SPARK PLUG
Hello guys, in this post we are going to explain to you about a little part of the engine called Spark plug. Now here we are going to see about What is Spark plug, types of spark plug, working of spark plug, and atlast why it is used only in petrol engine.
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Ok, first let's start with
What is a Spark plug?
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| (Spark plug) |
A device which is used for producing electric current from the ignition system of the engine to the combustion chamber of a engine for igniting the air-fuel mixture with the help of the created electric spark, is called Spark plug. It is also called Sparking plug or Sparker. It is placed in the head of an internal combustion engine.
A Spark plug carries two electrodes separated by a small gap, between this small gap the current produced by the ignition system is passed to ignite the air-fuel mixture. The spark plug must have a resistance for withstanding that high temperature and voltage. If the gap between the electrodes are long, it may affect the energy produced by the spark, and also affects the shape of the insulator. Either it may cause deposition of carbon in the plug or preignition of the air-fuel mixture.
Parts of a Spark Plug
A spark plug is comprised with the following parts.
- Plug terminal
- Insulator
- Metal Shell
- Central Electrode
- Ground electrode
- Sealing Gasket
- Insulator tip
- Electode gap
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| (Labelled Spark plug parts) Source: Marineengine digest |
A terminal which is present in the top of the spark plug to get connected to the ignition system is called plug terminal. It is responsible for conducting high voltage to the central electrode of the spark plug. It is the portion which is attached to the high tension cable passing out from the cap of the distributor.
It is the main part of the spark plug. This is made up of Aluminium Oxide(Al2O3) and ceramic material. It improves the temperature resistance of the spark plug. It posses high dielectric strength. Its main function is to provide mechanical support and insulation of central electrode. It can withstand upto 4000 volts.
It is made up of steel shell. The metal shell withstands the torque of the spark plug, it is used to remove the heat from the insulator and it passes the heat to the cylinder head. It also acts as earth for the spark passing through the central electrode and helps the plug to get cooled.
The central electrode of the spark plug is connected to the plug terminal through an wire and it connects to a resistance. The tip of the central electrode is made by the combination of nickel-iron, Chromium and copper. The voltage is supplied from the secondary winding to the central electrode through the distributor.
| The ground electrode is made up of high nickel and steel alloys. It is welded to the metal shell. It also has some platinumaand iridium alloys to increase the lifetime of the spark plug. |
Sealing Gasket
The spark plug also have a role in sealing the combustion chamber of the engine when it is fixed. It is necessary to ensure that there is no leakage form the combustion chamber. The sealing made with the cylinder head and it also plays a role in heat dissipation from the combustion chamber.
The extended part of the insulator into the combustion chamber is called insulator tip. It has a major influence in thermal rating of the spark plug.
The gap between the Spark plugs are typically designed, by bending the ground electrode. The gap between the electrode may vary for each plug. But generally Spark plugs in automobiles have a gap between 0.6 and 1.8 mm. The electrodes play a vital role in producing the spark. If proper gap was not provided, the spark plug won't produce spark with suitable energy for igniting the air-fuel mixture and it may cause misfiring.
How Spark Plugs Work
At one end, it is connected to a high voltage source like ignition coil or the magneto, in the other end it is connected with two electrodes. When a high tension current passes through the plug terminal and ibto the central electrode, thus a potential difference is created between the electrodes. The fuel mixture ocvupies the gap between the electrodes so that the electric current doesn't flow beyond the tip of the central electrode.
If the voltage increases, the gap will be energised. As soon as the voltage energise the gap it will get ionised. After ionised they begin to act as conductor and allows the current to pass through this insulating gap. When it reaches a certain amount, the electrons begin to surge through the gap. This sudden movement of electrons increases the heat in that region due to the heat they began to expand fastly and causes the small explosion. This small explosion results in the formation of the spark from the spark plug and then it will cause the power stroke where the fuel moves the piston downwards because the ignition of the air-fuel mixture.
Types of Spark plug
Based on Temperatures
After the combustion of the fuel mixture, the heat which is produced needs to dissipate from the combustion chamber. The heat dissipate through the exhaust gases, between the gap of the spark plug surface and the cylinder wall of the engine. On the basis of temperature and heat dissipation, the spark plugs are classified into two types:
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| (Hot and cold spark plug) Source: V-auto.org |
Hot Spark Plug
The name itself will explain the function of this type of spark plug, that is the hot spark plug operates in a higher temperature range. To reduce the effect of heat it is made up less amount ceramic coat. This type of spark plug dissipates lesser combustion heat so that it makes the tip and electrode stay hotter. This hotness prevents the deposition of burnt fuel mixture and it won't allows to stay for long time.
