AUTO IGNITION OF N-DODECANE WITH VARYING DROPLET DIAMETERS

A high-pressure combustion apparatus is used to auto ignite a fiber-supported n-dodecane droplet. N-dodecane, a normal alkane, exhibits two stage combustion under specific elevated temperatures and pressures. Generally, as the temperature increases, ignition delays decrease, however, there is a special range of temperatures in which the opposite occurs. This study focuses on some temperatures within this special temperature range. First (cool flame) and total (hot flame) induction times under normal gravity are measured. Droplets diameters of approximately 0.24 mm - 1.38 mm are inserted into an oven at varying temperatures (650 K, 700 K, and 750 K) at 5 atm. The ambient conditions within the oven are ~21% Oxygen and ~79% Nitrogen. As temperature and droplet size increase, it is expected to see longer ignition delay times. High-speed shadowgraph imagery is recorded to assist in determining both the first and total induction times. Cool flame auto ignition is of particular importance. Combustion byproducts are minimized under cool flame auto ignition. Due to their occurrence in low temperatures, implementation in engines will allow automobiles to burn fuel at cooler temperatures. Reduced engine temperatures provide a means to reduce thermal losses (increase in efficiency). Larger droplets tend to have higher first and total inductions times under the parameters set for each experiment. As the droplet size increases, there is a linear relationship with the increased delay time. There does not appear to be a consistent relationship between temperatures and the delay times. More experimentation may reveal a consistent relationship between differing temperatures. The experiments were conducted at NASA Glenn Research Centers Zero Gravity Facility (ZGF) in Cleveland, Ohio.