Wall Chemical Effects on the Ignition and Distribution of Premixed Cool Flames

Abstract

Cool flames, which are governed by the low-temperature chemistry, are responsible for multistage ignitions and knocking phenomenon of internal combustion (IC) engines. Recently, it has been shown that there exists more significant wall chemical effects on cool flames than on hot flames. Therefore, elucidation of such phenomenon is extremely important for further improvements in the thermal efficiency and reduction in pollutant emissions of IC engines. In this paper, we introduce recent progresses in the cool flame research focused on wall chemical effects. The cool flame was ignited and stabilized in the vicinity of the wall by impinging a mixture of Dimethyl Ether (DME) and oxygen on a heated wall. The wall was coated with a thin film of specific materials, so that the wall chemical boundary condition can be modified while keeping the thermal boundary condition identical. Distributions of the HCHO, CO, and gas temperature on different wall materials were measured through Planar Laser-Induced Fluorescence (PLIF), Gas Chromatography (GC), and thermocouple scanning, respectively. Furthermore, the cool flame ignition process was observed through HCHO-PLIF with ramping up the wall temperature. The results show that the wall chemical effect can significantly modify not only cool flame structures but also ignition profiles.