Submillimeter-scale combustion

Until recently, the concept of combustion within a confined space defined by a microburner was thought to be impossible. Extensive literature dating back to Davy's seminal work in 1817 has discussed how thermal and chemical quenching set a minimum size below which no flame can exist. In this report, though, it is shown that microcombustion is possible if the wall composition and structure are carefully controlled. It is suggested that there are three keys to obtaining microcombustion: (1) the walls of the microburner need to be fabricated from materials that do not quench radicals so that the gas-phase combustion reactions can occur unimpeded; (2) the device needs to be insulated well enough that the net heat generation is sufficient to keep the reacting mixture hot enough to sustain significant combustion; and (3) the flow pattern in the burner needs to be such that the temperature is low enough not to melt the walls, yet the flame fills the entire space. Using this design strategy, devices burning methane-air and propane-air mixtures in a 750-mum slot were designed and optimized to achieve high conversion. These results show that microcombustion is possible with consideration of microscale engineering challenges and fitting combustor design. (C) 2004 American Institute of Chemical Engineers.