The principal objective of this study was to investigate the effect of fuel oxygen on diesel particulate mass and number emissions using two different oxygenated blends. Jatropha biodiesel (JBD) and diglyme were used as oxygenates. Marine gas oil (MGO) was chosen as base fuel for its diesel like properties and frequent use in maritime transportations. Tests were conducted with a diesel engine at four different loads. Two blends were made maintaining same oxygen content in the blends. The diglyme blend is termed as Ox1, while JBD blend as Ox2. A dilution tunnel was used to collect the particle mass on glass fiber filter, while a scanning mobility particle sizer (SMPS) was used to determine the particle number concentrations. Smoke, carbon monoxide (CO), total unburnt hydrocarbon (THC), and oxides of nitrogen (NOx) were also measured. Experimental results showed that at high loads, for both oxygenated blends (Ox1, Ox2), fine particle number concentrations in the accumulation mode (AM) (peaking at around 73 nm) decreased markedly, compared to the reference MGO. However, the number concentrations, for the Ox2, in the nucleation mode (NM) (peaking at around 15 nm) blend increased significantly at all loads. The total particulate matter (TPM), which was measured by gravimetric method, was lower for both Ox1 and Ox2 compared to MGO. Ox1 and Ox2 also reduced CO, THC and smoke emissions. NOx emissions and exhaust temperatures were identical with the three blends. No significant changes in BSFC, brake thermal efficiency, CO2 and gas pressures were observed among the three fuels. (C) 2011 Elsevier Ltd. All rights reserved.