synthetic Paraffinic Mixtures

Aviation turbine fuel and diesel fuel were blended with synthetic paraffins produced via two pathways and the combustion properties measured. Both aviation and diesel fuel containing synthetics produced from the fermentation of sugars, had a linear response to blending with decreasing ignition delay times from 5.05 - 3.52 ms for F-34 and 3.84 - 3.52 ms for F-76. For the same fuels blended with synthetics produced from the fermentation of alcohols, ignition delay times were increased out to 18.66 ms. The derived cetane number of the blends followed an inversely similar trend. Additionally, simulated distillation using ASTM D2887 at high synthetic paraffinic kerosene blend ratios resulted in the recovery temperatures being incorrectly reported. In this case, higher recovery volumes were at lower temperatures than earlier recovery points i.e. T90< T50, for SIP-SPK.