Laboratory for Advanced Combustion & Energy Research
LACER Washington University St. Louis
A laminar inverse ethylene/air flame
In the inverse configuration the oxidizer stream exits from the innermost tube and the fuel exits from an outer concentric tube.
Particulate matter (PM) emissions from large scale combustion processes have both environmental and biological effects. For example, soot is the cause of reduced visibility in many U.S. cities and is responsible for thousands of deaths annually from inhalation. In the past, removal of PM has been accomplished by flowing exhaust gases through filters or electrostatic precipitators; however, the current objective for zero emission systems has sparked efforts to eliminate particulates in situ by redesigning the combustion process.
The flame structure, i.e. the relationship between the local temperature and local gas composition, in a non-premixed flame can be influenced by changing the concentrations of the fuel and oxidizer streams at the inlet boundary. Typically, these concentrations are controlled by the addition or removal of an inert species such as nitrogen, argon, or carbon dioxide to the individual streams. The level of inert dilution in the fuel and oxidizer streams can be quantified by the stoichiometric mixture fraction Zst .
In the relationship above Y represents the mass fraction of the fuel or oxidizer species at the boundary, W is the molecular weight and v is the stoichiometric coefficient. For a neat fuel air flame Zst = 0.064. If the nitrogen contained in the oxidizer stream is removed and used to dilute the fuel stream such that adiabatic flame temperature remains constant Zst increases and a dramatic effect on soot formation is observed.
diffusion flames @ 2370 K
a) ethylene/air
b) diluted ethylene/oxygen
The flame that appears completely blue has the same adiabatic flame temperature but has been designed to produce no soot.
(a)
(b)