<p>Turbulent nonpremixed combustion is widely used in the gas turbine combustors and in combustors attached to thermal power plant boilers. Improving the performance of these combustors is essential for reducing their CO₂ emissions. Understanding the effects of flame curvature on the local structure of turbulent nonpremixed flames is necessary for improving the accuracy of the laminar flamelet model and determining how the combustor performance can be improved. This study experimentally clarified the effects of the Lewis number of the fuel flow (<i>Le</i>_F) on curved counterflow nonpremixed flames using methane or propane as the fuel and air as the oxidizer. The effects of <i>Le</i>_F were isolated by comparing observations of methane–nitrogen fuel flows, for which <i>Le</i>_F is unaffected by the dilution rate, with observations of propane–nitrogen fuel flows, for which <i>Le</i>_F changes substantially with the dilution rate. Although it was previously believed that flame curvature effects could be neglected in hydrocarbon–nitrogen flames, this study revealed that even with hydrocarbon fuels, flame curvature can induce Lewis number effects when the flame radius is small. The effects of flame curvature on extinction were observed when the ratio of the flame zone thickness to the flame radius was on the order of 10^− 1, which is expected to occur in actual combustors. These results indicate that the effects of flame curvature should be considered when the laminar flamelet model is used to analyze turbulent nonpremixed flames at <i>Le</i>_F ≠ 1.</p>