- Author
-
Linteris, G. T.
|
Rumminger, M. D.
|
Babushok, V. I.
- Title
- Catalytic Inhibition of Laminar Flames by Transition Metal Compounds.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
Cleaire Advanced Emission Controls, LLC, San Leandro, CA
- Journal
-
Progress in Energy and Combustion Science,
Vol. 34,
No. 3,
288-329,
June 2008
- Sponsor
- Department of Defense, Washington, DC
- Keywords
-
laminar flames
|
metal compounds
|
flame extinguishment
|
catalytic inhibition
|
halon alternatives
|
fire suppression
|
nanoparticles
|
fuel additives
|
soot formation
|
premixed flames
|
flame retardants
|
ignition
|
nozzles
|
metals
|
vapor phases
|
iron
|
tin
|
manganese
|
kinetics
|
premixed flames
|
counterflow flames
|
diffusion flames
|
chemical inhibition
|
condensation
- Identifiers
- eeeengine knock; flame screening tests; radical recombination in post-flame region of premixed flames; catalytic efficiency of different metals in promoting radical recombination; radical recombination in rocket nozzles; other relevant investigations of metals compounds in flame systems; flame studies with iron-containing compounds; summary of demonstrated flame inhibition potential by transition metal compounds Based on the results presented above, we can assemble a list of transition metals which demonstrated; metals which have shown flame inhibiting properties; gas-phase mechanisms of flame inhibition by metallic compounds; inhibitor concentration required for 30% and 50% decreases of burning velocity for different models and experimental data; calculated maximum and equilibrium radical volume fractions in methane-air flame; effects of particle formation; potential for particle formation in flames inhibited by other metal compounds; current state of knowledge of inhibition potential of metals, and potential loss of effectiveness due to condensation
- Abstract
- Some of the most effective flame inhibitors ever found are metallic compounds. Their effectiveness, however, drops off rapidly with an increase of agent concentration, and varies widely with flame type. Iron pentacarbonyl, for example, can be up to two orders of magnitude more efficient than CF3Br for reducing the burning velocity of premixed laminar flames when added at low volume fraction; nevertheless, it is nearly ineffective for extinction of co-flow diffusion flames. This article outlines previous research into flame inhibition by metal-containing compounds, and for more recent work, focuses on experimental and modeling studies of inhibited premixed, counterflow diffusion, and co-flow diffusion flames by the present authors. The strong flame inhibition by metal compounds when added at low volume fraction is found to occur through the gas-phase catalytic cycles leading to a highly effective radical recombination in the reaction zone. While the reactions of these cycles proceed in some cases at close to collisional rates, the agent effectiveness requires that the inhibiting species and the radicals in the flame overlap, and this can sometimes be limited by gas-phase transport rates. The metal species often lose their effectiveness above a certain volume fraction due to condensation processes. The influence of particle formation on inhibitor effectiveness depends upon the metal species concentration, particle size, residence time for particle formation, local flame temperature, and the drag and thermophoretic forces in the flame.