Spark Plugs | How does spark plug work? | Spark plug problems and replacement

How does a spark plug works

Spark Plugs are the most important components of the vehicle's ignition system. They are used in SI or gasoline engines to ignite the air-fuel mixture. This small component is so vital for the vehicle that it can not even start without it.  The Spark Plugs generate spark by the phenomenon of Electric breakdown. They covert the high voltage from the ignition coil to spark which helps in the combustion of charge inside the engine. 

    How Spark Plugs Work?

    How does a spark plug work?

    The spark plug consists of a steel shell or covering. Inside the shell, lies a central electrode. The central electrode is positive and receives the high voltage current from the ignition coil. A ground electrode is mounted on the top of the shell appearing as a notch in front of the Spark Plug. These electrodes may be made of Nickel, Platinum or Iridium Alloys. The central electrode carries the high tension current from the ignition coil. It is insulated using Porcelain all over its surface, except the tip. This insulation is necessary in order to prevent the leaking of current from the central electrode. The ground electrode is mounted over the steel casing. It gets grounded when the spark plug is connected to the cylinder head. There lies a small gap between the naked tip of the central electrode and the ground electrode. The high tension current flows in the central electrode and develops a very high voltage across the electrodes. This voltages is so high that it ionizes the air molecules between the electrodes and produce electric sparks. This spark causes the air-fuel mixture inside the engine to ignite. 

    Types Of Spark Plug

    There are different types of spark plugs available in the market based on their design and use. On the basis of electrode material the Spark Plugs are classified as:

    1. Copper/Nickel Spark Plug

    Copper-Nickel Spark Plugs consists of copper electrodes coated with Nickel. The Copper in itself is very fragile and can not bear the heat of combustion. Hence it is coated with Nickel, which is a stronger material than the Copper. These spark plugs are cheaper and the most common among all. The problem with them is their short life. They wear out quickly, increasing the gap between the electrodes. This causes the weakening of spark which further leads to poor performance and mileage of the vehicle.

    2. Platinum Spark Plug

    Platinum is harder and more resistant to wear. Platinum Spark Plugs have a longer life and consistent performance. The tips of platinum electrodes do not wear out helping it to maintain the spark intensity in the long run. The only disadvantage of these Spark Plugs is their high cost. These Spark Plugs are available in two types:

    1. Single Platinum Electrode Spark Plug

    These type of Spark Plugs only have a platinum coating on the negative electrode.

    2. Double Platinum Electrode Spark Plug

    This type of Spark Plugs has a Platinum coating on central and the negative electrode both. These Spark Plugs are costlier but have better performance and a longer life. 

    3. Iridium Spark Plug

    Iridium is even harder than Platinum. It also has a high melting point which helps it, survive the high temperature and pressure of the combustion chamber. Iridium Spark Plugs have a thinner central electrode which allows them to conduct electricity in a superior way. These Spark Plugs have a longer life and lead to smoother engine performance.

    On the basis of the number of electrodes the spark plugs are classified as:

    1. Single Electrode Spark Plug

    These Spark Plugs have a single ground electrode and a single central electrode. They are very common and are used in almost in every vehicle.

    2. Multi Electrode Spark Plug

    These Spark Plugs have a single central Electrode while a multiple number of ground electrodes. They may have 2, 3 or even 4 ground electrodes depending upon their design. The presence of more number of ground electrodes increases the probability of spark generation. The greatest drawback of  Single Electrode Spark Plug is the deposition of carbon and shoot particles on the electrodes. This bridges the gap between the electrodes decreasing the probability of spark generation. The presence of multiple ground electrodes solves this problem by providing multiple paths for the spark generation. In case one of the Electrodes get fouled or wear out, other electrodes would keep on generating the sparks. Multi-Electrode Spark Plugs have a longer life and they help in maintaining the performance of the vehicle in long run.

    Heat Range For Spark Plugs

    Heat range of spark plugs

    The heat range of spark plugs represents how fast the spark plug is able to transfer heat from electrode tips to cylinder head. If a spark plug temperature is too low, it causes carbon and other materials to deposit on the electrodes.  This will cause misfiring and reduce engine performance. If the spark plug temperature is very high, it may cause pre-ignition or knocking. However, the hotter spark plugs have self-cleaning capabilities and they can burn off any deposits on the electrode tips.
     The heat range of spark plug is represented by heat rating. The heat rating of a spark plug indicates the level of heat transfer from it. It is generally represented by a number. The spark plugs with lower heat rating are called hot spark plugs while those with higher heat ratings are called cold spark plugs. 

    Hot Type Spark Plugs

    Hot spark plugs have a larger insulating nose. Larger insulating nose allows more amount of combustion gases to surround the nose decreasing the heat transfer from electrodes to the cylinder head. This causes their temperature to rise quickly. These spark plugs are used generally in light-duty engines. These engines operate at lower temperatures and hence need hot type spark plugs to prevent the fouling of spark plugs. 

