Abstract A study of the propagation of lean premixed ethyleneair flames in a divided-chamber combustion vessel was conducted to compare experimental observations with a numerical simulation based on a flame sheet-vortex dynamics model in axisymmetric coordinates. The temporal and spatial development of flames exiting a small cylindrical prechamber were observed in the experiments using laser-schlieren videography. The equivalence ratio of the ethyleneair mixture was varied from 0.5 to 0.65. The corresponding flame speeds S u for this range of equivalence ratios were measured in a complementary study and were shown to increase from 10 to 24 cm/s, respectively, while the ratio of unburned to burned gas densities varied by less than 20 %. The associated increase in gas velocity with equivalence ratio was used to change the estimated Reynolds number in the experiment from 1870 to 8090. Good agreement between the predicted and measured prechamber flame propagation rates was obtained. For the lowest Reynolds number experiment the calculated spatial and temporal development of the flame in the main combustion chamber agreed with the experimental observations. For all Reynolds numbers the numerical results scale with the characteristic time scale obtained by normalizing with the burned gas flame speed S u. In the experimental results this normalized time scale is not an accurate measure of similar flame development. As the Reynolds number was increased in the experiment the flame development was more rapid. At the highest Reynolds number conditions, a combination of the simplifying assumptions in the flame sheet-vortex dynamics model results in a slower development of the flame-vortex interaction without the experimentally observed shear layer instabilities.