Suitability of 2-Ethylhexyl Esters from Plant Oils in Diesel Engines 2012-01-1581
The suitability of caprylic (C8:0), lauric (C12:0), and palmitic (C16:0) acid 2-ethylhexyls derived from palm/coconut oil in diesel engine was evaluated. The pour point of each compound was approximately 40°C lower than that of the corresponding methyl ester due to the ethyl branch in the alcohol. All compounds possessed high oxidation stability, high lubricity, and a high cetane number. Engine bench test results demonstrated that 2-ethylhexyl laurate and palmitate result in shorter ignition delays compared to gas oil. The short ignition delays suppressed initial premix-like combustion. As a result, high brake thermal efficiency with low combustion noise was achieved. Furthermore, both laurate and palmitate produced less NOx emissions and less unburned gaseous emissions. The amount of soot emissions from palmitate was greater than that from gas oil despite the oxygen atoms in the fuel molecules, since air-fuel mixing during ignition delay was insufficient due to the short ignition delay and low volatility of palmitate. Laurate, however, showed the lowest soot emissions among fuel tested including gas oil under various fuel injection timings and engine loads. In addition, the low volatilities of laurate and palmitate led to large emission of soluble organic fractions in particulates, especially under low load conditions, and early injection timing with high engine load.