No abstract

The high cost and limited availability of emerging alternative fuels and/or fuel blending stocks with unknown compositions are often major impediments to the certification of these materials as Fit-For-Purpose (FFP) for the U.S. Navy. A method was desired whereby a candidate fuel could be rapidly prescreened to determine if it would be suitable for further, moreextensive FFP testing. The goal of this research was to employ statistical analysis strategies to establish linkages between the chemical constituency of any given fuel or fuel stock, regardless of type or source, and the resultant performance, and/or fuel properties. A chemical profiler developed during the course of this work has previously been used to quantify the constituencies of fuels using gas chromatography−mass spectrometry (GC-MS) data. These constituencies were then correlated to specification properties using partial least-squares regression modeling reconfigured into a multistep, iterative strategy. While this modeling strategy was shown to be successful at predicting the performance properties not only of the training data but also of uncalibrated alternative fuels, the underlying data abstraction strategy was determined to be inherently unsuitable for use with the disparate data from multiple GC-MS instruments due to instrument-based overfitting. The following report details a novel modeling strategy that makes use of normalized total ion chromatography (TIC) peak areas to both streamline the procedural complexity of the previous modeling strategy and more ably quantify chemical constituencies for the purposes of multi-instrument FFP fuel modeling.

This study was undertaken to address the need for an improved analytical method to detect and quantify hindered phenolic antioxidant additives in Navy mobility fuels that overcomes the limitations of currently available methods. It was demonstrated that hindered phenols in fuels can be accurately quantified using capillary gas chromatography−mass spectrometry with selected ion monitoring (GC−MS/SIM) of mass fragments unique to each analyte. Using this approach, three methods were developed for the analysis of antioxidants in fuels: (1) a single-column GC−MS/SIM method that, because of co-elution of fuel constituents, is only suitable for quantifying tri-tert-butylphenol, (2) a two-column heart-cutting method that overcomes the problem of co-eluting fuel components but requires modification of the instrument, and (3) a GC−MS/MS method that does not require modification of the instrument. The heart-cutting method was developed as a practical method for the routine determination of each of the five hindered phenolic antioxidants in any type of fuel, with a method quantitation limit (MQL) of 0.5 mg/L, with minimal interference from fuel. The GC−MS/MS method provides a lower MQL of 0.05 mg/L. Both methods offer a significant advantage over traditional high-performance liquid chromatography with electrochemical detection (HPLC− ECD) methods, which are more labor-intensive and not capable of separating each of the individual phenolic antioxidants.

A set of low-sulfur diesel fuels from the Western Pacific region were found to be unstable during storage although they passed all standard specification tests. This sample set was found to have high nitrogen content. Initially, liquid–liquid extractions with a mild aqueous acid were performed to separate basic and nonbasic nitrogen groups in an attempt to determine if these organonitrogen classes were responsible for the poor stability. The findings of this study indicate that there may be a correlation between the acid-extractable nitrogen compounds in these fuels and the formation of high levels of particulates in storage. To develop a more comprehensive understanding of the classes and distributions of organonitrogen compounds in fuels, a novel analytical method was developed using two-dimensional gas chromatography with nitrogen chemiluminescence detection (GCxGC-NCD). The GCxGC-NCD analyses revealed the presence of three distinct groups of nitrogen compounds. One group corresponded to the acid-extractable basic nitrogen compounds, one with the nonbasic nitrogen compounds, and a third early-eluting lighter polar organonitrogen fraction that had previously not been observed. This light organonitrogen fraction was unique to these particularly unstable fuels. If this is found to be universally applicable, this light polar nitrogen fraction may serve as an indicator of potentially unstable diesel fuels. Overall, the GCxGC-NCD method has been shown to be a valuable tool to enhance our understanding of the chemistry of organonitrogen species and their impact on fuel stability.