Cool diffusion flames in a stably stratified stagnation flow

Cool diffusion flames have been a growing research topic since their discovery in 2012. Until now their study has been hindered by the high cost of the experimental systems used to observe them. A method is presented here for observing cool diffusion flames inexpensively using a pool of liquid n-heptane and parallel plates heated so as to produce a stably stratified stagnation flow. The flames were imaged with a color camera and an intensified camera. Measurements included gas phase temperatures, fuel evaporation rates, and formaldehyde yields. These are the first observations of cool flames burning near the surfaces of fuel pools. The measured peak temperatures were between 705 and 760 K and were 70 K above the temperature of the surrounding air. Autoignition first occurred at 550 K.