Antiknock agent is a gasoline additive that works to reduce the engine knocking tendency while trying to accelerate the octane rating of the fuel. Mixture of gas and air in a conventional car engine has a problem with igniting too early and when this happens, it creates a knocking noise.
Commonly used antiknock agents are tetraethyl lead, ferrocene, toluene, iron pentacarbonyl, isooctane and methylcyclopentadienyl manganese tricarbonyl. Lead compounds have been used as an antiknock agent for many years. The most commonly used is tetraethyl lead, a transparent and highly toxic dense liquid. It easily dissolves in ethyl, acetone, gasoline and in some other solvents. It boils at around 250°Ð¡.
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Another commonly used lead antiknock agent is the tetramethyl lead. It is a liquid with pungent smell and boils at around 120°Ð¡. Due to the relatively low boiling temperature, this substance spreads more evenly in gasoline fractions. Tetramethyl lead is more stable than tetraethyl lead at around 700°Ð¡. This ensures higher and better efficiency of the tetramethyl lead as compared to tetraethyl lead in high pressure ratio internal combustion engine vehicles.
Commonly found drawback of both the compounds is the high toxicity of the agents, with high impact on the environment and negative influence on the exhaust gas after treatment devices. Hence, for these reasons the use of tetramethyl lead and tetraethyl lead is decreasing and intensive research is carried out for more efficient antiknock agents is in the pipeline.
Some of the antiknock agents which have already been tested and used at various times are cyclopentadienyl manganese tricarbonyl (CMT), methylcyclopentadienyl manganese tricarbonyl (MMT) and dicyclopentadienyl iron. In terms of higher and better efficiency, manganese compounds are analogous and iron compounds are inferior to lead. CMT is a highly volatile crystalline compound of yellow color. It is stable in air and is easily soluble in organic solvents and is completely insoluble in water. MMT is a low viscosity liquid of light amber color with a grassy smell and has a boiling point of 250°Ð¡. Ferrocene is a solid crystalline substance and has a melting temperature of 180°Ð¡. Iron pentacarbonyl is a straw color liquid with boiling temperature of 105°Ð¡ and freezing temperature of -2°Ð¡.
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Ferrocenyl dimethyl carbinol is a crystal powder with melting temperature of 70°Ð¡. Organometallic agents create sedimentation of metals on the walls of combustion chamber. Therefore, organometallic anti-knock additives are typically used in combination with materials which convert churly metal oxides into volatile compounds. Due to high toxicity of lead type anti-knock agents, significant disadvantages and high cost associated with it, the research for a special material, which does not comprise any toxic substance, is in the pipeline. Such anti-knock agents are organic amines containing, xylidine methylaniline and extralyne.