    Cold Type Spark Plugs

    Cold type spark plugs have a shorter insulating nose. This increases the rate of heat transfer from their firing ends as they have very less insulation from the combustion gases. Their temperature does not rise as quickly as the hot type spark plugs. They are used in heavy or high-performance engines. These engines operate at very high temperature and hence their spark plugs have to bear a huge amount of heat. Using cold spark plugs prevent their temperature from rising up quickly. This reduces the chances of pre-ignition and knocking in these engines.

    Spark Plug Problems

    Spark plug problems

    The Spark Plugs have to bear a huge amount of heat and pressure inside the engine. The sparks generated by them also cause erosion of material from the electrode surface. All these factors deform the basic design of Spark Plugs and causes the electrodes to wear out. Let's now discuss some of the problems in detail:

    1. Spark Plug Fouling

    Spark Plug fouling is a very common problem with Spark Plugs. Fouling may be done by deposition of Carbon, Dust or Fuel particles on the electrode tips. This reduces or bridges the gap between the electrodes allowing the current to pass easily to the ground electrode. This reduces the spark intensity leading to problems like Misfiring and poor startability. This may even reduce the throttle response, mileage and power output of the engine. There are many factors responsible for Spark Plug fouling. Burning of too rich Air-Fuel mixture is one of them. This leads to the deposition of Carbon on electrode tips. The Air-fuel mixture may become rich due to clogged air filters, wrong Carburetor settings or due to faulty injectors. The leaking piston rings may also cause Spark Plug fouling by the disposition of Engine Oil over the electrodes. The fouled electrodes are unable to generate sufficient voltage necessary for proper spark. This causes the engine to underperform reducing combustion efficiency. Poor combustion also leads to the loss of power and mileage. The fouled Spark Plugs need to be replaced soon to restore the engine performance.

    2. Melting Or Burning Of Spark Plug Electrodes

    The huge temperature inside the combustion chamber may even cause the electrodes to burn or melt down. This occurs generally when the temperature of the combustion chamber becomes abnormally high. This happens usually due to knocking/detonation, burning of lean Air-Fuel mixture, incorrect spark time etc. Once a spark plug melts or burns we must replace it as soon as possible and also diagnose the problem behind it 

    3. Wearing Out Of Spark Plug Electrodes

    The generation of sparks causes the removal of material from the electrode tips. Each time a spark generates, it erodes a small amount of material from the Electrode tip. The removal of material over the time, widens the electrode gap making it difficult for the spark to be generated.

    Symptoms Of A Bad Spark Plug

    The electrodes of Spark Plugs wear out with the time. This weakens the spark intensity causing poor combustion inside the engine. This may lead to various problems in the vehicle.  We can guess a faulty Spark Plug with the following symptoms:

    1. Misfiring

    It is the most common problem caused due to increased or decreased electrode gap. Misfiring leads to improper combustion and hence loss of fuel. It also reduces the throttle response and power of the engine.

    2. Reduced Mileage

    Due to faulty spark plug, improper combustion takes place inside the engine. This causes a large amount of fuel to go unburnt. This decreases the combustion efficiency and hence the mileage of the vehicle.

    3. Reduced Throttle Response

    If you feel that your vehicles Throttle response has got sluggish or your vehicle is not getting proper pick-up, a possible cause for it may be a faulty Spark Plug. The wearing out of Spark Plugs decreases their effectiveness leading to poor throttle response. So, whenever you feel your vehicle is not getting pick-up as earlier, do check the Spark Plugs first.

    4. Poor Startability

    The weakening of sparks also makes it difficult to start the engine. At the time of starting, the engine is cold and it is difficult to initiate the combustion. The weaker sparks aren't enough to fire the air-fuel mixture at the initial moments. Hence if you feel your vehicle has problems in starting, check your Spark Plugs.

    How To Clean A Spark Plug?

    How to clean a spark plug
    Emery Paper

    Cleaning a Spark Plug must be an essential part of your vehicle maintenance schedule. You must monitor the condition of Spark Plug on a regular basis. If you find any fouling or deposition you must try to clean it. To clean a spark plug you need Petrol and Emery Paper (Sand Paper). First of all, you must remove the Spark Plug from the Cylinder Head. Now clean its electrode tip area with Petrol. After cleaning with Petrol try to rub the electrodes with Emery Paper. This would help in the removal of surface deposits. After cleaning the electrodes thoroughly, wash it with Petrol again. Now leave it to dry for some times. 

    When To Change A Spark Plug?

    When to change  spark plug

    The electrodes of Spark Plugs wear out gradually over time. They face problems such as fouling, burning, melting and erosion. All these causes the Spark Plugs to underperform and reduce the quality of combustion inside the engine. This causes several problems like reduced power, lesser mileage, misfiring, poor startability etc. To fix this, we must inspect and clean the Spark Plug if necessary. For preventive maintenance, we must follow the Spark Plug maintenance schedule and replace it as per the guidelines mentioned in the owners manual.  Generally,  it is recommended to change the spark plug after 10000-16000 Kms. We can also replace them before the prescribed time if they are worn out.

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