An antiknock agent is a gasoline additive used to reduce engine knocking and increase the fuel's octane rating by raising the temperature and pressure at which auto-ignition occurs. The mixture known as gasoline or petrol, when used in high compression internal combustion engines, has a tendency to engine knocking (also called "pinging" or "pinking") and/or to ignite early before the correctly timed spark occurs ( pre-ignition, refer to engine knocking).
Notable early antiknock agents, especially tetraethyllead, added to gasoline included large amounts of Lead poisoning. The chemical was responsible for global negative impacts on health, and the phase out of leaded gasoline from the 1970s onward was reported by the United Nations Environmental Programme to be responsible for "$2.4 trillion in annual benefits, 1.2 million fewer premature deaths, higher overall intelligence and 58 million fewer crimes." Some other chemicals used as gasoline additives are thought to be less toxic.
Similar bans in other countries have resulted in sharply decreasing levels of lead in people's . findarticles.com
A side effect of the lead additives was protection of the poppet valve seats from erosion. Many ' engines have needed modification to use lead-free fuels since leaded fuels became unavailable. However, "lead substitute" products are also produced and can sometimes be found at auto parts storesThis is an example..
Gasoline, as delivered at the pump, also contains additives to reduce internal engine carbon buildups, improve combustion, and to allow easier starting in cold climates.
In some parts of South America, Asia, and the Middle East, leaded gasoline is still in use. Leaded gasoline was phased out in sub-Saharan Africa, starting 1 January 2006. A growing number of countries have drawn up plans to ban leaded gasoline in the near future.
Some experts speculate that leaded petrol was behind a global crime wave in the late 1980s and early 1990s.
To avoid deposits of lead inside the engine, lead scavengers are added to the gasoline together with tetraethyllead. The most common ones are:
Ethanol has several issues as an antiknock additive. It is hydrophilic, pulling water vapor out of moist air, and it also increases the level of free oxygen in the fuel significantly. Both of these cause significant degradation to traditionally constructed engines, posing both residue and corrosion issues in increasing proportion with increasing fractions of ethanol. Whereas age-degraded gasoline may simply polymerize, evaporate, and thus lose its flammability, age-degraded gasoline-ethanol blends can cause severe damage if allowed to sit in an engine. Automotive engines addressed this with the mandated shift over to ethanol-tolerant metals and seals, and with the use of smart electronic fuel injection, which has some flexibility to adjust combustion properties and timing. Automotive engines did not see major issues because of these factors, and because automobiles in active use typically cycle through their gas tank in a matter of weeks. In small carbureted engines, like generators and lawnmowers, ethanol damage became the dominant mode of failure.
A large Canadian study from 2002 (funded by automakers, who are against its use) concluded that MMT impairs the effectiveness of automobile emission controls and increases pollution from motor vehicles. However, a later study by the Canadian government found that "no Notice of Defect was found to be potentially caused by MMT."General Review of Emission-Related Notices of Defect and Recalls (Canada and the U.S.), Environment Canada (January 31, 2005)
Many studies have been undertaken over time that confirmed the use of MMT is compatible with vehicles and safe for human health and the environment. In particular, a 2013 risk assessment on MMT was undertaken by ARCADIS Consulting, following a methodology developed by the European Commission. This risk assessment was verified by an independent panel and found by the EU Commission to be compliant with their methodology. It concluded that "when MMT is used as a fuel additive in petrol, no significant human health or environmental concerns related to exposure to either MMT or its transformation combustion products (manganese phosphate, manganese sulphate and manganese tetroxide) were identified even in locations where MMT is approved for use at levels up to 18 mg Mn/L."Risk Assessment of Methylcyclopentadienyl Manganese Tricarbonyl (mmt) when used as a Fuel Additive, Arcadis (November 2013).
As stated by Health Canada in their risk assessment on the widespread use of MMT in Canadian gasoline, "all analyses indicate that the combustion products of MMT in gasoline do not represent an added health risk to the Canadian population"Risk Assessment for the Combustion Products of Methylcyclopentadienyl Manganese Tricarbonyl (MMT) in Gasoline," Health Canada (December 6, 1994)
MMT is manufactured by reduction of bis(methylcyclopentadienyl) manganese using triethylaluminium. The reduction is conducted under an atmosphere of carbon monoxide. MMT is a so-called half-sandwich compound, or more specifically a piano-stool complex (since the three CO ligands are like the legs of a piano stool). The manganese atom in MMT is coordinated with three carbonyl groups as well as to the methylcyclopentadienyl ring. These hydrophobic organic ligands make MMT highly lipophilic, which may increase bioaccumulation. While the structure of MMT suggests lipophilicity and potential to bioaccumulate, comparison of bioconcentration factors (BCF) reported for plant and animal species in comparison to regulatory-based cutoffs (i.e., US EPA and EU REACH) indicates a low bioaccumulative potential of MMT. Figures 2 and 3 of the study (pages 182 & 184) shows the BCF plotted against time and illustrates the potential BCF of MMT. From these figures, the upper curve (A) demonstrates the 9-day MMT BCF plateauing at approximately 400 in plants and 200 in fish, with both values well below the Bioaccumulative / Very Bioaccumulative (B/vB) thresholds of US EPA, EU REACH and Environment & Climate Change Canada.
