Oleic Methyl Ester Investigations in an Indirect Injection Diesel Engine; Stage One: Combustion Investigations

The authors investigated the injection and combustion characteristics of a methyl oleate (Methyl 9(Z)-octadecenoate C19H36O2; Mw 296.495), in blends with diesel No. 2 of 20-50% (wt./wt.) in order to evaluate the possibility of using it as an additive to full bodied biodiesel for performance improvement. The FAME test fuel has been injected in an experimental single cylinder separate combustion chamber engine with 77mm bore, with a compression ratio of 23.5:1 at a pressure of 147 bars, that proved capable of atomizing the higher viscosity fuel. The diesel fuel was blended with Methyl Oleate up to 50%, (O50) and the mixtures have shown favorable ignition characteristics, with the ignition delay of about 1.03 ms for petroleum diesel (D100) and slightly decreased for O50 at 2000rpm with about 1% or 0.01 ms. The heat release rate for O50 displayed a similar development compared with the reference diesel fuel, the premixed combustion phase being combined with the diffusion combustion and reaching a maximum of 17.5 J/deg for diesel versus 15.5 J/deg for O50. Maximum combustion pressure was approximately 73 bars for diesel compared with 75 bars for the O50 fuel, while the diesel instantaneous volume-averaged gas temperature reached 2120 K vs. 2150 K for the O50. The total heat flux calculated by Annand model produced values of 2.05MW/m² for diesel fuel compared with 2.07 MW/m² for O50. The convection flux for both petroleum diesel and 50% oleic FAME in diesel blend had values of 1.5 MW/m², and a maximum radiation flux of about 0.66 MW/m² for diesel versus 0.70 MW/m² for oleic FAME. Based on the heat fluxes, the heat loss in convection and radiation for both fuels throughout the cycle showed similar values, negligible during the combustion around TDC and increased losses during the power stroke especially from the convection phenomenon. The engine's mechanical efficiency with oleic FAME showed lower values than that in diesel combustion of 78% vs 86% at 4.78 bmep (100% load) while the engine overall efficiency obtained with any blend including diesel was constant at 32%. The study showed that the new biodiesel produced from methyl oleate proposed by the authors has favorable combustion properties and very similar to those of diesel No 2 showing good prospects as performance improver.