Industrial burners that use either fuel oil or natural gas are conside
red as candidates for implementing strategies for control of NOx. Two
burners, at 20 and 800 kW burning fuel oil are installed in a tunnel f
urnace and subjected to active control by way of introducing pulses in
to the air supply. Using optical diagnostics to identify the CH radica
l, the imaging reveals the evolution of the vortical structures within
flames: a non-premixed diffusion flame appearing in the braids of the
vortex and a premixed core region. Prompt NOx mechanisms are explored
, noting that thermal NOx in this case is not the predominant contribu
tor in the fuel burner. III the case of natural gas burners, thermal N
Ox control is achieved passively. The burners achieve significant redu
ctions in NOx by radically altering the fuel-air jet distribution from
the normal air-surrounding Fuel ports approach: the air and fuel jets
are arranged on a base circle, each low momentum fuel port alternatin
g with high momentum air port and each type pointing away from the bur
ner axis at a different, but constant, angle. The NOx reduction mechan
ism is speculated to be due to flue gas recirculation with concomitant
reduction in flame temperature. The burner has been tested in both si
ngle and multiple modes in a unique multi-burner furnace. Results obta
ined using both active and passive control and manipulation indicate t
hat significant enhancement of combustion can be achieved by applying
modern tools and new ideas. (C) 1998 Elsevier Science Inc. All rights
reserved.