Mixture temperature-controlled combustion: A revolutionary concept for ultra-low NOX emission

Abstract

Mixture Temperature-Controlled (MTC) combustion is a novel concept, offering 50% reduction in NOX emission compared to V-shaped flames without a known compromise. The essence of this concept is the central cold air injection, which is also the atomizing medium of the plain-jet airblast atomizer presently to delay fuel–air mixture ignition. Hence, the flame root is not anchored to the fuel nozzle or burner lip, facilitating distributed combustion through a homogeneous temperature field, ultimately leading to reduced NOX emission. The flame was stable up to an equivalence ratio of 0.57, which was followed by blowout as the lean flammability limit was approached. Lean combustion also means reduced flame propagation speed, being another key feature to keep the flame lifted and facilitating homogeneous mixture formation. It was observed that distributed combustion was easier to achieve under leaner conditions. Unlike flameless combustion or exhaust gas recirculation techniques, such as MILD combustion, the oxidizer can be ambient air, offering robust realization in practical applications. The distributed flame is characterized by low flame luminosity and noise. Its acoustic spectrum contains geometry-related components principally. Hence, it is hypothesized that this concept also has a lower tendency to thermoacoustic instabilities than V-shaped flames.