Oxygen combustion has a high energy efficiency because the unnecessary heating of nitrogen in air is eliminated: However, the high costs of oxygen and retrofitting limits the widespread application of oxygen combustion for existing conventional air/fuel combustion systems. This study modifies the conventional air/fuel combustion system to explore the influence of oxygen. concentration on combustion system performance when the oxygen concentration is limited between 21% O-2 and 30% O-2. Oxygen is only injected into atomised air in this study. The experimental results indicate that the increase of the oxygen concentration leads to less fuel consumption, because of the existence of less inert gas (N-2). Compared with 21% 02, fuel consumption is reduced 33.3%, for 30% O-2 when the furnace temperature is maintained at 1200 +/- 10 degrees C. Moreover, the NOx concentrations were increased 1.51 times but the total NOx emissions were decreased by 23% when the oxygen concentration increased from 21% to 30%. Meanwhile, the radiation heat flux per energy input was increased, along with the oxygen concentration.