Understanding Concentration and Pressure Changes during Ultrasonication-Enhanced Blending of Petrol-Ethanol Blended Fuel

Understanding Concentration and Pressure Changes during Ultrasonication-enhanced Blending of Petrol-Ethanol Blended Fuel

D. Nkazi, M.O. Daramola*, S Iyuke

School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Wits 2050, Johannesburg, South Africa

*Corresponding author; E-mail: Michael.daramola@wits.ac.za; +27117177536

Abstract

Increasing global energy demand as well as air quality concerns have in recent years led to the search for alternative clean fuels to replace fossil fuels. One such alternative is the blending of petrol (gasoline) with ethanol, which has numerous advantages such ethanol’s ability to act as oxygenate thus reducing the carbon monoxide emissions from the exhaust of internal combustion engines of vehicles. However, the hygroscopic nature of ethanol could cause phase separation of the blended fuel and this is a major concern in obtaining a perfectly homogenized petrol-ethanol fuel. Phase separated petrol-ethanol fuel could cause irreversible damages to internal combustion engines. Formation of perfectly homogenized petrol-ethanol blend is the key to solving the problem [1] and this depends on molecular diffusion and eddy diffusion in the vertical and horizontal direction during the process. Several mixing methods such as impinging-jet micro-mixing, high-pressure homogenization techniques have been proposed as a measure to overcome the problem [2], but ultrasonication is the most promising of all.

Ultrasonic cavitation generated during ultrasonication is an effective type of dynamic agitation due to the growth and implosive collapse of bubbles in liquid as a result of ultrasonic vibration [3]. Also designing a blender to achieve perfectly homogenized petrol-ethanol fuels via ultrasonication-enhanced blending depends on the in-depth understanding of concentration and pressure changes during the mixing. Therefore in this study, investigation was conducted to investigate effect of the position of ultrasonicator’s horn on the concentration and pressure changes during ultrasonication-enhanced blending of petrol-ethanol fuels. Understanding the concentration and pressure changes during the process could pave a way for the design of a blender to achieve a perfectly homogenized petrol-ethanol blend.

Petrol-ethanol mixtures were prepared and the ethanol concentrations in the mixtures were 10%, 20% and 30% v/v. A 2.5 l-beaker of diameter 1400 mm was using the blending. During the blending, the position of ultrasonicator’s horn was fixed in the beaker and the concentration and pressure were measured at distance ranging from 10 mm to 40 mm away from the position of the horn to understand effect on the homogenization of the mixture. The measurement was conducted at both horizontal and vertical distance away from the horn. The pressure during the ultrasonication-enhanced blending was measured with an oscilloscope and the ethanol and petrol concentrations in the samples withdrawn at time intervals during the mixing were analysed with a pre-calibrated high performance liquid chromatography (HPLC).

Concentration gradient, energy gradient (indicated by pressure) and diffusion rates were higher in the vertical direction when compared to the behaviour in the horizontal direction, therefore making the diffusion in the horizontal direction a rate-limiting step. This suggests that the dimensions of the blender that will ensure perfectly homogenized mixture should have larger height-to-diameter ratio. In addition, the results reveal variation of pressure with time due to the changes in the ultrasound energy at different vertical and horizontal distances away from the fixed position of the horn. Between 120 and 360 seconds of the ultrasonication-enhanced blending, the pressure gradient became zero (a plateau), indicating a constant distribution of ultrasound energy, hence perfectly homogenization of the petrol-ethanol blend. The concentration profile with distance during the blending follows a wave function but the concentration of ethanol as a function of time in the mixture remained constant in the both horizontal and vertical distance away from the fixed position of the horn of the ultrasonicator. The observed behaviour could be exploited towards designing a blender with high efficiency for ultrasonication-enhanced blending of petrol-ethanol fuels.

Keywords: Petrol-ethanol blends, Ultrasonication, Cavitation, blender

References

1. Neagu, M., Dinu, F. 2013. Rev. Chim. 64(10), 1160-1165
2. Thoma, G., Swofford, J., Popov, V., Som, M. 1997. Adv. Env. Res. 1, 178-193
3. Jansen et al. 2010.US Patent 7703698