COMBUSTION CHARACTERISTICS OF SPRAY FLAMES OF DIESEL AND PALM METHYL ESTER AT LEAN INLET CONDITIONS

Palm Methyl Ester (PME) is an attractive alternate fuel to petroleum diesel because it can be produced from a renewable source, is close to being carbon-neutral in the environment, and has many properties similar to those of petroleum fuels. Although a few engine studies have been completed using PME, basic studies on the combustion of PME sprays are limited. Hence, the objective of this investigation was to study the combustion characteristics of spray flames of PME and diesel at three equivalence ratios: 0.4, 0.6 and 0.8. The liquid fuel was atomized and combusted with air in a heated environment; the coflow air temperature was maintained at 65% of the midpoint of the boiling point range of the fuels. The equivalence ratio was changed by altering the fuel flow rate, while maintaining the atomizing and coflow air flow rates constant, thus maintaining the gas velocity field invariant. The PME flames were shorter and less luminous than the diesel flames and had significant near-burner homogeneous-gas-phase reaction zones. The global CO emission index of the PME flames was higher than that of diesel flames at equivalence ratios of 0.4 and 0.6. The NO emission index of the PME flames was almost twice that of the diesel flames. The in-flame concentration profiles highlighted the effects of the significant fuel-bound oxygen content in PME.