Pulsating combustion of ethylene in micro-channels with controlled temperature gradient

摘要

Nowadays with the demand for high-efficiency systems, there is a growing development and application of microelectromechanical systems (MEMS devices) which may generate more energy than the modern batteries. In this context, a new experimental device has been developed. It consists of a microtubular reactor with a controlled external temperature profile. The high gas temperature allows the autoignition of the mixture and the flame stabilization in reactors with inner diameter (id) smaller than the ordinary quenching diameter. The temperature profile along the tube is measured continuously using an infrared camera while an EMCCD camera is used to collect the CH* emission from the flame. The present experimental study on C_2H_4/air mixtures reacting in narrow channels has been undertaken to provide detailed information on flame combustion at microscale. Three kinds of flame behaviors were observed: (ⅰ) bright and stable flames under high flow velocity, (ⅱ) flames with repetitive extinction and ignition in the middle flow rates range, and (ⅲ) weak flames at low flow rates. The presence of oscillating transitional regimes was also investigated and a detailed analysis of the unstable regimes (determination of frequencies and characteristic times) was carried out. The effect of the inlet velocity, the equivalence ratio, and the tube id were also investigated. Numerical simulations were also conducted to study the ignition characteristics of unstable flames.