Understanding Spark Plug

Originally, with the perfect design of gasoline internal combustion engines, if the spark plug is eliminated then the combustion process won’t work. The device delivers electric current from an ignition system to the combustion chamber of spark-ignition engines. Compressed fuel/air mixture is igniting with the component.

As we’ve learnt the secret behind the mechanical movement of most automobiles in received from the combustion circle. For the small explosion to take place SI version spark plug is included.

The component is so small that people overlook is function in their car engine. it contains a metal threaded shell, electrically isolated from a central electrode by a porcelain insulator. The central electrode that may contain a resistor, is attached by a heavily insulated wire to the out terminal of an ignition coil or magneto.

spark plug types

The metal shell is screwed into the engine’s cylinder head, thus causes the ignition. Today we’ll be looking at the definition, functions, parts, types, working principle, bad symptoms, as well as advantages and disadvantages of spark plugs.

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Spark Plug Definition

A spark plug is an electrical device that is used in internal combustion engines to ignites compressed aerosol gasoline using an electric spark. The electrical component is highly used to perform mechanical jobs.

In simple term, spark plugs turn an energy source (gasoline) into movement. For instance, we have petrol which is highly flammable and also air, that could cause an explosion when mixed. The 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 Spark Plugs

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 plugs firing end must be low enough to prevent pre-ignition but should be high enough to prevent fouling. Spark plugs can serve as a heat exchanger by eliminating the unwanted thermal energy from the combustion chamber. The heat is then transferred to the engines 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.

Major Parts of a Spark Plug

Below are the various parts of a spark plug and their functions:


This part insulates the terminal, centre shaft and centre electrode from the housing. it helps to prevent the escape of high voltage from the electrodes. Because the bottom part of the insulated is inserted into the combustion chamber, high purity alumina with great heat-proof characteristic, mechanical strength, excellent insulation and thermal conductivity at high temperature must be used.


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.

Ring, Parking Washer:

This spark plug component helps the insulator and the housing tightly fit each other and maintain airtightness


The gasket makes the housing and the engine perfectly fit each other and also maintain the airtightness of the combustion chamber. Although, there is a procedure for tightening and the suitable locking margin must be secured.

Center Shaft (stem):

The centre shaft connects the terminal and the centre electrode. The part is made of steel and contains a role that allows high-voltage current to flow from the terminal to the centre electrode without loss.

Glass Seal:

The glass seal is located between the centre shaft and insulator to main the airtightness. It is made from a special mixture of glass powder and copper powder. They are charged in the installation section of the shaft and centre shaft and centre electrode and then melted at high temperature. This bond the centre shaft and the centre 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.

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Electrode with Copper:

A special nickel alloy is employed at the centre electrode to reduce electrode wear and copper is sealed into the centre section to enhance its thermal conductivity.


The housing creates an outer shell that surrounds and supports the insulator. It also allows the spark plug to be installed to the engine. at the bottom part, there is a ground electrode that makes current flow through the engine itself to the centre electrode over the gap.

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Center Electrode:

The centre electrode is laser welded to an iridium alloy tip usually with a diameter of 0.4mm to produce the centre electrode, iridium is a precious metal with extraordinarily superior properties for a spark plug electrode. These properties include high-temperature resistance, high strength, and low resistance etc. The purpose of a centre electrode is to lower the spark voltage, secure reliable spark improves ignition performance and reduces the quenching effect.

U-groove Ground Electrode:

This component serves a very important purpose as it allows large ignition energy to be obtained, widen the flame core (flame size) easily. The surface contacted by the air-fuel mixture is large and there is much edge section, and sparks easily occur. 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.

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Below is the complete diagram of a spark plug:

diagram of a spark plug

Types of Spark Plugs

Below are the various types of spark plugs available out there:

Copper Spark Plugs:

In these types of the spark plug, the centre electrode is copper core coated with a nickel alloy. There is a need for more voltage to produce sparks because the centre electrode has the largest diameter compared to others. Because nickel alloys are a soft material 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. Although some manufacturers see installing expensive spark plugs may be a waste of money.

