Antiknock agent
agent used to increase a fuel's octane rating
An antiknock agent (or knock inhibitor) 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 knock (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 toxic lead. 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.
In Europe, after the earlier ban of lead antiknock additives, an effective ban of other metal-contained additives (MFA, metallic fuel additives) was established in 2004 with a specific limit for methylcyclopentadienyl manganese tricarbonyl (MMT) of 6 mg/l from 2011, lowered to 2 mg/l in 2014. In recent years no use of MMT has been reported in the annual monitoring reports under the European fuel quality directive. By the end of the 1990s, North American refineries also voluntary stopped the use of MMT in petrol, since less contested antiknock additives and compounds, such as MTBE and ethanol, were available.
Research
Early research was led by A. H. Gibson and Harry Ricardo in England and Thomas Midgley Jr. and Thomas Boyd in the United States.
“Antiknock agent” enters the record as agent used to increase a fuel's octane rating. Crown Archives preserves that source wording while asking what Antiknock, agent and used can confirm, complicate or overturn.
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This entry incorporates text from “Antiknock agent” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.