Internal combustion engines use a spark plug, an electrical device that ignites compressed aerosol gasoline using an electric spark. Mechanical jobs heavily rely on the electrical component.
A spark plug has two major functions in internal combustion engines, which include igniting the fuel/air mixture and dissipating heat from its application. In this reading, we’ll explore what a spark plug is, its functions, diagram, parts, types, and how it works.
Let’s begin!
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What Is A Spark Plug?
Internal combustion engines use a spark plug, which is an electrical device that ignites compressed aerosol gasoline with an electric spark. Mechanical jobs heavily rely on electrical components. In simple terms, spark plugs turn an energy source (gasoline) into movement.
A ceramic insulator keeps the metal part of the spark plug away from the center electrode so they don’t touch electrically. A well-insulated wire links the center electrode, which might have a resistor, to the output terminal of the magneto or ignition coil.
Due to its attachment to the engine’s cylinder head, the metal shell of the spark plug has electrical grounding.
For instance, we have petrol, which is highly flammable, and also air, which could cause an explosion when mixed. The spark plug is like lighting a fire in the compressed gas. There are two types of spark plugs: regular replacements and performance ones.
One or more spark gaps form between the inner ends of the central electrode as it goes through the porcelain insulator and into the combustion chamber. The side, earth, or ground electrode(s) are usually bumps or parts attached to the inner end of the threaded shell.
The performance spark plugs are tougher, having the ability to withstand a greater change in temperatures and mechanical stresses. Regular types, on the other hand, cannot endure these extreme conditions. Well, we’ll further look into them below this article.
Functions of a Spark Plug
A spark plug has two major functions in internal combustion engines, which include
Igniting fuel/air mixture: as electrical energy is transmitted through the component, it ignites the gasoline/air mixture in the combustion chamber.
Spark plugs can only remove heat, not create it. The temperature of the plug’s firing end must be low enough to prevent pre-ignition, but it should be high enough to prevent fouling.
Spark plugs can serve as heat exchangers by eliminating unwanted thermal energy from the combustion chamber. The heat is then transferred to the engine cooling system.
Another discovered function of spark plugs is in Saab direct ignition. The device measures ionization in the cylinders when they are not firing. We use this ionic current measurement to replace the ordinary cam phase sensor, knock sensor, and misfire measurement function.
Furnaces, which require the ignition of a combustible fuel/air mixture, are another important application for spark plugs. We refer to them as flame igniters in this condition.
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Major Parts of a Spark Plug
A spark plug consists of several major parts, each playing a crucial role in its function. Here are the key components:
Insulator
This part insulates the terminal, center shaft, and center electrode from the housing. It helps prevent high voltage from escaping from the electrodes.
Because the bottom part of the insulation is inserted into the combustion chamber, high-purity alumina with great heatproof properties, mechanical strength, excellent insulation and thermal conductivity at high temperatures must be used.
Terminal
A high-tension cord attaches to a terminal, allowing high-voltage current to flow through the ignition system. It contained a terminal nut that supports almost any high-tension cord available. You can remove the terminal for vehicles that don’t require a nut.
Gasket
The gasket makes the housing and the engine perfectly fit each other and also maintains the airtightness of the combustion chamber. However, securing the suitable locking margin requires a specific procedure for tightening.
Glass Seal
The glass seal is located between the center shaft and the insulator to maintain airtightness. A special mixture of glass powder and copper powder makes up the seal.
They are charged in the installation section of the shaft and center electrode and then melted at high temperatures.
This bonds the center shaft and the center electrode and fuses the insulator and the metal. Their sealing is good, and the thermal expansion ratio is perfect. As a result, they maintain excellent airtightness and prevent gaps even in harsh conditions.
Electrode with Copper
A special nickel alloy is employed at the center electrode to reduce electrode wear and copper is sealed in the central section to enhance its thermal conductivity.
Housing
The housing creates an outer shell that surrounds and supports the insulator. It also allows the spark plug to be installed in the engine. At the bottom part, there is a ground electrode that makes current flow through the engine itself to the center electrode over the gap.
Center Electrode
We laser weld the center electrode to an iridium alloy tip, typically measuring 0.4 mm in diameter. Iridium is a precious metal with extraordinarily superior properties for a spark plug electrode.
These properties include high-temperature resistance, high strength, low resistance, etc. A center electrode serves the purpose of lowering the spark voltage, ensuring a reliable spark, improving ignition performance, and reducing the quenching effect.
U-groove Ground Electrode
This component plays a crucial role by facilitating the attainment of high ignition energies and effortlessly expanding the flame core, or flame size. The air-fuel mixture contacts a large surface with numerous edge sections, which facilitates the easy formation of sparks.
Tapered Cut Ground Electrode
This part features a finely tapered electrode tip. The purpose is to reduce the quenching effect, which enriches the ignition performance.
Diagram Of a Spark Plug
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Types of Spark Plug
There are several types of spark plugs, each designed for specific applications and engine requirements. Here are the main types:
Copper Spark Plug
In these types of spark plugs, the center electrode is a copper core coated with a nickel alloy. There is a need for more voltage to produce sparks because the center electrode has the largest diameter compared to others.
