For an engine to make the best use of the fuel, the spark should occur before the piston reaches the top of what?
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.
The speed of the pistons increases as the engine speed increases. This means that the faster the engine goes, the spark has to occur when?
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.
What is it called when the spark timing is moved closer to the top of the compression stroke?
Goals like minimizing emissions can be achieved 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.
According to the article, retarding the timing may also eliminate what?
Retarding the timing may also eliminate knocking; some cars that have knock sensors will do this automatically.
What is the difference between a "hot" spark plug and a "cold" spark plug?
Some cars require a hot spark plug. This type of plug is designed with a ceramic insert that has a smaller contact area with the metal part of the plug. This reduces the heat transfer from the ceramic, making it run hotter and thus burn away more deposits. Cold spark plugs are designed with more contact area, so they run cooler.
The coil is a simple device -- essentially a high-voltage transformer made up of ______ of wire.
The coil is a simple device -- essentially a high-voltage transformer made up of two coils of wire. One coil of wire is called the primary coil. Wrapped around it is the secondary coil. The secondary coil normally has hundreds of times more turns of wire than the primary coil.
The primary role of the distributor is to distribute high voltage from the ______ to the correct cylinder.
The distributor handles several jobs. Its first job is to distribute the high voltage from the coil to the correct cylinder. This is done by the cap and rotor. The coil is connected to the rotor, which spins inside the cap. The rotor spins past a series of contacts, one contact per cylinder. As the tip of the rotor passes each contact, a high-voltage pulse comes from the coil. The pulse arcs across the small gap between the rotor and the contact (they don't actually touch) and then continues down the spark-plug wire to the spark plug on the appropriate cylinder.
Spark plugs use this to isolate the high voltage at the electrode, ensuring that the spark happens at the tip of the electrode and not anywhere else on the plug.
Spark plugs use a ceramic insert to isolate the high voltage at the electrode, ensuring that the spark happens at the tip of the electrode and not anywhere else on the plug; this insert does double-duty by helping to burn off deposits. Ceramic is a fairly poor heat conductor, so the material gets quite hot during operation. This heat helps to burn off deposits from the electrode.
Spark timing is so critical to an engine's performance that most modern cars use a sensor to tell the engine control unit (ECU) what?
Spark timing is so critical to an engine's performance that most cars don't use points. Instead, they use a sensor that tells the engine control unit (ECU) the exact position of the pistons. The engine computer then controls a transistor that opens and closes the current to the coil.
In a distributorless ignition system, what component has total control over spark timing?
The coil in this type of system works the same way as the larger, centrally-located coils. The engine control unit controls the transistors that break the ground side of the circuit, which generates the spark. This gives the ECU total control over spark timing.
Automobile ignition systems rely on perfect timing. A simple spark, when delivered at precisely the right moment, can mean the difference between a smoothly running, powerful engine that operates cleanly and an engine that runs rough, lacks power and produces unnecessary emissions. Let's get your motor running.
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