Accurate Measurement of the Ratios of Biodiesel Blends

Biodiesel is a common fuel commodity mainly used as a blending component with diesel fuel. Fuel terminals, distributors, and regulatory agencies have to pay close attention to the concentration of biodiesel in diesel fuel to ensure that it meets regulatory limits. Diesel fuel containing too much biodiesel is likely to cause engine failures, while fuel with very little biodiesel will not comply with renewable fuel standards.

A simple on-site measurement tool for measuring biodiesel concentration which can be used by non-technical personnel in the field is required. ASTM D7371 and EN14078 are the widely accepted techniques used to analyze biodiesel in diesel; however to use these techniques, an expensive FTIR spectrometer, which is best suited for use in laboratories and is highly complex, is required.

The newly introduced ASTM D7861 technique along with InfraSpec analyzers now helps users avoid lengthy delays waiting for laboratory outputs, with immediate on-site testing and results. The InfraSpec analyzer is the ideal tool specifically developed to confirm the ASTM D7861 technique, and therefore has become the industry standard for on-site measurement of Fatty Acid Methyl Ester (FAME) blend percentages.

The InfraSpec VFA-IR Spectrometer for Biodiesel Blend Measurements

The InfraSpec VFA-IR spectrometer  is a portable device allowing highly reliable on-site investigation of biodiesel in diesel in under a minute. It weighs less than 5lbs, and its rechargeable battery can last for an entire shift before requiring a recharge. The InfraSpec VFA-IR is easy to operate, and is ideal for when a single, repetitive percent biodiesel in diesel analysis is required.

Figure 1 is a schematic illustrating the patented design of the system, where one end has an attenuated total reflection (ATR) sample plate with an electronically modulated source and the other end has a linear variable filter (LVF) covering a wavelength range of 5.4-10.8µm (1850-925 cm-1) integrated with a 128 pixel detector array. Unlike an FTIR spectrometer, an infrared analyzer does not have moving parts and an optical air path, thereby making it a portable, sturdy analyzer for use in a production or field environment.

The InfraSpec VFA-IR spectrometer also comprises a simple PC interface that can be used by non-technically trained personnel. It allows the complete data and spectral information to be transmitted to laboratory technicians for assessment as and when required. The spectral range of the analyzer also enables supplementary measurements such as ethanol in gasoline and water in ethanol, to be performed.

Compliance with ASTM D7861

The ASTM method D7861 was developed to provide a field test technique for measuring biodiesel in diesel that can be used by fuel terminals/distributors and regulatory agencies. The InfraSpec VFA-IR spectrometer shows complete compliance with the ASTM D7861 standard and was the main tool used to develop the accuracy statement for the technique. Some 27 independently developed samples of varying biodiesel content, ranging from 1-30%, was measured on twelve spectrometers.

The samples contained one of three types of biodiesel – canola, soy, and waste vegetable oil and one of three diesel fuels which varied in aromatic content. The samples were tested three times on each tool and the outcomes were transmitted to an independent, statistician for analysis.

The calculated reproducibility and repeatability compared favorably with that of D7371. Disparities in the biodiesel type or diesel type had no major effect on the established reproducibility and repeatability. Furthermore, the data did not indicate any major differences in accuracy between biodiesel types.

Comparison to D7371 and EN14078

All the samples were measured by an independent laboratory using an FTIR for ASTM D7371 and EN14078 and the InfraSpec VFA-IR spectrometer. The results from the InfraSpec VFA-IR spectrometer revealed a good correlation to the two FTIR methods with an r2 greater than 0.999.

Sample ID EN 14078 Nicolet iS10 ASTM D7371 Nicolet iS10 InfraSpec VFA-IR Spectrometer
1.0 STD 1.1 1.15 1.4
105-001 0.3 0 0.25
105-002 0.3 0 0.17
105-003 0.2 0 0.22
105-004 0.3 0 0.2
5.02 STD 5 4.99 5.12
30.0 STD 30.2 30.07 30.11
50.0 STD 50 50.06 50.6


The InfraSpec VFA-IR spectrometer is a portable solution, which is simple to use yet robust, and can be used for the measurement of biodiesel in diesel. Repeatable results can be attained within a minute thereby making the InfraSpec the perfect tool for on-site measurements. The InfraSpec complies with ASTM D7861 and has high correlation with ASTM D7371 and EN 14078, thus providing a superior alternative to more expensive FTIRs.

The key advantages are listed below:

  • ASTM D7861 compliant
  • Compares to ASTM D7371 and EN 14078
  • Results are ready within one minute
  • Ideal for fuel loading areas
  • Used by blenders, fuel terminals, and regulatory agencies

This information has been sourced, reviewed and adapted from materials provided by AMETEK Spectro Scientific.

For more information on this source, please visit AMETEK Spectro Scientific.


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