Knocking causes

In some circumstances, the octane number of the gasoline used in the engine must be increased to prevent knock caused by accumulated deposits. This phenomenon is called Octane Requirement Increase (ORI). Both prevention and reversal of ORI are difficult to achieve. 

Many workers have stated that tetraethyllead is effective in increasing the intrinsic resistance of fuels to surface ignition. Part of the effectiveness is due undoubtedly to the activity of tetraethyllead in suppressing subsequent knock caused by the premature ignition of the charge (91). With proper allowance for this effect, tetraethyllead appears to increase the surface ignition resistance of those fuels to which it contributes knock... 

Only in extreme cases is knocking caused by a true detonation wave.8 Brown and Watkins. state that the detonation wave as recognized in progressive homogeneous reactions is not the cause of knock.118... 

I knocking is the premature j spontaneous explosion of the petrol mixture during the com-I pression stroke in a petrol en-I ginc before the mixture is ig-j nited by a spark. Knocking causes significant loss of power I and may result in damage to i the engine. 

Knocking should be absolutely avoided because if allowed to continue it will cause severe mechanical and thermal problems (Eyzat et al., 1982), which can... 

The Octane Requirement Increase, ORI, is a phenomenon manifested by the appearance of knocking and is due to the increase in engine octane demand with time. This phenomenon is correlated with the increase of solid deposits in the combustion chamber. Although the causes have not been determined with certainty, some companies have patented additives which modify the deposits. The effect is to limit the increase in octane demand (Bert et al., 1983 Chevron, 1988 Nelson et al., 1989). 

Knock is caused by unwanted chemical reactions in the combustion chamber. These reactions are a function of the specific chemical species which make up the fuel and the environmental conditions to which the fuel is subjected during the compression and power stroke in the engine. Therefore, both the chemical makeup of the fuel and the engine design parameters must be considered when trying to understand knock. 

Chemical Factors. Because knock is caused by chemical reactions in the engine, it is reasonable to assume that chemical stmcture plays an important role in determining the resistance of a particular compound to knock. Reactions that produce knock are generally free-radical chain-type reactions which are different from those that occur in the body of the flame the former occur at lower temperatures and are called cool flame reactions. 

The octane number requirement (ONR) of a car is the octane number which causes barely audible, ie, trace knock when driven by a trained rater. The Coordinating Research Council (CRC), a research organi2ation funded joindy by the American Petroleum Institute (API) and the American Automobile Manufacturers Association (AAMA), has defined test procedures for measuring ONR. Each car is driven under a set of light and heavy accelerations until the most sensitive driving mode is determined. Then a series of fuels is mn in the car until trace knock is determined. Each year, CRC members measure ONR of more than 100 cars and pubHsh the results. 

Arrhythmias. The first solution to cardiovascular problems arising from arrhythmias came about as a result of a complication caused by open-heart surgery. During procedures to correct congenital defects in children s hearts, the electrical conduction system often became impaired, and until it healed, the heart could not contract sufficiently without outside electrical stimulation. A system that plugged into a wall outlet was considered adequate until an electrical storm knocked out power, lea ding to the development of the first battery-powered external pacemaker. 

This cycling process causes drastic variations in noise levels. These noises should not be regarded as problems, unless accompanied by severe knocking or squealing noises. Figure 41.11 shows a typical hydraulic unloader and its location on the compressor. 

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