Internal combustion engines use a spark plug, an electrical device, to ignite 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, an electrical device, to ignite compressed aerosol gasoline using an electric spark. The electrical component is highly used to perform mechanical jobs. In simple terms, spark plugs turn an energy source (gasoline) into movement.
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 to the compressed gas. There are two types of spark plugs: regular replacements and performance ones.
The performance spark plugs are tougher, having the ability to withstand a greater change in temperatures and mechanical stresses. However, regular types can’t withstand such 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.
Diagram Of a Spark Plug
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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 heat-proof 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. For some vehicles that do not require a terminal nut, the terminal can be removed.
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 ratio of expansion 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 center 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.
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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. Despite their shorter lifespan, some cars design them to use the plug. 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 great 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 is ignited in the cylinder of the compressor stroke, while the other is ignited in the cylinder of the exhaust stroke.
The air/fuel mixture has already burned in the previous stroke, wasting the spark at the end. This ignition system is not much affected by rain or debris.
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. But it has better thermal conductivity; it’s often used in older European performance cars and motorcycles.
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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.
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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.