Assessing water affinity properties of biodiesel, diesel fuel, and blends by measuring water saturation and water absorption

Abstract

Biodiesel has many advantages and technical aspects of being blended in any proportion with diesel fuel to support diversification energy policy. However, biodiesel absorbs more moisture than diesel fuel since methyl esters are hygroscopic compounds, and there is a limited amount of published information about water affinity properties. Water content can affect the fuel’s characteristics, reducing fuel quality if it accumulates into free, emulsion, or soluble water. This paper reports the water affinity properties of biodiesel, diesel fuel, and their blends through water saturation. It indicates a maximum water content value that the fuel can retain at a specific temperature and moisture absorption by controlled temperature and humidity. The results show that the pristine biodiesel has a water saturation range of (1366 to 1771) mg.kg-1 in the temperature range of (288.15 to 313.15) K. Therefore, diesel fuel has a maximum water saturation of 255 mg.kg-1 at a temperature of 313.15 K. The water saturation curve shows that biodiesel-diesel blends have a water saturation with a slope range of (12.20 to 15.11) mg.kg-1 water per 1%-vol biodiesel in diesel fuel blend in the temperature range (288.15 to 303.15) K. During eight days of observation on eight commercial biodiesels, the moisture absorption value was 1094 mg.kg-1 at a temperature of 298.15 K with a relative humidity of 90 %. It was also found that high moisture quickly affects the water content point in the storage period.