The present study aims at investigating the characteristics of oxy-combustion of heavy oil liquid fuel in a down-fired model furnace. Nonpremixed probability density function (PDF) mixture model was used to simulate the combustion characteristics and turbulence chemistry. The validation of the present model was performed against the experimental data and is found to be in good agreement. The results depict that the oxy-combustion of liquid fuels results in lower soot. It is observed that the soot formation is reduced when N2 in air-combustion is replaced by O2 in oxy-combustion. However, it increases as the amount of oxygen in oxy-combustion increases. Replacing nitrogen in the air-combustion by carbon dioxide in oxyfuel combustion tends to reduce the temperature levels in the upstream sections of the combustion chamber.