Iridium Spark Plugs:

The iridium types of spark plug last longer since iridium is harder and more durable material than platinum. The centre electrode is designed to be small which makes it requires less voltage to generate a spark. This is why it’s of the high cost compared to the first type. Nowadays, most vehicle features the iridium spark plug because it minimizes the amount of car breakdown.

Single Platinum Spark Plugs:

These types of the spark plug are similar to the copper/nickel version, only that, its centre 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 Plugs:

In these types, there is a platinum coating both at the centre 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 Plugs:

Because the material of silver spark plug is less durable, it does not last long as iridium or platinum spark plug. But it has beat thermal conductivity, it’s often used I older European performance cars and motorcycles.

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Working Principle of a Spark Plug

The working of a spark plug can be quite complex in some stage but can be very interesting to learn. As earlier mentioned, its purpose is to ignite the compressed air/fuel mixture of gasoline engines.

The device contains an insulated centre electrode that runs its length and there are one or more ground electrodes on the bottom end. This part is separated from the exposed end of the centre electrode which is called “spark gap”. Whenever voltage is supplied from the ignition coil to the spark plug, it is high enough, causing the electrical energy to jump the gap and produce a spark.

The electrodes were traditionally made of copper but it’s improve using high metals like iridium and platinum. The modern spark plugs are designed with smaller centre electrodes so that lower voltage will be required to generate sparks. This is because less voltage will make a more efficient ignition system.

The plug is installed to a high voltage generated by ignition or magneto. A voltage difference is developed between the centre electrode and side electrode when the electrons flow from the coil. At this stage, no current can flow because the air and fuel in the gap is an insulator, but as the voltage rises, the structure of the gas between the electrodes begins to change. Once the voltage exceeds the dielectric strength of the gases, it becomes ionized.

This ionized gas becomes a conductor and allows electrons to flow across the gap. Spark plugs usually required voltage of more than 2000 volts to properly ignites. As the current of electrons rises across the gap, the temperature of the spark channel to 60,000 k. With this immense heat in the spark channel, the ionized gas quickly expands, causing a small explosion in the chamber.

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 much 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.

watch the video to have more understanding of how spark plugs works:

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Symptoms of Bad or Failing Spark Plug

Below are the symptoms of bad or failing spark plug and their prevention:

Slow acceleration:

When spark plugs begin to fail, you begin to noticed poor acceleration on your car. Though in modern vehicles where the sensor is telling the most condition of the engine ignition system. The issue can be easily noted. Sometimes the issue can be from a faulty sensor, but in most cases, it’s a worn-out plug. Slow acceleration can be caused by several factors in the engine such as bad fuel filters, dirty or clogged fuel injector, or faulty oxygen sensor. This is why an expert needs to examine the situation as soon as it started.

Poor Fuel Economy:

A bad spark plug could make you spend more money on fuel. A good spark plug helps to burn fuel efficiently in the combustion cycle, which helps to achieve more than the average fuel economy. The problem occurs on the spark plug either because the gap between the electrodes is either too close or their much gap in-between. In most cases, mechanics adjust the gap when you complain of a similar issue. Well, it is better to change the plug instead to avoid such in the future.

Difficult Startup:

The issue is common as you find a DIY driver going straight losing his spark plug when he/she have trouble starting their car. In most time the device seems to be worn. But, different symptoms can affect an engine’s ignition system, an expert should be involved.

Engine Misfiring:

Misfiring of engines is an issue from the ignition system, often time in modern cars it’s a fault from a sensor. But it’s also caused by the spark plug wire or if the tip of the spark plug that connects the wire got damaged. If an engine misfire the driver will experience intermittent stumbling or sputtering sounds in the engine. if care is not taken and the misfiring continues, exhaust emissions will increase, fuel economy will drop, and engine power will decrease. So, a different problem is related to misfiring, consider seeing a mechanic immediately you notice misfire in the engine.

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In conclusion, a spark plug is a great component which we’ve seen effective working on gasoline engines. We’ve also examined two functions it offers which include igniting and removing heat from the chamber. Various spark plug parts and functions were revealed and also types as well as bad symptoms.

I hope you enjoyed the reading, if so, kindly comment, share and recommend this site to other technical students. Thanks!

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