The influence of the combustion air temperature, air to fuel ratio and the burner geometry on the emission of nitric oxide, carbon monoxide and soot from the combustion chamber was studied during liquid fuel combustion. Experiments with 50-kW burners showed that the geometry of the burner nozzles has a strong influence on the emission of pollutants and that it is possible to keep the nitric oxide emission below the limit (220 ppm) despite preheating of the combustion air to 300 degreesC. It was also demonstrated that a reasonable accuracy in NO and CO modelling can be obtained if the crucial parameters of the model are chosen on the basis of at least one experiment.