Experimental investigation on the effect of n-pentanol blending on spray, ignition and combustion characteristics of waste cooking oil biodiesel

Due to their excellent physicochemical properties, biodiesel and n-pentanol are regarded as two promising alternative biofuels for automobile. However, the fundamental data of spray and combustion characteristics of n-pentanol/biodiesel blends are still scarce. The objective of this work is to investigate the effects of n-pentanol addition to waste cooking oil (WCO) biodiesel in different ratios (0%, 20%, and 40% in volume) on spray, ignition and combustion characteristics in a constant volume combustion bomb (CVCB). Ignition and combustion tests were performed at five ambient temperatures (800, 900, 1000, 1100 and 1200 K) with three oxygen concentration (10%, 15% and 21%), and spray tests were conducted at the same temperature ranges but with no oxygen involved to prevent combustion happening. The result shows liquid length decreases with increase of ambient temperature, and the falling slope increases significantly with the blended n-pentanol concentration. The liquid length of B60P40 is about 6% longer than that of B100 at 800 K condition, while it becomes about 10% shorter than B100 when ambient temperature rises to 1200 K. Although the cetane number of n-pentanol is much less than biodiesel, an increase of n-pentanol ratio has a promoting effect on the ignition event under most conditions. Under these conditions, addition of 40% n-pentanol has cut the ignition delay of biodiesel, on average, by 30.2%. The natural flame luminosity is found to be reduced significantly with an increasing n-pentanol ratio, meaning that addition of n-pentanol could reduce the soot level under all conditions. For example, the time integrated natural luminosity (TINL) of B60P40 is only 41.2% of that of B100 under 1000 K temperature conditions. The result also suggests that, for multi-component fuels, flame lift-off length (FL) is the most reliable factor that influence the soot concentration level under spray combustion processes, rather than ignition delay or soot formation time. Overall, blending n-pentanol into biodiesel has a great soot oxidation potential and could maintain suitable ignition phase at the same time.