Copper spark plugs require more frequent replacement than other types due to the soft nature of nickel alloys. Some cars design them to use the plug, despite its shorter lifespan. However, some manufacturers see installing expensive spark plugs as a waste of money.
Iridium Spark Plug
The iridium-type spark plugs last longer since iridium is a harder and more durable material than platinum. The design of the center electrode minimizes the voltage required to generate a spark.
This is why it’s of high cost compared to the first type. Nowadays, most vehicles feature the iridium spark plug because it minimizes the amount of car breakdown.
Single Platinum Spark Plug
These types of spark plugs are similar to the copper/nickel version, only that their center electrode contains a platinum disc. This disc is welded to the tip rather than nickel alloy.
Single platinum plugs are expensive but last longer than nickel alloy before it has worn away. It generates more heat, which reduces carbon buildup. The plug is recommended for new cars with a coil-on-plug ignition system.
Double Platinum Spark Plug
In these types, there is a platinum coating on both the center and ground electrodes, which makes them more efficient and last longer. It is a fantastic choice for a wasted spark ignition system that exerts more wear on both electrodes.
In a wasted spark ignition system, each ignition coil ignites two spark plugs at a time. One spark plug ignites in the compressor stroke cylinder, the other in the exhaust stroke cylinder.
The air/fuel mixture has already burned in the previous stroke, wasting the spark at the end. Rain or debris do not significantly affect this ignition system.
Silver Spark Plug
Because the material of a silver spark plug is less durable, it does not last as long as an iridium or platinum spark plug. However, due to its superior thermal conductivity, older European performance cars and motorcycles frequently utilize it.
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How A Spark Plug Works
The plug connects to an ignition coil or magneto, which generates high voltage. It creates a voltage difference between the center electrode and the side electrode as the electrons flow out of the coil.
The fuel and air in the gap act as an insulator, preventing current flow until the voltage increases and the gases’ structure changes.
The gases ionize when the voltage is greater than their dielectric strength. Electrons can pass through the gap because the ionized gas turns into a conductor. For a spark plug to “fire” correctly, the voltage must typically be higher than 20,000 volts.
The spark channel’s temperature rises to 60,000 K as the electron current bursts through the gap.
A little explosion occurs when the ionized gas rapidly expands due to the extremely high temperatures in the spark channel. The heat and pressure cause the gases to react, resulting in a small ball of fire in the spark gap as they spontaneously ignite at the end of the spark event.
The particular makeup of the mixture between the electrodes, as well as the level of combustion chamber turbulence at the time of the spark, determines the size of this fireball or kernel.
An engine running with a small kernel will have delayed ignition timing, whereas an engine running with a large kernel will experience advanced timing.
Hot And Cold Plugs
The heat range of spark plugs is the temperature of the tip in the spark gap. The component is considered hot or cold depending on the temperature. Because the tip of the hot spark plugs stores more heat than the combustion chamber, they serve as good insulators.
It tends to last longer than the cold type because the temperature is high enough to burn off carbon deposits. This is why hot plugs work well on standard vehicles. Because cold spark plugs have significantly less insulation, they conduct more heat out of the tip and away from the chamber.
This keeps the combustion chamber cooler. However, too many hot cylinder chambers for perfect function can result in pre-ignition or knocking (uneven fuel burn), which can cause permanent damage to the engine.
Cold plugs are ideal for high-performance vehicles with high-temperature engines, those with high horsepower, high rpm, prolonged acceleration or high-speed driving, or forced induction.
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Conclusion
The spark plug is a critical component in the ignition system of internal combustion engines. It delivers the electric spark necessary to ignite the air-fuel mixture, enabling engine power and performance. A well-functioning spark plug ensures efficient fuel combustion, smoother engine operation, and better fuel economy.
Regular inspection and timely replacement are essential to avoid misfires, poor acceleration, and starting issues. Choosing the right type and gap size for your engine ensures optimal ignition and long-term reliability.
FAQs on Spark Plug
What is a spark plug?
A spark plug is a device that delivers an electric spark to ignite the air-fuel mixture in the combustion chamber of an internal combustion engine.
How often should spark plugs be replaced?
Most spark plugs should be replaced every 30,000 to 100,000 miles, depending on the type and vehicle manufacturer’s recommendations.
What are signs of a bad spark plug?
Common symptoms include engine misfires, poor fuel economy, difficulty starting, rough idling, and reduced acceleration.
Are all spark plugs the same?
No. Spark plugs come in various types such as copper, platinum, double platinum, and iridium, each with different performance and lifespan characteristics.
Can I clean and reuse a spark plug?
While cleaning is possible, it’s generally better to replace spark plugs to ensure reliable ignition and performance.
What happens if the spark plug gap is incorrect?
An incorrect gap can cause weak sparks, misfires, rough running, or even engine damage due to inefficient combustion.