Emulsions that mix two or more immiscible phases are broadly applied in pharmaceutics, chemistry, and industries. The phase inversion temperature (PIT) method is an emulsifying approach to preparing an emulsion with low energy consumption and cheap equipment. The effects of surfactant characteristics and processes of cooling or heating on the fuel properties of emulsions composed of silicone oil by the emulsifying method, such as mean droplet sizes of the de-ionized water phase, were considered herein. The application of the silicone oil emulsion as engine fuel was first evaluated. The results show that the emulsions added with the polyol surfactant mixture appeared to have a larger mean water-droplet size, a larger number of dispersed water droplets, a wider range of dispersed-water sizes, and lower kinematic viscosity than those with Brij 30 surfactant. Increasing the surfactant concentration of either Tween 20 mixed with Span 80 or Brij 30 surfactant increased kinematic viscosity and the number of dispersed droplets while decreasing mean droplet sizes. After being subjected to fast heating and then fast cooling, the silicone oil emulsion appeared to form many smaller dispersed droplets than those being proceeded with slow cooling. The emulsion of silicone oil was found to have adequate engine fuel properties.

The engine performance and emission characteristics of burning emulsions of soybean oil biodiesel in a compression-ignition diesel engine prepared through the phase inversion temperature method were compared with those of neat soybean oil biodiesel and the emulsion prepared by the mechanical homogenization method. The engine torque was set constantly at 98 N·m with varying engine speeds. The experimental results show that the emulsion prepared by the method of phase inversion temperature had higher O2 and NOx emissions, a higher excess air ratio, a higher exhaust gas temperature, and a higher brake fuel conversion efficiency than the emulsion prepared by the mechanical homogenization method, which had lower CO and CO2 emissions, a lower equivalence ratio, and lower brake-specific fuel consumption. While the neat soybean oil biodiesel was found to have the lowest fuel consumption rate, brake-specific fuel consumption, and CO and CO2 emissions, it had the highest exhaust gas temperature and brake fuel conversion efficiency, NOx and O2 emissions, and excess air ratio among those three fuels. Therefore, the phase inversion temperature method is considered promising for preparing fuel emulsions as an alternative to petro-derived diesel for compression-ignition engines.

The effects of emulsification variables, such as surfactant type and heating/cooling emulsion processes, on the emulsification characteristics of silicone oil’s emulsions prepared by the phase inversion temperature method were investigated in this study. The water-in-oil (W/O) emulsions have been widely applied to enhance burning efficiency and reduce both pollutant emissions and fuel consumption. The silicone oil was emulsified with de-ionized water with the assistance of nonionic surfactants to form oil-in-water (O/W) emulsions. The hydrophilic–lipophilic balance (HLB) value of the Span 80 and Tween 20 surfactant mixture was set equal to 10 based on their weight proportions and the respective HLB values of the two surfactants. The experimental results show that the emulsions with the Span 80/Tween 20 surfactant mixture appeared to have a higher phase inversion temperature and a larger electrical conductance. On the other hand, it has a lower emulsification stability and a narrower range of phase inversion temperature than the emulsions prepared with a Brij 30 surfactant (polyoxyethylene (4) lauryl ether). The increase in surfactant concentration from 1 wt.% to 10 wt.% decreased the electrical conductance and phase inversion temperature while increasing the suspensibility and absorbance value for the emulsions prepared with either Span 80/Tween 20 mixture or Brij 30.