Sooting behavior of ethanol droplet combustion at elevated pressures under microgravity conditions

Liquid ethanol is widely used in practical fuels as a means to extend petroleum-derived resources or as a fuel additive to reduce emissions of carbon monoxide from spark ignition engines. Recent research has also suggested that ethanol and other oxygenates could be added to diesel fuel to reduce particulate emissions. In this cursory study, the combustion of small ethanol droplets in microgravity environments was observed to investigate diffusion flame characteristics at higher ambient pressures and at various oxygen indices, all with nitrogen as the diluent species. At the NASA Glenn Research Center 2.2-second drop tower free ethanol droplets were ignited in the Droplet Combustion Experiment (DCE) apparatus, and backlit and flame view data were collected to evaluate flame position and burning rate. Profuse sooting was noted above 3 atm ambient pressure. In experiments performed at the Japan Microgravity Center 10-second (JAMIC) drop shaft with Sooting Effects in Droplet Combustion (SEDC) apparatus, the first data that displayed a spherical soot shell for ethanol droplet combustion was obtained. Because of the strong sensitivity of soot formation to small changes in an easily accessible range of pressures, ethanol appears to be a simple liquid fuel suitable for fundamental studies of soot formation effects on spherical diffusion flames. The results impact discussions regarding the mechanism of particulate reduction by ethanol addition to fuels in high-pressure practical combustors