Spark Plug

Spark Plug

Here is the complete guide about Spark Plug. Here you can get Spark Plug working principle, and also other important topics like Main Parts, types and Applications of Spark Plug.

A spark plug is a device used to ignite the air/fuel mixture in an engine cylinder. It is generally used in petrol engines, as the combustion of fuel requires a spark to initiate the combustion process.

What Is Spark Plug

A spark plug is an electrical device that fits into the cylinder head of a few inner combustion engines and ignites compressed aerosol fuel via an electric powered spark. Spark plugs have an insulated middle electrode linked with the aid of using a heavily insulated wire to an ignition coil or magneto circuit at the outside, forming, with a grounded terminal on the bottom of the plug, a spark gap inside the cylinder.

Main Parts of Spark Plug


This component insulates the terminal, center shaft and center electrode from the housing. it enables to prevent the escape of excessive voltage from the electrodes. Because the lowest a part of the insulated is inserted into the combustion chamber, excessive purity alumina with great heat-proof characteristic, mechanical strength, incredible insulation and thermal conductivity at excessive temperature must be used.


A terminal is connected to a high-tension cord which allows high-voltage current to flow through the ignition system. It contained a terminal nut that helps nearly any high-tension cord available. For a few automobiles that don’t require a terminal nut, the terminal may 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 additionally maintain the airtightness of the combustion chamber. Although, there is a procedure for tightening and the perfect locking margin must be secured.

Center Shaft (stem):

The center shaft connects the terminal and the center electrode. The component is made of metallic and consists of a position that allows high-voltage current to flow from the terminal to the center electrode with out loss.

Glass Seal:

The glass seal is placed among the center 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 center shaft and center electrode and then melted at high temperature. This bond the center shaft and the center electrode and fuses the insulator and the metal. Their sealing is good and the thermal ratio of growth is perfect. Because of this, even below harsh situations gaps do now no longer arise and good airtightness may 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 phase to enhance its thermal conductivity.


The housing creates an outer shell that surrounds and helps the insulator. It additionally lets in the spark plug to be installed to the engine. at the lowest part, there’s a ground electrode that makes current flow via 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 0.4mm to provide the center electrode, iridium is a treasured metallic with extraordinarily advanced properties for a spark plug electrode. These houses encompass high-temperature resistance, high strength, and low resistance etc. The reason of a center electrode is to lower the spark voltage, stable reliable spark improves ignition overall performance and reduces the quenching effect.

U-groove Ground Electrode:

This component serves a very important reason because it allows large ignition energy to be obtained, widen the flame core (flame size) easily. The surface contacted through the air-gasoline combination 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 reason is to reduce the quenching effect, which enriches the ignition overall performance.

Working Principle of a Spark Plug

  • When a high voltage current from the distributor is passes to the spark plug.
  • The central electrode and ground electrode is applied to a very high voltage as much as 40000 V.
  • Due to this high voltage difference between the central electrode and ground electrode, the air in among the electrode hole receives ionized.
  • The ionized gas will become conductor and conducts contemporary from central electrode to the ground electrode producing spark.
  • The spark produced is used to ignite the air-gasoline mixture in the engine cylinder.

Types of Spark Plugs

Spark plugs can be put into two different primary classifications, based on their operating temperatures and construction.

Based on their operating temperatures

Once the combustion process is completed in the combustion cycle, the heat generated needs to dissipate. The heat escapes through the exhaust gases, the cylinder wall of the engine and the spark plug surface. Based on the operating temperature and level of heat dissipation, spark plugs can be classified into two types:

1. Hot spark plug:

A hot spark plug operates in a higher temperature range. It has a lesser ceramic area used to insulate the heat. A hot spark plug dissipates lesser combustion heat and lets in the tip and electrode to stay hotter. This ensures that any deposit accumulation is burned off and isn’t allowed to stay for long.

2. Cold spark plug:

For high-overall performance engines that run hot with the aid of using default, the use of a hot spark plug will cause pre-ignition. In extreme cases, it may additionally cause the end melting off. In such cases, a cold spark plug is used. Here the ceramic insulation area is higher and this it will dissipate more heat. But at the flip side, it is prone to more deposit accumulation. Be sure to follow your instruction manual and use the correct type of plug recommended for your engine for optimum overall performance.

Based on material used

Spark plugs are further classified based on the material used on the ends of the electrodes.

They are of four types:

(i)Copper- nickel type:

These are the maximum fundamental types of spark plugs. Here the centeR electrode is made of a copper-nickel alloy as copper on its very own is weak and will melt off because of engine heat. Nickel is introduced to strengthen the plug however even then these are the weakest types available in the market. They are also required to be made with a larger diameter and hence require more voltage for operation.

(ii) Single platinum type:

These plugs have a small platinum disc on the tip of the center electrode. This platinum tip is exponentially stronger than a copper-nickel coating making this type of plug to last long as well. They are also less prone to debris build up.

(iii) Double platinum type:

These plugs have platinum tips on each the center electrode and the side electrode. They spark up twice in the combustion cycle, as soon as earlier than the combustion and as soon as throughout the exhaust stroke. The 2d spark is wasted and so this spark plug can only be used in case your automobile is prepared with a waste spark ignition kind distributor.

(iv)Iridium type:

These are the best spark plugs available in the market. Here the end of the center electrode is made of Iridium which is the strongest out of nickel, copper, and platinum. Hence, they are the least prone to deposits and damage. They also have a small sized electrode which requires much less voltage for operation as well. Iridium plugs are much more expensive than the opposite sorts however then again you pay for what you get.

Requirements of a Spark Plug

  1. It have to be reliable at high voltage transmission i.e. as much as 40,000 V.
  2. It must have desirable insulation functionality even at temperatures of a thousand 0C, and prevention of arcing and flashover.
  3. It should possess resistance to thermal shock (Hot exhaust gases-cold intake mixtures)
  4. It need to make pressure-tight and gas-tight sealing with the combustion chamber.
  5. It have to be capable to withstand oscillating pressures as much as approx. 100 bar.
  6. It should have high mechanical strength for reliable installation.
  7. It need to have good thermal conduction with the aid of using insulator tip and electrodes.
  8. It must possess resistance to spark erosion, combustion gases and residues.
  9. It have to be capable of preventing of build-up of deposits at the insulator.

Symptoms of Bad or Failing Spark Plug

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.


It is used in all petrol engines of scooters, motorcycles, cars, etc. where the petrol is burnt with the help of spark.


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