Influence of Storage Conditions on Fuel Functionality of Palm Oil Methyl Ester

The stability of biodiesel generally depends on the nature of the fatty acid composition of the parent oil. Unsaturated compounds are significantly more reactive to oxidation than saturated compounds. The palm olein vegetable oil, derived from crude palm oil, contains higher unsaturated compounds in comparison to other forms of palm oils. An experiment was intended to investigate the impact of storage degradation of palm oil methyl ester in terms of fuel chemical properties, engine performance and exhaust emission. The degradation study was carried out by keeping methyl ester of palm oil, derived from raw palm olein oil through base catalytic trans-esterification, in two different environment conditions (one in a transparent closed-lid container exposed to light and another in a container exposed to air and light) at three different temperature (5°C, 25°C and 38°C) over 10 months. It was observed that degradation of biodiesels through oxidative reaction led to a series of changes in its properties, with severely increase in peroxide value, acid value and decrease in heating value at higher temperature storage irrespective of storage conditions. The fuel sample with the highest degradation rate, after 10 months of storage, was considered for the evaluation of engine performance and emission by making blends with petroleum diesel at a different proportion. And the comparisons were made with fresh biodiesel blends and diesel fuel. The engine performance of the biodiesels (fresh and oxidized) and their blends were similar to that of diesel fuel with a non-significant difference in thermal efficiency, but higher fuel consumption. The emission quality (CO and smoke density) of oxidized biodiesel was significantly better than that of fresh biodiesel and diesel fuel. But, the NOx emission was comparatively higher than diesel fuel for both the biodiesel. The effect of fuel oxidation on the NOx emissions was also found to be 3% to 4% higher.