This study investigates the combustion characteristics of methyl oleate (oleic FAME) produced from oleic acid. This compound is the main fatty acid component of peanut FAME, a potential renewable biofuel. Methyl oleate has been suggested in our previous work as a reference fuel or surrogate for biodiesel for advanced research (simulation and experiments), or as an enrichment compound to improve biodiesel’s fuel properties. This investigation compares the combustion and emissions characteristics of methyl oleate to peanut FAME and ultra-low sulfur diesel No. 2 (ULSD), in a single-cylinder indirect injection diesel engine intended for use as an auxiliary power unit. The dynamic viscosity of peanut FAME (P100) and Methyl Oleate (O100) was found to be 5.2 cP and 4.3 cP, respectively, at 40°C. It was determined from the ASTM standards for biodiesel that up to 50% FAME could be run in the engine. The lower heating value of P100 and O100 was 36 MJ/kg and 37 MJ/kg respectively, compared to 42.7MJ/kg for ULSD. With a combustion time of 2ms, P50 and O50 have shown similar combustion characteristics with ignition delays of about 1 ms at 2200rpm, 6.2 imep (100% load). The P50, O50, and ULSD heat release, with premixed phase combining with diffusion combustion, produced maximum values of 20.3 J/CAD, 22.7 J/CAD, and 21.9 J/CAD respectively. The heat fluxes were calculated by the Annand model, and a 2% increase in maximum total heat flux was observed for O50 compared with a maximum value of 1.95 MW/m2 for ULSD and P50. The mechanical efficiency of 77% was similar for all tested FAME blends and ULSD. The NOx increased for P20 by 6% compared with ULSD while for P50 it was similar to the ULSD values. The NOx emissions of methyl oleate showed a similar trend with that of ULSD. The soot values were relatively constant for all of the methyl oleate blends and increased by 14% for P50 when comparing both fuels to ULSD.
The findings support the use of methyl oleate as a reference or model fuel for combustion modeling, and as a compound for enriching biodiesel.