Air Entrainment Studies for a Supersonic Micro-Ejector System

Micro-ejectors offer a unique way of entraining relative large quantities of air without any moving parts, which when mixed with fuel can provide the necessary fuel-air mixture to power a micro-combustion system. Together, the micro-ejector and the micro-combustion systems can make up components of a unique air-breathing propulsion system. Larger scale ejector-based propulsion systems that operate a rocket ejector cycle have been constructed and operated in the past, dating back to the 1960s. Only very recently this same ejector system has been scaled down to the micro-size domain for use in applications other than propulsion, more specifically as a way of entraining and mixing fuel and air for use in micro-combustor applications. The present study involved the use of propane as ejector primary fluid, chosen for its high vapor pressure which allowed us to operate a March 2 nozzle with a throat height of 31 microns under high pressure and thus achieve various degrees of air entrainment based on the area ratio between the primary nozzle and ejector secondary duct. Experimental data showed the performance of the ejector system under the various area ratios studied. The degree of mixing of the primary jet is reviewed, specifically as it pertains to air entrainment performance.