is right tech a, tech b, neither or both??
Garden
Experienced gardeners share their insights in answering this question :
Tech A is wrong, fuel will not ignite before the firing of the spark plug. The spark ignites fuel air mixture causing detonation. Tech B is correct by saying detonation occurs after spark plug has fired, which in turn ignites fuel air mixture causing detonation.
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Pre-ignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to incandescence by previous engine combustion events.
Pre-ignition is the ignition of the air- fuel charge while the piston is still compressing the charge. The ignition source can be caused by a cracked spark plug tip, carbon or lead deposits in the combustion chamber, or a burned exhaust valve, anything that can act as a glow plug to ignite the charge prematurely.
This high combustion pressure can cause ignition earlier than the normal timing. This abnormal phenomenon, called pre-ignition, is combustion that occurs outside the specified ignition timing, and it can instantaneously generate abnormal combustion and combustion pressure, causing fatal damage to the engine.
Pre-Ignition can occur alone or as a result of detonation. Hot spots from detonation, improper heat range spark plugs and glowing carbon deposits from lean mixtures are common causes of pre-ignition.
Preignition is caused by the presence of something in the cylinder hot enough to act as an ignition source. Detonation is caused by anything that adds heat to the last small volumes of unburned mixture out near the cylinder wall.
Detonation is an uncontrolled combustion event which occurs after the spark event. Pre-ignition is an uncontrolled combustion event which occurs before the spark event. Knock (pinging) is the actual noise that can be audibly heard if detonation is bad enough.
An oscilloscope is used to identify preignition; detonation is determined by its audible knock. With increase in compression ratios and power output necessitating study of these phenomena, it is expected that proper instrumentation for differentiating between the two will be extremely useful.
This is generally caused by some type of glowing ignition source such as a hot exhaust valve, too-hot spark plug, or carbon residue. Pre-ignition is especially damaging to engine components like pistons and head gaskets, since excessive cylinder pressures can occur even before the piston reaches top dead center (TDC).
What Are the Symptoms of Detonation? Detonation—sometimes called knock or pre-ignition—is a pinging sound that can sometimes be heard during acceleration and throttle tip-in. Unlike normal exhaust noise, detonation is a higher-pitched, raspy note that emanates from the engine compartment.
It could be one or more of the following things: too low a fuel octane, an insufficient cooling system, a poorly designed combustion chamber, too hot a spark plug, too much static compression, too little overlap between the cam`s intake and exhaust lobe, too lean an air/fuel ratio, too much preheating of the intake …
Damage from pre-ignition is much more severe and instantaneous than that from detonation. Typically, with pre-ignition, you will see holes melted in pistons, spark plugs melted away, and engine failure happens pretty much immediately.
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http://www.manddsmallengine.com/briggs/info/plug7.html
http://www.manddsmallengine.com/briggs/info/plug7.html
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