Engines knock

Before its use as a fuel additive to reduce engine knock was banned in the United States, tetraethyllead was produced in enormous quantities. One method of producing the compound was the reaction between lead and ethyl chloride, in which the reactivity of lead was enhanced by its amalgamation with sodium. 

Chemical reaction rates, 14 607. See also Kinetic measurements Chemical reactions. See also Chemical processes Reaction entries with absorption, 2 47-48, 71-76 activated carbon for control of, 4 755 on adsorbents, 2 629-630, 650-651 atomic level of, 16 736 contexts of, 22 336 engine knock and, 22 390—391 heterogeneous, 22 331-332, 339 homogeneous, 22 339 independent and dependent, 22 336—337 mass-transfer coefficients with, 20 753-755... 

Source Some unleaded gasoline may contain isopropyl ether and other oxygenates as an octane booster and to prevent engine knock. 

In the past, tetraethyl lead was added to gasoline to slow its burning rate in order to prevent engine knock and increase performance. This caused serious and harmful pollution, and lead has since been eliminated as a gasoline additive in most countries. Most exterior (and some interior) house paints once contained high levels of lead as well. Today, the amount of lead in paint is controlled, with not more than 0.05% allowed in the paint material. 

What is engine knock What causes the engine knock problem ... 

Does the Diesel engine have engine knock problem Why ... 

The Otto cycle is a spark-ignition reciprocating engine consisting of an isentropic compression process, a constant-volume combustion process, an isentropic expansion process, and a constant-volume cooling process. The thermal efficiency of the Otto cycle depends on its compression ratio. The compression ratio is defined as r= Fmax/f min- The Otto cycle efficiency is limited by the compression ratio because of the engine knock problem. 

Of these chemicals, the EPA has traditionally focused its monitoring efforts on only one, lead. The reason is that lead (in the form of tetraethyl lead (C2H5) Pb) was once used extensively as a fuel additive to reduce the problems of engine "knocking in automotive vehicles. Because of the health problems posed by lead, however, tetraethyl lead was banned from use in automotive fuels in 1976. 

Engine knock is measured by two ASTM methods, ASTM D-2699 and D-2700. Method ASTM D-2699 is identified as the research octane number (RON) and method ASTM D-2700 is identified as the motor octane number (MON). The primary differences between these two methods are summarized in TABLE 3-3. 

Engine knock and vibration can be due to the rapid pressure rise resulting from the combustion of low-cetane-number fuels. 

The deposit mass acts to reduce the physical volume of the combustion chamber through air displacement. As a result, during the compression-ignition cycle the cylinder air volume is compressed to a higher pressure. When ignition occurs, engine knock will be enhanced due to higher cylinder pressures. 

Problems related to engine knock can be readily diagnosed by measuring the octane number of gasoline. However, it is also possible to look at the distillation profile of gasoline and anticipate problems linked to engine knock. 

In practice, short-chain alkanes and alkenes are normally used as feedstock for shape-selective catalytic formation of isooctanes at relatively low temperatures. Until the 1980s, lead alkyls (Section 18.1) were added to most automotive fuels to help suppress engine knock, but they have been phased out in North America because of the chronic toxicity of lead and lead compounds. The most commonly used nonlead antiknock additive is now methyl tert-butyl ether [MTBE CH30C(CH3)3], which is made by the reaction of methanol with 2-methylpropene, (CHs C—CH2 (see Section 7.4). The latter is obtained by catalytic cracking of petroleum fractions to give 1-butene, which is then shape-selectively isomerized on zeolitic catalysts. 

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