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| Ignition System Diaphragm |
REQUIREMENTS OF IGNITION SYSTEM
The three following elements are essential for effective engine operation:
* A good air-fuel mixture
* A high compression pressure
* Proper ignition timing and powerful sparks
Ignition Timing
The ignition system on your car has to work in perfect concert with the rest of the engine. The goal is to ignite the fuel at exactly the right time so that the expanding gases can do the maximum amount of work. If the ignition system fires at the wrong time, power will fall and gas consumption and emissions can increase.
When the fuel/air mixture in the cylinder burns, the temperature rises and the fuel is converted to exhaust gas. This transformation causes the pressure in the cylinder to increase dramatically and forces the piston down.
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| The 4 Stroke Cycle of The Piston |
There is a small delay from the time of the spark to the time when the fuel/air mixture is all burning and the pressure in the cylinder reaches its maximum. If the spark occurs right when the piston reaches the top of the compression stroke, the piston will have already moved down part of the way into its power stroke before the gases in the cylinder have reached their highest pressures.
To make the best use of the fuel, the spark should occur before the piston reaches the top of the compression stroke, so by the time the piston starts down into its power stroke the pressures are high enough to start producing useful work.
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| The Power Stroke Formation of the Piston |
Force = Pressure - Area of the piston
Distance = Stroke length So when we're talking about a cylinder, work = pressure - piston area - stroke length. And because the length of the stroke and the area of the piston are fixed, the only way to maximize work is by increasing pressure.
The timing of the spark is important, and the timing can either be advanced or retarded depending on conditions.
The time that the fuel takes to burn is roughly constant. But the speed of the pistons increases as the engine speed increases. This means that the faster the engine goes, the earlier the spark has to occur. This is called spark advance: The faster the engine speed, the more advance is required.
Other goals, like minimizing emissions, take priority when maximum power is not required. For instance, by retarding the spark timing (moving the spark closer to the top of the compression stroke), maximum cylinder pressures and temperatures can be reduced. Lowering temperatures helps reduce the formation of nitrogen oxides (NOx), which are a regulated pollutant. Retarding the timing may also eliminate knocking; some cars that have knock sensors will do this automatically.
Next we'll go through the components that make the spark.
The basic function of the ignition system is to generate sparks that can ignite the air-fuel mixture in the cylinders, so the following conditions must be satisfied:
1. W/ A STRONG SPARK
When the air-fuel mixture is compressed in the cylinders, it becomes difficult for the spark to pass through the air.(This is because even air has electrical resistance, and this resistance rises as the air is compressed.)
For this reason, the voltage that is supplied to the plugs must be high enough to ensure the generation of a powerful spark between the electrodes of the spark plug.
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| The Powerful Sparks Between Air-Fuel Mixtures |
In order to obtain the most effective combustion of the air-fuel mixture, there must be some means of varying the ignition timing in accordance with engine rpm and load (that is, of varying the crankshaft angle at which each plug fires.)
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| Proper Ignition Timing |
If the ignition system fails, the engine will stop running. The ignition system must therefore have sufficient reliability to endure.
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