Development of an advanced MEMS sensor for the simultaneous measurement of ion current and heat flux during flame–wall interactions

Flame–wall interactions have been extensively investigated using optical diagnostic techniques or numerical simulations. However, these techniques tend to be costly and complex, making their application to actual combustor challenging. Therefore, a measurement technique that is easy to use and applicable to practical systems is required. In this study, a thin-film sensor for the simultaneous measurements of ion current and heat flux was developed using the micro-electro-mechanical systems (MEMS) technology. The MEMS sensor comprised two ion current sensors and a resistance temperature detector for evaluating flame behaviors and heat transfer during transient flame–wall interactions. The MEMS sensor was tested under a head-on quenching condition. Consequently, the ion current and heat flux were clearly measured. Compared with the flame images recorded by a high-speed camera, the ion current began to rise when the flame entered the flame-detectable zone (approximately 600 μm in this study) of the sensor and reached its peak when the flame was closest to the sensor. Subsequently, the ion current began to decrease and finally disappeared when the flame was completely quenched. In addition, the ion current and heat flux showed dispersions in their peak values and phases. Through the validation using simple numerical simulations, the reason for the dispersions was presumed to be the local heat release rate. The MEMS sensor detected the local ion current and heat flux. Therefore, it can be used to evaluate the near-wall characteristics of flame behaviors and heat transfer during flame–wall interactions.