Flame structure, which includes the radiation power and temperature profiles, soot concentration profiles, and pollutants emissions (NO, NO x , CO, and CO 2 ) of propane and propylene gas diffusion flames with and without ahydrogen pilot flame in crossflow is presented. All of the profiles were obtained at a distance of 50% of the total flame length from the burner. The purpose was to investigate the effects of a pilot flame on the structure of flames in crossflow. The fuel was injected vertically into a horizontal airstream through a burner. The flames at nonpiloted conditions were partially or completely detached form the burner. For the piloted flames, hydrogen was added to completely attach the flames to the burner. Experiments were conducted at two different crossflow speeds, 2.68 m/s and 3.58 m/s. The piloted flames, in general, had lower emissions of NO, NO x , and CO 2 . The temperature profiles in all flames showed a peak near the flame center. The pilot flame did not significantly influence the flame temperature profiles at the crossflow speed of 2.68 m/s. However, at 3.58 m/s, the overall flame temperature for both fuels was lower in the piloted flames. The nonpiloted detached flame showed higher concentrations of NO x , CO 2 , and O 2 , but had a lower soot concentration. All of the piloted flames appeared to be longer and narrower compared to detached flames. Piloted flames also produced higher radiation, produced more smoke, and appeared more luminous than detached flames.