Detection of flame radicals using light-emitting diodes

Lasers are common tools in the field of combustion diagnostics. In some respects, however, they have disadvantages. Therefore, there is a need for new light sources delivering radiation in the required wavelength regions with high stability and reliability at low cost. Light-emitting diodes (LED) in the near- and mid-infrared spectral region have proven their potential for spectroscopic applications in the past. In the present work we demonstrate the feasibility of using ultraviolet LEDs for flame diagnostics. For this purpose, OH and CH radicals are detected in premixed methane/air flames. The LED emission is found to be stable after thermal equilibrium is reached. This was the case after a warming-up period in the order of minutes. The spectral characteristics were stable during a 24-h test.