A variety of related complexes are known, including ferrocene, which is also under consideration as an additive to gasoline.
Ferrocene and its numerous derivatives have no large-scale applications, but have many niche uses that exploit their unusual structure (ligand scaffolds, pharmaceutical candidates), robustness (anti-knock formulations, precursors to materials), and redox reactions (reagents and redox standards). Use for global cooling has been proposed.
Ferrocene and its derivatives are antiknock agents added to the petrol used in motor vehicles, and are safer than the now-banned tetraethyllead. Application of fuel additives Petrol additive solutions containing ferrocene can be added to unleaded petrol to enable its use in vintage cars designed to run on leaded petrol. The iron-containing deposits formed from ferrocene can form a conductive coating on the spark plug surfaces.
This compound is a common precursor to diverse iron compounds, including many that are useful in organic synthesis.Samson, S.; Stephenson, G. R. "Pentacarbonyliron" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. . Fe(CO)5 is prepared by the reaction of fine iron particles with carbon monoxide. Fe(CO)5 is inexpensively purchased.
Iron pentacarbonyl is one of the homoleptic ; i.e. metal complexes bonded only to carbon monoxide ligands. Other examples include octahedral Cr(CO)6 and tetrahedral nickel carbonyl.
Most metal carbonyls have 18 valence electrons, and Fe(CO)5 fits this pattern with 8 valence electrons on Fe and five pairs of electrons provided by the CO ligands. Reflecting its symmetrical structure and charge neutrality, Fe(CO)5 is vapour pressure; it is one of the most frequently encountered liquid metal complexes.
Fe(CO)5 adopts a trigonal bipyramidal structure with the Fe atom surrounded by five CO : three in equatorial bond positions and two axially bound. The Fe-C-O linkages are each linear.
Fe(CO)5 is the archetypal fluxional molecule due to the rapid interchange of the axial and equatorial CO groups via the Berry mechanism on the NMR spectroscopy. Consequently, the13C NMR spectrum exhibits only one signal due to the rapid interchange between nonequivalent CO sites.
In Europe, iron pentacarbonyl was once used as an anti-knock agent in petrol in place of tetraethyllead. Two more modern alternative fuel additives are ferrocene and methylcyclopentadienyl manganese tricarbonyl. Fe(CO)5 is used in the production of "carbonyl iron", a finely divided form of iron used in of high-frequency coils for electronics, and for manufacture of the active ingredients of some radar absorbent materials (e.g. iron ball paint). It is famous as a chemical precursor for the synthesis of various iron-based .
Iron pentacarbonyl has been found to be a strong flame speed inhibitor in oxygen based flames.
Toluene and benzene were used as octane rating boosters for aviation fuel by the Royal Air Force in the World War Two. Tetraethyl lead was manufactured in the USA and was on short supply, so Rolls-Royce engineers built the Rolls-Royce Merlin to work with fuel affed with benzene and toluene. This was called as "aromatic fuel". The Allison V-1710 engine would not run with the RAF fuels as it required tetraethyl lead for lubrication of its valvetrain, but the Packard-built Merlins would. This is why the Merlin-engine P-51 Mustangs had a text "Suitable for Aromatics" on their USAAF type description.
Toluene can be used as an octane rating in gasoline fuels used in internal combustion engines. Toluene at 86% by volume fueled all the turbo Formula 1 teams in the 1980s, first pioneered by the Honda team. The remaining 14% was a "filler" of n-heptane, to reduce the octane to meet Formula 1 fuel restrictions. Toluene at 100% can be used as a fuel for both two-stroke and four-stroke engines; however, due to the density of the fuel and other factors, the fuel does not vaporize easily unless preheated to 70 degrees Celsius (Honda accomplished this in their Formula 1 cars by routing the fuel lines through the exhaust system to heat the fuel). Toluene also poses similar problems as alcohol fuels, as it eats through standard rubber fuel lines and has no lubricating properties as standard gasoline does, which can break down fuel pumps and cause upper cylinder bore wear.
Toluene has also been used as a coolant for its good heat transfer capabilities in sodium cold traps used in nuclear reactor system loops.
Properties of xylenes and ethylbenzene are nearly identical to toluene, with the latter advertised by a refinery as "component of high performance fuels".
Isooctane is produced on a massive scale in the petroleum industry, usually as a mixture with related hydrocarbons. The alkylation process alkylates isobutane with isobutylene using a strong acid catalyst. In the NExOCTANE process, NExOCTANE - Neste Jacobs isobutylene is dimerized into isooctene and then hydrogenated to isooctane.
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