Ferrocene: A Smokeless Additive
Ferrocene is an iron-based additive discovered in the early 1950's. It is an unusually stable orange crystalline solid with a formula of FeC10H10. The compound is soluble in common organic solvents and stable towards acids and bases. One of the most important applications for ferrocene is its use as an additive for promoting the smokeless combustion of fuels. Comparatively low concentrations of ferrocene have a marked effect upon carbon formation. Further, ferrocene has demonstrated antiknock properties for use in fuels for spark-ignition engines. Ferrocene has been evaluated for its performance in compression-ignition, internal combustion engines by a number of independent sources including Southwest Research Institute and the University of Minnesota. Southwest Research Institute tested ferrocene in the early 1980s. The study was conducted in a gas turbine engine. The additive was tested to determine its affect upon flame radiation (fuel efficiency) and soot formation. The study determined ferrocene had a dramatic effect upon the oxidation and removal of soot, but had no measurable effect upon combustion efficiency. It was also discovered that ferrocene oxidized to form iron oxide. The iron oxide coated the exposed combustion chamber components forming a red rouge or rust. The rouge could act as a polishing agent, and in high concentrations, could create excessive wear to valve stems. The rouge buildup can probably be prevented with the use of a detergent additive. The University of Minnesota study also determined the addition of ferrocene had little impact upon fuel consumption. The study intended to show ferrocene created greater improvements in specific fuel consumption and soot particle reduction over time (as the engine conditioned or was coated with reactive iron). This study also shows ferrocene additized fuel produces soot particles that are lower in mass, but greater in number. Ferrocene is typically added to fuel at 500 to 5000 times the concentration of ferrous picrate, and the iron content of the ferrocene compound is 3 times greater than the iron content of the ferrous picrate compound. Ferrocene is the active ingredient for a number of additive brands. These include additives sold by Econalytic Systems, Parish Chemical, Octel, and Exxon/Nalco. Brand names that I am familiar with include Catane and Ferox.
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