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Time: 2016-10-16
Pre-ignition happens when the air and fuel mixture in the cylinder of an engine is ignited before the spark plug fires. This is typically caused from a hot spot in the compression chamber or by a spark plug that is too hot.
Many high-compression racing engines suffer from pre-ignition. The fuel enters the engine and is ignited early by the heat generated from the ultra-high compression pressures, much like a diesel engine. This often causes the engine to break pistons or bend connecting rods as the other cylinders attempt to fire in the correct timing sequence. The best-case scenario will result in engine knocking or pinging.
During pre-ignition, the air and fuel mixture ignites prior to the spark plug firing.
In some early engines, this run-on was due to excess fuel being drawn into the engine by poorly functioning carburetors after the ignition was turned off. The engine would continue to stutter and pop as the raw fuel entered the hot combustion chamber and pre-ignition occurred. The advent of fuel injection has all but stopped this type of engine behavior.
Pre-ignition as well as engine knock both drastically increase the temperature within the combustion chamber. This virtually ensures that the occurrence of one of these conditions will bring on the other. Pre-ignition results in poor engine performance and is often accompanied by a rough running engine. The pre-ignition problem is often easy to correct and can be eliminated with minimal effort. Changing to a cooler operating spark plug can often cure pre-ignition in an engine.
Proper adjustment of the carburetor and a corrected air-fuel mixture can also cure most pre-ignition conditions. Another cure for the problem can be the addition of a cleaning agent to the vehicle's fuel supply. Also, cleaning the combustion chambers of carbon deposits will often solve the problem. The timing sequence of combustion in a piston engine is an exact science. Any combustion occurring either too early or too late can cause severe problems. The fuel-air mixture entering the engine must be allowed to travel to its intended destination before igniting. Any variance of this timed event can result in engine damage or destruction.
Engine builders often spend many hours removing sharp edges from engine components. This is done not only to reduce stress risers and prevent parts breakage, but also to prevent hot spots that can cause pre-ignition. By removing the sharp edges with sand paper or other methods, the builder can continue assembling the engine with less fear of problems later on.
How does an electronic ignition work? Ignition systems based upon the concept of the generation of measured and timed electrical impulses have existed since the early 1900s. Modern day electronic ignition no longer requires as many electro-mechanical parts in the system, the key one being the distributor.
It is built upon a solid state circuit of sensors that trigger a switch, which passes current through the ignition coil. These regularly passed electrical impulses travel to spark plugs that then ignite the fuel. Such an electronic system is more efficient and can support higher engine horsepower levels than older distributor or mechanically-controlled systems.
The primary advantage offered by an electronic ignition that is circuit-based instead of mechanically-controlled is in how the electrical impulse is distributed to the spark plugs. Utilizing transistors, sensors, and electrical switches, such as the thyristor, to control electrical flow is more accurate, reliable, and durable than a breaker-point system controlled by a mechanically-rotating distributor head. Since it is highly precise, this also prevents incomplete combustion of fuel in the piston chamber of an engine, leading to better fuel efficiency and reducing pollution.
An electronic ignition automates several of the processes of ignition control that had to be manually adjusted or set in the past. Early magneto systems required hand-cranking instead of an electric start, and these were first replaced by non-rechargeable dry cell batteries that had a limited life span. Earlier systems were also limited by the amount of voltage they could generate, and such systems had imprecise timing of the distribution of electrical current overall. This kept early automotive vehicles operating at lower speeds and consuming more fuel than is the case with a newer electronic ignition.
Cars built prior to the mid 1970s that utilized a distributor-controlled electronic ignition can also be retrofitted with newer technology which combines the ignition system to the fuel injection system as one more efficient unit. Where such retrofitting is not possible on a particular model, kits exist for upgrading a classic distributor-controlled vehicle without fuel injection to electronic ignition.
Source: www.wisegeek.com