A spark plug is an electrical device that is used in internal combustion engines to ignite compressed aerosol gasoline using an electric spark. The electrical component is highly used to perform mechanical jobs. A spark plug has two major functions in internal combustion engines, which include igniting 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 get started!
What Is A Spark Plug?
A spark plug is an electrical device that is used in internal combustion engines 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 fire to the compressed gas. Spark plugs are either regular (replacement) or performance.
The performance spark plugs are tougher, having the ability to withstand a greater change in temperatures and mechanical stresses. However, regular types can’t. 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.
- Removing of heat: spark plugs cannot create heat, but they can only be used to remove heat. The temperature of the end of the plug’s firing end must be low enough to prevent pre-ignition but 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. When they are not firing, the device is used to measure ionization in the cylinders. This ionic current measurement is used to replace the ordinary cam phase sensor, knock sensor, and misfire measurement function.
Other great purposes of spark plugs include furnaces wherein a combustible fuel/air mixture must be ignited. In this condition, they are referred to as flame igniters.
Diagram Of a Spark Plug
Related: What Is An Automobile Engine? Its Diagram, Parts & How it works
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 to prevent the escape of high voltage from the electrodes. Because the bottom part of the insulation is inserted into the combustion chamber, high-purity alumina with great heat-proof characteristics, mechanical strength, excellent insulation and thermal conductivity at high temperatures must be used.
Terminal
A terminal is attached to a high-tension cord, which allows 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, there is a procedure for tightening and the suitable locking margin must be secured.
Glass Seal
The glass seal is located between the center shaft and the insulator to maintain air tightness. It is made from a special mixture of glass powder and copper powder. They are charged in the installation section of the shaft and center 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. Because of this, even under harsh conditions, gaps do not occur and good airtightness can be protected.
Electrode with Copper
A special nickel alloy is employed at the center electrode to reduce electrode wear and copper is sealed into 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
The center electrode is laser welded to an iridium alloy tip, usually with a diameter of 0.4 mm to produce the center electrode. 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. The purpose of a center electrode is to lower the spark voltage, secure a reliable spark improve ignition performance, and reduce the quenching effect.
U-groove Ground Electrode
This component serves a very important purpose as it allows large ignition energy to be obtained and widens the flame core (flame size) easily. Sparks easily happen because the surface that the air-fuel mixture contacts is large and has a lot of edge sections. Finally,
Tapered Cut Ground Electrode
In this part, the electrode tip is cut to a finely tapered shape. The purpose is to reduce the quenching effect, which enriches the ignition performance.
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.
Because nickel alloys are soft materials and not very durable, copper spark plugs need to be replaced more frequently than other types. Some cars are designed to use the plug despite their shorter lifespan. However, some manufacturers see installing expensive spark plugs as a waste of money.
Iridium Spark Plug
The iridium types of spark plugs last longer since iridium is a harder and more durable material than platinum. The center electrode is designed to be small, which makes it require less voltage 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 both at 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 in the compressor stroke’s cylinder and the other in the exhaust stroke’s cylinder. At last, the spark gets wasted because the air/fuel mixture is already burnt in the previous stroke. This ignition system is not much affected by rain or debris.
Silver Spark Plug
Because the material of silver spark plug is less durable, it does not last as long as iridium or platinum spark plug. But it has better thermal conductivity; it’s often used in older European performance cars and motorcycles.
Related: What Is A Fuel Injection System? Its Diagram and How It Works
How A Spark Plug Works
An ignition coil or magneto produces high voltage, which is connected to the plug. It creates a voltage difference between the center electrode and the side electrode as the electrons flow out of the coil. As the voltage increases, the structure of the gases between the electrodes changes, but not before the fuel and air in the gap act as an insulator, preventing any current from flowing.
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 make-up of the mixture between the electrodes, as well as the level of combustion chamber turbulence at the time of the spark, determine 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. The hot spark plugs are good insulators because more heat is stored in the tip and therefore in the combustion chamber.
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. Cold spark plugs are much less insulated, which is why more heat is conducted 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.