On July 25, 2003, the Chemical Engineering Department of Hong Kong University of Science and Technology conducted a research to determine the water droplets size distribution in “F2-21 eeFuel” fuel additive.

This research was aimed at identifying the distribution of suspended water particles in diluted F2-21 eeFuel additive, which is an oil-in-water microemulsion.

The test procedure is presented below:

  • A concentrated fuel additive was diluted with motor oil (Caltex Havoline Energy) before measuring particle size distribution (dispersion structure);
  • 0.5 milliliters of concentrated additive was mixed with 2,000 ml of motor oil;
  • The fuel additive at 1:4000 concentration to motor oil mixture was poured in a control chamber of a Coulter Delsa 440SX measuring device and then the water particles size distribution was analyzed.

It is commonly known that distributed water particles are in suspension due to Brownian agitation. The diffuseness of each particle depends on its size (as shown in modal equation 1). In the Coulter Delsa 440SX device, suspended particles were illuminated with a laser beam, and the laser light was diffused. The laser beam diffused from particles varied by intensity degree with their diffuseness. The variation level was characterized with the help of this measurement device and was «self-correlated» (mathematical process) in order to receive information on particle size distribution. Particles with similar spherical diameter ranging from 3 nanometers to 30 μm could be detected by analyzer.

D = k8T / 3 πηd   (Equation 1)


k8 = Boltzmann's constant

Т = temperature

η = solvent viscosity

d= equivalent spherical diameter

Refraction index (RI) and dynamic viscosity (Vis) of solvent (i.e. motor oil) was required for measuring distribution. Refraction index ranging within 1.3974-1.4300, and dynamic viscosity ranging within 0.392-0.448, that were calculated on the basis of gasoline values, were applied. Repetitive measurements were made using the same refraction index and dynamic viscosity values (Run 1 and Run 2). The instrument allowed making a simultaneous multi-angular analysis. The measurements were made with 24.4° and 32.7° laser beam tilt angle.

Theoretically, the results measured with both tilt angles should be identical, but they may vary in practice.

The results are as follows:

Particle size distribution measurement results are shown in Figure 2a-b. The similarity of repetitive measurement results (run 1 and run 2) demonstrates that the measurements are sufficiently repeatable. According to analyzer, the size of suspended water particles is generally ranging from 3 to 9 nanometers. There is a large amount of particles of size less than 4 nanometers among them. Since the measurement device range is limited and ranges from 3 nanometers to 30 μm, the particles of less than 3 nanometers cannot be detected where they are present. The comparison of particles distributions received with different refraction indices and dynamic viscosity values shows that a different entry value can result in varying measurement results. However, the appearing variations are insignificant.

The report on the work which had been carried out was prepared by Alex H.K. Chan, Emily S.M. Lay and Professor K.M. Ng (consortium of chemical products and processes, Chemical Engineering Department, Hong Kong University of Science and Technology)