How to Measure Fuel Composition Using FT-IR Instruments?

From the very first stage of fuel characterization, infrared spectroscopy was extensively applied in fuel analysis. AMETEK Grabner Instruments — an industry trendsetter with its IROX 2000 and MINISCAN IRXpert fuel analyzers — launched its latest product, the MINISCAN IR VISION FTIR analyzer, in 2017.

Whether a fuel is a diesel, jet fuel, or gasoline, it is made up of a complex mixture of hydrocarbons, most of which do not have characteristic absorption in the IR. They make up the “background” or “matrix”. On the contrary, olefins, aromatics, and the various additives used to compose a fuel, exhibit absorption bands and are used to characterize it. The content of aromatics, such as benzene, is rigorously monitored by authorities, and IR standard procedures, such as ASTM D6277 or ISO EN238, exist to evaluate their concentrations.

The Ever-Growing Complexity of Fuel Composition

The number of additives used to improve fuel properties also needs regulation — firstly for optimized blending, and secondly for environmental purposes. A variety of components that improve the oxygen content and promote better combustion have been developed, and, as the chemical bond between carbon and oxygen atoms can be accessed easily with IR radiation, IR spectroscopy has turned out to be the most preferred method for detecting such substances (for example, ASTM D5845). At present, the US Environmental Protection Agency (EPA) lists nearly 7,400 different branded substances from different vendors that are used as fuel additives.

Typically, a definite number of specific additives are used to adjust important fuel properties, such as the octane number (or cetane number in diesel fuel). In due course, it became apparent that a fuel spectrum must correlate with usual additives determining its properties. As the standardized methods for acquiring information about fuel properties are expensive and time-consuming (for example, CFR Knock Engines), chemometric methods connecting the IR method with fuel properties became widespread.

Portable FTIR Spectrometers

In the 1990s, Dr Werner Grabner, founder of Grabner Instruments in Vienna, Austria, created the first portable FTIR spectrometer, called IROX, to determine the concentration of oxygenates in gasoline with the help of mid-IR. In 2000, another instrument dedicated to diesel was launched. Both instruments were used to determine the concentrations of various fuel components, and also to predict typical fuel properties, by creating a strong prediction model for different regions worldwide.

Still, during the first 10 years of the 2000s, the manufacturers of standard benchtop IR analyzers identified the fuel market as a new business field and designed similar specific applications for fuel analysis. These producers also applied Raman IR spectroscopy to complement standard IR. Other technologies, such as attenuated total reflection (ATR) IR spectroscopy, were launched. However, Raman, FTIR, and ATR technologies are basically different methods to view the same thing from slightly different perspectives.

No technique was superior or inferior to another. Every technology had its own advantages and limitations for the purpose it is used for. ATR was easily applied in a process for online applications, and FTIR instruments were usually designed compactly and sturdily for use in mobile fuel labs. The actual differentiators come from available support, ease of use, flexibility and application range, robustness, quality of instrument design, and, finally, the accuracy and precision of the device, which are direct functions of spectrometer design, its stability, the spectral range, resolution, and intensity of the IR light source.

The Need for More

With the evolution of the oil market and more diversity in fuel compositions, there was a demand for a flexible analyzer, instead of a specialized analyzer. This trend to versatile fuel composition remains strong even now. On one hand, fuel technology struggles for increasingly more efficient fuels with better combustion and ever more efficient fuels, and, on the other hand, environment requires low-emission fuels with least environmentally controversial substances in the exhaust.

Therefore, in 2017, 17 years after the introduction of the IROX, Grabner Instruments launched a powerful, flexible FTIR spectrometer, the MINISCAN IR Vision. The MINISCAN IR VISION is a compact, high speed, and rugged FTIR fuel analyzer designed for complete and automatic measurement of jet, gasoline, and diesel fuels. The analyzer is set to measure over 100 fuel parameters and components for fuel blending. It is developed to carry out quality inspection and check compliance with specifications of fuels directly at the point of sale.

A compound analysis is carried out as per international standards: ASTM D6277 and EN 238 for benzene, EN 14078 for biodiesel blends, and ASTM D5845 for oxygenates. An integrated temperature-regulated density meter enables precise determination and stability of fuel density. Fuel properties such as octane and cetane number, vapor pressure, distillation, and others are automatically determined from the complete IR spectrum, using Partial Least Square (PLS) analysis and sophisticated chemometric models, conforming to ASTM E1655. Several thousand data points are employed to obtain the best prediction accuracy.

The MINISCAN IR Vision portable fuel analyzer from Grabner Instruments is unparalleled in its class. With the thermoelectric temperature regulation of the instrument’s filling system, built-in density meter, and measuring cells, the accuracy in measuring volume and mass percent of fuel compounds is considerably increased.

MINISCAN IR Vision Portable Fuel Analyzer

The durability of the instrument makes it suitable for the problems faced during field or mobile testing. The MINISCAN IR Vision portable fuel analyzer includes Grabner Instruments’ robust, proven, and bubble-free metal filling system. A shock-and-vibration-tested VISION platform housing shields the instrument. Its double interferometer is attached with a self-aligning mirror system that enables automatic correction of intensity shifts after a rough drive on an uneven road. In addition, a robust, 10” full-color industrial touch screen ensures ease of use and highest visibility even under harsh environmental conditions. For field applications, the instrument can be operated on a 12 V car adapter.

This information has been sourced, reviewed and adapted from materials provided by Grabner Instruments.

For more information on this source, please visit Grabner Instruments.