Cold Spark Plug
In the case if high performable engines, it has heat production by default engine function. If we use hot spark plug in those kind of engine it will cause pre-ignition of the engine. In some extreme cases, it may lead to the melting of electrode tip. So, to avoid melting cold spark plugs are used. In these cold spark plug the ceramic coat insulation is large in amount, so that the dissipation of heat is high. These kind of spark plugs are used for high performable engines.
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| (Melting of spark plug) |
Based on Material Used
Based on the types of materials used the spark plugs are classified into four types
Copper- Nickel Type
This type of spark plug is the most basic type. In this type the central electrode is made up of copper- nickel alloys. This type is not suited for high performance engine because copper is a weak metal, nickel is added to provide strength to the copper. Even after the addition of nickel, this types are very weak for withstanding the high heat and temperature. It also has a larger diameter and requires high voltage to perform. So, it will surely melt off when plugged in a high performance engine.
Single Platinum Type
In this type, the spark plug have a small size of platinum disc at the end of the central electrode. This platinum end strengthens the plug more than the copper-nickel alloy coating. It also reduce the accumulation of burnt slags.
Double Platinum Type
In this type the platinum tips are provided on both the central electrode as well as the ground electrode. These spark plug will spark twice ina combustion cycle. One at the compression stroke and the next at the beginning exhaust stroke. There won't be any ignition in the second spark. It is just wasted. It is used in the ignition system having waste spark distributor. The advantage of this waste spark is that, it is not affected by rain season or any dampness and it also reduces the accumulation of waste between the gap.
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| (Platinum spark plug) Source: Marine Engine digest |
Iridium Type
It is the best type of spark plug among all the types. In this type the central electrode tip is made up of metal called iridium. The iridium is one of the strongest metal. It is more stronger than all the other metal type spark plugs like copper, nickel and platinum. It has a small diameter therefore it requires only small amount of voltage for performance of spark. It has the capacity for withstanding the high heat. The only disadvantage in this type is that the cost of the spark plug. Since it is the strongest it is much more expensive when compared all the other types of spark plug available in the market.
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| (Iridium spark plug) Source: Marine engine digest |
Why spark plug are used only in petrol engines?
In the case of a diesel engine, the fuel is burned when the fuel is injected at high pressure to the hot compressed air in the cylinder. This hot compressed air reaches the engine cylinder with the help of a turbocharger or natural respiration. And with the help of the Fuel pump, the fuel reaches the combustion chamber. And hence both fuel and air enter the combustion chamber separately. Thus with the help of that hot compressed air, the combustion process takes place in a diesel engine.
But in the case of a petrol engine, the combustion will occur only when the air-fuel mixture gets ignited by the spark from spark plug which is present inside the engine cylinder. So in petrol engines, we are using spark plug to ignite the air-fuel mixture in yhe combustion chamber of the engine.
Symptoms of spark plug deterioration
After some times the span of the spark plug reduces and it will begin to Over time your car spark plug’s health will begin worsed. Generally, the span of a spark will be mentioned by the manufacturers. Ideally you have to change it after a runtime of 15,000 km. There are some symptoms that will indicate you about the deterioration of your spark plug. Some of the symptoms of deterioration of your spark plugs are
- Rough idle condition when you start vehicle. once you turn on your vehicle
- False firing of engine
- High consumption of fuel
- Low throttle power
- Sudden rise in power
These are the some indications that your spark plug is losing its value.
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| (Spark plug deterioration) |
How to improve your spark plug life?
- Choose the right type of plug according to the performance of your engine.
- Clean the tip of Electrodes regularly because sometimes there will be a chance for deposition of burnt gas. It may reduce the effectiveness of the spark plug.
- Regularly monitor the spark plug gap. It should be between 0.6 to 1.8mm as I mentioned earlier.
- Clean the mounting area of spark plug periodically.
Conclusion
That's all about the spark plug and types, construction and working of spark plug. Also, I had given some symptoms for deterioration of spark plug and ways to improve the spark plug.
I hope that you understand the definitions, types, construction, working, symptoms of deterioration of spark plug.
If you have any queries or doubts or need improvements in this article put that in the below-mentioned comments section we will reply and rectify as fast as possible.
Spark your brain and Throttle your knowledge!