XBEE improves fuel stability according to ASTM D 4740 spot test by Intertek

Fuel instability often occurs when the aromatic solvency of the fuel is disturbed, typically by paraffinic solvents used as cutter stocks, or fuels based on paraffinic crudes. Bunkers from different fuel sources may separately pass ISO 8217 certification tests, yet when blended and subjected to age and heat on board the vessel, the bunkers become incompatible. Heavy sludge affects the fuel system, causing increased maintenance costs and operational problems.

ASTM D 4740 measures fuel compatibility and resistance of mixed fuels to form sludge under a ship’s high-temperature fuel handling conditions. Demonstrated in this test by Intertek Caleb Brett laboratory in California, USA, a mixture of 3.5% sulphur HFO 380 bunker samples that were initially ISO 8217 compliant, but when aged and mixed, became highly unstable.

XBEE enzymes improved the compatibility rating from an unusable “5” to a usable “2 to 3”.

Fuel test - Intertek Caleb Brett and HFO XBEE stability

In February 2019, Intertek Caleb Brett was commissioned to study our enzymes’ effects on improving stability in unstable HFO. To simulate a realistic shipboard fuel scenario of blended fuels with different ages, five individual 1-litre and 750-ml laboratory retains from five different bunkering operations were acquired from a California fuel jobber. Fuel certifications (ISO 8217-2017) had been performed between February 2018 and August 2018. The HFO came from a sole source. The refinery and crude oil source is not known.

The five samples were blended together, totalling approximately 3.8 litres. An additional 200 ml of an aged IFO 380 sample from a different vendor was added. The total volume was approximately 4 litres. The fuel samples were mixed and delivered to Intertek. The Laboratory split the fuel into two equal portions, and additized one sample at 0.5 ml (~4,000:1). The fuel was set aside for one week.

The primary goal of this test was to create a blend of HFO that was unstable due to commingling of different batches of different aged fuels, in order to determine what characteristics XBEE is likely to improve, at the most economical dose rate.


The most remarkable response was the ASTM D 4740 Compatibility rating going from a “5” to a “3”. This indicates the blended fuel went from being unsafe to use to being safe to use, but with warnings to not overheat the fuel. Ratings can be subjective, as there are no fractional ratings. The “5” for the neat fuel is obvious. The treated fuel falls in between “2” and “3”. As it does lean closer to “3” (not easily visible in the photograph), the rating must go to the higher number. (See images, chart, and description below.)

The other notable change was ASTM D 445, which is viscosity. The neat fuel was 374.3 cSt, and the treated fuel was 357.7 cSt. This represents a 4.5% reduction in viscosity, with no reduction in fuel density.

Other results of interest include:

  • ASTM D 664: a 12% reduction in acidity
  • ASTM D 6560: a 3% reduction in asphaltenes
  • ASTM D 482: a 45% reduction in ash

These fuel characteristics are known to contribute to fuel instability, sludge formation, corrosion, and injector fouling or even injector damage. While these are small improvements, collectively they are all contributing factors towards the total improvement of this fuel blend.

Fuel test - Intertek Caleb Brett and HFO XBEE
Neat fuel · Rating ‘5’
Fuel test - Intertek Caleb Brett and HFO XBEE
XBEE treated fuel · Rating ‘3’


In this study, XBEE Enzyme Fuel Technology greatly improved the compatibility and stability in an unstable HFO blend. For shipboard applications, XBEE can significantly reduce sludge formation due to commingling and aged fuel, and improve fuel system function and engine cleanliness. (Following are photographs of the ASTM D 4740 compatibility spot tests, as well as the full Intertek Caleb Brett Report of Analysis.)

Fuel test - Intertek Caleb Brett and HFO XBEE