Ignition surface

As a guide, because of convection that occurs from hot surfaces, ignition by a hot surface in open air should not be assumed unless the surface temperature is at least 200°C above the published minimum autoignition temperature (American Petroleum Institute, Ignition Risk of Hot Sui faces, API PSD 2216, Washington, 1980). 

Lc Length of acoustic cavity To, Propellant-surface ignition... 

Note Where normal process and compressor operating temperatures are low and there are no nearby hot surface ignition sources, the probability of fire may be low. In these cases, specific compressor water spray protection may not be needed. 

Calculation of hot surface ignition temperature is complex and depends on many variables. From a safety perspective, it is often safest to assume that a surface with a normal temperature slightly below the autoignition temperature is a potential ignition source. 

Mixtures of natural gas and air are similarly unpredictable, being quite stable and unreactive until a spark or a hot surface ignites reaction, and then thermal and chain branching autocatalysis takes off and so does the building. 

A combustion process in which a flame front may be started by hot combustion-chamber surfaces either prior to or after spark ignition, or a process in which some part, or all. of the charge may be consumed at extremely high rates. This term, therefore, includes any surface ignitions of the charge, and it includes ordinary knock or knock which is induced by surface ignition phenomena, either prior to or after spark. 

A knock which is recurrent and repeatable in terms of audibility. It is controllable by the spark advance advancing the spark increases the knock intensity and retarding the spark reduces the intensity. This definition does not include surface-ignition induced knock. 

Hot Spots. Combustion-Chamber Deposits) Surface ignition is the initiation of a flame front by any hot surface other than the spark discharge prior to the arrival of the normal flame front. The flame front or fronts so established propagate at normal velocities. This phenomenon can be further subdivided into preignition and postignition. 

Surface ignition before the oc- Surface ignition which occurs... 

Knocking Surface Ignition Knock which has been preceded by surface ignition. It is not controllable by spark advance. It may or may not be recurrent and repeatable. 

Nonknocking Surface Ignition Surface ignition which does not result in knock. 

Knocking surface ignition characterized by one or more erratic sharp cracks. It probably is the result of comparatively early surface ignition from deposit particles. 

A low-pitched thudding noise different from knock and accompanied by engine roughness. One of the causes probably is the high rate of pressure rise associated with very early ignition or multiple surface ignition. 

The earliest method of detecting surface ignition was based on the occurrence of abnormal noise. Ricardo mentions that in 1904 preignition was accompanied by a dull thud, but no trace of the ringing knock was found (72). Pressure-time records of combustion also have been used since the early days to detect the occurrence of surface ignition (8). A sudden increase in temperature of the cylinder head also has been taken... 

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