Knock gasoline

An objection to this theory is that it has been based on data from the saturated vapors of the fuels and not from dilute air-vapor mixtures. The existence of liquid drops in the dilute fuel mixture drawn through the carburetor, hot intake manifold, and mixed with the hot residual gases in the hot cylinder is doubtful. Also, the fact that such extremely volatile fuels as ethyl ether knock strongly cannot be explained. The fact that some of the most volatile gasolines knock more readily than heavier grades has been attributed to the presence of impurities in the latter which act in an antiknock capacity. 

Most of the ethylene dichloride produced is utilized for the manufacture of vinyl chloride, which may be obtained from it by pyrolysis or the action of caustic soda. Large quantities are also used in anti-knock additives for gasoline. As a solvent It has been displaced by trichloroethylene and tetrachloroelhyJene. U.S. production 1978 4-75 megatonnes. 

Product characterization aims at defining their end-use properties by means of conventional standard measurements related as well as possible — and in any case, being the object of a large consensus— to end-use properties. We cite for example that octane numbers are supposed to represent the resistance of gasoline to knocking in ignition engines. 

Octane rating (Section 2 16) The capacity of a sample of gasoline to resist knocking expressed as a number equal to the percentage of 2 2 4 trimethylpentane ( isooctane ) in an isooctane-heptane mixture that has the same knocking characteristics... 

Eor a considerable period, >90% of the new cars in Brazil operated on E96 fuel, or a mixture of 96% ethanol and 4% water (82). The engines have high compression ratios (ca 12 1) to utilize the high knock resistance of ethanol and deUver optimum fuel economy. In 1989 more than one-third of Brazil s 10 million automobiles operated on 96% ethanol/4% water fuel. The remainder ran on gasoline blends containing up to 20% ethanol (5). 

Octane number is a measure of a fuel s abiUty to avoid knocking. The octane number of a gasoline is deterrnined in a special single-cylinder engine where various combustion conditions can be controlled. The test engine is adjusted to give trace knock from the fuel to be rated. Various mixtures of isooctane (2,2,4-trimethyl pentane) and normal heptane are then used to find the ratio of the two reference fuels that produce the same intensity of knock as that by the unknown fuel. 

Proc ing Anti-knock Gasoline y Synihctic Resins... 

Chemical additives first entered the industry in the first decade of the centuiy. These additives sewed a number of uses. For example, they lessened the capacity of gasoline to vaporize out of the gas tank or to polymerize (i.e., produce gummy residues) in the engine. In the early 1920s, the most important application for these substances was to eliminate knocking. Tetraethylead (TEL) was the first major gasoline additive to be commercialized for this purpose. 

The Ethyl Corp. and DuPont held the TEL patent, and controlled the TEL monopoly. The company held the sole right to the only known material that could eliminate automotive knocking. And it used its influence in the gasoline market to manipulate prices. Over the next few years, the company wielded its monopoly power to maintain a 3—5 cent differential between its ethyl gasoline and the regular, unleaded gasoline sold by the rest of the industiy. 

The shortage of petroleum after World War I induced an intense search for a gasoline substitute in the form of alcohol. The trade press felt alcohol would definitely replace gasoline as a fuel at some point. The advantages ot alcohol cited in the technical press included greater power and elimination of knocking. 

Once gasoline is refined, chemicals ore added to reduce knocking and prevent the formation of gum in the engine. 

An octane rating scale was devised for fuels to quantify their knock resistance. Further research led to cataloguing the antiknock qualities of the myriad individual hydrocarbon species found in gasoline. 

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