Identification of Cool and Blue Flames in Compression Ignition

Low-temperature ignition of hydrocarbon fuels is characterized by weak, pale blue light emission. It has been difficult to distinguish the low-temperature flame; cool flames, the first onset of the lowtemperature flames, and blue flame, the second, from the other and final hot flame. The present paper shows how to identify the compression-ignition flames spectroscopically. Cool, blue, or hot flame is identified by the HCO band emission, blue and red colorations. 329.8 nm wave lebngh emission in the HCO Vaidya band is almost the only tool for identifying the blue flame. Visible red spectrum near 600 nm is most effective to perceive the hot-flame appearance. Autoignited hot flames turn yellow or red. The H2O emission at 632.8 nm and soot formation would be plausible cause of red coloration. Carbon formation starts in compression-ignition low-temperature flame just after the cool flame has degenerated.