Flame Structure of Turbulent Quasi-Premixed Flames Produced by Rapid Mixing

Abstract

Lean premixed combustion is one of the attractive ways to reduce nitric oxide emission as well as greenhouse gases from combustion devices, and the industrial demand on lean premixed combustion seems expanding to the field of regenerative combustion or heat recovery combustion where premixed combustion has not been attempted due to the fear of auto-ignition or flash-back. For the purpose, we have developed a unique mixing nozzle to create a quasi-premixture of fuel and air by rapid mixing, and applied this rapid mixing nozzle to an opposed jet type and a Bunsen type burners to observe combustion characteristics of the quasi-premixture. As a result, the quasi-premixed flame showed the same flame structure and combustion characteristics as the perfectly premixed flame even though the mixing time was extremely short as a few milliseconds. Therefore, the rapid mixing nozzle in this paper can be used to imitate highly preheated premixed flames, which may be impossible in a usual way, that is, the quasi-premixture of fuel and highly preheated air can be a substitution for highly preheated premixed combustion as far as the mixing time is shorter than the ignition delay of the fuel.